From the Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Científicas and Department of Biochemistry, School of Medicine, Autonoma University, 28029 Madrid, Spain
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Members of the Rho family of small GTPases
activate the nuclear factor B (NF-
B) (Perona, R., Montaner, S.,
Saniger, L., Sánchez-Pérez, I., Bravo, R., and Lacal,
J. C. (1997), Genes & Dev. 11, 463-475). We have
investigated whether different members of the family of exchange
factors specific for Rho proteins (Dbl family) could activate the
transcription factor NF-
B and have explored both their specificity
under in vivo conditions and the mechanisms involved.
Activated forms of Dbl, Ost, and Vav proteins induce NF-
B
activation. While the activation induced by the Vav oncogen was
efficiently inhibited by a dominant negative mutant of Rac1, the
corresponding mutant of Cdc42Hs was able to block selectively NF-
B
activation mediated by Dbl. Finally, mutants of RhoA and Cdc42Hs, but
not that of Rac1, inhibited the activation of NF-
B by Ost. Thus,
under in vivo conditions, different members of the Dbl
family are related to specific Rho GTPases for the regulation of
NF-
B. Activation of NF-
B by Rho or Ras proteins is mutually
independent. However, there is a link between the NF-
B and the c-Jun
N-terminal kinase/stress-activated protein kinase (JNK/SAPK) cascades
since a dominant negative mutant of MEKK1 is able to inhibit NF-
B
activation induced by Rac1 and Cdc42Hs proteins, but not by RhoA. These
results indicate that, in mammalian cells, multiple pathways coexist
for the activation of NF-
B, some of which are mediated by specific
members of the Ras and Rho families of small GTPases.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
The Rho family of small GTPases are involved in the regulation of critical cellular functions, such as cell growth, apoptosis, invasion, and cytoskeleton organization, and in several aspects of development (2, 3). During the last few years, a growing body of evidence has emerged revealing the implication of RhoA, Rac1, and Cdc42Hs proteins in signal transduction cascades that regulate the activity of different transcription factors. Constitutively activated forms of Rac1 and Cdc42Hs GTPases are able to induce the activity of the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK)1 in COS-7, NIH-3T3, and HeLa cells (4, 5). However, RhoA, RhoB, RhoC, and Cdc42Hs, but not Rac1, induce the activation of JNK/SAPK in human kidney 293T cells (6). Activated Rac1 and Cdc42Hs mutants have also been shown to activate the p38/Mpk2 pathway, which is induced by different stress conditions (5). Furthermore, Hill et al. (7) have reported the regulation of the transcriptional activity of the serum response factor (SRF) by RhoA, Rac1 and Cdc42Hs mediated by, at least, two independent mechanisms.
Recently, our group has described the activation of the nuclear factor
B by members of the Rho family of small GTP binding proteins (1).
The NF-
B complex is composed of different homodimers and
heterodimers of the members of the Rel/NF-
B family of transcription factors. In its inactive state, NF-
B is located in the cytoplasm where it is retained by a third inhibitory protein denominated I
B
(8, 9). Activation by multiple external stimuli triggers the
phosphorylation and proteolytic degradation of the I
B protein, releasing the NF-
B dimer, which translocates to the nucleus and binds DNA. We have reported that RhoA, Rac1, and Cdc42Hs GTPases induce
the transactivation of the NF-
B-dependent HIV promoter in COS-7, NIH-3T3, and Jurkat cells. Rho proteins activate the translocation of NF-
B complexes by inducing the phosphorylation of
the I
B
isoform in Ser-32 and Ser-36 residues. Furthermore, RhoA
and Cdc42Hs seem to mediate specifically the activation of NF-
B by
certain physiological stimuli such as tumor necrosis factor
(TNF
) (1).
The activity of Rho proteins is regulated by guanine nucleotide exchange factors that promote the transition between the inactive, GDP-bound state and the active, GTP-bound state of these GTPases (10). Rho-related exchange factors acquire tumorigenic activity by deletion of their N-terminal region, and in fact, most of them have been identified as potent oncogenes isolated from different transformed cell lines. The ability of catalyzing the GDP/GTP exchange is critically mediated by two conserved regions of these molecules, designated as the Dbl homology (DH) domain and the Pleckstrin homology (PH) domain (11). Because of these features, these exchange factors have been enclosed in a rapidly growing family known as the Dbl family, which includes the Dbl protein itself, identified in 1985 from a diffuse B-cell lymphoma (12), Ost, isolated from a rat osteosarcoma (13) and Vav, cloned as a transforming gene from a human hematopoietic cell line (14).
