From the Department of Pathology and Laboratory Medicine, Mount
Sinai Hospital, Toronto, Ontario M5G 1X5, Canada, the § Department of
Laboratory Medicine and Pathobiology, University of Toronto, Toronto,
Ontario, M5G 1L5 Canada, the ¶ Department of Urology, University
Hospital Charite, Humboldt University, Berlin, 10048, Germany, and the
Biology and Biotechnology Program, Lawrence Livermore National
Laboratory, Livermore, California 94551
Received for publication, June 21, 2000, and in revised form, September 15, 2000
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ABSTRACT |
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Kallikreins are a subgroup of serine proteases
with diverse physiological functions. Growing evidence suggests that
many kallikreins are implicated in carcinogenesis. By using molecular
cloning techniques, we identified a new human kallikrein gene,
tentatively named KLK15 (for kallikrein 15 gene). This new gene maps to chromosome 19q13.4 and is located between
the KLK1 and KLK3 genes. KLK15 is
formed of five coding exons and four introns, and shows structural
similarity to other kallikreins and kallikrein-like genes.
KLK15 has three alternatively spliced forms and is
primarily expressed in the thyroid gland and to a lower extent in the
prostate, salivary, and adrenal glands and in the colon testis and
kidney. Our preliminary results indicate that the expression of
KLK15 is up-regulated by steroid hormones in the LNCaP
prostate cancer cell line. The KLK15 gene is also
up-regulated, at the mRNA level, in prostate cancer in comparison
to normal prostatic tissue. KLK15 up-regulation was found
to be associated with more aggressive forms of prostate cancer. This
newly discovered gene has the potential of being used as a diagnostic
and/or prognostic marker for prostate cancer.
Kallikreins are a group of serine proteases that are found in
diverse tissues and biological fluids. The term "kallikrein" was
first introduced by Werle and colleagues (1, 2) who found high levels
of their original isolates in the pancreas (in Greek, the
"kallikreas"). Kallikreins are divided into two main groups; the
plasma kallikrein, which is a single gene (3), and the tissue
kallikreins, which are encoded by a large multigene family in rodents
(4, 5). Until recently, the human kallikrein gene family was thought to
consist of only three members (6). However, we and others have
identified 11 new members of the kallikrein gene family (7-18). The
progress in this area of investigation has recently been reviewed
(7).
Prostate-specific antigen
(PSA),1 currently the most
useful tumor marker for prostate cancer diagnosis and monitoring, is a member of the human kallikrein gene family of serine proteases (19,
20). In addition to PSA, human glandular kallikrein 2 (hK2, encoded by
the KLK2 gene) has been proposed as an adjuvant diagnostic
marker for prostate cancer (21, 22). Moreover, accumulating evidence
indicates that other members of the expanded kallikrein gene family may
be associated with malignancy (7). The normal epithelial cell-specific
1 gene (NES1; KLK10, according to the approved
human tissue kallikrein gene nomenclature) was found to be a novel
tumor suppressor, which is down-regulated during breast cancer
progression (23). Other gene family members, including zyme
(KLK6), neuropsin (KLK8), and human stratum
corneum chymotyrptic enzyme (HSCCE; KLK7) were also found to
be differentially expressed in certain types of malignancies (24-26).
The diagnostic usefulness of PSA in prostate cancer led us to speculate
that other, related molecules might be valuable biomarkers for prostate cancer and other malignancies.
During our efforts to identify new kallikrein genes that might be
involved in malignancy, we cloned a new gene, tentatively named
kallikrein 15 gene (KLK15). Here, we describe the
identification of the new gene, its genomic and mRNA structure, its
location in relation to other known kallikreins, and its tissue
expression pattern. The KLK15 gene has another three
alternatively spliced forms, expressed in many tissues. Our preliminary
data suggest that KLK15 is up-regulated in prostate cancer
and that it is under steroid hormone regulation in the LNCaP prostate
cancer cell line. Higher expression of KLK15 is associated
with more aggressive (higher stage and higher grade) prostate tumors.
