Protein phosphatase 2A is a critical regulator of protein kinase C zeta signaling targeted by SV40 small t to promote cell growth and NF-kappaB activation.
We have reported that inhibition of protein phosphatase 2A (PP2A) by expression of SV40 small t stimulates the mitogenic MAP kinase cascade. Here, we show that SV40 small t can substitute for tumor necrosis factor-alpha (TNF-alpha) or serum and stimulate atypical protein kinase C zeta (PKC zeta) activity, resulting in MEK activation, cell proliferation and NF-kappaB-dependent gene transcriptional activation in CV-1 and NIH 3T3 cells. These effects were abrogated by co-expression of kinase-deficient PKC zeta and inhibition of phosphatidylinositol 3-kinase p85alpha-p110 by wortmannin, LY294002 and a dominant-negative mutant of p85alpha. In contrast, expression of kinase-inactive ERK2 inhibited small t-dependent cell growth but was unable to abolish small t-induced NF-kappaB transactivation. Our results provide the first in vivo evidence for a critical regulatory role of PP2A in bifunctional PKC zeta signaling pathways controlled by phosphatidylinositol 3-kinase. Constitutive activation of PKC zeta and NF-kappaB following inhibition of PP2A supports new mechanisms by which SV40 small t promotes cell growth and transformation. By establishing PP2A as a key player in the response of cells to growth factors and stress signals like TNF-alpha, our findings could explain why PP2A is a primary target utilized during SV40 infection to alter cellular behavior.
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Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX 75235, USA. esonta@mednet.swmed.edu
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D016475:3T3 Cells; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D000957:Antigens, Viral, Tumor / Q000378:metabolism*; D001769:Blood; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002455:Cell Division; D002460:Cell Line; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017930:Genes, Reporter; D008156:Luciferases / Q000378:metabolism; D048369:MAP Kinase Kinase 1; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases; D016328:NF-kappa B / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013539:Simian virus 40 / Q000276:immunology; D014162:Transfection; D000077191:Wortmannin; D000099221:Protein Kinase C zeta
D000730:Androstadienes; D000957:Antigens, Viral, Tumor; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D008156:Luciferases; D048369:MAP Kinase Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D016328:NF-kappa B; D019869:Phosphatidylinositol 3-Kinases; D010749:Phosphoprotein Phosphatases; D011493:Protein Kinase C; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011994:Recombinant Proteins; D000077191:Wortmannin; D000099221:Protein Kinase C zeta; C482127:Map2k1 protein, mouse