Affiliations of authors: M. T. Furlong, C. D. Hough, C. A. Sherman-Baust, P. J. Morin, Laboratory of Biological Chemistry, Gerontology Research Center, National Institute on Aging, Baltimore, MD; E. S. Pizer, Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore.
Correspondence to: Patrice J. Morin, Ph.D., Laboratory of Biological Chemistry, Gerontology Research Center, National Institute on Aging, 5600 Nathan Shock Dr., Baltimore, MD 21224 (e-mail: morinp{at}grc.nia.nih.gov).
Cancer cell lines are an essential tool of cancer research, but their origin can sometimes be difficult to determine with certainty. In addition to contamination with other cell lines during in vitrocultivation, errors can arise during the initial resection from the patient because the organ of origin can sometimes be difficult to determine. This is particularly problematic for ovarian cancer, where a substantial fraction of the cases represent metastases from distant nongenital sites (1). Once in culture and without detailed patient data, it can be difficult or impossible to trace the origin of a particular cell population. The difficulty arises from the fact that cells tend to lose their tissue-specific markers during tumorigenesis and in vitro establishment.
In the course of our study of ß-catenin signaling in ovarian cancer, we discovered
several ovarian cancer lines that have constitutively elevated ß-catenin-mediated
transcription (Furlong MT, Morin PJ: unpublished results). Deregulation of this pathway results
in inappropriate activation of T-cell factor-responsive genes and, in colon cancer, is due to
mutations either in ß-catenin or in the tumor suppressor gene adenomatous polyposis coli
(APC) (2,3). Our finding of ovarian cell lines with an activated
ß-catenin/T-cell factor pathway is consistent with a recent report (4)
that ß-catenin is mutated in a subset of ovarian cancers. SW626, a well-studied ovarian
cancer cell line, showed high levels of ß-catenin-mediated transcriptional activation but
contained a wild-type ß-catenin gene, as assessed by direct sequencing. Surprisingly,
however, when a cell lysate of SW626 was probed by immunoblotting with an anti-APC
antibody, full-length APC was not detected (Fig. 1, A). Instead, SW626
expressed a truncated product of approximately 110 kd. The APC tumor suppressor gene is
mutated in the vast majority of all colon cancers (5) but has never been
found to be altered in ovarian cancer. Indeed, APC was previously analyzed in 40 sporadic
ovarian carcinomas, and no mutations were found (6).
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Because the above results suggested that SW626 may be of colonic origin, we decided to
investigate this issue further by using immunologic markers often used to differentiate ovarian
from colonic primary tumors. SW626 cells were stained with antibodies against cytokeratin (CK)
20, CK7, estrogen receptor/progesterone receptor, CA125, carcinoembryonic antigen, and
Calretinin. It has been reported that CK20 and CK7 are the best markers to differentiate colonic
from ovarian carcinoma (9,10). Typically, colonic carcinomas are
positive for CK20 and negative for CK7; in contrast, ovarian carcinomas are usually positive for
CK7 and negative for CK20. The staining pattern of SW626 was completely consistent with a
colonic origin because it was positive for CK20 and negative for CK7 (Table 1). These staining data were confirmed by examining the results of an ongoing serial
analysis of gene expression (11) in our laboratory. The CK20 transcript
was found at relatively high levels in SW626 (0.1% of the total messenger RNAs),
whereas the CK7 messenger RNA was not detected in more than 5000 transcripts. The other
markers shown in Table 1
are not as consistently reliable for
differentiating ovarian from colonic carcinomas but are still of interest. Estrogen
receptor/progesterone receptor, CA125, and Calretinin, which are sometimes positive in ovarian
cancer, were negative in SW626, and carcinoembryonic antigen, a marker that is positive in up to
50% of colon cancer specimens (10), was negative in SW626.
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Manuscript received December 28, 1998; revised May 14, 1999; accepted June 8, 1999.
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