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.

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 G(i), we show that also the pertussis toxin-insensitive GTPase G(q/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. G(q/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 (AlF(4)(-))-induced adhesion to ICAM-1 requires RhoA and contraction; 3) constitutively active G(q) 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 zeta-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 zeta-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.