Common reduction of the Raf kinase inhibitory protein in clear cell renal cell carcinoma.

Despite the recent progress in our understanding of clear cell renal cell carcinomas (ccRCCs), the etiology of ccRCC remains unclear. We reported here a prevailing reduction of the raf kinase inhibitory protein (RKIP) in ccRCC. In our examination of more than 600 ccRCC patients by western blot and immunohistochemistry, RKIP was significantly reduced in 80% of tumors. Inhibition of RKIP transcription in ccRCC occurs to greater levels than VHL transcription based on the quantification analysis of their transcripts in six large datasets of DNA microarray available in Oncomine™ with the median rank of suppression being 582 and 2343 for RKIP and VHL, respectively. Collectively, the magnitude of RKIP reduction and the levels of its downregulation match those of VHL. Furthermore, RKIP displays tumor suppressing activity in ccRCC. While modulation of RKIP expression did not affect the proliferation of A498 and 786-0 ccRCC cells and neither their ability to form xenograft tumors in NOD/SCID mice, ectopic expression or knockdown of RKIP inhibited or enhanced A498 and 786-0 ccRCC cell invasion, respectively. This was associated with robust changes in vimentin expression, a marker of EMT. Taken together, we demonstrate here that downregulation of RKIP occurs frequently at a rate that reaches that of VHL, suggesting RKIP being a critical tumor suppressor for ccRCC. This is consistent with RKIP being a tumor suppressor for other cancers.

Clear cell renal cell carcinoma induces fibroblast-mediated production of stromal periostin.

OBJECTIVES: Increase in periostin (PN) was reported in clear cell renal cell carcinoma (ccRCC). But how PN contributes to ccRCC pathogenesis remains unclear. This research will investigate the underlying mechanism. METHODS: The PN protein in 37 adjacent non-tumour kidney (ANK) tissues, their respective ccRCCs, 16 cases of metastasised ccRCC and xenograft tumours was analysed by immunohistochemistry. PN expression in ccRCC cells and NIH3T3 fibroblasts was examined by real time PCR (polymerase chain reaction) and western blot. RESULTS: PN was detected at low levels in the tubular epithelial cells of ANKs. PN was robustly increased in the ccRCC-associated stroma of both organ-confined and metastasised ccRCCs. Furthermore, despite A498 ccRCC cells and their-derived xenograft tumour cells expressing a low level of PN, a strong presence of stromal PN was observed especially in the boundary region between xenograft tumour mass and non-tumour tissue. Collectively, these results suggest that the ccRCC-associated PN was derived from stroma instead of tumours. This notion was supported by the co-existence of PN with α-smooth muscle actin (αSMA), a marker of activated fibroblasts, in both local and metastasised ccRCC. Furthermore, co-culture of NIH3T3 mouse fibroblasts with either human A498 or 786-0 ccRCC cells dramatically enhanced PN transcription only in NIH3T3 cells as well as NIH3T3 cell-mediated accumulation of extracellular PN. In return, extracellular PN significantly enhanced A498 cell attachment. Elevation of PN promotes NIH3T3 cell proliferation and enhanced AKT activation. CONCLUSIONS: ccRCC induces fibroblast-mediated accumulation of stromal PN; stromal PN enhances ccRCC cell attachment and fibroblast proliferation.