Identification of a novel family of targets of PYK2 related to Drosophila retinal degeneration B (rdgB) protein

The protein tyrosine kinase PYK2 has been implicated in signaling pathways activated by G-protein-coupled receptors, intracellular calcium, and stress signals. Here we describe the molecular cloning and characterization of a novel family of PYK2-binding proteins designated Nirs (PYK2 N-terminal doma in-interacting receptors). The three Nir proteins (Nir1, Nir2, and Nir3) bi nd to the amino-terminal domain of PYK2 via a conserved sequence motif loca ted in the carboxy terminus. The primary structures of Nirs reveal six puta tive transmembrane domains, a region homologous to phosphatidylinositol (PI ) transfer protein, and an acidic domain. The Nir proteins are the human ho mologues of the Drosophila retinal degeneration B protein (rdgB), a protein implicated in the visual transduction pathway in flies, We demonstrate tha t Nirs are calcium-binding proteins that exhibit PI transfer activity in vi vo. Activation of PYK2 by agents that elevate intracellular calcium or by p horbol ester induce tyrosine phosphorylation of Nirs. Moreover, PYK2 and Ni rs exhibit similar expression patterns in several regions of the brain and retina. In addition, PYK2-Nir complexes are detected in lysates prepared fr om cultured cells or from brain tissues. Finally, the Nir1-encoding gene is located at human chromosome 17p13.1, in proximity to a locus responsible f or several human retinal diseases. We propose that the Nir and rdgB protein s represent a nem family of evolutionarily conserved PYK2-binding proteins that play a role in the control of calcium and phosphoinositide metabolism downstream of G-protein-coupled receptors.