Concomitant deregulation of HIF1α and cell cycle proteins in VHL-mutated renal cell carcinomas

Abstract

Renal cell carcinomas (RCCs) of the clear cell type are associated with alteration of the von Hippel-Lindau (VHL) tumour suppressor gene as well as subsequent stabilization and over-expression of hypoxia inducible factor (HIF), which causes up-regulation of cyclin D1. On the basis of their ability to interact with cyclin D1 we investigated a number of cell cycle proteins to shed further light on the downstream effects of HIF dysregulation. Expression of HIF1alpha, cyclin D1, cyclin-dependent kinase 4 and cyclin-dependent kinase inhibitors p16, p21 and p27 was studied by immunohistochemistry. Since NFkappaB1/RelA have been shown to bind to the cyclin D1 promoter, mRNA expression of these transcription factors was further analysed by quantitative PCR. In RCCs harbouring VHL mutations/hypermethylation, over-expression of HIF1alpha was parallelled by up-regulation of cyclin D1 and CDK4 and down-regulation of p21 and p27. Moreover, p27 expression was inversely correlated with tumour cell differentiation. Comparison of non-tumorous autologous kidney tissues revealed a significant down-regulation of NFkappaB1 mRNA expression in patients harbouring RCC with VHL mutations/hypermethylation. Our data support the notion of a link between VHL deficiency/HIF dysfunction and disturbances of cell cycle control in the tumorigenesis of VHL-negative RCC.

Characterizing Vascular Parameters in Hypoxic Regions: A Combined Magnetic Resonance and Optical Imaging Study of a Human Prostate Cancer Model

“…As evident in Fig. 1B, HIF-1 activity was nondetectable under normoxic growth conditions showing the absence of aberrant signaling pathways resulting in stable expression of HIF-1 (10). The immunoblot data show that these cells produced large amounts of EGFP following treatment with CoCl 2 , with optimal concentrations in the range of 200 to 300 Amol/L.…”

“…However, another caveat of using the HRE system in tumors is the variation of normal HIF-1a expression levels in cancer cell lines where the expression can be independent of oxygen tension (10). This dysregulation is brought about by several pathways.…”

“…For example, insulin growth factor-1 can stimulate HIF-1a expression through a posttranscriptional mechanism (21). In addition, cell lines that express mutated VHL can prevent HIF-1a from degrading and promote HIF-1a subunit accumulation (10). More recently, it was shown that the proangiogenic factor interleukin-8 can stimulate VEGF expression in HIF-1a-deficient colon cancer cells (22).…”

“…Solid tumors were derived from HRE-EGFP PC-3 cells by inoculating 10 6 cells in 0.05 mL of Hanks Balanced Salt solution (Sigma) s.c. in the right flank of male severe combined immunodeficient mice. Tumor volumes used in the study were 100 to 200 mm 3 and developed within 5 weeks of inoculation.…”

Understanding the Importance of Smart Drugs in Renal Cell Carcinoma

“…Thus, it has been shown that over-expression of HIF-1a induced by hypoxia was paralleled by down-regulation of the cyclin-dependent kinase inhibitor p27. In the same way, reduction or absence of p27 abrogated the hypoxia-induced G1 checkpoint, also suggesting that p27 is a key regulator of G1/S transition in hypoxic cells [23,24].…”