Identification of the New Gene--
We previously constructed
the first contiguous map for the human kallikrein gene locus extending
from the KLK1 gene (centromere) to the KLK14 gene
(telomere) (7, 8, 11, 12, 27). Overlapping bacterial artificial
chromosome (BAC) clones spanning this area were identified by screening
of a human BAC library using different radiolabeled gene-specific
probes. An area of ~300 kb of genomic sequence was established using
different techniques, as described previously (11, 27). By performing
an EcoRI restriction analysis, we were able to orient the
kallikrein locus along the EcoRI restriction map of
chromosome 19q13 available from the Lawrence Livermore National
Laboratory (LLNL). A BAC clone that extends more centromerically (BC
781134) was then identified. Contigs of linear genomic sequences from
this clone are available from the LLNL. Initially, we have used these
contig sequences to predict the presence of novel genes, using
bioinformatic approaches, as described previously (8, 12), and a
putative new serine protease was identified. The sequence of the
putative gene was then verified by different approaches, including
sequencing, EST data base search, PCR screening of tissues, as
described below.
Expressed Sequence Tag Searching--
The predicted exons of the
putative new gene were subjected to homology search using the BLASTN
algorithm (28) from the National Center for Biotechnology Information
web server against the human EST data base (dbEST). Clones with
>95% homology were obtained from the IMAGE consortium (29) through
Research Genetics Inc. (Huntsville, AL). The clones were propagated,
purified as described elsewhere (30), and sequenced from both
directions with an automated sequencer, using insert-flanking vector primers.
Prostate Cancer Cell Line and Hormonal Stimulation
Experiments--
The LNCaP prostate cancer cell line was purchased
from the American Type Culture Collection (ATCC), Manassas, VA. Cells
were cultured in RPMI media (Life Technologies, Inc., Gaithersburg, MD)
supplemented with glutamine (200 mM), bovine insulin (10 mg/liter), fetal bovine serum (10%), antibiotics, and antimycotics, in
plastic flasks, to near confluency. The cells were then aliquoted into 24-well tissue culture plates and cultured to 50% confluency. 24 h before the experiments, the culture media were changed into phenol
red-free media containing 10% charcoal-stripped fetal bovine serum.
For stimulation experiments, various steroid hormones dissolved in
100% ethanol were added into the culture media at a final
concentration of 10 RT-PCR for the KLK15 Gene--
Total RNA was extracted from the
LNCaP cell line or from prostate tissues using Trizol reagent (Life
Technologies, Inc.) following the manufacturer's instructions. RNA
concentration was determined spectrophotometrically. 2 µg of total
RNA was reverse-transcribed into first-strand cDNA using the
Superscript preamplification system (Life Technologies, Inc.). The
final volume was 20 µl. Based on the combined information obtained
from the predicted genomic structure of the new gene and the EST
sequences (see below), two gene-specific primers were designed
(KLK15-F1 and KLK15-R1) (Table I), and PCR was carried out in a
reaction mixture containing 1 µl of cDNA, 10 mM
Tris-HCl (pH 8.3), 50 mM KCl, 1.5 mM
MgCl2, 200 µM dNTPs (deoxynucleoside
triphosphates), 150 ng of primers, and 2.5 units of HotStar DNA
polymerase (Qiagen Inc., Valencia, CA) on a PerkinElmer Life Sciences
9600 thermal cycler. The cycling conditions were 95 °C for 15 min to
activate the Taq DNA polymerase, followed by 35 cycles of
94 °C for 30 s, 64 °C for 30 s, 72 °C for 1 min, and
a final extension step at 72 °C for 10 min. Equal amounts of PCR
products were electrophoresed on 2% agarose gels and visualized by
ethidium bromide staining. All primers for RT-PCR spanned at least two
exons to avoid contamination by genomic DNA. To verify the identity of
the PCR products, they were cloned into the pCR 2.1-TOPO vector
(Invitrogen, Carlsbad, CA) according to the manufacturer's
instructions. The inserts were sequenced from both directions using
vector-specific primers, with an automated DNA sequencer.
