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Filamin A Is Required for T Cell Activation Mediated by Protein Kinase C-¹

Division of Cell Biology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121

Induction of T cell responses following engagement of the Ag-specific TCR depends on TCR-initiated rearrangements of the cellular actin cytoskeleton and highly coordinated and tightly regulated interactions and of diverse intracellular signaling proteins. In this study, we show that filamin A (FLNa), an actin-binding and signal mediator scaffolding protein, is required for T cell activation. Following Ag stimulation, FLNa was recruited to the T cell-APC contact area, where it colocalized with protein kinase C- (PKC). Depletion of FLNa by RNA interference did not affect TCR-induced early tyrosine phosphorylation or actin polymerization but, nevertheless, resulted in impaired IL-2 expression by human primary T cells and reduced activation of NF-B, AP-1, and NFAT reporter genes in transfected T cells. TCR stimulation induced stable physical association of FLNa with PKC. Furthermore, the TCR/CD28-induced membrane translocation of PKC was inhibited in FLNa-depleted T cells. These results reveal novel role for FLNa in the TCR/CD28 signaling pathway leading to transcription factor activation and IL-2 production, and suggest that this role is mediated, in part, through the inducible interaction of FLNa with PKC.