Interaction of γ1-Syntrophin with Diacylglycerol Kinase-ζ

Abstract

Syntrophins are modular adapter proteins that link ion channels and signaling proteins to dystrophin and its homologues. A yeast two-hybrid screen of a human brain cDNA library using the PDZ domain of γ1- syntrophin, a recently identified brain-specific isoform, yielded overlapping clones encoding the C terminus of diacylglycerol kinase-ζ (DGK-ζ), an enzyme that converts diacylglycerol into phosphatidic acid. In biochemical assays, the C terminus of DGK-ζ, which contains a consensus PDZ-binding motif, was found to be necessary and sufficient for association with γ1-syntrophin. When coexpressed in HeLa cells, DGK-ζ and γ1-syntrophin formed a stable complex that partitioned between the cytoplasm and nucleus. DGK-ζ translocates from the cytosol to the nucleus, a process negatively regulated by protein kinase C phosphorylation. We found that DGK-ζ recruits γ1-syntrophin into the nucleus and that the PDZ-binding motif is required. Disrupting the interaction altered the intracellular localization of both proteins; DGK-ζ accumulated in the nucleus, whereas γ1-syntrophin remained in the cytoplasm. The level of endogenous syntrophins in the nucleus of HeLa cells also reflected the amount of nuclear DGK-ζ. In the brain, DGK-ζ and γ1-syntrophin were colocalized in cell bodies and dendrites of cerebellar Purkinjie neurons and other neuronal cell types, suggesting that their interaction is physiologically relevant. Moreover, coimmunoprecipitation and pull-down experiments from brain extracts and cells suggest that DGK-ζ, γ1-syntrophin, and dystrophin form a ternary complex. Collectively, our results suggest that γ1-syntrophin participates in regulating the subcellular localization of DGK-ζ to ensure correct termination of diacylglycerol signaling.