A functional role for mitochondrial protein kinase Calpha in Bcl2 phosphorylation and suppression of apoptosis.
Phosphorylation of Bcl2 at serine 70 may result from activation of a classic protein kinase C (PKC) isoform and is required for functional suppression of apoptosis by Bcl2 in murine growth factor-dependent cell lines (Ito, T., Deng, X., Carr, B., and May, W. S. (1997) J. Biol. Chem. 272, 11671-11673). Human pre-B REH cells express high levels of Bcl2 yet remain sensitive to the chemotherapeutic agents etoposide, cytosine arabinoside, and Adriamycin. In contrast, myeloid leukemia-derived HL60 cells express less than half the level of Bcl-2 but are >10-fold more resistant to apoptosis induced by these drugs. The mechanism responsible for this apparent dichotomy appears to involve a deficiency of mitochondrial PKCalpha since 1) HL60 but not REH cells contain highly phosphorylated Bcl2; 2) PKCalpha is the only classical isoform co-localized with Bcl2 in HL60 but not REH mitochondrial membranes; 3) the natural product and potent PKC activator bryostatin-1 induces mitochondrial localization of PKCalpha in association with Bcl2 phosphorylation and increased REH cell resistance to drug-induced apoptosis; 4) PKCalpha can directly phosphorylate wild-type but not phosphorylation-negative and loss of function S70A Bcl2 in vitro; 5) stable, forced expression of exogenous PKCalpha induces mitochondrial localization of PKCalpha, increased Bcl2 phosphorylation and a >10-fold increase in resistance to drug-induced cell death; and () PKCalpha-transduced cells remain highly sensitive to staurosporine, a potent PKC inhibitor. Furthermore, treatment of the PKCalpha transformants with bryostatin-1 leads to even higher levels of mitochondrial PKCalpha, Bcl2 phosphorylation, and REH cell survival following chemotherapy. While these findings strongly support a role for PKCalpha as a functional Bcl2 kinase that can enhance cell resistance to antileukemic chemotherapy, they do not exclude the possibility that another Bcl2 kinase(s) may also exist. Collectively, these findings identify a functional role for PKCalpha in Bcl2 phosphorylation and in resistance to chemotherapy and suggest a novel target for antileukemic strategies.
Ruvolo
P P
PP
Sealy Center for Oncology and Hematology and the Department of Internal Medicine, University of Texas Medical Branch, Galveston, Texas 77555, USA.
Deng
X
X
Carr
B K
BK
May
W S
WS
D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002460:Cell Line; D003561:Cytarabine / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051571:Protein Kinase C-alpha; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D019311:Staurosporine / Q000494:pharmacology; D014162:Transfection
D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D019253:Proto-Oncogene Proteins c-bcl-2; D003561:Cytarabine; D005047:Etoposide; D004317:Doxorubicin; C496628:PRKCA protein, human; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha; D019311:Staurosporine