Actions and interactions of glucocorticoids and transforming growth factor beta on two related human myeloma cell lines

To evaluate possible involvement of a paracrine/ autocrine inhibitory growth fador in myeloma cell growth, we studied the expression and actions of two forms of transforming growth factor fi (TGF-$1 and TGF-�92) on two closely related myeloma cell lines, OPM-1 and OPM-2. Earlier studies showed that both cell lines contain glucocorticoid receptors, but only OPM-2 cells are growth inhibited by dexamethasone (Dex). We found that OPM-2 growth was inhibited by TGF-$, with TGF-$1 exerting a greater effect than TGFI�2, and Dex plus TGF-�91 acting synergistically. In OPM-1 (Dex insensitive), TGF-/3 mRNA was not expressed, whereas it was induced by Dex in OPM-2. It was also possible to block partially the growth inhibition of Dex in OPM-2 cells by the addition of anti-TGF-fl1 antibodies. These data suggest that the glucocorticoid effect(s) on myeloma cells may be mediated at least in part through modulation of internal and/or external levels of TGF-fl1.