Results derived from in vitro experiments have shown that the members of the Dbl family have a wide specificity regarding their nucleotide exchange activity for the different Rho proteins. Nevertheless, during the last few years, a considerable effort has been made in order to identify which processes these Dbl-related proteins could mediate in vivo. Overexpression of some of these exchange factors induces cytoskeleton arrangements that had previously been related to RhoA, Rac1, or Cdc42Hs (15-18). Tiam1 is able to induce membrane ruffling in fibroblasts and COS cells (19, 20), whereas Lbc is implicated in stress fiber formation (21) and Fgd1 induces the extension of filopodia (22). On the other hand, there is also abundant information relating activation of Rho proteins with signaling events. Thus, activation of the 70-kDa S6 kinase is induced by overexpression of the Dbl and Fgd1 proteins (22, 23), and several members of the Dbl family such as Dbl, Ost, Vav, Tiam1, and Fgd1 have been found to activate the JNK/SAPK cascade (4, 20, 22, 24). Moreover, activation of JNK/SAPK induced by Vav and Tiam1 oncogenes seems to be inhibited by the dominant negative mutant of Rac1, Rac1/Asn-17 (20, 24). These results indicate that the Dbl-related guanine nucleotide exchange factors have a limited specificity for Rho proteins in vivo.
Although it is well established that Rho GTPases are regulated by
specific nucleotide exchange factors that generically belong to the Dbl
family of proteins, little is known about their specificity under
physiological conditions. In this study, we have investigated further
the pathways leading to the activation of NF-B where Rho proteins
are implicated. Both specificity by some members of the family of
exchange factors for Rho proteins and the mechanisms involved are
addressed.
![]() |
EXPERIMENTAL PROCEDURES |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
Cell Lines and Transfections-- Simian COS-7 fibroblast-like cells were maintained in Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum and 1 mM glutamine. Cells were transfected by the calcium phosphate precipitation method in 60-mm dishes (25). The total amount of DNA was adjusted to 5-6 µg/plate.
DNA Constructs--
(453/+80) HIV-LUC reporter containing the
two NF-
B binding sites of the HIV enhancer region and the same
plasmid with 3-base pair substitutions in the
B sites (
HIV-LUC)
were previously described (26). The 5 × Gal4-LUC reporter and the
plasmids GAL4-c-Jun(1-223) and GAL4-c-Jun(1-223;A63/73) were kindly
provided by Dr. M. Karin (University of California, San Diego).
GAL4-c-Jun(1-223) and GAL4-c-Jun(1-223;A63/73) expression vectors
encode for fusion proteins containing the GAL4 DNA binding domain and
the c-Jun activation domain (5). Both phosphorylation sites by JNK/SAPK
are substituted by alanine residues in GAL4-c-Jun(1-223;A63/73)
protein. The plasmids pJ5
-MEKK1 WT and pJ5
-MEKK
(K432M) were
also kindly provided by Dr. M. Karin. The vector
pJ5
-MEKK
(K432M) codifies for a catalytically inactive MEKK1
mutant (5). PCDNAIIIB-derived vectors containing cDNAs for
constitutively activated RhoA, Rac1, and Cdc42Hs proteins (QL) and
pCEV27-derived vectors encoding the dominant mutants RhoA/Asn-19,
Rac1/Asn-17 and Cdc42Hs/Asn-17 were kindly provided by Drs. T. Miki
(NCI, National Institutes of Health) and S. Gutkind (National Institute
of Dental Research, Bethesda, MD). Plasmids pZIP-Neo-Ras/Asn-17 and
pZip-Neo-C4-Raf were a generous gift from L. Feig (Tufts University
School of Medicine, Boston) and U. Rapp (Universitat Wurzburg,
Germany), respectively, and have been previously described (1).
