Inhibin/ activin subunits and activin receptor are co-expressed 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 α-subunit gene was highly expressed in Leydig tumor cell lines except LC-540. Both inhibin /gb-A- and /gb-B-subunit mRNAs were present in low levels. The 6.5-kb β-A-subunit mRNA was detected in MA-10, R2C and LC-540 cells, and not in I-10 cells. The expression of the two species of /gb-B-subunit mRNA is cell specific. In MA-10 and I-10 cells, 4.4-kb /gb-B-subunit mRNA was the predominant species, while in R2C and LC-540 cells both 4.4-kb and 3.3-kb mRNA were present in equal quantities. By contrast, two species (6 and 3 kb) of activin receptor ActRII mRNA were identified in equal intensity 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 increase in inhibin α-subunit mRNA levels, and small or no significant change in inhibin /gb-B-subunit and ActRII mRNAs. However, a 70–80% reduction in inhibin β-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) the three inhibin/activin subunit genes are expressed differently, while the activin receptor gene is expressed identically in the four cell lines.