Phosphorylated Grb14 Is an Endogenous Inhibitor of Retinal Protein Tyrosine Phosphatase 1B, and Light-Dependent Activation of Src Phosphorylates Grb14

Abstract

Growth factor receptor-bound protein 14 (Grb14) is an adapter protein implicated in receptor tyrosine kinase signaling. Grb14^−/− studies highlight both the positive and negative roles of Grb14 in receptor tyrosine kinase signaling in a tissue-specific manner. In this study, we made a novel finding that Grb14 inhibits the activity of PTP1B, the major negative regulator of insulin receptor (IR) signaling, in a phosphorylation-regulated manner. Phosphorylation of Tyr-347 in the BPS domain of Grb14 is critical for interaction with PTP1B, resulting in the competitive inhibition of PTP1B activity. We also found that rhodopsin-regulated Src kinase activation in retina leads to the phosphorylation of Grb14. Further, ablation of Grb14 resulted in significantly elevated retinal PTP1B activity in vivo. PTP1B is known to be regulated by oxidation, glutathionylation, phosphorylation, and SUMOlyation, and our study for the first time demonstrates the inhibition of PTP1B activity in vivo by protein molecule Grb14 in a tissue-specific manner.

ACKNOWLEDGMENTS

This work was supported by grants from the NIH (EY016507-05; EY00871; EY12190).

We appreciate the technical help of Dustin Allen. We thank Roger J. Daly (Garvan Medical Institute, Sydney, Australia) for providing us the Grb14^−/− mice. We thank Benjamin Neel (Ontario Cancer Institute, Canada) for providing PTP1B floxed mice and Yun Le (University of Oklahoma Health Science Center) for providing opsin-Cre mice. We acknowledge Jian-xing Ma (University of Oklahoma Health Sciences Center) for providing Rpe65^−/− mice.