Collagenous repeat containing sequence of 26 kDa protein (CORS-26) is a recently discovered novel member of the TNF/C1q/adiponectin superfamily. CORS-26 has been detected in chondrocytes and osteoblasts, but its functional properties are largely unknown. As CORS-26 shows structural analogies to adiponectin, which has been shown to exert proinflammatory and destructive properties in arthritic synovium, the goal of the present study was to examine the expression and regulation of CORS-26 in adipocyte differentiation.

Gene expression of 3T3-L1-preadipocyte cultures were examined on the protein and mRNA level by real-time PCR, Western blot, electrophoretic mobility shift assay and luciferase-reporter gene assay.

CORS-26 showed numerous homologies to adiponectin such as a C-terminal globular domain and a N-terminal collagen domain. CORS-26 mRNA expression could not be detected in preadipocytes and in early adipocytes after 48 hours of culture. After 4–9 days of adipocyte differentiation, however, upregulation of CORS-26 mRNA and protein could be detected. CORS-26 promoter activity and RNA expression could be stimulated by troglitazone and fenofibrate but not by 15-deoxy-prostaglandin J2. In addition, PPARγ, but not PPARα, binds specifically to a promoter response element at position -641/-596.

CORS-26 appears to be a novel adiponectin with strong homologies to the other members of the C1q/TNF/adiponectin superfamily, which includes its functional properties that may be as proinflammatory in the arthritic joint as those of adiponectin.