Oncogenic versions of guanine nucleotide exchange factors for Rho
proteins are as follows: pMEX-derived vector encoding for a truncated
Vav protein that lacks the helix-loop-helix domain (PJC7) was kindly
provided by Dr. X. Bustelo (SUNY, Stony Brook); pZipNeo-derived vector
encoding for a truncated Dbl protein (12) and PCEV27-derived vector
encoding for a truncated Ost protein (13) were kindly provided by Drs.
S. Gutkind and T. Miki, respectively.
Gene Expression Analysis--
Cells were transfected as
described above and harvested 24 h after transfection. Protein
extracts for luciferase and -galactosidase activity were obtained as
described previously (1). Transfection of the (
453/+80) HIV-LUC
reporter was used for the determination of the NF-
B activity.
Analysis of c-Jun transcriptional activation by JNK/SAPK was performed
by transfection of the 5 × Gal4-LUC reporter and the plasmids
GAL4-c-Jun(1-223) or GAL4-c-Jun(1-223;A63/73). Transfection
efficiencies were routinely corrected by obtaining the ratio of the
luciferase and the
-galactosidase activities observed in the same
sample. Results are expressed as -fold induction considering 1 as the
luciferase activity of the cells transfected with the corresponding
empty vector or as percentage of maximal induction.
![]() |
RESULTS AND DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|
We have recently described that members of the Rho family of small
GTP binding proteins are capable of activating the transcription factor
NF-B (1). Overexpression of either normal or constitutively activated forms of RhoA, Rac1, and Cdc42Hs induced the transactivation of the human immunodeficiency virus (HIV) promoter, which is mostly mediated by the presence of two
B binding sites in its enhancer region (26). Moreover, the activation of NF-
B by Rho proteins implicated the translocation of RelA/p50 and p50/p50 dimers to the
nucleus and was observed in a variety of cell types, such as simian
COS-7, murine NIH-3T3, and human T-cell lymphoma Jurkat cells.
Overexpression of Rho GTPases has been useful to reveal the possible
role of these molecules in the regulation of NF-B. However, it could
also induce artifacts that are not representative of their
physiological role due to improper localization or other indirect
effects. Activation of Rho proteins is catalyzed under physiological
conditions by the activation of certain specific nucleotide exchange
factors that belong to the Dbl family of proteins. Thus, we
investigated whether some of these Dbl-related molecules, which are
known specific exchange factors for Rho proteins, were able to activate
NF-
B. COS-7 cells were transfected with the HIV-LUC plasmid as a
reporter along with the expression vectors encoding for the
constitutively activated forms of Dbl, Ost, and Vav proteins or their
corresponding empty vectors. These oncogenic versions contain a
deletion in their N-terminal domain that confers transforming potential
to these molecules. As shown in Fig.
1A, transient expression of
either Dbl, Ost, or Vav oncogenes was able to induce the
transactivation of the HIV promoter, as we had observed for the
constitutively activated Rho proteins (QL-mutants). This activation was
mostly due to the presence of the two
B sites located in the HIV
enhancer domain because this effect was blocked when a mutant plasmid
HIV-LUC with 3-base pair substitutions in the
B sites was used
(data not shown). By contrast, while a significant activation was
obtained with the corresponding Rho proteins as previously reported
(1), no effect was observed by the overexpression of the PKC
isoenzyme, in keeping with previous reports (27-29).
|
Activation of the transcriptional activity of c-Jun induced by all
these proteins was also assayed in parallel experiments. The
corresponding vectors for the activated forms of Rho GTPases and
the truncated versions of Dbl, Ost, and Vav were cotransfected in COS-7
cells along with the 5 × GAL4-LUC reporter and the plasmid GAL4-c-Jun(1-223) encoding for a fusion protein containing the GAL4
DNA binding domain and the c-Jun activation domain (5). As shown in
Fig. 1B, expression of either Rac1 or Cdc42Hs was able to
induce the c-Jun transcriptional activity while expression of RhoA was
negative as the expression of PKC, in agreement with previous
reports (1, 4, 5). The oncogenic forms of Dbl, Vav, and Ost proteins
were also able to induce the activation of the c-Jun transcription
factor. This effect was mediated by the phosphorylation of c-Jun at
residues serines 63 and 73, since activation was efficiently blocked by
cotransfection of the plasmid GAL4-c-Jun(1-223;A63/73). These results
indicate that members of the family of specific exchange factors for
Rho proteins, in addition to the JNK/SAPK cascade, are able to activate
the transcription factor NF-
B. These results provide further
evidence to support the concept that Rho proteins may be involved in
the physiological regulation of NF-
B.
