Differential expression of caveolin-1 in renal neoplasms

Caveolin-1 is a major component of membrane caveolae, which are specialized lipid raft microdomains on cell membrane that are implicated in molecular transport, cell adhesion, and signal transduction. The overexpression of caveolin-1 recently was associated with a poor outcome in patients with clear-cell renal cell carcinoma (CCRCC) and was proposed as a useful diagnostic marker. In the current study, the authors used immunohistochemistry to investigate the membranous and cytoplasmic expression of caveolin-1 and its correlation with other pathologic parameters in different subtypes of renal neoplasms.

A tissue microarray (TMA) was constructed from 60 normal kidneys, 22 CCRCCs, 20 papillary renal cell carcinomas (PRCCs), 16 chromophobe renal cell carcinomas (ChRCCs), and 19 oncocytomas (ONCs). The TMA was immunostained for caveolin-1 protein. Both membranous and cytoplasmic caveolin-1 expression levels were measured and were correlated with tumor size, Fuhrman nuclear grade, and pathologic stage.

Caveolin-1 was expressed normally in distal convoluted tubules, collecting ducts, parietal cells of Bowman capsule, smooth muscle, and vascular endothelial cells. Membranous caveolin-1 expression was detected in 19 of 22 CCRCCs (86.4%), which was significantly higher than the membranous caveolin-1 expression detected in PRCCs (1 of 20 tumors; 5%), ChRCCs (0 of 16 tumors; 0%), and ONCs (1 of 19 tumors; 5.3%). Cytoplasmic caveolin-1 expression was detected in 16 of 22 CCRCCs (72.7%), in 13 of 20 PRCCs (65%), in 8 of 16 ChRCCs, (50%), and in 13 of 19 ONCs (68.4%). The percentage of tumors that expressed cytoplasmic caveolin-1 did not differ significantly among the different types of renal tumors (P = .1). Only membranous caveolin-1 expression was correlated with tumor size (Pearson correlation = 0.266; P = .043). There was no correlation between membranous or cytoplasmic caveolin-1 expression and other pathologic parameters, including Fuhrman nuclear grade and staging according to the American Joint Committee on Cancer tumor, lymph node, metastasis classification system.

Caveolin-1 expression has 2 distinctive patterns in renal neoplasms: membranous and cytoplasmic. In the current study, membranous caveolin-1 expression was detected predominantly in CCRCCs and only rarely in other subtypes of renal neoplasms. Thus, the current results indicated that caveolin-1 expression may have potential both as a diagnostic marker in the differential diagnosis of renal tumors and as a therapeutic target, especially for CCRCC.