Expression of human mucin genes in normal kidney and renal cell carcinoma

Aims: Human mucins are large O-glycoproteins expressed by epithelial cells. Mucins are thought to be implicated in cell protection, cell adhesion and signalling. The aim of this study was to investigate the expression of the human mucin genes (MUC1-4, 5AC, 5B, 6-7 ) in normal kidney and renal cell carcinoma. Methods and results: We analysed by in-situ hybridization, immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR) the expression of these genes in normal adult kidney (n = 14) and renal cell carcinomas (n = 29). MUC1, MUC3 and MUC6 were expressed both in normal kidney and in renal carcinomas. In normal kidney, MUC1 was expressed in the distal convoluted tubules and in collecting ducts, whereas MUC3 was restricted to the proximal tubules. MUC4 was strongly expressed in epithelial urothelial cells of pyelocalyceal cavities. MUC6 was only detected by RT-PCR. In renal carcinoma, we showed a heterogeneous expression of MUC1 and MUC3 with an over-expression of MUC3 in renal clear cell carcinoma. The level of MUC3 expression by in-situ hybridization was associated with the nuclear grade in clear cell carcinoma. Conclusions: This study is the first large series investigating human mucin gene expression in the kidney. MUC1, MUC3 and MUC6 are expressed in normal and tumour kidney. The over-expression of MUC3 in renal cell carcinomas favours its implication in renal tumorigenesis.