Carcinogenesis Advance Access published online on October 8, 2008
Carcinogenesis, doi:10.1093/carcin/bgn231
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Impaired DNA double-strand break repair contributes to chemoresistance in HIF-1
-deficient mouse embryonic fibroblasts
Institute of Physiology and Zürich Center for Integrative Human Physiology ZIHP, University of Zürich, CH-8057 Zürich, Switzerland
Correspondence: Roland H. Wenger, Institute of Physiology, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland. Phone: +41 (0)44 6355065, Fax: +41 (0)44 6356814, E-mail: roland.wenger{at}access.uzh.ch
A mismatch between metabolic demand and oxygen delivery leads to microenvironmental changes in solid tumors. The resulting tumor hypoxia is associated with malignant progression, therapy resistance and poor prognosis. However, the molecular mechanisms underlying therapy resistance in hypoxic tumors are not fully understood. The hypoxia-inducible factor (HIF) is a master transcriptional activator of oxygen-regulated gene expression. Transformed mouse embryonic fibroblasts (MEFs) derived from HIF-1
-deficient mice are a popular model to study HIF function in tumor progression. We previously found increased chemotherapy and irradiation susceptibility in the absence of HIF-1. Here, we show by single-cell electrophoresis, histone 2AX phosphorylation and nuclear foci formation of 
H2AX and 53BP1, that the number of DNA double-strand breaks (DSB) is increased in untreated and etoposide-treated HIF-deficient MEFs. In etoposide-treated cells, cell cycle control and p53-dependent gene expression were not affected by the absence of HIF-1. Using a candidate gene approach to screen 17 genes involved in DNA repair, mRNA and protein of three members of the DNA-dependent protein kinase (DNA-PK) complex were found to be decreased in HIF-deficient MEFs. Of note, residual HIF-1 protein in cancer cells with a partial HIF-1 mRNA knock-down was sufficient to confer chemoresistance. In summary, these data establish a novel molecular link between HIF and DNA-DSB repair. We suggest that selection of early, non-hypoxic tumor cells expressing low levels of HIF-1 might contribute to HIF-dependent tumor therapy resistance.
Received June 17, 2008; revised September 24, 2008; accepted September 28, 2008.
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  S. Lehmann, D. P. Stiehl, M. Honer, M. Dominietto, R. Keist, I. Kotevic, K. Wollenick, S. Ametamey, R. H. Wenger, and M. Rudin Longitudinal and multimodal in vivo imaging of tumor hypoxia and its downstream molecular events PNAS, August 18, 2009; 106(33): 14004 - 14009. [Abstract] [Full Text] [PDF]
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