Specific Role for Protein Kinase C j3 in Cell Differentiation1

A critical role for protein kinase C (PKC) in signal transdudion 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 fundions. In human leukemia cell line HL-60, the adion of 1 ,25-dihydroxyvitamin D3 results in transcriptional up-regulation of PKC 3 (within 8-1 2 h) (1. M. Obeid et al., J. Biol. Chem., 265: 2370-2374, 1990). In this study, the role of PKC fi in the regulation of proliferation and differentiation was studied. 1 ,25-Dihydroxyvitamin D3 caused an increase in PKC I, lI, and, to a lesser extent, PKC a, as determined by Western blot analysis. This increase was accompanied by inhibition of proliferation and indudion of differentiation. The addition of a 25-base pair antisense oligonucleotide direded against the 5’ coding sequence of PKC 3 attenuated up-regulation of PKC 3l and 3ll levels in response to 1 ,25-dihydroxyvitamin D3. This antisense oligonucleotide, but not sense oligonucleotide or antisense oligonucleotide to PKC a, caused inhibition of 1 ,25-dihydroxyvitamin D3-induced differentiation by 2545%. On the other hand, inhibition of cell proliferation by 1,25-dihydroxyvitamin D3 was minimally affeded by the addition of antisense oligonucleotides. These results identify a role for PKC J in cell differentiation and underscore the significance of transcriptional adivation 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.