Expression and modulation of protein kinase C isoforms in differentiation-competent and differentiation-resistant...

We have investigated eight of the protein kinase C (PKC) isoforms in Friend virus immortalized erythroleukemia cells. Using Western analysis, we detected the presence of the alpha, delta, epsilon, zeta and theta isoforms with no beta, gamma eta. We compared levels and modulations of these isoforms among 2 lines with different susceptibilities to DMSO-induced differentiation, a cell line rendered differentiation resistant by constitutive expression of an exogenous c-myb gene and cell lines naturally resistant to differentiation. These comparisons have shown that DMSO-induced differentiation is associated with downregulation of the delta, epsilon and theta isoforms. High levels of c-myb expression prevent the downregulation of epsilon, but not delta and theta, and also appear to have resulted in lower constitutive levels of PKC alpha. These results help define which isoforms are important and provide clues as to what point in the signal transduction pathway they may be acting relative to another element, c-myb.