Casein kinases are operationally defined by their preferential utilization of acidic proteins such as caseins as substrates. They can phosphorylate a large number of proteins. Participates in Wnt signaling.

Apelin is a neuropeptide expressed in the supraoptic and paraventricular nuclei and is an endogenous ligand for APJ, a G protein-coupled orphan receptor which is an alternative coreceptor with CD4 for HIV-1. Apelin and APJ