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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.

Original publication

DOI

10.1007/s11033-012-1975-3

Type

Journal article

Journal

Mol Biol Rep

Publication Date

12/2012

Volume

39

Pages

10811 - 10822

Keywords

Activating Transcription Factor 4, Apoptosis Regulatory Proteins, Autophagy, Breast Neoplasms, Cell Hypoxia, Cell Line, Tumor, Cell Survival, Female, Gene Expression Regulation, Neoplastic, Gene Knockdown Techniques, Genes, Neoplasm, Humans, Oligonucleotide Array Sequence Analysis, Promoter Regions, Genetic, Protein Binding, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-bcl-2, Stress, Physiological