Erythropoietin stimulates nuclear localization of diacylglycerol and protein kinase C βII in B6SUt.EP cells

Abstract

Erythropoietin (EPO) is a hormone, as well as a hematopoietic growth factor, that specifically regulates the proliferation and differentiation of erythroid progenitor cells. Although the membrane-bound receptor for EPO has no intrinsic kinase activity, it triggers the activation of protein kinases via phospholipases A₂, C, and D. A cascade of serine and threonine kinases, including Raf-1, MAP kinase and protein kinase C (PKC) is activated following tyrosine phosphorylation. In this study, we have examined whether changes in nuclear PKC and 1,2-diacylglycerol (DAG) are induced following EPO treatment of the murine target cell line, B6SUt.EP. Western blot analysis using isoform-specific antibodies demonstrated the presence of PKCβII, but not PKC α, βI, γ, ε, δ, η, or ζ in the nuclei of cells stimulated with EPO. The increase in nuclear βII levels was accompanied by an immediate rise in DAG mass levels with both of the increases peaking by 1 min. These rapid increases in nuclear DAG and PKCβII expression suggest a mechanism for EPO-induced changes in gene expression necessary for cell proliferation.