The relationship of erythropoietin overexpression with von Hippel-Lindau tumour suppressor gene mutations

Decreased levels of von Hippel-Lindau (VHL) tumour suppressor protein are associated with up-regulation of hypoxia-inducible factor (HIF), leading to increased tumour proliferation, angiogenesis and progression. The role of erythropoietin (EPO), a target gene for HIF, remains unknown for sporadic clear cell renal cell carcinoma (sCCRCC). In this study, we determined expression levels of EPO, and its correlation with VHL mutations and HIF-1· and HIF-2· expression in 82 patients identified with sCCRCC following nephrectomy. We identified VHL gene alterations using multiplex polymerase chain reaction, purifying products of polymerase chain reaction, and direct sequencing. Immunohistochemical staining for HIF-1·, HIF-2· and EPO was performed for tumour and corresponding normal tissues. Data were analyzed with respect to clinicopathological factors. EPO was detected in 87.8% of sCCRCC tumours versus 7.3% for normal tissues. EPO expression was related to tumours demonstrating VHL gene abnormalities. Of specimens with VHL alterations 95.6% tested positive for EPO, versus 78.3% when VHL gene expression was normal (P<0.01). EPO was identified in 96.2 and 94.2% of HIF-1· and HIF-2· positive specimens, respectively, compared to 72.4 and 53.8% for HIF-1· and HIF-2· negative groups (p<0.01). Moreover, EPO expression correlated significantly with increasing nuclear grade (p<0.05). HIF-2· was identified in 84.1% of sCCRCC, compared to 64.6% for HIF-1·. Expression of HIF-1·, HIF-2· and EPO is common in sCCRCC. Although both forms of HIF up-regulate expression of EPO, the relationship to HIF-2· appears to be more pronounced. The VHL-HIF-EPO pathway requires further study, as it may represent a potential molecular target for therapy of sCCRCC.