Epithelial ovarian carcinomas are thought to arise from cells of ovarian surface epithelium (OSE) covering the free surface of the human ovary. Two immortalized human cell lines, OSE2a (non-tumorigenic) and OSE2b-2 (tumorigenic), were previously established from normal OSE cells of a reproductive-age patient. In the present study, we found that expression of luteinizing hormone (LH)/chorionic gonadotropin (CG) receptor (LH/CGR) is present in OSE2a cells and absent in OSE2b-2 cells. In OSE2a cells, a low concentration (10(3) mIU/ml) of CG enhanced anchorage-dependent growth via up-regulation of insulin-like growth factor-1 (IGF1), whereas a high concentration (10(5) mIU/ml) of CG induced anchorage-independent growth and down-regulation of IGF1 expression. To investigate involvement of other genes in LH/CGR-related tumorigenicity, we compared cDNA expression arrays of OSE2a and OSE2b-2 cells, and found that the following genes had lower expression in OSE2b-2 than in OSE2a: integrin beta 1, intercellular adhesion molecule-1 (ICAM1), and Waf1/Cip1. Subsequent semiquantitative reverse transcription polymerase chain reaction using OSE2a cells showed that expression of integrin beta 1 was down-regulated by a high concentration (10(5) mIU/ml) of CG. These results suggest that LH/CGR affects anchorage-dependent and -independent growth by mediating up- and down-regulation of IGF1 and integrin beta 1. Repetitive and excessive activation of LH/CGR may cause genetic alteration of its signal transduction pathway, resulting in stimulation of growth of OSE cells, initiation of ovarian carcinogenesis, and cancer progression.