Hypoxia prevents etoposide-induced DNA damage in cancer cells through a mechanism involving hypoxia-inducible factor 1

Abstract

Intratumoral hypoxia is associated with resistance to therapy in many human cancers, and preexposure of tumor cells to hypoxia confers multidrug resistance. Whereas most anticancer drugs kill proliferating tumor cells by causing DNA damage, a role for hypoxia in the prevention and/or repair of drug-induced DNA damage has not been clear. Using the alkaline comet assay, we provide direct evidence that hypoxia-induced resistance to etoposide in human tumor cells (MDA-MB-231 breast carcinoma and DU-145 prostatic adenocarcinoma) is mainly due to prevention of drug-induced DNA damage (i.e., strand breaks) and that the amount of DNA damage present immediately after etoposide exposure is a good independent predictor of clonogenic survival. Our results also revealed that preexposure to hypoxia did not affect the apparent DNA repair capacity of cells. These findings indicate that the extent of DNA damage resulting from etoposide exposure is a more important determinant of survival than subsequent events after DNA damage. Furthermore, immunofluorescence analysis showed that, in a subpopulation of cells, preexposure to hypoxia decreased the levels of topoisomerase IIα, an enzyme that generates DNA strand breaks when poisoned with etoposide. Treatment of cells with small interfering RNA targeting hypoxia-inducible factor 1 prevented the hypoxia-induced decreases in topoisomerase IIα levels, abolished the protective effect of hypoxia against etoposide-induced DNA damage, and inhibited hypoxia-induced etoposide resistance. These findings support a model of hypoxia-induced drug resistance in which etoposide-induced DNA damage is prevented by HIF-1-dependent adaptations to hypoxia.

Jumonji domain-containing protein 2B silencing induces DNA damage response via STAT3 pathway in colorectal cancer

“…Our data suggest that HIF-1 α knockdown induced the DDR in cells exposed to 1% hypoxia for 24 h, accompanied by JMJD2B downregulation; furthermore, this change coincided with the suppression of JMJD2B (Figure 2A). It has also been reported that HIF-1 could restrain etoposide-induced DNA damage in hypoxia (Sullivan and Graham, 2009). Thus, it is very likely that HIF-1 α may partially regulate the DDR through JMJD2B.…”

Hypoxia-inducible factors: mediators of cancer progression and targets for cancer therapy

“…Third, HIF-1 inhibits expression of pro-apoptotic mitochondrial proteins ( BAX, BID ) and caspases ( CASP3, CASP8, CASP10 ) and induces expression of anti-apoptotic proteins ( BCL2 , BIRC5 ) [80–84]. Fourth, HIF-1 prevents chemotherapy-induced DNA damage by inhibiting the expression of topoisomerase IIα protein [85] or the DNA-dependent protein kinase complex [86]. Fifth, HIF-1-dependent metabolic reprogramming [16, 17, 30, 44, 45, 87, 88] may decrease ROS levels and thereby inhibit chemotherapy-induced cell death [89].…”

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

“…Many of these HIF-1 inducible genes such as VEGF, Glut-1, MDR, and Bcl-2 directly or indirectly mediate chemoresistance 19 .Therefore, in a wide range of different tumor types, e.g. hepatocellular carcinoma, neuroblastoma, and lung cancer, inhibition of HIF-1α resensitizes cells to drug treatment in hypoxia and is then a valid target to reverse hypoxia-induced drug resistance 8,9,15,19,21,25,[27][28][29][30]56 . HIF-1α accumulation has been associated with shorter survival in patients with early stage cervical, breast, ovarian, endometrial, oropharyngeal squamous cell carcinoma, and oligodendroglioma.…”

“…In this context, the most studied transcription factor is hypoxia-inducible factor-1 (HIF-1). HIF-1 is an important factor in the adaptation of cells to hypoxic environments, and significantly contributes to the aggressiveness and chemoresistance of number of different tumours 5,[7][8][9]15,19,21,[25][26][27][28][29][30] . However, these changes can be independent of HIF-1 (ref.…”