Using NF-B activation as a reporter assay, we next investigated
whether distinct proteins of the Dbl family of exchange factors had any
degree of specificity for different members of the Rho family of small
GTPases. This information may be very useful to identify the
physiological pathways where each Rho protein may exert its regulatory
function on NF-
B-dependent transcription. The product of
the vav proto-oncogen is mostly expressed in hematopoietic cell lines, and this exchange factor has been found to be critical for
antigen receptor-mediated activation and proliferation of B and T
lymphocytes (14, 30, 31). Recently it has been described that a
truncated Vav protein could efficiently activate the JNK/SAPK by a
Rac1-dependent pathway since a dominant negative
mutant of Rac1, Rac/Asn-17, inhibited the activation induced by
this exchange factor (24). Moreover, Rac1 GDP/GTP exchange reaction
catalyzed by Vav is dependent on tyrosine phosphorylation (32). Thus, we investigated the specificity for this exchange factor regarding the
activation of NF-
B. COS-7 cells were cotransfected with the corresponding expression vectors encoding for the constitutively activated form of Vav and the dominant negative mutants of Rho proteins, RhoA/Asn-19, Rac1/Asn-17, and Cdc42Hs/Asn-17, along with the
HIV-LUC reporter. As shown in Fig. 2,
only the dominant negative mutant Rac1/Asn-17 was able to block
efficiently the activation of NF-
B mediated by the overexpression of
Vav. Neither RhoA/Asn-19 nor Cdc42Hs/Asn-17 expression had a
significant inhibitory effect on this assay. These results corroborate
that this exchange factor seems to be selective for Rac1 GTPase.
|
Similar studies were also carried out with the Dbl exchange factor. The
Dbl protein had previously shown in vitro exchange activity
for both RhoA and Cdc42Hs GTPases (33, 34) and is capable of activating
the JNK/SAPK cascade in COS-7 cells and phosphoprotein 70 S6 kinase in
NIH-3T3 cells (4, 23). COS-7 cells were cotransfected with the
expression vector of the activated form of Dbl and the different
dominant negative mutants of Rho proteins, along with the HIV-LUC
reporter. As shown in Fig. 3, the
dominant negative mutant of Cdc42Hs was capable of efficiently interfering the activation of NF-B induced by overexpression of Dbl.
By contrast, no significant inhibitory effect in the activation of
NF-
B by Dbl was observed by the expression of the RhoA mutant, RhoA/Asn-19 or the Rac1 mutant, Rac1/Asn-17. Thus, even though there is
in vitro evidence for exchange activity of Dbl for both GTPases, Cdc42Hs but not RhoA play a role in the activation of NF-
B
induced by Dbl. These results also indicate that Dbl oncogen could
induce the NF-
B transcriptional activity by catalyzing the GDP/GTP
transition for Rho proteins in a selective manner.
|
Finally, the specificity for the Ost exchange factor was also
investigated. Horii et al. (13) reported the in
vitro GDP/GTP exchange activity of Ost for RhoA and Cdc42Hs.
Furthermore, this molecule was able to bind specifically to the
Rac1-GTP form, suggesting that Ost could also serve as an effector
molecule for this GTPase. In keeping with these results, in
vivo experiments have shown that Ost is able to activate the
JNK/SAPK cascade in COS-7 cells (4). However, no evidence is available
to link Ost to RhoA under in vivo conditions since RhoA is
not able to activate the JNK/SAPK in this cell system. COS-7 cells were
cotransfected with the encoding vector for the activated Ost protein
along with the dominant negative mutants of the Rho proteins and the
HIV-LUC reporter. As shown in Fig. 4,
both RhoA/Asn-19 and Cdc42Hs/Asn-17 could efficiently block the
transactivation of the HIV promoter induced by Ost. Thus both RhoA and
Cdc42Hs seem to mediate the activation of NF-B induced by this
exchange factor. By contrast, we did not see any significant effect due
to the expression of Rac1/Asn-17 with less than 20-25% inhibition.
