Activin and activin receptors in a rat osteogenic-sarcoma cell-line, umr-106

We have localized immunocytochemically activin-A-like reactivity in UMR-106 osteogenic cells with a characterized, specific antiserum against synthetic fragment of subunits of activin-A, a member of transforming growth factor B (TGFB) superfamily. No staining was seen when the activin BA-subunit antisera were replaced by immunoneutralized sera, antiserum dilution buffer, or normal rabbit serum. Using in situ hybridization and the reverse transcription polymerase chain reaction (RT-PCR), we have observed the expression of the BA-subunit of activin and activin receptors II & IIB, DNA sequencing data show that the RT-PCR product corresponds to the predicted fragments of activin-A and activin receptors, respectively. In addition, exogenously administered activin inhibited cell growth in cultured UMR-106 cells. Our findings have shown that (a) activin-A was localized immunohistochemically to UMR-106 cells, (b) expression of activin-A and its receptors are detected by in situ hybridization and RT-PCR in UMR-106 cells, and (c) activin may have an inhibitory autocrine function in the proliferation of these cells.