Search

Most sporadically occurring renal tumors include a functional loss of the tumor suppressor von Hippel Lindau (VHL). Development of VHL-deficient renal cell carcinoma (RCC) relies upon activation of the hypoxia-inducible factor-2α (HIF2α), a master transcriptional regulator of genes that drive diverse processes, including angiogenesis, proliferation, and anaerobic metabolism. In determining the critical functions for HIF2α expression in RCC cells, the NADPH oxidase NOX4 has been identified, but the pathogenic contributions of NOX4 to RCC have not been evaluated directly. Here, we report that NOX4 silencing in VHL-deficient RCC cells abrogates cell branching, invasion, colony formation, and growth in a murine xenograft model RCC. These alterations were phenocopied by treatment of the superoxide scavenger, TEMPOL, or by overexpression of manganese superoxide dismutase or catalase. Notably, NOX4 silencing or superoxide scavenging was sufficient to block nuclear accumulation of HIF2α in RCC cells. Our results offer direct evidence that NOX4 is critical for renal tumorigenesis and they show how NOX4 suppression and VHL re-expression in VHL-deficient RCC cells are genetically synonymous, supporting development of therapeutic regimens aimed at NOX4 blockade. Cancer Res; 74(13); 3501–11. ©2014 AACR.

The early growth response gene 1, EGR1, is an important transcriptional regulator and acts as the convergent point between a variety of extracellular stimuli and activation of target genes resulting in diverse responses such as cell growth, proliferation, and apoptosis. Unlike other tumor types, in prostate tumor tissues EGR1 expression is elevated relative to normal tissues. However, the mechanism(s) of regulation of EGR1 in prostate tumor cells are unknown. As EGR1 expression and epidermal growth factor (EGF) signaling are frequently upregulated in prostate tumors, we tested the hypothesis that EGF induces EGR1 expression in prostate cancer cells. Using real-time PCR to quantify EGR1 transcripts, EGF induced EGR1 expression levels in a dose and time-dependent manner; and kinase inhibitors, PD98059 and wortmannin, abrogated the EGF-mediated EGR1 response. Analysis of the EGR1 promoter using reporter constructs identified an EGF-responsive region in the proximal promoter containing three potential serum response element (SRE) sites. In vivo chromatin immunoprecipitation assays demonstrated that EGF enhanced Elk-1 binding at the SRE sites of the EGR1 promoter in PC3 cells, and Elk-1 also bound in the absence of stimulus. Overexpression of Elk-1 enhanced activation of the EGF-responsive region indicating that Elk-1 is sufficient to activate EGR1 in PC3 cells. Similarly, a dominant-negative Elk-1 suppressed EGR1 promoter activity indicating that Elk-1 is necessary for EGF-induced EGR1 transcription in both PC3 and LNCaP cells. Taken together, these results demonstrate that EGR1 expression in prostate cancer cells is mediated through an EGF-ERK-Elk-1 signaling cascade. Since elevated EGF and EGF receptor are associated with prostate cancer progression, these results may explain elevated EGR1 in high-grade prostate tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4013. doi:10.1158/1538-7445.AM2011-4013