Overview:

ALK4 is a member of the subfamily of receptor ser/thr kinases that mediates signaling by the Activins. ALK4 is expressed in many human tissues, including kidney, pancreas, brain, lung, and liver. Truncated ALK4, predominantly expressed in human pituitary adenomas, function as dominant negative receptors to interfere with wild-type receptor function and blocks the antiproliferative effect of activin possibly contributing to development of human pituitary tumors (1). ALK4 is able to mediate Nodal signaling in the presence of Cripto during vertebrate development (2).

References:

1. Zhou, Y. et al: Truncated activin type I receptor Alk4 isoforms are dominant negative receptors inhibiting activin signaling. Mol Endocrinol. 2000 Dec;14(12):2066-75.

2. Reissmann, E. et al: The orphan receptor ALK7 and the Activin receptor ALK4 mediate signaling by Nodal proteins during vertebrate development. Genes Dev. 2001 Aug 1; 15(15):2010-22.