Factor inhibiting HIF (FIH-1) promotes renal cancer cell survival by protecting cells from HIF-1α-mediated apoptosis

BACKGROUND: Clear cell renal cell carcinoma (CCRCC) is the commonest form of kidney cancer. Up to 91% have biallelic inactivation of VHL, resulting in stabilisation of HIF-alpha subunits. Factor inhibiting HIF-1 is an enzyme that hydroxylates HIF-alpha subunits and prevents recruitment of the co-activator CBP/P300. An important question is whether FIH-1 controls HIF activity in CCRCC. METHODS: Human VHL defective CCRCC lines RCC10, RCC4 and 786-O were used to determine the role of FIH-1 in modulating HIF activity, using small interfering RNA knockdown, retroviral gene expression, quantitative RT-PCR, western blot analysis, Annexin V and propidium iodide labelling. RESULTS: Although it was previously suggested that FIH-1 is suppressed in CCRCC, we found that FIH-1 mRNA and protein are actually present at similar levels in CCRCC and normal kidney. The FIH-1 inhibition or knockdown in the VHL defective CCRCC lines RCC10 and RCC4 (which express both HIF-1 alpha and HIF-2 alpha) resulted in increased expression of HIF target genes. In the 786-O CCRCC cell line, which expresses only HIF-2 alpha, FIH-1 attenuation showed no significant effect on expression of these genes; introduction of HIF-1 alpha resulted in sensitivity of HIF targets to FIH-1 knockdown. In RCC4 and RCC10, knockdown of FIH-1 increased apoptosis. Suppressing HIF-1 alpha expression in RCC10 prevented FIH-1 knockdown from increasing apoptosis. CONCLUSION: Our results support a unifying model in which HIF-1 alpha has a tumour suppressor action in CCRCC, held in check by FIH-1. Inhibiting FIH-1 in CCRCC could be used to bias the HIF response towards HIF-1 alpha and decrease tumour cell viability. British Journal of Cancer (2011) 104, 1151-1159. doi: 10.1038/bjc.2011.73 www.bjcancer.com Published online 8 March 2011 (c) 2011 Cancer Research UK