FNDC1, also known as MEL4B3, Ags8, Expressed in synovial lining protein and Activation-associated cDNA protein, is a 1888 amino acid secreted protein that contains five fibronectin type-III domains. FNDC1 is moderately expressed in skeletal muscle, pancreas, heart, kidney, spinal cord, ovary and lung. Expression of FNDC1 is induced in response to hypoxia in ventricular cardiomyocytes. Since FNDC1 interacts with G??? and G©, it is likely that FNDC1 is an activator for G-protein signaling. Though normally absent in healthy skin, FNDC1 expression is induced by TGF-beta signaling in skin tumors and psoriasis. There are two isoforms of FNDC1 that are produced as a result of alternative splicing events.