Purpose: The purpose of this study was to examine ovarian cancer cells for the expression of decorin, a proteoglycan component of the cell matrix that can inhibit cancer cell growth.
Experimental design: Cultured ovarian cancer cells and surgically excised tumors were examined by immunohistochemistry and Western blot analysis for decorin expression. Reverse transcription-polymerase chain reaction analysis was used to analyze cultured cells for decorin transcripts.
Results: We detected decorin transcripts in two ovarian cancer cell lines by reverse transcription-polymerase chain reaction analysis. However, no decorin was found in conditioned culture medium from those cell lines. Cells treated with the proteasome inhibitor MG132 showed strong perinuclear staining with a decorin-specific monoclonal antibody by immunohistochemistry. Also, Western blot analysis showed the presence of a ladder of decorin-specific bands that were intensified by treatment with MG132, suggesting that de novo synthesized decorin was degraded by the ubiquitination pathway. The decorin component of tumor stroma was previously shown to contain high levels of chondroitin sulfate as opposed to dermatan sulfate side chains, and those molecules contained unusually high levels of O- and 6-sulfate linkages. We provided immunohistochemical evidence that these chondroitin sulfate side chains may have been produced by myofibroblasts.
Conclusions: Decorin protein expression was not detected in ovarian cancer cells. Decorin transcripts were produced and probably translated, but the protein was probably degraded by the ubiquitination pathway. We present evidence that stromal decorin of ovarian tumors was made by myofibroblasts. We also propose that decorin may be a tumor suppressor gene that is inactivated during epithelial cell development.