STIMULATION OF THE PLATELET-DERIVED GROWTH-FACTOR-BETA RECEPTOR SIGNALING PATHWAY ACTIVATES PROTEIN-KINASE C-DELTA

The murine myeloid progenitor cell line 32D was recently shown to unde rgo monocytic differentiation when protein kinase C-delta (PKC-delta) was overexpressed and activated by 12-O-tetradecanoylphqrbol-13-acetat e (TPA) (H. Mischak, J. Il. Pierce, J. Goodnight, M; G. Kazanietz, P. M. Blumberg, and J. F. Mushinski, J. Biol. Chem. 268:20110-20115, 1993 ). Tyrosine phosphorylation of PKC-delta occurred when PKC-delta-trans fected 32D cells were stimulated by TPA (W. Li, H. Mischak, J.-C. Yu, L.-M. Wang, J. F; Mushinski, M. A. Heidaran, and J. H. Pierce, J. Biol . Chem. 269:2349-2352, 1994). In order to elucidate the role played by PKC-delta in response to activation of a receptor tyrosine kinase, we transfected platelet-derived growth factor beta receptor (PDGF-beta R ) alone (32D/PDGF-beta R) or together with PKC-delta (32D/PDGF-beta R/ PKC-delta) into 32D cells. NIH 3T3 cells which endogenously express bo th PDGF-alpha R and PDGF-beta R were also transfected with PKC-delta ( NIH 3T3/PKC-delta). Like TPA treatment, PDGF-BB stimulation caused str iking phosphorylation of PKC-delta in vivo and translocation of some P KC-delta from the cytosol fraction to the membrane fraction in both ce ll systems. Some of the phosphorylation induced by PDGF-BB treatment w as found to be on a tyrosine residue(s). Tyrosine-phosphorylated PKC-d elta was observed only for the membrane fraction after stimulation wit h PDGF-BB or TPA. The enzymatic activity of PKC-delta in the membrane fraction also increased after stimulation with TPA or PDGF, providing a positive correlation between PKC-delta tyrosine phosphorylation and its activation. Overnight treatment Of 32D/PDGF-beta R/PKC-delta cells with PDGF-BB induced monocytic differentiation as judged by an increa se in expression of cell surface microphage differentiation markers. P DGF-BB had much weaker effects on 32D/PDGF-beta R cell differentiation , suggesting that increased PKC-delta expression enhanced monocytic di fferentiation. These results indicate that PKC-delta is a downstream m olecule in the PDGFR signaling pathway and may play a pivotal role in PDGF-beta R-mediated cell differentiation.