Tissue Expression--
Total RNA isolated from 26 different
human tissues was purchased from CLONTECH (Palo
Alto, CA). We prepared cDNA as described above for the tissue
culture experiments and used it for PCR reactions. Tissue cDNAs
were amplified at various dilutions using two gene-specific primers
(KLK15-F2 and KLK15-R1) (Table I). Due to the high degree of homology
between kallikreins, and to exclude nonspecific amplification, PCR
products were cloned and sequenced.
Prostate Cancer Tissues--
Prostate tissue samples were
obtained from 29 patients who had undergone radical retropubic
prostatectomy for prostatic adenocarcinoma at the Charite University
Hospital, Berlin, Germany. The patients did not receive any hormonal
therapy before surgery. The use of these tissues for research purposes
was approved by the Ethics Committee of the Charite Hospital. Fresh
prostate tissue samples were obtained from the cancerous and
non-cancerous parts of the same prostates that had been removed. Small
pieces of tissue were dissected immediately after removal of the
prostate and stored in liquid nitrogen until analysis. Histological
analysis from all the tissue pieces was performed as described
previously (31) to ensure that the tissue was either malignant or
benign. The tissues were pulverized with a hammer under liquid
nitrogen, and RNA was extracted as described above, using Trizol reagent.
Statistical Analysis--
Statistical analysis was performed
with SAS software (SAS Institute, Cary, NC). The analysis of
differences between KLK15 expression in non-cancerous
versus cancerous tissues from the same patient was performed
with the non-parametric McNemar test. The binomial distribution was
used to compute the significance level. Prostate tumor KLK15
mRNA levels were qualitatively classified into two categories
(KLK15-low and KLK15-high groups), and associations between KLK15
status and other variables were analyzed using the Fisher's exact test.
Structure Analysis--
Multiple alignment was performed using
the ClustalX software package and the multiple alignment program
available from the Baylor College of Medicine (Houston, TX).
Phylogenetic studies were performed using the Phylip software package.
Distance matrix analysis was performed using the Neighbor-Joining/UPGMA
program, and parsimony analysis was done using the Protpars program.
Hydrophobicity study was performed using the Baylor College of Medicine
search launcher. Signal peptide was predicted using the SignalP server. Protein structure analysis was performed by the SAPS (structural analysis of protein sequence) program.
Cloning of the KLK15 Gene--
A contiguous map for the human
kallikrein gene locus extending from the KLK1 gene
(centromere) to the KLK14 gene (telomere) was previously
established (7, 8, 11, 12, 27). To investigate the presence of other
kallikrein-like genes centromeric to KLK1, a BAC clone (BC
781134) was obtained as described under "Materials and Methods."
According to the published genomic sequence of prostate specific
antigen (PSA) and human renal kallikrein (KLK1)
genes, we designed gene-specific primers for each of these genes (Table
I) and developed polymerase chain
reaction (PCR)-based amplification protocols, which allowed us to
generate specific PCR products with genomic DNA as a template. PCR
screening of the BAC clone by these gene-specific primers indicated
that this clone is positive for KLK1 but negative to PSA,
thus, confirming its location to be centromeric to PSA.
A putative new serine protease was predicted from the sequence of this
clone by computer programs as described previously (12). This clone was
digested, blotted on a membrane, and hybridized with gene-specific
primers for the putative KLK15 gene (according to the
predicted sequence), and positive fragments were subcloned and
sequenced to verify the structure of the putative gene. This putative
gene sequence was then compared using the BLASTN program against
the human EST data base, and two EST clones were identified (GenBankTM
accession numbers AW274270 and AW205420). These two clones were 99%
identical to the last exon and the 3'-untranslated region of the gene,
and the second EST ends with a stretch of 17 adenine (A) nucleotides
that were not found in the genomic sequence, thus verifying the 3'-end
of the gene and the position of the poly(A) tail.
To identify the full mRNA structure of the gene and to determine
the exon/intron boundaries, PCR reactions were performed using primers
located in different computer-predicted exons, using a panel of 26 human tissue cDNAs as templates. PCR products were sequenced. Two
of these primers (KLK15-F1 and KLK15-R1) (Table I) were able to amplify
the full coding region of the gene from different tissues. Comparing
the mRNA with the genomic structure indicated the presence of a
gene formed from five coding exons with four intervening introns.
