Inhibition of T Cell Activation and Function by the Adaptor Protein CIN85.

The adaptor CIN85 inhibits T cell activation through its association with the phosphatase Sts-2 after TCR stimulation. Thou shalt not CIN The ubiquitously expressed adaptor protein CIN85 has distinct roles in different cell types. This adaptor inhibits the activation of the receptor tyrosine kinases EGFR and PDGFR but promotes B cell receptor signaling. To determine its function in T cells, Kong et al. compared the activation of mouse T cells lacking CIN85 or the highly related adaptor CD2AP. Only loss of CIN85 augmented T cell growth and IL-2 production. CIN85 associated with the inhibitory phosphatase Sts-2 and promoted its recruitment to T cell receptor microclusters after activation. These data define a previously unknown inhibitory interaction, which could be targeted to augment T cell function in cancer and immunity. T cell activation is initiated by signaling molecules downstream of the T cell receptor (TCR) that are organized by adaptor proteins. CIN85 (Cbl-interacting protein of 85 kDa) is one such adaptor protein. Here, we showed that CIN85 limited T cell responses to TCR stimulation. Compared to activated wild-type (WT) T cells, those that lacked CIN85 produced more IL-2 and exhibited greater proliferation. After stimulation of WT T cells with their cognate antigen, CIN85 was recruited to the TCR signaling complex. Early TCR signaling events, such as phosphorylation of ζ-chain–associated protein kinase 70 (Zap70), Src homology 2 (SH2) domain–containing leukocyte protein of 76 kDa (SLP76), and extracellular signal–regulated kinase (Erk), were enhanced in CIN85-deficient T cells. The inhibitory function of CIN85 required the SH3 and PR regions of the adaptor, which associated with the phosphatase suppressor of TCR signaling–2 (Sts-2) after TCR stimulation. Together, our data suggest that CIN85 is recruited to the TCR signaling complex and mediates inhibition of T cell activation through its association with Sts-2.