Inhibitory role of prohibitin in human ovarian epithelial cancer

To characterize the exact individual roles of gonadotropins on ovarian epithelial carcinogenesis, an earlier study showed that prohibitin was significantly up-regulated by luteinizing hormone (LH). To further clarify the role of prohibitin in ovarian carcinogenesis and its association with LH, herein we studied the expression of prohibitin in various ovarian tissues including different developmental stages of ovarian epithelial tumors.

A total of 135 samples were studied by immunohistochemistry. These included benign ovarian cases with follicles, ovarian surface epithelia and ovarian epithelial inclusions (OEI) (n=30), serous cystadenoma (n=14), serous borderline tumor (n=12), serous carcinoma (n=20), mucinous cystadenoma (n=10), mucinous borderline tumor (n=10), mucinous carcinomas (n=10), endometrioid carcinomas (n=12), poorly/undifferentiated carcinomas (n=5), and fallopian tube (n=12).

Strong and diffuse staining of prohibitin was detected in luteinized ovarian stromal cells, follicular cells, fallopian tube, and OEI with serous differentiation. A significantly higher prohibitin expression in luteinized stromal cells than in non-luteinized stromal cells was observed (P<.01). Within the ovarian epithelium, the level of prohibitin expression was basically negative in ovarian surface epithelia, but highly expressed in OEI. However, compared to the level of prohibitin expression in OEI, it showed a trend of gradual loss from benign ovarian tumors, to borderline tumors and to carcinomas (P<.0001). Compared to the serous tumors, epithelial tumors with mucinous differentiation showed a significant lower level of prohibitin (P<.0001). An inverse correlation was noted between prohibitin expression and cancer grade. It is interesting to note that a high prohibitin expression level was seen in the fallopian tube, which is similar to OEI.

These data further suggest that prohibitin plays a tumor suppressing role, which is probably associated with LH mediated protection role against ovarian epithelial carcinoma. In addition to the tumor suppressive role of prohibitin, it also plays a role in cellular differentiation, which may be helpful to differentiate ovarian mucinous tumors from the tumors with serous differentiation in clinical settings. More importantly, our findings are supportive that the ovarian epithelial cancers, particularly the serous cancers including those precursors with serous differentiation are likely to be derived from fallopian tube instead of ovarian surface epithelia.