Paxillin binding to the cytoplasmic domain of CD103 promotes cell adhesion and effector functions for CD8+ resident memory T cells in tumors

CD8+/CD103+ tissue resident memory T cells (TRM cells) accumulate in several human solid tumors where they have been associated with a favorable prognosis. However, the role of CD103 - the α subunit of the integrin αEβ7 (also known as CD103) - in the retention and functions of these TRM is undefined. In this report, we investigated the role of CD103 cytoplasmic domain and the focal adhesion-associated protein paxillin (Pxn) in downstream signaling and functional activities triggered through αE/CD103 chain. Binding to immobilized recombinant (r)E-cadherin-Fc of CD103 integrin expressed on tumor-specific CTL clones promotes phosphorylation of Pxn and Pyk2 and binding of Pxn to the αE/CD103 subunit tail. Inhibition of Pxn phosphorylation by the Src inhibitor saracatinib or its knockdown via shRNA dramatically altered adhesion and spreading of freshly isolated CD8+/CD103+ lung-tumor-infiltrating lymphocytes (TIL) and CD103+ tumor-specific CTL clones. Inhibition of Pxn phosphorylation with saracatinib in these CTL clones also severely compromised their functional activities toward autologous tumor cells. Using Jurkat T cells as a model to study CD103 integrin activation, we demonstrated a key role of serine residue S1163 of the αE chain intracellular domain in polarization of CD103 and recruitment of lysosomes and Pxn at the contact zone of T lymphocytes with rE-cadherin-Fc-coated beads. Overall, our results show how Pxn binding to the CD103 cytoplasmic tail triggers αEβ7 integrin outside-in signaling that promotes CD8+ T-cell migratory behavior and effector functions. These results also explain the more favorable prognosis associated with retention of TRM cells in the tumor microenvironment.

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