Vav Activation and Function as a Rac Guanine Nucleotide Exchange Factor in Macrophage Colony-Stimulating Factor-Induced Macrophage Chemotaxis

Abstract

Signal transduction mediated by phosphatidylinositol 3-kinase (PI 3-kinase) is regulated by hydrolysis of its products, a function performed by the 145-kDa SH2 domain-containing inositol phosphatase (SHIP). Here, we show that bone marrow macrophages of SHIP^−/− animals have elevated levels of phosphatidylinositol 3,4,5-trisphosphate [PI (3,4,5)P₃] and displayed higher and more prolonged chemotactic responses to macrophage colony-stimulating factor (M-CSF) and elevated levels of F-actin relative to wild-type macrophages. We also found that the small GTPase Rac was constitutively active and its upstream activator Vav was constitutively phosphorylated in SHIP^−/− macrophages. Furthermore, we show that Vav in wild-type macrophages is recruited to the membrane in a PI 3-kinase-dependent manner through the Vav pleckstrin homology domain upon M-CSF stimulation. Dominant inhibitory mutants of both Rac and Vav blocked chemotaxis. We conclude that Vav acts as a PI 3-kinase-dependent activator for Rac activation in macrophages stimulated with M-CSF and that SHIP regulates macrophage M-CSF-triggered chemotaxis by hydrolysis of PI (3,4,5)P₃.

ACKNOWLEDGMENTS

We thank Koji Nakamura for preparing viral vectors and for his considerable intellectual input. We also thank Vishwanath Ramachandran, Brian Ceresa, and Susheela Tridandapani for critical review of the manuscript.

We have no conflicts of interest to disclose.

This study was supported by National Institutes of Health grants AI49264 and CA64268.