D120 and K152 within the PH Domain of T Cell Adapter SKAP55 Regulate Plasma Membrane Targeting of SKAP55 and LFA-1 Affinity Modulation in Human T Lymphocytes

ABSTRACT

The β2-integrin lymphocyte function-associated antigen 1 (LFA-1) is needed for the T cell receptor (TCR)-induced activation of LFA-1 to promote T cell adhesion and interaction with antigen-presenting cells (APCs). LFA-1-mediated cell-cell interactions are critical for proper T cell differentiation and proliferation. The Src kinase-associated phosphoprotein of 55 kDa (SKAP55) is a key regulator of TCR-mediated LFA-1 signaling (inside-out/outside-in signaling). To gain an understanding of how SKAP55 controls TCR-mediated LFA-1 activation, we assessed the functional role of its pleckstrin homology (PH) domain. We identified two critical amino acid residues within the PH domain of SKAP55, aspartic acid 120 (D120) and lysine 152 (K152). D120 facilitates the retention of SKAP55 in the cytoplasm of nonstimulated T cells, while K152 promotes SKAP55 membrane recruitment via actin binding upon TCR triggering. Importantly, the K152-dependent interaction of the PH domain with actin promotes the binding of talin to LFA-1, thus facilitating LFA-1 activation. These data suggest that K152 and D120 within the PH domain of SKAP55 regulate plasma membrane targeting and TCR-mediated activation of LFA-1.

KEYWORDS:

• LFA-1
• SKAP55
• adhesion

Supplemental material for this article may be found at https://doi.org/10.1128/MCB.00509-16.

ACKNOWLEDGMENTS

We thank Anke Ramonat for excellent technical assistance and Nirdosh Dadwal for purification of proteins.

This work was supported by the medical faculty of the Otto von Guericke University (stipend for A.W.) and DFG grants CRC 854 (B10, B12, B19, and Z01 for C.F., S.K., B.S., A.J.M., and/or L.P.) and CRC 958/765 (A7 or C4 for C.F.).

We declare no competing financial interest.