Expression of regulator of G protein signalling protein 5 (RGS5) in the tumour vasculature of human renal cell carcinoma

The gene expression profiles of tumour and normal vasculature are distinctively different. The altered expression of various angiogenesis-related genes in tumour-derived endothelial cells has been investigated intensively, but there may be as yet unidentified molecules that regulate tumour angiogenesis. In the present study, the distinctive expression of regulator of G protein signalling protein 5 (RGS5) in tumour vessels in human renal cell carcinoma (RCC) has been clarified. RGS5 is a member of the RGS superfamily and acts as a negative regulator of heterotrimeric G protein-mediated signalling through G protein-coupled receptors (GPCRs). RT-PCR showed strong expression of RGS5 in all RCCs examined, but expression was very weak or undetectable in normal kidneys. By real-time RT-PCR, the ratio of RGS5 mRNA in RCC to that in normal kidney was 6.6 : 1 (p = 0.0012). In situ hybridization showed strong expression of RGS5 in vessels within tumour cell nests. It was expressed neither in tumour cells nor in normal renal capillaries. Immunohistochemical staining using serial sections for endothelial cell markers (CD31 and CD34) and smooth muscle cell markers (alpha-SMA and desmin), as well as fluorescence double staining, strongly suggested that tumour endothelial cells were the main location of RGS5 in RCC. These findings suggest that RGS5 may be involved in G protein-mediated signalling in tumour vessels in human RCC.