Translation of the mRNA sequence in all possible reading frames
revealed the presence of only one frame that gives an uninterrupted
polypeptide chain, which also contains the highly conserved structural
motifs of the kallikreins, as discussed below.
Structural Characterization of the KLK15 Gene--
As shown in
Fig. 1, the KLK15 gene is
formed of five coding exons and four intervening introns, although, as
with other kallikrein genes, the presence of further upstream
untranslated exon(s) could not be ruled out (17, 32, 33). All of the
exon/intron splice sites conform to the consensus sequence for
eukaryotic splice sites (34). The gene further follows strictly the
common structural features of other members of the human kallikrein
multigene family, as described below. The predicted protein-coding
region of the gene is formed of 771 bp, encoding a deduced 256-amino
acid polypeptide with a predicted molecular mass of 28.1 kDa.
The potential translation initiation codon matches the consensus Kozak
sequence (35), moreover, there is a purine at position
Nucleotides 7764-7769 (ATTAAA) (the numbers refer to our GenBankTM
submission number AF242195) closely resemble a consensus polyadenylation signal (37) and are followed, after 17 nucleotides, by
the poly(A) tail. No other potential polyadenylation signals were
discernible in the 3'-untranslated region, suggesting that the above
sequence is the actual polyadenylation signal. Although AATAAA is
highly conserved, natural variants do occur, and the ATTAAA sequence is
reported to occur as a natural polyadenylation variant in 12% of
vertebrate mRNA sequences (38). The presence of glutamic acid (E)
at position 203 suggests that KLK15 will likely possess a
unique substrate specificity. PSA has a serine (S) residue in the
corresponding position and has chymotryptic-like activity. Many other
kallikreins usually have aspartate (D) in this position, indicating a
trypsin-like activity (Fig. 2) (6).
Although the KLK15 protein sequence is unique, comparative
analysis revealed that it has a considerable degree of homology with
other members of the kallikrein multigene family. KLK15 shows 51%
protein identity and 66% similarity with the trypsin-like serine
protease (TLSP) and 49% and 48% identity with the neuropsin and
KLK-L3 proteins, respectively. Hydrophobicity analysis revealed that
the amino-terminal region is quite hydrophobic (Fig.
3), consistent with the possibility that
this region harbors a signal sequence, analogous to other serine
proteases. Computer analysis of the KLK15 protein sequence predicted a
cleavage site between amino acids 16 and 17 (TAA-QD). Sequence
alignment (Fig. 2) also revealed another potential cleavage site
(Lys21), at a site homologous to the activation site of
other serine proteases (lysine (K) or arginine (R) is present in most
cases) (39). Several evenly distributed hydrophobic regions throughout the KLK15 polypeptide are consistent with a globular protein, similar
to other kallikreins and serine proteases. Thus, as is the case with
other kallikreins, and although direct experimental evidence is
lacking, KLK15 is presumably translated as an inactive 256-amino acid
preproenzyme precursor. Prepro-KLK15 has 21 additional residues, which
constitute the preregion (the signal peptide formed of 16 residues),
and the propeptide (5 residues).
The dotted area in Fig. 2 indicates an 11-amino acid loop
characteristic of the classical kallikreins (PSA, KLK1, and KLK2) but
not found in KLK15 or other members of the kallikrein multigene family
(10, 11, 13, 14). However, KLK15 has a unique 8-amino acid loop
(HNEPGTAG) at positions 148-155, not found in any other kallikrein
(Fig. 2). 29 "invariant" amino acids surrounding the active site of
serine proteases have been described (40). Of these, 28 are conserved
in KLK15. One of the unconserved amino acids (Ser173
instead of Pro) is also found in prostase, KLK-L2, and KLK-L5 proteins,
and represents a conserved evolutionary change to a protein of the same
group, according to protein evolution studies (41). Twelve cysteine
residues are present in the putative mature KLK15 protein; 10 of them
are conserved in all kallikreins and would be expected to form
disulfide bridges. The other two (Cys131 and
Cys243) are not found in PSA, KLK1,
KLK2, or KLK-L4, however, they are found in
similar positions in all other kallikrein genes and are expected to
form an additional disulfide bond.
