Biological activity of hβc mutants in BAF-B03 cells. (A) Factor-dependent and -independent proliferation of BAF-B03 cells infected with retroviruses encoding the indicated β subunits and subsequently superinfected with a retrovirus encoding the hGMR subunit. Proliferation assays were performed using triplicates of 5 × 103 cells in the presence of mIL-3 or hGM-CSF or in the absence of either factor, as indicated. The asterisk by A459D indicates that, in this case, the cells were not superinfected with the hGMR retrovirus. A459D(FI) represents a population of A459D-infected cells that were selected for factor-independent growth before analysis. For comparison, assays of uninfected BAF-B03 cells and cells infected with the hGMR virus alone are shown. (B) Flow cytometric analysis of hβc and hGMR expression on the BAF-B03 cells used in (A). In each case, the cells infected with the indicated β subunits were stained with an irrelevant control antibody (dashed line), an anti-hβc antibody (thin solid line), and an anti-hGMR antibody (thick solid line) by standard indirect immunofluorescence. Axes are as for Fig2B.
