Activation of β-isozyme of protein kinase C (PKCβ) is necessary and sufficient for phorbol ester-induced differentiation of HL-60 promyelocytes: Studies with PKCβ-defective pet mutant

12-O-Tetradecanoylphorbol-13-acetate (TPA) induces growth arrest and differentiation of a number of leukemia cell lines including HL-60 human promyelocytic leukemia. We investigated the involvement of protein kinase C (PKC) isotypes in phorbol ester-induced differentiation using the phorbol ester-tolerant PET mutant of HL-60 cells, which (in contrast to the parent phorbol ester-sensitive (wild-type) S variant of HL-60 cells) does not growth-arrest, become adherent, or undergo apoptosis when exposed to TPA (Macfarlane, D. E., Gailani, D., and Vann, K. (1988) Br. J. Haematol. 68, 291-302). In comparison to S cells, we found that proliferating PET cells markedly underexpress mRNA for PKCβ, but do express PKCα and PKCδ. The PKCβ-selective activator 12-deoxyphorbol 13-phenylacetate 20-acetate induces growth arrest, adherence, surface expression of CD11a, and apoptosis in S cells, but not in PET cells. Expression of PKCβ in PET cells can be restored by exposing them to dihydroxyvitamin D3, and this treatment restores the ability of subsequently added 12-deoxyphorbol 13-phenylacetate 20-acetate or TPA to induce immediate cell adherence and growth arrest of PET cells. These data led us to conclude that activation of PKCβ is both necessary and sufficient for phorbol ester-induced growth arrest and adherence in these myeloid cells.