¹Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, Maryland, MD 20892, USA

²Department of Pharmacology, Columbia University, New York, NY 10032, USA

Correspondence to: Weiqun Li, Stem Cell Research Laboratory, Lombardi Cancer Center, Georgetown University Medical Center, 3970 Reservoir Road NW, NRB W309, Washington DC 20007, USA

^aCurrent address: Molecular and Clinical Hematology Branch, NIDDK

To investigate the role of protein kinase C (PKC) in apoptotic signaling induced by cytokine withdrawal, we expressed PKC-, - and - individually in the 32D myeloid progenitor cells. The parental and PKC-- and PKC-- transfected 32D cells underwent apoptosis within 24 h in the absence of interleukin 3. In contrast, expression of PKC- inhibited the onset of apoptosis as determined by genomic DNA fragmentation and flow cytometric analysis. Correlating with the inhibition of apoptosis, PKC- transfectants exhibited increased activity of the endogenous Akt serine/threonine kinase. Furthermore, PKC-, but not PKC- or -, specifically activated overexpressed Akt. PKC--induced Akt activity was partially dependent on phosphoinositol 3' kinase (PI 3'K) since a PI 3'K inhibitor was able to suppress PKC--induced Akt activation. Both basal and interleukin 3-stimulated phosphorylation of Akt on serine 473 was enhanced in the PKC- and Akt contransfectants. Coexpression of wild type Akt and PKC- resulted in greater suppression of apoptosis than PKC- expression alone. Together, our results demonstrate that suppression of apoptosis by PKC- correlates with its ability of activating endogenous Akt. Furthermore, activation of overexpressed Akt by PKC- is consistent with their synergistic effect on suppressing apoptosis, providing the strong evidence of cross talk between Akt and PKC-.

apoptosis; Akt/protein kinase B; protein kinase C-

FCS, fetal calf serum; [³H]TdR, [³H]thymidine; HA, hemagglutinin; IL-3, interleukin 3; PH, pleckstrin homology; PI, propidium iodide; PI 3'K, phosphoinositol 3' kinase; PKC, protein kinase C; SDS - PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TPA, 12-O-tetradecanoylphorbol-13-acetate; WT, wild type