Our characterization of molecules enriched at the plasma membrane of peripheral blood T-cells, identified a previously unstudied molecule EPI64C (TBC1D10C). The available data provided two clues regarding potential function of EPI64C. First, it contains a TBC domain, which often serves as a RabGAP. Second, it belongs to a family of 3 related protein of which the best defined, EPI64 (also referred to as EPI64A), regulates microvilli in choriocarcinoma cells and is a GAP for Rab27a. We investigated function of EPI64C and its potential relevance to T-cell recognition, envisioning two possible roles: regulation of cortical cytoskeleton architecture or regulation of receptor recycling. Our subsequent analysis supports the 2nd possibility: a role in receptor recycling as follows. Upon antigen recognition, T-Cell Receptor (TCR/CD3) and other signaling molecules become enriched in a specialized contact site between the T-cell and antigen-presenting cell, i.e. the immunological synapse (IS). Enrichment occurs via mechanisms that include polarized secretion from recycling endosomes, but the Rabs and RabGAPs which regulate this are unknown. Rab35 is one of the 16 Rabs identified by our proteomic profiling of peripheral blood T-cells. Our in-cell assays suggested that Rab35 might be a substrate for EPI64C Rab-GAP activity. Follow-up studies confirmed that EPI64C is a Rab35-GAP based both on in vitro Rab35-specific GAP activity and findings in transfection assays. EPI64C and Rab35-dominant negative (DN) constructs each impaired transferrin export from a recycling pathway in Jurkat T-cells and induced large vacuoles marked by transferrin receptor (TfR), TCR and SNAREs implicated in TCR polarized secretion. Rab35 localized to the plasma membrane and to intracellular vesicles where it substantially colocalized with TfR and with TCR. Rab35 was strongly recruited to the IS. Conjugate formation was impaired by transfection with Rab35-DN or EPI64C, and by EPI64C knockdown. TCR enrichment at the IS was impaired by Rab35-DN. Thus, EPI64C and Rab35 regulate a recycling pathway in T-cells and contribute to IS formation, most likely by participating in TCR transport to the IS.
Showing the most recent 10 out of 16 publications
