SPARC (secreted protein acidic and rich in cysteine, also called osteonectin, BM-40, and 43K protein) is a matricellular protein and is associated with cell-matrix interactions during cell proliferation and extracellular remodeling. It is also implicated in the neovascularization, invasion, and metastasis of human malignancies. To investigate a potential role of the SPARC in renal tumorigenesis, we examined primary renal cell carcinomas (RCCs) for SPARC expression by Northern blot analysis and for protein distribution by immunohistochemistry. We found that 6 (100%) of 6 sarcomatoid and 25 (70%) of 36 clear-cell carcinomas had enhanced SPARC transcription compared with that of the corresponding normal kidney tissue. In contrast, papillary and chromophobe RCCs characterized by a hypovascular or avascular tumor phenotype had undetectable SPARC expression. Immunohistochemical analysis showed that SPARC was strongly stained in the cytoplasm of the sarcomatoid neoplastic cells in sarcomatoid RCCs, whereas it was expressed only in the vascular endothelial cells and fibroblasts in clear-cell RCCs. SPARC staining intensity in the stromal cells was increased in the invading portion in some clear-cell RCCs. These findings suggest that tumor development, including neovascularization and invasion in clear-cell RCCs, might be regulated by SPARC from stromal endothelial cells and fibroblasts and that sarcomatoid transformation from common-type RCCs is associated with upregulation of SPARC expression; SPARC may contribute to its aggressive tumor phenotype.
Copyright 2001 by W.B. Saunders Company