INTEGRIN ALPHA(5) IS EXPRESSED ON HUMAN LUTEINIZING GRANULOSA-CELLS DURING CORPUS-LUTEUM FORMATION, AND ITS EXPRESSION IS ENHANCED BY HUMANCHORIONIC-GONADOTROPIN IN-VITRO

We previously reported that human granulosa cells (GC) express integri n alpha(6) beta(1) in large follicles and early corpus luteum (CL). In this study, we examined the expression of integrin alpha(5) and fibro nectin (FN) by immunohistochemistry. Integrin alpha(5) was undetectabl e on human GC in preovulatory follicles, but it was intensely expresse d on luteinizing GC of CL in the early luteal phase, and it was weakly expressed on large luteal cells (LL) in the midluteal phase. FN was s imilarly expressed between GC/LL. Thus, integrin alpha(5) and FN were stage-specifically expressed on/between luteinizing GC in the early lu teal phase. Next we examined the effect of human chorionic gonadotroph in (HCG) on expression of integrin alpha 5 on luteinizing GC in vitro. GC obtained from preovulatory follicles were cultured for 3 days with out (control) or with HCG (1 IU/ml), and expression of integrin alpha( 5) was examined by flow cytometry. Although the positivity rate did no t differ, the mean relative fluorescence intensity was 3.4-fold higher in the HCG-treated group (n = 8, P < 0.01). These findings indicate t hat integrin as is rapidly expressed on GC during luteinization, proba bly under LH stimulation, and suggest that integrin alpha(5) is involv ed in CL formation via interaction with its ligand FN.