To predict the phylogenetic relatedness of the KLK15 protein with other
serine proteases, the amino acid sequences were aligned together using
the Unweighted Pair Group Method with Arithmetic mean (UPGMA) and the
Neighbor-Joining distance matrix methods, and the Protpars parsimony
method. All phylogenetic trees obtained agreed that other serine
proteases (non-kallikreins) can be grouped together as a separate
group, indicating that kallikreins represent a separate step in the
evolution of serine proteases. KLK15 was grouped with the
KLK-L3 and TLSP (Fig. 4) and
the classical kallikreins (hK1, hK2, and PSA) are grouped together in
all trees, suggesting that the separation between classical kallikreins
and the kallikrein-like genes occurred early during evolution,
consistent with suggestions of previous studies (13).
Splice Variants of the KLK15 Gene--
PCR screening for
KLK15 transcripts using gene-specific primers (KLK15-F2 and
KLK15-R2) (Table I) revealed the presence of three bands in most of the
tissue cDNAs examined (Fig. 7). These bands were gel-purified,
cloned, and sequenced. The upper band represents the
classical form of the gene, and the lower band is splice
variant 3 (Fig. 5). The middle band represents other two-splice variants. Restriction digestion of the PCR product of the
middle band with StuI, followed by gel
separation, purification, and sequencing, revealed that it is composed
of splice variants 1 and 2, which have approximately the same length
(splice variant 1 has exon 4 (137 bp) but is missing 118 bp from exon
3, whereas splice variant 2 has an additional 118 bp of exon 3 but
missing exon 4. All splice variants are expected to encode for
truncated protein products (Fig. 5).
Chromosomal Localization of the KLK15 Gene--
Restriction
analysis study of a number of overlapping BAC clones spanning the human
kallikrein locus followed by comparison with the EcoRI
restriction map of the area (available from the LLNL web site) enabled
us to identify a BAC clone (BC 25479) that is telomerically adjacent to
BC 781134 (which harbors the KLK15 gene). A BLASTN search of
the sequences of the two clones showed that the ends of these clones
are overlapping. By identifying the position of the KLK1,
KLK3, and KLK15 genes along these clones, we were
able to precisely define the relative location and the direction of
transcription of these three genes. KLK1 is the most centromeric, and its direction of transcription is from telomere to
centromere, followed by KLK15, which is more telomeric and transcribes in the same direction. The distance between the two genes
is a length of 1501 bp. The KLK3 gene is more telomeric, located at a distance of 23,335 bp from the position of
KLK15, and is transcribed in the opposite direction (Fig.
6). These results are consistent with
previous reports where the distance between KLK3 and
KLK1 was roughly estimated to be ~31 kb (6, 27).
Tissue Expression and Hormonal Regulation of the KLK15
Gene--
As shown in Fig. 7, the
KLK15 gene is expressed at highest levels in the thyroid
gland. Lower levels of expression are also seen in the prostate,
salivary, and adrenal glands and in the colon, testis, and kidney. To
verify the RT-PCR specificity, representative PCR products were cloned
and sequenced. Fig. 8 shows that the KLK15 gene is up-regulated by steroid hormones in the human
LNCaP prostate cancer cell line.
KLK15 Expression in Prostate Cancer--
The expression of the
KLK15 gene in normal and cancerous prostatic tissues was
examined by RT-PCR. Actin was included as a control gene to ensure the
quality and amount of the cDNA used. To examine the relative
expression of the KLK15 gene in normal compared with
malignant tissues, we analyzed 29 pairs of prostatic tissues. Each pair
represented normal and cancerous tissue obtained from the same patient.
The intensity of the PCR band was compared between each pair of
normal/cancerous tissue to establish if the expression was higher or
lower in cancer, compared with normal tissue. The results are
summarized in Table II. Thirteen out of 29 patients had significantly higher KLK15 expression in the
cancer tissue and only three had the expression of KLK15 higher in
non-cancer than to cancer tissues. Analysis by the McNemar test
indicated that the differences between normal and cancerous tissues are statistically significant (p = 0.021). Because of the
small number of cases, the binomial distribution was used to compute
the significance level. We have further qualitatively classified the
prostate cancer patients in two groups: (a) KLK15
expression-positive (n = 21) and (b)
KLK15 expression-negative (or very low) (n = 8). When we compared the association of KLK15 expression
with clinicopathological prognostic variables, we found that higher
KLK15 expression was more frequent in patients with late
stage disease and tumors of higher grade (Table
III).
