Protein kinase C-a isoform is involved in erythropoietin-induced erythroid differentiation of CD341 progenitor cells from human bone marrow

Protein kinase C (PKC) is a family of serine/threonine protein kinases involved in many cellular responses. Although the analysis of PKC activity in many systems has provided crucial insights to its biologic function, the precise role of different isoforms on the differentiation of normal hematopoietic 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 CD341 progenitor cells from human bone marrow. Freshly isolated CD341 cells were found to express PKC-a, PKC-b2, and PKC-e, whereas PKC-d, PKC-g, and PKC-z were not detected. Treatment with erythropoietin (EPO) or with EPO and stem cell factor (SCF) induced a predominantly erythroid differentiation of CD341 cells that was accompanied by the up-regulation of PKC-a and PKC-b2 protein levels (11.8and 2.5-fold, respectively) compared with cells cultured in medium. Stimulation with EPO also resulted in the nuclear translocation of PKC-a and PKC-b2 isoforms. Notably, none of the PKC isoforms tested were detectable in CD341 cells induced to myeloid differentiation by G-CSF and SCF stimulation. The PKC inhibitors staurosporine and calphostin C prevented EPOinduced erythroid differentiation. Downregulation of the PKC-a, PKC-b2, and PKC-e expression by TPA pretreatment, or the down-regulation of PKC-a with a specific ribozyme, also inhibited the EPOinduced erythroid differentiation of CD341 cells. No effect was seen with PKC-b2– specific ribozymes. Taken together, these findings point to a novel role for the PKC-a isoform in mediating EPO-induced erythroid differentiation of the CD341 progenitor cells from human bone marrow. (Blood. 2000;95:510-518)