Role of the EHD Family of Endocytic Recycling Regulators for TCR Recycling and T Cell Function.

T cells use the endocytic pathway for key cell biological functions, including receptor turnover and maintenance of the immunological synapse. Some of the established players include the Rab GTPases, the SNARE complex proteins, and others, which function together with EPS-15 homology domain-containing (EHD) proteins in non-T cell systems. To date, the role of the EHD protein family in T cell function remains unexplored. We generated conditional EHD1/3/4 knockout mice using CD4-Cre and crossed these with mice bearing a myelin oligodendrocyte glycoprotein-specific TCR transgene. We found that CD4+ T cells from these mice exhibited reduced Ag-driven proliferation and IL-2 secretion in vitro. In vivo, these mice exhibited reduced severity of experimental autoimmune encephalomyelitis. Further analyses showed that recycling of the TCR-CD3 complex was impaired, leading to increased lysosomal targeting and reduced surface levels on CD4+ T cells of EHD1/3/4 knockout mice. Our studies reveal a novel role of the EHD family of endocytic recycling regulatory proteins in TCR-mediated T cell functions.

EHD1 and RUSC2 Control Basal Epidermal Growth Factor Receptor Cell Surface Expression and Recycling.

Epidermal growth factor receptor (EGFR) is a prototype receptor tyrosine kinase and an oncoprotein in many solid tumors. Cell surface display of EGFR is essential for cellular responses to its ligands. While postactivation endocytic trafficking of EGFR has been well elucidated, little is known about mechanisms of basal/preactivation surface display of EGFR. Here, we identify a novel role of the endocytic regulator EHD1 and a potential EHD1 partner, RUSC2, in cell surface display of EGFR. EHD1 and RUSC2 colocalize with EGFR in vesicular/tubular structures and at the Golgi compartment. Inducible EHD1 knockdown reduced the cell surface EGFR expression with accumulation at the Golgi compartment, a phenotype rescued by exogenous EHD1. RUSC2 knockdown phenocopied the EHD1 depletion effects. EHD1 or RUSC2 depletion impaired the EGF-induced cell proliferation, demonstrating that the novel, EHD1- and RUSC2-dependent transport of unstimulated EGFR from the Golgi compartment to the cell surface that we describe is functionally important, with implications for physiologic and oncogenic roles of EGFR and targeted cancer therapies.