Kallikreins are a subgroup of serine proteases. The term
"kallikrein" is usually utilized to describe an enzyme that acts upon a precursor molecule (kininogen) for release of a bioactive peptide (kinin) (3, 42). However, the generic term "tissue kallikrein" is not restricted to the functional definition of the
enzyme. This term is now used to describe a group of enzymes with a
highly conserved gene and protein structure, which also co-localizes in
the same chromosomal locus. Among the three classical human kallikrein
genes, only KLK1 encodes for a protein with potent kininogenase activity. The enzymes encoded by KLK2 and
KLK3 genes have very weak kininogenase activity. The already
cloned 14 members of the human kallikrein gene family have a number of
similarities (7, 11) as follows: 1) All genes localize to the
same chromosomal region (proximal19q13.4). 2) All genes encode for
putative serine proteases with a conserved catalytic triad in the
appropriate positions, i.e. histidine near the end of the
second coding exon, aspartic acid in the middle of the third exon, and
serine at the beginning of the fifth (last) exon. 3) All genes have
five coding exons (some members contain one or more 5'-untranslated
exons). 4) Coding exon sizes are similar or identical. 5) Intron phases are fully conserved. 6) All genes have significant sequence homologies at the DNA and amino acid levels (30-80%). 7) Many of these genes are
regulated by steroid hormones.
Figs. 2 and 9 show that the newly
identified KLK15 gene shares all the above similarities and
is thus suggested to be a new member of the human kallikrein multigene
family. We named this gene KLK15 based on the
recommendations for the new kallikrein gene nomenclature, as approved
by the Human Gene Nomenclature Committee and available on the
Web (43).
INTRODUCTION
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ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
MATERIALS AND METHODS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
8 M. Cells stimulated with
100% ethanol were included as controls. The cells were cultured for
24 h, then harvested for mRNA extraction.
RESULTS
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ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES
Primers used for genomic PCR amplification
3, which
occurs in 97% of vertebrate mRNAs (36). It should also be noted
that, like most other kallikrein-like genes, KLK15 does not
have the consensus G nucleotide at position +4.
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Fig. 1.
Genomic organization and partial genomic
sequence of the KLK15 gene. Intronic sequences are not
shown except for the splice junction areas. Introns are shown with
lowercase letters and exons with capital letters.
The coding nucleotides are shown in boldface and the
3'-untranslated region follows the TGA stop codon
(encircled). The translated amino acids of the coding region
are shown underneath by a single letter abbreviation. For the full
sequence, see GenBankTM accession number AF242195. The start and stop
codons are encircled, and the exon-intron junctions are
underlined. The catalytic residues are boxed. The
putative polyadenylation signal is underlined. The exact
start of the first coding exon was not determined.
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Fig. 2.
Alignment of the deduced amino acid sequence
of KLK15 with members of the kallikrein multigene family.
Dashes represent gaps to bring the sequences to better
alignment. The residues of the catalytic triad (H,
D, and S) are shown in italics.
Identical amino acids are highlighted in black and similar
residues in are gray. The 29 invariant serine protease
residues are marked by the symbol on the bottom and the
cysteine residues by the + symbol on top of each
block. The predicted cleavage sites of the signal and activation
peptides are indicated by arrows. The dotted area
represents the kallikrein loop sequence. The trypsin-like cleavage
pattern predicted by the presence of the Asp residue is indicated by an
asterisk. KLK15 has a Glu in this position. A
unique 8-amino acid sequence, HNEPGTAG, is present at positions
148-155 of the KLK15 gene.
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Fig. 3.
Plot of hydrophobicity and hydrophilicity of
the KLK15 protein, as compared with the prostate specific antigen
(PSA). Note the hydrophobic region at the amino terminus,
suggesting presence of a signal peptide. For details, see text.
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Fig. 4.
