Carcinogenesis Advance Access originally published online on April 1, 2008
Carcinogenesis 2008 29(8):1493-1499; doi:10.1093/carcin/bgn088
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Published by Oxford University Press 2008.
Regulation of hypoxia-inducible genes by ETS1 transcription factor
1 Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, Frederick, MD 21702, USA
2 Laboratory of Tumor and Stem Cell Biology, National Cancer Institute, Bethesda, MD 20892, USA
3 Department of Cardiothoracic Surgery
4 Department of Pathology, New York University School of Medicine, New York, NY 10016, USA
* To whom correspondence should be addressed. Tel: +1 301 846 5623; Fax: +1 301 846 5946; Email: salnikow{at}ncifcrf.gov
Hypoxia-inducible factor (HIF-1) regulates the expression of genes that facilitate tumor cell survival by making them more resistant to therapeutic intervention. Recent evidence suggests that the activation of other transcription factors, in cooperation with HIF-1 or acting alone, is involved in the upregulation of hypoxia-inducible genes. Here we report that high cell density, a condition that might mimic the physiologic situation in growing tumor and most probably representing nutritional starvation, upregulates hypoxia-inducible genes. This upregulation can occur in HIF-independent manner since hypoxia-inducible genes carbonic anhydrase 9 (CA9), lysyloxidase like 2 (LOXL2) and n-myc-down regulated 1 (NDRG1)/calcium activated protein (Cap43) can be upregulated by increased cell density under both normoxic and hypoxic conditions in both HIF-1
-proficient and -deficient mouse fibroblasts. Moreover, cell density upregulates the same genes in 1HAEo– and A549 human lung epithelial cells. Searching for other transcription factors involved in the regulation of hypoxia-inducible genes by cell density, we focused our attention on ETS1. As reported previously, members of v-ets erythroblastosis virus E26 oncogene homolog (ETS) family transcription factors participate in the upregulation of hypoxia-inducible genes. Here, we provide evidence that ETS1 protein is upregulated at high cell density in both human and mouse cells. The involvement of ETS1 in the upregulation of hypoxia-inducible genes was further confirmed in a luciferase reporter assay using cotransfection of ETS1 expression vector with NDRG1/Cap43 promoter construct. The downregulation of ETS1 expression with small interfering RNA (siRNA) inhibited the upregulation of CA9 and NDRG1/Cap43 caused by increased cell density. Collectively, our data indicate the involvement of ETS1 along with HIF-1 in regulating hypoxia-inducible genes.
Abbreviations: CA9, carbonic anhydrase 9; Cap43, calcium activated protein; ETS, v-ets erythroblastosis virus E26 oncogene homolog; HD, high density; HIF-1, hypoxia-inducible factor; LD, low density; LOX, lysyloxidase; LOXL2, lysyloxidase like 2; NDRG1, n-myc-down regulated 1; PCR, polymerase chain reaction; siRNA, small interfering RNA
Received November 15, 2007; revised February 25, 2008; accepted March 15, 2008.
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