Vav1 Controls the Stability and Function of SLP-76 Containing Signaling Microclusters.
Generation of productive immune responses requires T cell activation and differentiation
into various effector and helper subsets. T cell activation is mediated by signaling
events that originate at the T cell receptor (TCR) and result in the phosphorylation of
several critical adapter and effector molecules. These early signaling events result in
the formation of multisubunit struc... read moretures known as SLP-76-containing signaling
microclusters (SLP-76 MC). These SLP-76 MC are the structures responsible for T cell
signaling; their formation and persistence are closely linked with productive T cell
signaling. I propose that SLP-76 MC perform two functions to facilitate T cell
activation. First, they act as a central `hub' where enzymes contact and act upon their
substrates. Recruiting these proteins to a common location increases access to
substrates and the efficiency with which they are activated. Second, they act as
molecular adhesion points that connect the T cell receptor to the cytoskeleton.
Interaction with the cytoskeletal machinery increases the efficiency with which SLP-76
MC are formed and provides a mechanism to explain the centralized movement of SLP-76 MC.
To gain further insight into the structure and function of SLP-76 MC, I have analyzed a
critical component of the microcluster: the Rho family guanine-nucleotide exchange
factor (GEF) Vav1. Here, I show that Vav1 is recruited to the N-terminal tyrosines of
SLP-76 and is required for the structural stability of the microcluster. Vav1 possesses
a C-terminal cassette composed of Src homology (SH) domains that directs recruitment
into SLP-76 MC and contributes to multivalent interactions that are required for
microcluster persistence. However, these domains are insufficient to mediate
microcluster persistence, indicating that the N-terminal domains of Vav1 also make
structural contributions. Consistent with a model in which the microcluster is a hub of
enzymatic activity, Vav1 recruitment to SLP-76 MC is required for its phosphorylation
and activation. In turn, Vav1 also acts on downstream GTPases within microclusters. The
enzymatic GEF activity of Vav1, while not required for structural stabilization of
microclusters, acts as a downstream effector required for full T cell activation. In
addition, I show that the N-terminal domains, which are associated with regulating the
enzymatic activity of Vav1, are required to link Vav1 to the translocation machinery of
the cell and allow SLP-76 MC to act as attachment points between the TCR and
cytoskeleton. I conclude that Vav1 mediates T cell activation by increasing SLP-76 MC
persistence and function through multiple non-catalytic scaffolding interactions.
Analysis of this critical SLP-76 MC component has revealed novel aspects of how SLP-76
MC mediate T cell activation.
Thesis (Ph.D.)--Tufts University, 2011.
Submitted to the Dept. of Immunology.
Advisor: Stephen Bunnell.
Committee: Mercio Perrin, Henry Wortis, Joan Mecsas, Larry Feig, and Jennifer Cannons.
Keywords: Immunology, and Cellular biology.read less