The Calponin Homology Domain of Vav1 Associates with Calmodulin and Is Prerequisite to T Cell Antigen Receptor-induced Calcium Release in Jurkat T Lymphocytes

Zhuo Zhou,Jie Yin,Zhixun Dou,Jun Tang,Cuizhu Zhang,Youjia Cao

doi:10.1074/jbc.m702975200

Abstract

Vav1 is a guanine nucleotide exchange factor that is expressed specifically in hematopoietic cells and plays important roles in T cell development and activation. Vav1 consists of multiple structural domains so as to facilitate both its guanine nucleotide exchange activity and scaffold function following T cell antigen receptor (TCR) engagement. Previous studies demonstrated that the calponin homology (CH) domain of Vav1 is required for TCR-stimulated calcium mobilization and thus downstream activation of nuclear factor of activated T cells. However, it remained obscure how Vav1 functions in regulating calcium flux. In an effort to explore molecules interacting with Vav1, we found that calmodulin bound to Vav1 in a calcium-dependent and TCR activation-independent manner. The binding site was mapped to the CH domain of Vav1. Reconstitution of vav1-null Jurkat T cells (J.Vav1) with CH-deleted Vav1 exhibited a severe deficiency in calcium release to the same extent as that of Jurkat cells treated with the calmodulin inhibitor or J.Vav1 cells. The defect persisted even when phospholipase-Cgamma1 was fully activated, indicating a prerequisite role of Vav1 CH domain in calcium signaling. The results suggest that Vav1 and calmodulin function cooperatively to potentiate TCR-induced calcium release. This study unveiled a mechanism by which the Vav1 CH domain is involved in calcium signaling and provides insight into our understanding of the role of Vav1 in T cell activation.

Highlights

Cium plays a central role in this process and has been studied intensively [1,2,3,4]
Vav1 Is Prerequisite to T cell antigen receptor (TCR)-induced Intracellular Calcium Release—T cell stimulation evokes a biphasic calcium flux, the calcium release followed by calcium depletion-activated calcium entry [7, 19]
Vav1 Interacts with Calmodulin via calponin homology (CH) Domain in a Ca2ϩdependent and Activation-independent Manner—To explore the possible mechanisms that Vav1 modulates calcium release, we looked for Vav1 binding partners

Summary

Introduction

Cium plays a central role in this process and has been studied intensively [1,2,3,4]. The deficiency in TCR-stimulated Ca2ϩ release in J.Vav1 cells is thought to be the consequence of the impaired activation of PLC-␥1, represented by tyrosine phosphorylation on both Tyr-783 [38] and Tyr-775 residues [39]. When we treated J.Vav1 cells with pervanadate (PV), a potent protein-tyrosine phosphatase inhibitor, to induce PLC-␥1 phosphorylation [40], the calcium defects still remained in J.Vav1 cells (Fig. 2A).

Results

Conclusion