Osborne, Douglas G.

Abstract A key component in T cell activation is the endosomal recycling of receptors to the cell surface allowing for continual integration of signaling and antigen recognition. Multiple early endosomal associated proteins have been found to interact with T cell surface receptors and play a role in the recycling and transport of these receptors to the cell surface. One endosomal protein possibly involved in T cell receptor transport is sorting nexin 17 (SNX17). SNX17 has been found to bind with receptors involved in T cell activation, but its role in receptor recycling and T cell activation is unknown. Using lentivirus shRNA against SNX17, we have found that the knockdown of the SNX17 protein resulted in fewer T-APC conjugates, lower CD69, TCR, and LFA-1 surface expression, as well as lower overall TCR recycling compared to control T cells. Using immunofluorescence, we have found that SNX17 colocalizes with TCR and localizes to the peripheral-SMAC at the immune synapse in T-APC conjugates. This data suggest that SNX17 plays a synergistic role in the maintenance of normal surface levels of activating receptors and integrins to permit optimum T cell activation at the immune synapse.

Key Points T-cell activation induces TCR transactivation of CXCR4 to stabilize cytokine mRNA transcripts via a PREX1-Rac1–signaling pathway. Inhibition of the TCR-CXCR4–signaling pathway impairs TCR-dependent and TCR-independent cytokine secretion by CTCL cells.

Abstract A key component in T cell activation is the endosomal recycling of receptors to the cell surface, thereby allowing continual integration of signaling and Ag recognition. One protein potentially involved in TCR transport is sorting nexin 17 (SNX17). SNX proteins have been found to bind proteins involved in T cell activation, but specifically the role of SNX17 in receptor recycling and T cell activation is unknown. Using immunofluorescence, we find that SNX17 colocalizes with TCR and localizes to the immune synapse in T– conjugates. Significantly, knockdown of the SNX17 resulted in fewer T–APC conjugates, lower CD69, TCR, and LFA-1 surface expression, as well as lower overall TCR recycling compared with control T cells. Lastly, we identified the 4.1/ezrin/radixin/moesin domain of SNX17 as being responsible in the binding and trafficking of TCR and LFA-1 to the cell surface. These data suggest that SNX17 plays a role in the maintenance of normal surface levels of activating receptors and integrins to permit optimum T cell activation at the immune synapse.

COMMD1 deficiency results in defective copper homeostasis, but the mechanism for this has remained elusive. Here we report that COMMD1 is directly linked to early endosomes through its interaction with a protein complex containing CCDC22, CCDC93, and C16orf62. This COMMD/CCDC22/CCDC93 (CCC) complex interacts with the multisubunit WASH complex, an evolutionarily conserved system, which is required for endosomal deposition of F-actin and cargo trafficking in conjunction with the retromer. Interactions between the WASH complex subunit FAM21, and the carboxyl-terminal ends of CCDC22 and CCDC93 are responsible for CCC complex recruitment to endosomes. We show that depletion of CCC complex components leads to lack of copper-dependent movement of the copper transporter ATP7A from endosomes, resulting in intracellular copper accumulation and modest alterations in copper homeostasis in humans with CCDC22 mutations. This work provides a mechanistic explanation for the role of COMMD1 in copper homeostasis and uncovers additional genes involved in the regulation of copper transporter recycling.