Protein kinase C-alpha isoform is involved in erythropoietin-induced erythroid differentiation of CD34(+) progenitor cells from human bone marrow

Protein kinase C (PKC) is a family of serine/threonine protein kinases invo lved in many cellular responses, Although the analysis of PKC activity in m any systems has provided crucial insights to its biologic function, the pre cise role of different isoforms on the differentiation of normal hematopoie tic progenitor cells into the various lineages remains to be investigated. The authors have assessed the state of activation and protein expression of PKC isoforms after cytokine stimulation of CD34(+) progenitor cells from h uman bone marrow. Freshly isolated CD34(+) cells were found to express PKC- alpha, PKC-beta 2, and PKC-epsilon, whereas PKC-delta, PKC-gamma, and PKC-z eta were not detected. Treatment with erythropoietin (EPO) or with EPO and stem cell factor (SCF) induced a predominantly erythroid differentiation of CD34(+) cells that was accompanied by the up-regulation of PKC-alpha and P KC-beta 2 protein levels (11.8- and 2.5-fold, respectively) compared with c ells cultured in medium. Stimulation with EPO also resulted in the nuclear translocation of PKC-alpha and PKC-beta 2 isoforms. Notably none of the PKC isoforms tested were detectable in CD34(+) cells induced to myeloid differ entiation by G-CSF and SCF stimulation. The PKC inhibitors staurosporine an d calphostin C prevented EPO-induced erythroid differentiation. Downregulat ion of the PKC-alpha, PKC-beta 2, and PKC-epsilon expression by TPA pretrea tment, or the down-regulation of PKC-alpha with a specific ribozyme, also i nhibited the EPO-induced erythroid differentiation of CD34(+) cells, No eff ect was seen with PKC-beta 2-specific ribozymes, Taken together, these find ings point to a novel role for the PKC-alpha isoform in mediating EPO-induc ed erythroid differentiation of the CD34(+) progenitor cells from human bon e marrow. (Blood.2000;95:510-518) (C) 2000 by The American Society of Hemat ology.