title: The increase in BIK expression following ERK1/2 pathway inhibition is a consequence of G₁ cell-cycle arrest and not a direct effect on BIK protein stability.
abstract: BIK (BCL2-interacting killer) is a pro-apoptotic BH3 (BCL2 homology domain 3)-only protein and a member of the BCL2 protein family. It was proposed recently that BIK abundance is controlled by ERK1/2 (extracellular-signal-regulated kinase 1/2)-catalysed phosphorylation, which targets the protein for proteasome-dependent destruction. In the present study, we examined ERK1/2-dependent regulation of BIK, drawing comparisons with BIM(EL) (BCL2-interacting mediator of cell death; extra long), a well-known target of ERK1/2. In many ERK1/2-dependent tumour cell lines, inhibition of BRAF(V600E) (v-raf murine sarcoma viral oncogene homologue B1, V600E mutation) or MEK1/2 (mitogen-activated protein kinase/ERK kinase 1/2) had very little effect on BIK expression, whereas BIM(EL) was strongly up-regulated. In some cell lines we observed a modest increase in BIK expression; however, this was not apparent until ~16 h or later, whereas BIM(EL) expression increased rapidly within a few hours. Although BIK was degraded by the proteasome, we found no evidence that this was regulated by ERK1/2 signalling. Rather, the delayed increase in BIK expression was prevented by actinomycin D, and was accompanied by increases in BIK mRNA. Finally, the delayed increase in BIK expression following ERK1/2 inhibition was phenocopied by a highly selective CDK4/6 (cyclin-dependent kinases 4 and 6) inhibitor, which caused a strong G₁ cell-cycle arrest without inhibiting ERK1/2 signalling. In contrast, BIM(EL) expression was induced by ERK1/2 inhibition, but not by CDK4/6 inhibition. We conclude that BIK expression is not subject to direct regulation by the ERK1/2 pathway; rather, we propose that BIK expression is cell-cycle-dependent and increases as a consequence of the G₁ cell-cycle arrest which results from inhibition of ERK1/2 signalling.
authors: *Signalling Programme, The Babraham Institute, Babraham Research Campus, Cambridge CB22 3AT, U.K.
authors: Matthew J
authors: MJ
authors: Sale
authors: *Signalling Programme, The Babraham Institute, Babraham Research Campus, Cambridge CB22 3AT, U.K.
authors: Simon J
authors: SJ
authors: Cook
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D051017:Apoptosis Regulatory Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D045744:Cell Line, Tumor; D051358:Cyclin-Dependent Kinase 4 / Q000037:antagonists & inhibitors / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6 / Q000037:antagonists & inhibitors / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048370:MAP Kinase Kinase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D024101:Mitochondrial Proteins; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D009369:Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D055550:Protein Stability / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; C096820:BIK protein, human; D000072224:Bcl-2-Like Protein 11; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D009363:Neoplasm Proteins; D061988:Proteasome Inhibitors; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; C482128:MAP2K2 protein, human; C495900:CDK4 protein, human; C495911:CDK6 protein, human; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D046988:Proteasome Endopeptidase Complex