PROTEIN-KINASE C-EPSILON IS NECESSARY FOR ERYTHROPOIETINS UP-REGULATION OF C-MYC AND FOR FACTOR-DEPENDENT DNA-SYNTHESIS - EVIDENCE FOR DISCRETE SIGNALS FOR GROWTH AND DIFFERENTIATION

Erythropoietin regulates the transcription of the protooncogenes c-myc and c-myb by discrete protein kinase C (PKC)-dependent and protein se rine/threonine phosphatase-dependent pathways, respectively (Spangler, R., Bailey, S. C., and Sytkowski, A. J. (1991) J. Biol. Chem. 266, 68 1-684; Patel H. R. Choi H.-S, and Sytkowski A. J. (1992) J. Biol. Chem . 267, 21300-21302), In the present study we demonstrate that up-regul ation of c-myc requires the PKC-epsilon isoform and that this pathway is required for erythropoietin-induced DNA synthesis (growth) but appa rently not for beta-globin expression (differentiation), Treatment of Rauscher murine erythroleukemia cells resulted in phosphorylation of p hospholipase C-gamma 1 and activation of PKC-epsilon as evidenced by i ts translocation from soluble to particulate subcellular fractions, Ar tificial down-regulation of PKC-epsilon with anti-sense oligodeoxynucl eotides blocked erythropoietin's up-regulation of c-myc in a concentra tion-dependent manner, In contrast, antisense oligodeoxynucleotides to PKC-alpha, -beta, -gamma, -delta, and -zeta had no effect, Although d own-regulation of PKC-epsilon blocked the increase in c-myc expression , it did not inhibit erythropoietin induction of beta-globin expressio n, a marker of erythroid differentiation, However, down-regulation of PKC-epsilon did block factor-dependent DNA synthesis quantified by mea surement of [H-3]thymidine incorporation into newly synthesized DNA of normal murine erythroid cells, The results are consistent with discre te intracellular signals regulating erythroid cell growth and differen tiation.