The functional activity of integrins is dynamically regulated by T cell receptor stimulation and by protein kinase C (PKC). We report a novel function for the PKC effector protein kinase D1 (PKD1) in integrin activation. Constitutively active and kinase-inactive PKD1 mutants lacking the PKD1 pleckstrin homology (PH) domain block phorbol ester- and TCR-mediated activation and clustering of β1 integrins. The PH domain of PKD1 mediates the association of PKD1 with the GTPase Rap1 and is central to Rap1 activation and membrane translocation in T cells. Furthermore, PKD1 and Rap1 associate with β1 integrins in a manner that is dependent on the carboxy-terminal end of the β1 integrin subunit cytoplasmic domain. β1 integrin expression is required for Rap1 activation and membrane localization of the PKD1-Rap1 complex. Therefore, PKD1 promotes integrin activation in T cells by regulating Rap1 activation and membrane translocation via interactions with the β1 integrin subunit cytoplasmic domain.
Bibliographical noteFunding Information:
We thank R. Johnson and P. Champoux for technical assistance; Drs. E. Peterson, P. Schwartzberg, S. Matthews, and D. Cantrell for helpful discussions and advice; and Drs. D. Cantrell, S. Matthews, M. Ginsberg, D. Rose, J. Bos, J. Miller, M. Mescher, M. Jenkins, E. Peterson, M. Philips, and D. Mueller for providing reagents and DNA constructs. We also thank J. Ojia and J. Sedgewick from the Biomedical Image Processing Lab of the University of Minnesota for assistance with confocal microscopy and image analysis and J. Sederstrom and G. Veltri from the University of Minnesota Cancer Center Flow Cytometry Core Facility for assistance with cell sorting. This work was supported by National Institutes of Health (NIH) grants AI31126 and AI38474 (to Y.S.), NIH grant T32 CA009138 (to R.B.M. and D.M.D.), American Heart Association grant 0120599Z (to D.M.D), and NIH grant T32 HL07741 (to A.C.Q.).