ALK-7, also known as ALK7 and ACVR1C, belongs to the ALK family. It is a type I receptor for the TGFB family of signaling molecules. TGF-β is the prototype of a protein superfamily which, in humans, contains at least 35 members, including activins, inhibins, bone morphogenetic proteins, growth/differentiation factors, and Müllerian inhibiting substance. ALK-7 is a serine-threonine kinase that can cause the activation of one of the SMAD signal transducers, SMAD2. ALK-7 has a ligand known as Nodal. Nodal stimulates the secretion of TIMP-1 and inhibits matrix metalloproteinases MMP-2 and MMP-9 activity. The overexpression of Nodal or constitutively active ALK-7 decreases cell migration and invasion, whereas knock-down of Nodal and ALK-7 has the opposite effects.