SPECIFIC ROLE FOR PROTEIN-KINASE-C-BETA IN CELL-DIFFERENTIATION

A critical role for protein kinase C (PKC) in signal transduction even ts has been well established. On the other hand, emerging evidence als o 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 D-3 results in transcriptional up-regulation of P KC beta (within 8-12 h) (L. M. Obeid et al., J. Biol. Chem., 265: 2370 -2374, 1990). In this study, the role of PKC beta in the regulation of proliferation and differentiation was studied. 1,25-Dihydroxyvitamin D-3 caused an increase in PKC beta I, beta II, and, to a lesser extent , PKC alpha, as determined by Western blot analysis. This increase was accompanied by inhibition of proliferation and induction of different iation. The addition of a 25-base pair antisense oligonucleotide direc ted against the 5' coding sequence of PKC beta attenuated up-regulatio n of PKC beta I and beta II levels in response to 1,25-dihydroxyvitami n D-3. This antisense oligonucleotide, but not sense oligonucleotide o r antisense oligonucleotide to PKC alpha, caused inhibition of 1,25-di hydroxyvitamin D-3-induced differentiation by 25-45%. On the other han d, inhibition of cell proliferation by 1,25-dihydroxyvitamin D-3 was m inimally affected by the addition of antisense oligonucleotides. These results identify a role for PKC beta in cell differentiation and unde rscore the significance of transcriptional activation of PKC as a mech anism for long-term regulation of PKC. The results also distinguish si gnaling pathways involved in cell differentiation from those involved in antiproliferation.