FIG. 8.

Dependence of the growth inhibition effect of Bα on functional TGF-β receptors. (A) The growth inhibition effect of Bα is TGF-β receptor dependent. R1B cells, an Mv1Lu derivative lacking functional TβRI, or DR26 cells, an Mv1Lu derivative lacking functional TβRII, were cotransfected with the pCal2 cyclin A-luciferase plasmid and pRK7 expression plasmids for Bα, TβRI/R4 (in R1B cells), or TβRII (in DR26 cells). Luciferase expression from the cyclin A promoter was measured in the absence (−) or presence (+) of TGF-β. (B) Dominant-negative inhibition of TβR1/R4 activity blocks growth inhibition by Bα. Mv1Lu cells were cotransfected with the pCal2 cyclin A-luciferase plasmid and pRK7 expression plasmids for Bα or a cytoplasmically truncated form of TβRI (DN R4) or both. Luciferase expression from the cyclin A promoter was measured in the absence or presence of TGF-β. Luciferase values, normalized for transfection efficiency, are presented relative to those of untreated, control transfected cells. Standard deviations were based on triplicate measurements.