Specific role for protein kinase C β in cell differentiation

A critical role for protein kinase C (PKC) in signal transduction events has been well established. On the other hand, emerging evidence also suggests a role for regulation of PKC levels in mediating long term cellular functions. In human leukemia cell line HL-60, the action of 1,25- dihydroxyvitamin D₃ results in transcriptional up-regulation of PKC β (within 8-12 h) (L. M. Obeid et al., J. Biol. Chem., 265: 2370-2374, 1990). In this study, the role of PKC β in the regulation of proliferation and differentiation was studied. 1,25-Dihydroxyvitamin D₃ caused an increase in PKC βI, βII, and, to a lesser extent, PKC α, as determined by Western blot analysis. This increase was accompanied by inhibition of proliferation and induction of differentiation. The addition of a 25-base pair antisense oligonucleotide directed against the 5' coding sequence of PKC β attenuated up-regulation of PKC βI and βII levels in response to 1,25-dihydroxyvitamin D₃. This antisense oligonucleotide, but not sense oligonucleotide or antisense oligonucleotide to PKC α, caused inhibition of 1,25- dihydroxyvitamin D₃-induced differentiation by 25-45%. On the other hand, inhibition of cell proliferation by 1,25-dihydroxyvitamin D₃ was minimally affected by the addition of antisense oligonucleotides. These results identify a role for PKC β in cell differentiation and underscore the significance of transcriptional activation of PKC as a mechanism for long- term regulation of PKC. The results also distinguish signaling pathways involved in cell differentiation from those involved in antiproliferation.