Enhances bone morphogenetic protein (BMP) signaling in a paracrine manner. In contrast, it inhibits both the activin-A and TGFB1-mediated signaling pathways (By similarity). Interacts with BMP7 and, by doing so, enhances binding to the type I receptors that contains cytoplasmic serine/threonine protein kinase domains. Also able to interact with activin-A and TGFB1 (By similarity). May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay.