Hypoxia-induced p53 modulates both apoptosis and radiosensitivity via AKT
Katarzyna B. Leszczynska, … , Francesca M. Buffa, Ester M. Hammond
Katarzyna B. Leszczynska, … , Francesca M. Buffa, Ester M. Hammond
Published May 11, 2015
Citation Information: J Clin Invest. 2015;125(6):2385-2398. https://doi.org/10.1172/JCI80402.
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Hypoxia-induced p53 modulates both apoptosis and radiosensitivity via AKT

Abstract

Restoration of hypoxia-induced apoptosis in tumors harboring p53 mutations has been proposed as a potential therapeutic strategy; however, the transcriptional targets that mediate hypoxia-induced p53-dependent apoptosis remain elusive. Here, we demonstrated that hypoxia-induced p53-dependent apoptosis is reliant on the DNA-binding and transactivation domains of p53 but not on the acetylation sites K120 and K164, which, in contrast, are essential for DNA damage–induced, p53-dependent apoptosis. Evaluation of hypoxia-induced transcripts in multiple cell lines identified a group of genes that are hypoxia-inducible proapoptotic targets of p53, including inositol polyphosphate-5-phosphatase (INPP5D), pleckstrin domain–containing A3 (PHLDA3), sulfatase 2 (SULF2), B cell translocation gene 2 (BTG2), cytoplasmic FMR1-interacting protein 2 (CYFIP2), and KN motif and ankyrin repeat domains 3 (KANK3). These targets were also regulated by p53 in human cancers, including breast, brain, colorectal, kidney, bladder, and melanoma cancers. Downregulation of these hypoxia-inducible targets associated with poor prognosis, suggesting that hypoxia-induced apoptosis contributes to p53-mediated tumor suppression and treatment response. Induction of p53 targets, PHLDA3, and a specific INPP5D transcript mediated apoptosis in response to hypoxia through AKT inhibition. Moreover, pharmacological inhibition of AKT led to apoptosis in the hypoxic regions of p53-deficient tumors and consequently increased radiosensitivity. Together, these results identify mediators of hypoxia-induced p53-dependent apoptosis and suggest AKT inhibition may improve radiotherapy response in p53-deficient tumors.

Authors

Katarzyna B. Leszczynska, Iosifina P. Foskolou, Aswin G. Abraham, Selvakumar Anbalagan, Céline Tellier, Syed Haider, Paul N. Span, Eric E. O’Neill, Francesca M. Buffa, Ester M. Hammond

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Figure 4

p53 targets PHLDA3 and INPP5D mediate apoptosis in hypoxia.

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p53 targets PHLDA3 and INPP5D mediate apoptosis in hypoxia. (A and B) Ap...
(A and B) Apoptosis detected morphologically or by Western blotting for PARP cleavage, respectively, in H1299 cells transfected with 5xHRE-PHLDA3 and exposed to 24 hours of hypoxia. The bar graph shows mean ± SEM (n = 3; 2-tailed Student’s t test [**P < 0.01]). For Western blotting, the lanes were run on the same gel but were noncontiguous. (C and D) Apoptosis detected morphologically or by Western blotting for cleaved PARP or caspase-3 (cl. Casp3) in RKO cells treated with nonspecific (Scr), PHLDA3, or p53 siRNA and exposed to 18 hours of hypoxia or normoxia. The bar graph shows mean ± SEM (n = 3, 2-way ANOVA test [P < 0.0001] followed by 2-tailed Student’s t test [***P < 0.01]). (E and F) Apoptosis detected in RKO cells treated with nonspecific, PHLDA3, INPP5D, or p53 siRNA as indicated and exposed to 14 hours of hypoxia or normoxia. The bar graphs show mean ± SEM (n = 3, 2-way ANOVA tests [P < 0.0001 for both graphs] followed by 2-tailed Student’s t test [**P < 0.01; ****P < 0.0001]). (G) Apoptosis detected morphologically in RKO cells treated with nonspecific, p53, or PHLDA3 siRNA and exposed to 14 hours of hypoxia or normoxia in the presence or absence of INPP5D/SHIP-1 inhibitor 3AC. The bar graph shows mean ± SEM (n = 3, 2-way ANOVA test [P < 0.0001] followed by 2-tailed Student’s t test [*P < 0.05; **P < 0.01]).