PLC-GAMMA ACTIVATION IS REQUIRED FOR PDGF-BETA-R-MEDIATED MITOGENESISAND MONOCYTIC DIFFERENTIATION OF MYELOID PROGENITOR CELLS

To investigate the molecular mechanisms mediating hematopoietic cell d ifferentiation and mitogenesis by activation of the platelet-derived g rowth factor beta receptor (PDGF-beta R), the mild type PDGF-beta R (P DGF-beta RWT) and tyrosine to phenylalanine mutants of the PDGF-beta R , including F751, F966, F970, F1009, F1021 and F1009/F1021 were overex pressed in FDC-P2 myeloid progenitor cells by retroviral-mediated gene transfer. Stimulation of PDGF-beta RWT and F966, F970 and F1009 infec tants with PDGF-BB led to the increased expression of monocytic differ entiation markers, In contrast, activation of PDGF-beta R in the paren tal line or the F1021 or F1009/F1021 mutant infectants failed to induc e monocytic differentiation, PDGF-BB stimulation of PDGF-beta RWT, F75 1, F966, F970 and F1009 infectants led to pronounced DNA synthesis, wh ereas F1021 and F1009/F1021 infectants did not reveal any increase in mitogenesis when compared to that of the FDC-P2 line, While PDGF stimu lation of FDC-2 cells overexpressing PDGF-beta RWT led to a pronounced increase in inositol phosphate formation due to phospholipase C-gamma (PLC-gamma) activation, PDGF-BB induced phosphoinositol hydrolysis wa s completely abolished in the F1021 and F1009/F1021 infectants, GF 109 203X, a specific inhibitor of protein kinase C (PKC) activation, fully blocked PDGF-beta R-mediated monocytic differentiation and mitogenesi s, Taken together, these results suggest that stimulation of the PDGF- beta R signaling pathway can mediate monocytic differentiation when PD GF-beta R is expressed at sufficient levels and that activation of PLC -gamma and PKC plays a pivotal role in PDGF-beta R-mediated differenti ation and mitogenesis in FDC-P2 cell system.