Tumor suppressor effect of follistatin-like 1 in ovarian and endometrial carcinogenesis: a differential expression and functional analysis.

Endometrial and ovarian cancers are the most common and the most lethal gynecologic malignancies worldwide, respectively. By performing differential expression analysis using annealing control primer (TM)-based reverse transcription (RT)-polymerase chain reaction (PCR) on pooled complementary DNA (cDNA) from 45 endometrial and 36 ovarian cancers and their non-tumor samples, reduced expression of the follistatin-like 1 (FSTL1) was identified. Downregulation of FSTL1 was further confirmed on individual samples and cell lines by quantitative real-time RT-PCR and western blotting. For in vitro functional study, full-length cDNA of FSTL1 was cloned and transiently transfected into the ovarian cancer cell line Ovca420 and endometrial cancer cell line AN3CA. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and cell count demonstrated significantly slower proliferation rate. By terminal uridine deoxynucleotidyl transferase dUTP nick end labeling and flow cytometric analysis, higher apoptotic activity and a remarkable increase in sub-G(1) cell population were observed in transfected cells, suggesting that FSTL1 induced apoptosis in cancer cells. Subsequent messenger RNA and protein expression analysis on downstream apoptotic molecules revealed upregulation and/or activation of FAS, FASLG, TRADD, Caspase-3, Caspase-7 and PARP by FSTL1 transfection, suggesting that FSTL1-induced apoptosis may be initiated mainly by FAS/FASLG death receptor-ligand binding. Cell migration and invasion assays demonstrated a remarkably lower cell migration and invasion capability in FSTL1-transfected cells in relation to downregulation of matrix metallopeptidase-2. Our findings suggested that a tumor suppressor role of FSTL1 may be important in ovarian and endometrial carcinogenesis.