Dendrogram of the predicted phylogenetic tree
for 15 kallikreins and a few other serine proteases. The
Neighbor-Joining method was used to align KLK15 with other
serine proteases and members of the kallikrein gene family. The tree
grouped the classical kallikreins (hK1, hK2, and PSA) together and
aligned KLK15 in one group with TLSP and
KLK-L3 genes. Other serine proteases were aligned in
different groups, as shown. For full gene names, see the abbreviations
footnote.
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Fig. 5.
Schematic presentation of the different
splice variants of the KLK15 gene. Exons are
shown by boxes and introns by the connecting
lines. Numbers inside boxes represent the
exons lengths in base pairs. The arrowhead points to the
common start codon and stars to the stop codon positions.
The length of the predicted polypeptide product is indicated beside
each variant in amino acids (AA). For full sequence
information, see our GenBankTM submission number AF242195. The
alternative splicing and/or exon skips create a frameshift, which leads
to a premature termination.
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Fig. 6.
The relative locations of
KLK1, KLK15, and KLK3
genes on chromosome 19q13.4. The two overlapping BAC clones
are identified, and the overlap region is hatched. Genes are
represented by horizontal arrows denoting the direction of
the coding sequence. Distances between genes are given in base pairs.
The figure is not drawn to scale.
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Fig. 7.
Tissue expression of the KLK15
gene, as determined by RT-PCR. KLK15 is primarily expressed
in the thyroid gland, and to a
lower extent in the prostate, salivary, and adrenal glands and in
the colon, testis, and kidney. For an explanation of the
multiple PCR bands (alternatively spliced forms) see text. PCR was
performed with primers KLK15-F2 and KLK15-R1.
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Fig. 8.
Hormonal regulation of the KLK15
gene in the LNCaP prostate cancer cell line. DHT,
dihydrotestosterone. Steroids were added at 10 8
M final concentrations. -ve, negative control.
Actin was used as a control gene. For more details, see text.
KLK15 expression in 29 pairs of cancerous and non-cancerous prostatic
tissues
Relationship between KLK15 expression and other clinicopathological
variables in 29 patients with primary prostate cancer
DISCUSSION
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ABSTRACT
INTRODUCTION
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DISCUSSION
REFERENCES
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Fig. 9.
Schematic diagram showing the comparison of
the coding regions of the 15 kallikrein genes. Exons are shown by
solid bars and introns by the connecting lines.
Letters above boxes indicate relative positions
of the catalytic triad that was found to be conserved in all genes;
H denotes histidine, D aspartic acid, and
S serine. Roman numerals indicate intron phases.
The intron phase refers to the location of the intron within the codon;
I denotes that the intron occurs after the first nucleotide
of the codon, II the intron occurs after the second
nucleotide, and 0 the intron occurs between codons. The
intron phases are conserved in all genes. Numbers inside
boxes indicate exon lengths in base pairs. Names
inside brackets represent the official nomenclature approved
by the Human Gene Nomenclature Committee. Untranslated 3'- and
5'-regions and 5'-untranslated exons are not shown.
Many kallikrein genes are related to the pathogenesis of human diseases, depending on the tissue of their primary expression. The KLK1 gene is involved in many disease processes, including inflammation (3), hypertension (44), renal nephritis and diabetic renal disease (45, 46), The connections of HSCCE (KLK7) with skin diseases, including pathological keratinization and psoriasis, have already been reported (47, 48). Little et al. suggested that zyme (KLK6) is amyloidogenic and plays a role in the development of Alzheimer's disease (14). There are other reports describing connection of neuropsin (KLK8) expression with diseases of the central nervous system, including epilepsy (49, 50). Being primarily expressed in the thyroid, KLK15 may play an important role in the normal physiology and pathophysiology of this gland. Among all other discovered kallikreins, many are expressed in the thyroid but none at the highest levels in this tissue (7, 11).
Our preliminary findings indicate that the KLK15 gene is up-regulated, at the mRNA level, in a subset of prostate cancers. The distributions of KLK15 qualitative expression status (high or low) between subgroups of patients differing by disease stage, tumor grade, and Gleason score indicated that high KLK15 expression was found more frequently in grade 3 tumors as well as in stage III and Gleason score >6 patients. These findings suggest that overexpression of KLK15 is associated with more aggressive forms of the disease and may be an indicator of poor prognosis. These findings require verification, because our patient population was relatively small (Table III).
