The Ubiquitously Expressed Csk Adaptor Protein Cbp Is Dispensable for Embryogenesis and T-Cell Development and Function

Abstract

Regulation of Src family kinase (SFK) activity is indispensable for a functional immune system and embryogenesis. The activity of SFKs is inhibited by the presence of the carboxy-terminal Src kinase (Csk) at the cell membrane. Thus, recruitment of cytosolic Csk to the membrane-associated SFKs is crucial for its regulatory function. Previous studies utilizing in vitro and transgenic models suggested that the Csk-binding protein (Cbp), also known as phosphoprotein associated with glycosphingolipid microdomains (PAG), is the membrane adaptor for Csk. However, loss-of-function genetic evidence to support this notion was lacking. Herein, we demonstrate that the targeted disruption of the cbp gene in mice has no effect on embryogenesis, thymic development, or T-cell functions in vivo. Moreover, recruitment of Csk to the specialized membrane compartment of “lipid rafts” is not impaired by Cbp deficiency. Our results indicate that Cbp is dispensable for the recruitment of Csk to the membrane and that another Csk adaptor, yet to be discovered, compensates for the loss of Cbp.

ACKNOWLEDGMENTS

We thank Ingrid Mecklenbräuker, Laura Donlin, Eva Besmer, and Sukhvinder Sahota for critical reading of the manuscript.

This work was supported by The Irene Diamond Fund/Professorship Program (A.T.) and by National Institutes of Health grants 5-RO1-AI050867 and 5-RO1-AI053545 (A.T.). This work was supported in part by The Cancer Research Institute Predocotoral Emphasis Pathway in Tumor Immunology (M.-W.D.).