These results suggest that the Ost exchange factor can indeed promote
the GDP/GTP transition, under in vivo conditions, for either
RhoA or Cdc42Hs, and this activity seems to mediate the activation of
NF-
B, but it does not affect Rac1, in agreement with the in
vitro experiments reported by Horii et al. (13).
|
From all these experiments, we can conclude that different exchange
factors such as Dbl, Ost, and Vav proteins induce the activation of
NF-B by the regulation of specific members of the Rho family of
GTPases. These data also indicate that these exchange factors,
regardless of their activities under in vitro conditions, have a selective activity for these GTPases in vivo. Since
each exchange factor may respond to the activation of specific
receptors for growth factors and cytokines under physiological
circumstances, they provide valuable information in order to identify
the specific pathways where Rho GTPases may play a functional role in
the regulation of NF-
B. As an extension of these results, Rho
proteins can be related to the biological functions also described for
NF-
B, such as regulation of cell proliferation and apoptosis, in
agreement with previous results from our group (25, 35, 36) and others (37-40).
We next investigated the mechanisms by which Rho GTPases and their
exchange factors mediate the activation of NF-B. It is important to
note that Ras proteins do also activate the transcription factor
NF-
B (41-43) and that several groups have recently reported that
Rho, Rac1, and Cdc42Hs proteins mediate in the signaling cascades which
confer transforming activity to the H-RasVal12 oncogene (37-40).
However, this is not a universal effect since several signaling
pathways which regulate the activity of different transcription factors
activated by Rho and Ras have shown to be independent (4, 7).
Therefore, we investigated whether the H-Ras/Raf kinase pathway was
involved in the activation of NF-
B induced by Rho proteins. As shown
in Fig. 5A, we were not able to detect any effect of the overexpression of the dominant negative mutants of H-Ras and Raf kinase (H-Ras/Asn-17 and Raf-C4) in the transactivation of the HIV promoter induced by RhoA, Rac1, or Cdc42Hs
proteins. These results indicate that Rho-mediated activation of
NF-
B is either independent of the Ras/Raf pathway or that it is
located downstream of Ras.
|
We then studied whether the Rho proteins could affect the activation of
NF-B mediated by the H-Ras protein. To that end, COS-7 cells were
cotransfected with the expression vectors of H-Ras-Val12 and the
dominant negative mutants of Rho proteins, RhoA/Asn-19, Rac1/Asn-17,
and Cdc42Hs/Asn-17 along with the HIV-LUC plasmid. In keeping with our
previous results (1), the induction of the HIV-LUC reporter in response
to TNF
was efficiently inhibited by the overexpression of the
dominant negative mutants of RhoA and Cdc42Hs proteins (Fig.
5B), indicating that these two GTPases were implicated in
this pathway. However, neither of the three Rho mutants had any
significant effect in the activation of NF-
B induced by the
H-Ras-Val12 protein. These results provide strong evidence that the
signal transduction cascades regulated by H-Ras and Rho GTPases for
NF-
B activation are mutually independent.
It has also been shown that cytokines such as TNF or environmental
stress such as UV irradiation can induce both c-Jun and NF-
B
activities simultaneously, a result that could suggest a cross-talking
among these two signaling events. Thus, we then explored the
possibility of a common link between the Rho-dependent signal transduction pathways that regulate the activity of c-Jun and
NF-
B transcription factors. In this regard, it has been reported that overexpression of MEKK1 (JNKKK) is able to induce the
transactivation of the HIV and IL-2R
promoters in Jurkat cells in an
NF-
B-dependent manner (44). On the other hand, a
kinase-defective, dominant negative mutant of MEKK1 inhibits the
transactivation of a
B-CAT reporter induced by TNF
in NIH-3T3
cells (45). Lee et al. (29) have also observed that MEKK1 is
able to activate the I
B
kinase complex, which is responsible of
the site-specific phosphorylation of I
B
in Ser-32 and Ser-36
residues. Thus, we investigated whether MEKK1 was involved in the
activation of the nuclear factor
B induced by members of the Rho
family of small GTP binding proteins. To that end, COS-7 cells were
cotransfected with the HIV-LUC plasmid and the derived expression
vectors encoding for the wild type form of the kinase MEKK1, along with
the constitutively activated forms (QL) of RhoA, Rac1, and Cdc42Hs
proteins or their corresponding empty vectors. As shown in Fig.
