The role of nuclear protein kinase C in the proliferaton and differentiation of hematopoietic cells
Description
Protein kinase C (PKC) is a family of phospholipid-dependent protein kinases that play a central role in mediating the signal transduction events of growth, differentiation, multidrug resistance, and many other cellular processes. The nuclear localization of PKC may be a key factor in determining if PKC has a direct role in the control of gene transcription and the activation/deactivation of transcription factors. PKC is an important signaling molecule in the well-described hematopoietic cell system. Because the role of specific PKC isoforms and their localization have not been elucidated in this system, studies were designed to test the hypothesis that nuclear localization of specific PKC isoforms are critical for the proliferation and differentiation of hematopoietic cells. The stimulation of proliferation in a factor-dependent murine hematopoietic cell line (B6SUt.EP) by erythropoietin (EPO) and interleukin-3 (IL-3), two critical hematopoietic cytokines, was shown to be associated with the localization of PKC $\beta$ in the nucleus of these cells after 24 hours of stimulation. Both diacylglycerol (DAG), which directly stimulates PKC, and PKC $\beta$ were present in the nucleus of B6SUt.EP cells after 1 min of stimulation with EPO. Additionally, PKC $\beta$ in a growth factor-independent hematopoietic cell line, GM-86 Friend erythroleukemia cells, bound to exogenous chromatin and DNA, and was extracted from the chromatin of these cells. PKC $\alpha$, the predominant classical isoform in GM-86 cells, localized to the nucleus only when differentiation was induced with hexamethylene bisacetamide (HMBA), a putative chemotherapeutic drug that also decreases proliferation in these cells. With the same treatment, nuclear PKC $\beta$ levels declined in parallel with reduced proliferation, suggesting an association of localization of PKC $\alpha$ to the nucleus during differentiation and nuclear PKC $\beta$ with proliferation. When antisense PKC $\alpha$ was transfected into these cells, HMBA-induced differentiation was reduced as much as 50% compared to vector-only transfected cells. Taken together, these studies show that distinct PKC isoforms are localized to the nucleus during differentiation and proliferation of hematopoietic cells and that PKC $\beta$ may interact with DNA during this nuclear localization