Expression of CD9/motility-related protein 1 (MRP-1) in renal parenchymal neoplasms: consistent expression in papillary and chromophobe renal cell carcinomas

Abstract

CD9 is a glycoprotein that is abundant in hematopoietic cells. Recently, it has been reported that CD9 is also present in the human kidney. In this article, we investigated the expression of CD9 using an immunohistochemical technique. We also studied the expression of CD9 protein and messenger RNA (mRNA) in tissue samples of some renal tumors using immunoblotting and reverse-transcription polymerase chain reaction (RT-PCR) analysis. Immunohistochemically, all tumors of papillary and chromophobe renal cell carcinomas (RCCs) and oncocytomas expressed CD9. In addition, CD9 was expressed in 31 of 66 conventional RCCs and 1 of 4 collecting duct carcinomas. On immunoelectron microscopy, CD9 was identified on the plasma membrane of a conventional RCC. The presence of CD9 protein in normal kidneys and various renal tumors, except for a collecting duct carcinoma and an oncocytoma, was confirmed by immunoblotting. On RT-PCR analysis, the expression of CD9 mRNA was observed in 1 normal kidney, 2 conventional RCCs, and 1 oncocytoma. The frequency of immunohistochemical CD9 positivity was significantly higher in papillary and chromophobe RCCs than in collecting duct carcinomas and conventional RCCs, respectively. These results suggest that CD9 may be a beneficial marker in the differential diagnosis between papillary RCCs and collecting duct carcinomas and also between chromophobe and conventional RCCs.