Hypoxia-Inducible Factor 1α Determines Gastric Cancer Chemosensitivity via Modulation of p53 and NF-κB

Abstract

BackgroundReduced chemosensitivity of solid cancer cells represents a pivotal obstacle in clinical oncology. Hence, the molecular characterization of pathways regulating chemosensitivity is a central prerequisite to improve cancer therapy. The hypoxia-inducible factor HIF-1α has been linked to chemosensitivity while the underlying molecular mechanisms remain largely elusive. Therefore, we comprehensively analysed HIF-1α's role in determining chemosensitivity focussing on responsible molecular pathways.Methodology and Principal FindingsRNA interference was applied to inactivate HIF-1α or p53 in the human gastric cancer cell lines AGS and MKN28. The chemotherapeutic agents 5-fluorouracil and cisplatin were used and chemosensitivity was assessed by cell proliferation assays as well as determination of cell cycle distribution and apoptosis. Expression of p53 and p53 target proteins was analyzed by western blot. NF-κB activity was characterized by means of electrophoretic mobility shift assay. Inactivation of HIF-1α in gastric cancer cells resulted in robust elevation of chemosensitivity. Accordingly, HIF-1α-competent cells displayed a significant reduction of chemotherapy-induced senescence and apoptosis. Remarkably, this phenotype was completely absent in p53 mutant cells while inactivation of p53 per se did not affect chemosensitivity. HIF-1α markedly suppressed chemotherapy-induced activation of p53 and p21 as well as the retinoblastoma protein, eventually resulting in cell cycle arrest. Reduced formation of reactive oxygen species in HIF-1α-competent cells was identified as the molecular mechanism of HIF-1α-mediated inhibition of p53. Furthermore, loss of HIF-1α abrogated, in a p53-dependent manner, chemotherapy-induced DNA-binding of NF-κB and expression of anti-apoptotic NF-κB target genes. Accordingly, reconstitution of the NF-κB subunit p65 reversed the increased chemosensitivity of HIF-1α-deficient cells.Conclusion and SignificanceIn summary, we identified HIF-1α as a potent regulator of p53 and NF-κB activity under conditions of genotoxic stress. We conclude that p53 mutations in human tumors hold the potential to confound the efficacy of HIF-1-inhibitors in cancer therapy.

Hypoxia-induced chemoresistance in cancer cells: The role of not only HIF-1

“…82 ). Inhibition of the phosphoinositol-3-kinase (PI3K) pathway, nuclear factor kappa-B (NF-κB), cycloxygenase-2 (COX-2), activator protein-1 (AP-1), cjun, Pim-1, and STAT-3 can reverse resistance to cytostatics in hypoxia, implying a role for these pathways in hypoxia-induced drug resistance 10,18,22,23,33,77,83,84 . However, the degree in which they are dependent on functional HIF-1 is uncertain.…”

Up‐regulation of survivin by AKT and hypoxia‐inducible factor 1α contributes to cisplatin resistance in gastric cancer

“…The a-subunits, HIF-1a and HIF-2a, are degraded by the proteasome system in an oxygen-dependent manner [15]. HIF-1a has been reported to contribute to the chemoresistance of a wide range of solid tumors, including gastric cancer [16,17]. We reported that antisense HIF-1a therapy enhances the efficacy of doxorubicin in the treatment of hepatocellular carcinoma [18], and prevents acquired resistance to anti-angiogenic therapy in lymphomas [19].…”

The Role of Hypoxia-Inducible Factors in Cancer Resistance

“…The molecular nature of this phenomenon was mostly explained by HIF1α anti-apoptotic target gene-induction (Bak, Bax, Bcl-xL, Bcl-2, Bid, Mcl-1, NF-κB, p53 and survivin), but also by suppression of p53 activation in response to chemotherapeutic agents [71], as it can be seen in Figure 3. HIF2α was recently shown to act in a similar manner, namely suppressing p53 activation and apoptosis in response to radiation-induced DNA damage in clear cell kidney cancer cells [69].…”