NF-kappaB/RelA transactivation is required for atypical protein kinase C iota-mediated cell survival.
In chronic myelogenous leukemia (CML), the oncogene bcr-abl encodes a dysregulated tyrosine kinase that inhibits apoptosis. We showed previously that human erythroleukemia K562 cells are resistant to antineoplastic drug (taxol)-induced apoptosis through the atypical protein kinase C iota isozyme (PKC iota), a kinase downstream of Bcr-Abl. The mechanism(s) by which PKC iota mediates cell survival to taxol is unknown. Here we demonstrate that PKC iota requires the transcription factor nuclear factor-kappaB (NF-kappaB) to confer cell survival. At apoptosis-inducing concentrations, taxol weakly induces IkappaB(alpha) proteolysis and NF-kappaB translocation in K562 cells, but potently induces its transcriptional activity. Inhibition of NF-kappaB activity (by blocking IkappaB(alpha) degradation) significantly sensitizes cells to taxol-induced apoptosis. Likewise, K562 cells expressing antisense PKC iota mRNA or kinase dead PKC iota (PKC iota-KD) are sensitized to taxol; these cells are rescued from apoptosis by NF-kappaB overexpression. Expression of constitutively active PKC iota (PKC iota-CA) upregulates NF-kappaB transactivation and rescues cells from apoptosis in the absence of Bcr-Abl tyrosine kinase activity. Using a chimeric GAL4-RelA transactivator, we find that taxol potently activates GAL4-RelA-dependent transcription. This activation was further upregulated by expression of PKC iota-CA and inhibited by expression of PKC iota-KD. Our results indicate that RelA transactivation is an important downstream target of the PKC iota-mediated Bcr-Abl signaling pathway and is required for resistance to taxol-induced apoptosis.
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Department of Internal Medicine, University of Texas Medical Branch, 301 University Blvd., Galveston, Texas, TX 77555-1060, USA.
Jamieson
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Brasier
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D002470:Cell Survival; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D016044:Fusion Proteins, bcr-abl / Q000502:physiology; D006801:Humans; D051550:I-kappa B Kinase; D020672:I-kappa B Proteins; D007527:Isoenzymes / Q000502:physiology*; D020014:K562 Cells; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000502:physiology*; D017239:Paclitaxel / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D051996:Transcription Factor RelA; D015533:Transcriptional Activation; D000099293:Protein Kinase C-lambda
D004247:DNA; D004268:DNA-Binding Proteins; D016044:Fusion Proteins, bcr-abl; D051550:I-kappa B Kinase; D020672:I-kappa B Proteins; D007527:Isoenzymes; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B; D017239:Paclitaxel; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D051996:Transcription Factor RelA; D000099293:Protein Kinase C-lambda; C000606204:NFKBIA protein, human; C496559:CHUK protein, human; C496560:IKBKB protein, human; C496565:IKBKE protein, human