Stromal Cell-Derived Factor-1-Induced LFA-1 Activation During In Vivo Migration of T Cell Hybridoma Cells Requires Gq/11, RhoA, and Myosin, as well as Gi and Cdc42

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Abstract
Dissemination of T cell hybridomas in mice, a model for in vivo migration of memory T cells and for T lymphoma metastasis, depends on the chemokine stromal cell-derived factor-1 (SDF-1) and the integrin LFA-1 and correlates well with invasion into fibroblast cultures. In addition to the known role of the pertussis toxin-sensitive heterotrimeric GTPase Gi, we show that also the pertussis toxin-insensitive GTPase Gq/11 is required for dissemination and invasion. Furthermore, we show that the small GTPases, Cdc42 and RhoA, are involved, and that invasion is blocked by inhibitors of actinomyosin contraction. Gq/11, RhoA, and contraction are specifically required for LFA-1 activation, since 1) they are essential for LFA-1-dependent migration toward low SDF-1 concentrations through ICAM-1-coated filters, but not for migration toward high SDF-1 levels, which is LFA-1 independent; 2) G protein (AlF4−)-induced adhesion to ICAM-1 requires RhoA and contraction; 3) constitutively active Gq induces aggregation, mediated by LFA-1. We previously reported that binding of this activated LFA-1 to ICAM-1 triggers a signal, transduced by the ζ-associated protein 70 tyrosine kinase, that activates additional LFA-1 molecules. This amplification of LFA-1 activation is essential for invasion. We show here that ζ-associated protein 70-induced LFA-1 activation requires neither Cdc42 and RhoA nor contraction and is thus quite different from that induced by SDF-1. We conclude that two modes of LFA-1 activation, with distinct underlying mechanisms, are required for the in vivo migration of T cell hybridomas.