May act as an inhibitor of TGF-beta signaling. Interacts with TGFB1, TGFB2 and TGFB3. Expression begins at 10.5 dpc and increases as development progresses to 17.5 dpc. Expression rises in parallel with the differentiation of vascular smooth muscle cells (VSMCs) of the aorta. Upon retinoic acid-induced differentiation of smooth muscle cells in vitro. N-glycosylated.