A NOVEL SERUM-PROTEIN SIMILAR TO C1Q, PRODUCED EXCLUSIVELY IN ADIPOCYTES

We describe a novel 30-kDa secretory protein, Acrp30 (adipocyte complement-related protein of <(30)under bar> kDa), that is made exclusively in adipocytes and whose mRNA is induced over 100-fold during adipocyte differentiation. Acrp30 is structurally similar to complement factor Clq and to a hibernation-specific protein isolated from the plasma of Siberian chipmunks; it forms large homo-oligomers that undergo a series of post-translational modifications, Like adipsin, secretion of Acrp30 is enhanced by insulin, and Acrp30 is an abundant serum protein. Acrp30 may be a factor that participates in the delicately balanced system of energy homeostasis involving food intake and carbohydrate and lipid catabolism. Our experiments also further corroborate the existence of an insulin regulated secretory pathway in adipocytes.