title: Overexpression of MEKK3 confers resistance to apoptosis through activation of NFkappaB.
abstract: Many cancers have constitutively activated NFkappaB, the elevation of which contributes to cancer cell resistance to chemotherapeutic agent-induced apoptosis. Although mitogen-activated protein kinase/extracellular-regulated kinase kinase kinase-3 (MEKK3) has been shown to participate in the activation of NFkappaB, its relations to apoptosis and cancer are unclear. In this study, we established cell model systems to examine whether stable expression of MEKK3 could lead to increased NFkappaB activity and confer resistance to apoptosis. In addition, we investigated in breast and ovarian cancers whether MEKK3 expression may be altered and correlated with aberrant NFkappaB activity. We show that stable cell lines overexpressing MEKK3 not only had elevated levels of NFkappaB binding activity but also were more responsive to cytokine stimulation. These stable cells showed 2-4-fold higher basal expression of Bcl-2 and xIAP than the parental cells. Consistent with this increased expression of cell survival genes, MEKK3 stable cells showed reduced activation of caspases 3 and 8 and poly(ADP-ribose) polymerase cleavage and dramatically increased resistance to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand, doxorubicin, daunorubicin, camptothecin, and paclitaxel. Intriguingly, analysis of human breast and ovarian cancers showed that a significant fraction of these samples have elevated MEKK3 protein levels with corresponding increases in NFkappaB binding activities. Thus, our results established that elevated expression of MEKK3 appears to be a frequent occurrence in breast and ovarian cancers and that overexpression of MEKK3 in cells leads to increased NFkappaB activity and increased expression of cell survival factors and ultimately contributes to their resistance to apoptosis. As such, MEKK3 may serve as a therapeutic target to control cancer cell resistance to cytokine- or drug-induced apoptosis.
authors.affiliation: Department of Biochemistry and Molecular Biology, Program in Genes and Development, University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Ajoy K
authors.initials: AK
authors.lastname: Samanta
authors.forename: Helen J
authors.initials: HJ
authors.lastname: Huang
authors.forename: Robert C
authors.initials: RC
authors.lastname: Bast
authors.forename: Warren S-L
authors.initials: WS
authors.lastname: Liao
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins; D001943:Breast Neoplasms / Q000737:chemistry / Q000378:metabolism; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D002470:Cell Survival; D004351:Drug Resistance; D019008:Drug Resistance, Neoplasm; D004622:Embryo, Mammalian; D005260:Female; D015870:Gene Expression; D005910:Glioma; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D007668:Kidney; D008113:Liver Neoplasms; D008156:Luciferases / Q000235:genetics; D048748:MAP Kinase Kinase Kinase 3; D020930:MAP Kinase Kinase Kinases / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D008562:Membrane Glycoproteins / Q000494:pharmacology; D016328:NF-kappa B / Q000032:analysis / Q000502:physiology*; D010051:Ovarian Neoplasms / Q000737:chemistry / Q000378:metabolism; D011506:Proteins / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D011993:Recombinant Fusion Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; D014162:Transfection; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D051017:Apoptosis Regulatory Proteins; D007375:Interleukin-1; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D008156:Luciferases; D048748:MAP Kinase Kinase Kinase 3; D020930:MAP Kinase Kinase Kinases; C482625:MAP3K3 protein, human