6A, the MEKK1 wild type
protein was capable of activating NF-
B in COS-7 cells, acting in a
cooperative manner in the transactivation of the HIV promoter when
coexpressed with Rac1 (QL) or Cdc42Hs (QL). By contrast, the activation
by the expression of the RhoA (QL) protein was not affected by the MEKK1 cotransfection. Furthermore, when the constitutively activated forms of RhoA, Rac1, and Cdc42Hs were coexpressed with a catalytically inactive, dominant negative mutant of MEKK1, MEKK
(K432M), the transactivation of the HIV promoter by Rac1 (QL) and Cdc42Hs (QL) was
efficiently inhibited, whereas this dominant negative mutant had no
effect on the activation mediated by RhoA (QL) (Fig. 6B). These results suggest that Rac1 and Cdc42Hs, but not RhoA, activate the
transcription factor NF-
B through a MEKK1-dependent
cascade. A further conclusion from these results is that activation of MEKK1 by Rac1 and Cdc42Hs can be a common link between the JNK/SAPK pathway and the NF-
B pathway. Therefore, agonists that activate Rac1
or Cdc42Hs may simultaneously activate these two pathways through
MEKK1. On the other side, RhoA seems to follow an MEKK1-independent mechanism for the activation of NF-
B, and in keeping with this, it
does not activate the JNK/SAPK pathway in the COS-7 cells (Fig. 1B).
|
In summary, we have found that constitutively activated forms of Dbl,
Ost and Vav proteins, known exchange factors for Rho GTPases, induce
the transactivation of the NF-B-dependent HIV promoter.
We have investigated the in vivo specificity of these molecules for the different Rho GTPases and found that Dbl activates NF-
B in a Cdc42Hs-dependent manner while Vav seems to be
selective for Rac1. Finally, both RhoA and Cdc42Hs are required for the activation of NF-
B by Ost. We have also concluded that Rho and H-Ras
GTPases activate NF-
B by mutually independent cascades. We report
that the wild type form of MEKK1 induces the transactivation of the HIV
promoter in COS-7 cells. Activation of NF-
B by Rac1 and Cdc42Hs
GTPases, but not that of RhoA, can be efficiently blocked by a
kinase-defective mutant of MEKK1, indicating that Rac1 and Cdc42Hs
activate the transcription factor NF-
B by a MEKK1-dependent pathway while RhoA follows an
MEKK1-independent mechanism. Our study provides evidence for a
cross-talking between NF-
B and JNK/SAPK pathways in COS-7 cells
where specific members of the Rho family of GTPases are involved. All
these results can be summarized in the scheme shown in Fig.
7, where some of the signaling cascades
in which the Ras and Rho GTPases participate are depicted. The results
shown here open a new perspective in deciphering the relevance of Rho
proteins in the regulation of multiple signal transduction pathways
that control gene regulation and trigger diverse responses in mammalian
cells.
|
![]() |
FOOTNOTES |
---|
* This work was supported by Grants 96/2135 and 96/2136 from Fondo de Investigación Sanitaria (FIS) from Spanish Department of Health, Grant PB94-0009 from DGICYT, and Grant 07-114-96 from the Consejería de Educación of Comunidad de Madrid.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.
§ Fellow from Fundación Ramón Areces.
¶ To whom correspondence should be addressed: Instituto de Investigaciones Biomédicas, Arturo Duperier 4, 28029 Madrid, Spain. Tel.: 34-91-585-4607; Fax: 34-91-585-4606; E-mail: jclacal{at}iib.uam.es.
1
The abbreviations used are: JNK/SAPK, c-Jun
N-terminal kinase/stress-activated protein kinase; SRF, serum response
factor; TNF, tumor necrosis factor
; HIV, human immunodeficiency
virus; MEKK1, c-Jun N-terminal kinase kinase kinase; MEKK1 WT, MEKK1 wild-type.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() |
---|