The RNA-binding protein Staufen from rat brain interacts with protein phosphatase-1

In mammalian neurones, homologues of the Drosophila RNA-binding protein Staufen are part of ribonucleoprotein complexes that move bidirectionally along dendritic microtubules and appear to regulate mRNA translocation and translation. In this study, putative components of Staufen granules were identified in a yeast two-hybrid screen of a rat brain cDNA library with a rat Staufen bait. Protein phosphatase-1 was found as an interacting partner. Binding appears to be mediated by a five amino acid residue sequence motif (R-K-V-T-F) in Staufen that is conserved in a number of proteins interacting with the phosphatase. A two amino acid residue mutation within this motif (R-K-V-G-A) disrupted the interaction. A cytoplasmic interaction of both proteins was shown by coimmunoprecipitation of rat Staufen and protein phosphatase-1 from the cytoplasm of transfected cells and rat brain homogenates. In mammalian brain, the phosphatase represents the first described endogenous interaction partner of Staufen. In primary hippocampal neurones, both proteins partially colocalize in somata and neuronal processes. Staufen does not modulate the in vitro protein phosphatase activity. These findings show that protein phosphatase-1 is a native component of Staufen particles. Cellular functions of Staufen may be regulated via phosphorylation or Staufen may recruite the phosphatase into specific ribonucleoprotein complexes.