Immunolocalization and mRNA expression of bone morphogenetic protein-6 in human clear cell renal carcinoma

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta superfamily of proteins. Dysregulation of BMP signaling has been suggested in the carcinogenesis of different organs. We determined BMP-6 mRNA and protein expression in localized human clear cell renal carcinoma (CCRC), obtained from 20 patients who underwent nephrectomy, by the real-time polymerase chain reaction and immunohistochemistry. 15/20 patients exhibited higher BMP-6 mRNA expression in malignant than in healthy renal tissue relative to the PBGD expression (p < 0.05). Immunostaining intensity for BMP-6 in healthy renal tissue ranged from 0 to 2 (average 0.9), as well as in renal clear cell carcinoma (average 1.1). Seven of 20 (35%) healthy tissue samples failed to stain with BMP-6 antibody, compared to 2/20 (10%) tumor samples (p < 0.05). BMP-6 immunostaining was positive in 18/20 CCRC samples. Staining was localized in the cytoplasm and/or membrane of malignant cells. Malignant tissue had significantly higher BMP-6 mRNA expression than healthy tissue. There was no significant correlation between BMP-6 mRNA and protein expression with disease presentation, disease progression and patients' characteristics. Long-term follow-up of our patients is needed to determine the possible role of increased expression of BMP-6 in CCRC.