title: ATF4 orchestrates a program of BH3-only protein expression in severe hypoxia.
abstract: Intratumoral hypoxia is associated with poor prognosis, regardless of the mode of therapy. Cancer cells survive this condition through activating several adaptive signaling pathways, including the integrated stress response (ISR) and autophagy. Activating transcription factor 4 (ATF4) is the major transcriptional mediator of the ISR, which we have shown to be involved in autophagy regulation to protect cells from severe hypoxia. Here we demonstrate that ATF4 orchestrates a program of BH3-only protein expression in severe hypoxia. We find that the BH3-only proteins HRK, PUMA, and NOXA are transcriptionally induced in severe hypoxia and that their expression is abrogated by RNA interference against ATF4. In particular, we show that the BH3-only protein harakiri (HRK) is transactivated by ATF4 in severe hypoxia through direct binding of ATF4 to the promoter region. Furthermore, we demonstrate through siRNA knockdown that HRK induces autophagy and promotes cancer cell survival in severe hypoxia.
authors.affiliation: Growth Factor Group, Cancer Research UK, Molecular Oncology Laboratories, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Headington, Oxford, OX3 9DS, UK. lrgpike@gmail.com
authors.forename: Luke R G
authors.initials: LR
authors.lastname: Pike
authors.forename: Kanchan
authors.initials: K
authors.lastname: Phadwal
authors.forename: Anna Katharina
authors.initials: AK
authors.lastname: Simon
authors.forename: Adrian L
authors.initials: AL
authors.lastname: Harris
mesh_terms: D051701:Activating Transcription Factor 4 / Q000378:metabolism*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001343:Autophagy; D001943:Breast Neoplasms / Q000235:genetics / Q000473:pathology; D015687:Cell Hypoxia / Q000235:genetics; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D052138:Genes, Neoplasm / Q000235:genetics; D006801:Humans; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological / Q000235:genetics
chemical_list: C497109:ATF4 protein, human; D051017:Apoptosis Regulatory Proteins; C438378:BBC3 protein, human; C484586:HRK protein, human; C498702:PMAIP1 protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051701:Activating Transcription Factor 4