There is now growing evidence that many kallikreins and kallikrein-like genes are related to malignancy. PSA is the best marker for prostate cancer so far (20). Recent reports suggest that hK2 (encoded by the KLK2 gene) could be another useful diagnostic marker for prostate cancer (21, 51). NES1 (KLK10) appears to be a novel tumor suppressor gene (23). The zyme (KLK6) gene was shown to be differentially expressed in primary breast and ovarian tumors (24), and the human stratum corneum chymotryptic enzyme (HSCCE, KLK7) has been shown to be expressed at abnormally high levels in ovarian cancer (25). Another recently identified kallikrein-like gene, tentatively named the tumor-associated differentially expressed gene-14 (TADG-14/neuropsin) (KLK8) was found to be overexpressed in about 60% of ovarian cancer tissues (26). prostase/KLK-L1/(KLK4), another newly discovered kallikrein-like gene, is speculated to be linked to prostate cancer (13). Two newly discovered kallikreins, KLK-L4 (KLK13) and KLK-L5 (KLK12), were also found to be down-regulated in breast cancer (10). Thus, extensive new literature suggests multiple connections of various kallikrein genes to many forms of human cancer.
The existence of multiple alternatively spliced mRNA forms is frequent among the kallikreins. Distinct RNA species are transcribed from the PSA gene, in addition to the major 1.6-kb transcript (19, 52, 53). Also, Reigman et al. (54) reported the identification of two alternatively spliced forms of the human glandular kallikrein 2 (KLK2) gene. A novel transcript of the tissue kallikrein gene (KLK1) was also isolated from the colon (55). Neuropsin, a recently identified kallikrein-like gene, was found to have two alternatively spliced forms, in addition to the major form (26, 56). KLK-L4 was also found to have different alternatively spliced forms (10). Because the splice variants of KLK15 have an identical 5'-sequence required for translation, secretion, and activation, it is possible to assume that they encode for a secreted protein (53). These proposals need experimental verification, and the role, if any, of these isoforms in tissue physiology and pathophysiology are worth examining in the future.
In conclusion, we characterized a new member of the human kallikrein
gene family, KLK15, which maps to the human kallikrein locus
(chromosome 19q13.4). This gene has three related splice forms in
addition to the classical form. KLK15 is expressed in a
variety of tissues but predominantly in the thyroid, it appears to be
up-regulated in more aggressive forms of prostate cancer, and its
expression is influenced by steroid hormones. Because a few other
kallikreins are already used as valuable tumor markers, we speculate
that KLK15 may also find similar clinical applications. This
possibility, as well as the physiological function of this protein in
various tissues need further investigation.
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ACKNOWLEDGEMENTS |
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We thank Maria Diamandis, Linda Grass, and Antoninus Soosaipillai for valuable technical assistance.
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FOOTNOTES |
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* The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) AF242195.
** To whom correspondence should be addressed: Mount Sinai Hospital, Dept. of Pathology and Laboratory Medicine, 600 University Ave., Toronto, Ontario M5G 1X5, Canada. Tel.: 416-586-8443; Fax: 416-586-8628; E-mail: ediamandis@mtsinai.on.ca.
Published, JBC Papers in Press, September 28, 2000, DOI 10.1074/jbc.M005432200
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ABBREVIATIONS |
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The abbreviations used are: PSA, prostate-specific antigen; KLK, kallikrein; KLK-L, kallikrein-like; PCR, polymerase chain reaction; hK2, human glandular kallikrein 2; dNTPs, deoxynucleoside triphosphates; LLNL, Lawrence Livermore National Laboratory; RT, reverse transcription; EST, expressed sequence tag; TLSP, trypsin-like serine protease; HSCCE, human stratum corneum chymotryptic enzyme; NES1, normal epithelial cell-specific 1 gene; kb, kilobase(s); BAC, bacterial artificial chromosome; contig, group of overlapping clones.
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