Intracellular trafficking of tim-1 to cell-cell contacts in the context of lymphocyte activation

Laburpena

T cell/Transmembrane Immunoglobulin and Mucin domain protein-1 (TIM-1) has been linked to asthma, allergy and atopic diseases. TIM-1 preferentially locates in intracellular compartments. Our results have demonstrated that both human and mouse TIM-1 locate in different types of endosomes and TIM-1 structural domains are important for TIM-1 sorting in intracellular vesicles. BALB/c variant of mouse TIM-1 has a longer mucin domain and it is more efficiently sorted to intracellular vesicle than C57BL/6 variant with shorter mucin domain. High-affinity ligands of TIM-1 such as PtdSer increase the amount of TIM-1 at cell surface. TIM-1 accumulates at intercellular junctions of transfected cells (homotypic TIM1-TIM1 interaction) and cellular contacts with apoptotic cells and it could be transferred through exosomes to recipient (apoptotic) cells. TIM-1 accumulation at cell-cell contacts is N-terminal domain and MILIBS dependent. This interaction could be mediated by PtdSer or by an undetermined co-factor that induces direct interaction between molecules of opposite cells. It has been reported that TIM-1 is physically associated with CD3, a major component of T cell receptor (TCR). Our results show that major intracellular pool of TIM-1 translocates to immunological synapse (IS) and colocalizes with CD3 in central supramolecular activation cluster (cSMAC), where it can enhance antigen-dependent T cell response in association with CD3-TCR. Nevertheless, cell surface TIM-1 does not translocate to IS and locates away from it, in the distal pole complexe. Hence, cellular localization of TIM-1 determines its differential trafficking in T cells during IS formation. Increase of cell surface TIM-1 by interaction with liposomes exposing PtdSer prevents its translocation to IS. This could explain why TIM-1 has been described to have a dual function as a T cell costimulatory molecule.