INHIBIN ACTIVIN SUBUNITS AND ACTIVIN RECEPTOR ARE COEXPRESSED IN LEYDIG TUMOR-CELLS

The expression of genes encoding inhibin/activin subunits and activin receptor was examined in four cultured Leydig tumor cells (MA-10, I-10 , R2C, and LC-540). Inhibin a-subunit gene was highly expressed in Ley dig tumor cell lines except LC-540. Both inhibin beta-A- and beta-B-su bunit mRNAs were present in low levels. The 6.5-kb beta-A-subunit mRNA was detected in MA-10, R2C and LC-540 cells, and not in I-10 cells. T he expression of the two species of beta-B-subunit mRNA is cell specif ic. In MA-10 and I-10 cells, 4.4-kb beta-B-subunit mRNA was the predom inant species, while in R2C and LC-540 cells both 4.4-kb and 3.3-kb mR NA were present in equal quantities. By contrast, two species (6 and 3 kb) of activin receptor ActRII mRNA were identified in equal intensit y in all four Leydig tumor cell lines. Addition of cAMP derivative to MA-10 cells at 0.1 mM for 17 h or 1 mM for 5 h produced a two-fold inc rease in inhibin a-subunit mRNA levels, and small or no significant ch ange in inhibin beta-B-subunit and ActRII mRNAs. However, a 70-80% red uction in inhibin beta-A-subunit mRNA was observed by 1 mM cAMP for 5 h. We concluded that (1) the inhibin/activin subunit genes and activin receptor gene are co-expressed in Leydig tumor cell lines, and (2) th e three inhibin/activin subunit genes are expressed differently, while the activin receptor gene is expressed identically in the four cell l ines.