Signal Transduction in Lymphocyte Activation
Our work over the last decade has demonstrated that the modifications of signals emanating from the T cell antigen receptor complex (TcR/CD3) mediated by accessory activation molecules (AAM) including CD4/8, CD45, CD28 and glycosylphosphatidylinositol anchored proteins (GPI-AP) can be extreme, resulting in perturbation of cell growth control, anergy, or death. Our global objectives are to: characterize the ordered interaction of AAM with TcR/CD3; define the sequence and temporal engagement of the second messenger generating systems engaged; and to characterize the TcR/CD3/AAM induced spatial re-distribution of second messenger generating systems supporting cellular activation and growth. Our approach utilizes primary T cells; T cell clonal variants and transgenesis: enabling a genetic analysis and facilitating the biochemical characterization underpinning the signaling phenotype.
The AAMs CD4 and CD8 play fundamental roles in
the initiation of the earliest signals induced upon TcR/CD3
engagement through their regulation of activity and delivery of
function of Src family PTK. We have discovered the interdependent
temporal and spatial regulation of Lck and Fyn during
proximal TcR signaling. Specifically, in primary CD4+ peripheral
lymph node T cells lipid rafts (LR) function to segregate Lck and
Fyn. Upon antigen receptor engagement, Lck is activated within
seconds outside LR, followed by its translocation into LR and the
ensuing activation of co-localized Fyn.
Genetic models and structure function analyses have enabled the formal demonstration that Fyn activation is predicated by its physical interaction with kinase active Lck within LR, and revealed a c-terminal sequence common to all members of the Lck subfamily of Src family PTK that predicates their partitioning to LR.
Our current working model proposes a biological framework based on structural distinctions amongst Src family subfamilies that rationalizes the involvement and regulation of function of multiple Src-family PTK reported to be critically involved in a variety of receptor-mediated signaling pathways.
Selected References:
Link to Pubmed Publications-
Filipp, D., Zhang, J., Leung, B. L., Shaw, A., Levin, S. D., Veillette, A. and Julius, M. 2003. Regulation of Fyn Trough Translocation of Activated Lck into LR. J. Exp. Medicine 197: 1221.
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Filipp, D., Leung, B. L., Zhang, J., Veillette, A. and Julius, M. 2004. Enrichment of Lck in LR Regulates Co-localized Fyn Activation
and the Initiation of Proximal Signals Through TcRab. Journal of Immunology 172:4266-4274. -
Filipp, D. and Julius, M. LR: Resolution of “Fyn problem”? 2004. Molecular Immunology 41: 645-656.
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Dominik Filipp, Behrouz Moemeni, Alessandra Ferzoco, Kirishanthy Kathirkamathamby, Jenny Zhang, Domenique Davidson, André Veillette, and Michael Julius. 2007. Lck Dependent Fyn Activation requires C-terminus dependent targeting of kinase active Lck to lipid rafts. Journal of Biological Chemistry (in press)
