title: Ras-related tumorigenesis is suppressed by BNIP3-mediated autophagy through inhibition of cell proliferation.
abstract: Autophagy plays diverse roles in Ras-related tumorigenesis. H-ras(val12) induces autophagy through multiple signaling pathways including Raf-1/ERK pathway, and various ERK downstream molecules of autophagy have been reported. In this study, Bcl-2/adenovirus E1B 19-kDa-interacting protein 3 (BNIP3) is identified as a downstream transducer of the Ras/Raf/ERK signaling pathway to induce autophagy. BNIP3 was upregulated by H-ras(val12) at the transcriptional level to compete with Beclin 1 for binding with Bcl-2. H-ras(val12)-induced autophagy suppresses cell proliferation demonstrated both in vitro and in vivo by expression of ectopic BNIP3, Atg5, or interference RNA of BNIP3 (siBNIP3) and Atg5 (shAtg5) using mouse NIH3T3 and embryo fibroblast cells. H-ras(val12) induces different autophagic responses depending on the duration of Ras overexpression. After a short time (48 hours) of Ras overexpression, autophagy inhibits cell proliferation. In contrast, a longer time (2 weeks) of Ras overexpression, cell proliferation was enhanced by autophagy. Furthermore, overexpression of mutant Ras, BNIP3, and LC3-II was detected in bladder cancer T24 cells and the tumor parts of 75% of bladder cancer specimens indicating a positive correlation between autophagy and tumorigenesis. Taken together, our mouse model demonstrates a balance between BNIP3-mediated autophagy and H-ras(val12)-induced tumor formation and reveals that H-ras(val12) induces autophagy in a BNIP3-dependent manner, and the threshold of autophagy plays a decisive role in H-ras(val12)-induced tumorigenesis. Our findings combined with others' reports suggest a new therapeutic strategy against Ras-related tumorigenesis by negative or positive regulation of autophagic activity, which is determined by the level of autophagy and tumor progression stages.
authors.affiliation: Institute of Basic Medical Sciences, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Shan-Ying
authors.initials: SY
authors.lastname: Wu
authors.forename: Sheng-Hui
authors.initials: SH
authors.lastname: Lan
authors.forename: Da-En
authors.initials: DE
authors.lastname: Cheng
authors.forename: Wei-Kai
authors.initials: WK
authors.lastname: Chen
authors.forename: Cheng-Huang
authors.initials: CH
authors.lastname: Shen
authors.forename: Ying-Ray
authors.initials: YR
authors.lastname: Lee
authors.forename: Roberto
authors.initials: R
authors.lastname: Zuchini
authors.forename: Hsiao-Sheng
authors.initials: HS
authors.lastname: Liu
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001343:Autophagy / Q000235:genetics*; D059447:Cell Cycle Checkpoints / Q000235:genetics; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D006801:Humans; D020935:MAP Kinase Signaling System; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D008869:Microtubule-Associated Proteins / Q000235:genetics; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D041681:NIH 3T3 Cells; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics* / Q000378:metabolism; D001749:Urinary Bladder Neoplasms / Q000235:genetics / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C090121:BNIP3 protein, human; C508686:BNip3 protein, mouse; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D024101:Mitochondrial Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras)