The antiapoptotic protein, FLIP, is regulated by heterogeneous nuclear ribonucleoprotein K and correlates with poor overall survival of nasopharyngeal carcinoma patients.
Heterogeneous nuclear ribonucleoprotein K (hnRNP K) mediates antiapoptotic activity in part by inducing downstream antiapoptotic genes. To systematically identify hnRNP K targets in nasopharyngeal carcinoma (NPC), affymetrix chips were used to identify genes that were both overexpressed in primary NPC and downregulated by hnRNP K knockdown in NPC-TW02 cells. The resulting gene set included the antiapoptotic gene, FLIP, which was selected for further study. In cells treated with hnRNP K siRNA, TRAIL-induced apoptosis was enhanced and the FLIP protein level was reduced. Promoter, DNA pull-down and chromatin-immunoprecipitation assays revealed that hnRNP K directly interacts with the poly(C) element on the FLIP promoter, resulting in transcriptional activation. Through iTRAQ-mass spectrometric identification of proteins differentially associated with the poly(C) element or its mutant, nucleolin was determined to be a cofactor of hnRNP K for FLIP activation. Furthermore, FLIP was highly expressed in tumor cells, and this high-level expression was significantly correlated with high-level hnRNP K expression (P=0.002) and poor overall survival (P=0.015) as examined in 67 NPC tissues. A multivariate analysis confirmed that FLIP was an independent prognostic factor for NPC. Taken together, these findings indicate that FLIP expression is transcriptionally regulated by hnRNP K and nucleolin, and may be a potential prognostic and therapeutic marker for NPC.
Chang Gung Molecular Medicine Research Center, Chang Gung University, Taoyuan, Taiwan.
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Chen
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Chung
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Hsueh
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Tsang
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Chi
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Liang
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Chen
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LJ
Wang
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Chang
D000328:Adult; D000368:Aged; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001665:Binding Sites / Q000235:genetics; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics / Q000378:metabolism*; D002277:Carcinoma; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D015870:Gene Expression / Q000235:genetics; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000175:diagnosis / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D011379:Prognosis; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000502:physiology; D034741:RNA, Small Interfering / Q000235:genetics; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology; D050656:Transcription Factor AP-2 / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000235:genetics; D000097796:Nucleolin
D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D010750:Phosphoproteins; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D053221:TNF-Related Apoptosis-Inducing Ligand; D050656:Transcription Factor AP-2; D000097796:Nucleolin; C505653:TNFSF10 protein, human; C072074:HNRNPK protein, human