T cell adhesion to TCR and Beta-1 integrin ligands is differentially controlled by the SKAP55 N-terminus.
immune responses require optimal T cell activation. T cell activation is dependent on
TCR-initiated signaling events that occur within compartmentalized signaling complexes
known as SLP-76 microclusters. SLP-76 microclusters are sites of active tyrosine
phosphorylation and enzymatic activity at the immune synapse. Furthermore, SLP-76
microclusters recruit a variety of ada... read moreptor molecules that provide scaffolding functions
to maintain the integrity of the complex and to protect against the actions of
down-regulating kinases, phosphatases, caspases and ubiquitin ligases. I propose that in
addition to acting as hubs of catalytic activity that are required for calcium flux and
changes in the transcriptional profile of T cells, SLP-76 microclusters act as points of
adhesion that bridge the TCR to the actin cytoskeleton and influence the topology of the
immune synapse so as to maintain stable T cell-APC conjugates. I hypothesize that SLP-76
microclusters act as T cell-specific podosomes that reinforce areas of tight contact
with the APC surface, thereby enabling the TCR to act as an adhesion receptor that
stabilizes the immune synapse for prolonged T cell-APC conjugate formation and optimal
TCR signal transduction. In addition, I hypothesize that SLP-76 microclusters integrate
inside-out signals from the TCR to integrins to reinforce the adhesive capability of the
immune synapse during antigen recognition. Here I show that one key regulator of
inside-out signaling, SKAP55, recruits to TCR-induced SLP-76 microclusters and impacts
microcluster dynamics, TCR- mediated contact stability and T cell retention to
anti-CD3-coated substrates or Beta1 integrin ligands. These are the first data to
demonstrate a role for SKAP55 in T cell spreading and adhesion downstream of solo TCR
ligation. I demonstrate that dimerization of the SKAP55 SH3 domains is sufficient for
these processes but is not sufficient for communication to Beta1 integrins. Inside-out
signaling to integrins is dependent on scaffolding interactions between the SKAP55
N-terminal dimerization motif (DM) and the adaptors RIAM and talin. In addition, I
demonstrate that the SKAP55 DM is required for optimal expression of paxillin, an
important regulator of Beta1 integrin-mediated adhesion and migration. Analysis of
SKAP55 function within the context of SLP-76 microclusters has revealed diverse roles
for this molecule in TCR and integrin-dependent adhesion and promises to provide
important insight with respect to how diverse arms of TCR signaling are coordinated in
space and time to promote T cell activation and ensuing immune
Thesis (Ph.D.)--Tufts University, 2014.
Submitted to the Dept. of Immunology.
Advisor: Stephen Bunnell.
Committee: Henry Wortis, Ralph Isberg, David Thorley-Lawson, Cheleste Thorpe, and Kenneth Swanson.
Keyword: Immunology.read less