Human leukemia cell lines with comparable receptor binding characteristics but different phenotypic responses to...

Phorbol diester (PDE) tumor promoters have differing effects on normal and neoplastic hematopoietic cells in vitro. The effects of PDEs on cells are apparently mediated by specific cellular receptors for these ligands. The purpose of this study was to determine if the different phenotypic responses of cells of different human leukemia cell lines were due to differences in the PDE receptors in these cells. All cells of the different lines studied [HL-60 (promyelocytic), HL-60Bll (undifferentiated blastic), U-937 (monoblastic), H-SB2 (T-lymphoblastoid), and SB (B-lymphoblastoid) bound the [20-3H]phorbol-12,13-dibutyrate in a specific manner. The ligand bound to the cells rapidly, reaching a maximum by 10 to 20 min at 37 degrees or by 60 min at 4 degrees. The bound [20-3H]phorbol-12,13-dibutyrate could be fully dissociated from the cells by adding unlabeled phorbol-12,13-dibutyrate; the kinetics of this dissociation paralleled association kinetics. Scatchard analysis of the binding data, derived from experiments done at 4 degrees, revealed linear plots, indicating, most likely, that only single classes of receptors existed on all of these lines. The dissociation constants for binding were all comparable (46 to 152 nM), and the calculated numbers of binding sites were comparable (4.8 to 8.1 X 10(5)/cell). None of the cells could degrade [20-3H]phorbol-12-myristate-13-acetate or [20-3H]phorbol-12,13-dibutyrate as determined by thin-layer chromatographic analysis of cells or supernatants of the cell cultures. PDEs inhibited the proliferation of U-937 and HL-60 cells but not that of the HL-60Bll, SB, or H-SB2 cells. The incorporation of tritiated thymidine into HL-60 cells (but not HL-60Bll cells) was dramatically inhibited by various PDEs, and the potency in causing this inhibition paralleled that known for the potency of the phorbol analogues to cause tumor promotion in vivo or to elicit other in vitro responses from hematopoietic cells. [20-3H]Phorbol-12-myristate-13-acetate caused the HL-60 and U-937 cells to adhere to the plastic, spread, and develop vacuoles, but the other cells displayed no changes. These results suggest that the differing phenotypic responses to PDEs are most likely related to postreceptor factors.