THE CHEMOKINE MONOCYTE CHEMOTACTIC PROTEIN-1 TRIGGERS JANUS KINASE-2 ACTIVATION AND TYROSINE PHOSPHORYLATION OF THE CCR2B RECEPTOR

The chemokines are a growing family of low m.w., 70- to 80-residue pro inflammatory cytokines that operate by interacting with G protein-coup led receptors, Chemokines are involved in cell migration and in the ac tivation of specific leukocyte subsets. Using the Mono Mac 1 monocytic cell line, we show that monocyte chemotactic protein 1 (MCP-1) trigge rs activation of the Janus kinase 2 (JAK2)/STAT3 pathway and CCR2 rece ptor tyrosine phosphorylation. Both Ca2+ mobilization and cell migrati on are blocked in Mono Mac 1 cells by tyrphostin B42, a specific JAK2 kinase inhibitor. Within seconds of MCP-I activation, JAK2 phosphoryla tes CCR2 at the Tyr(139) position and promotes JAK2/STAT3 complex asso ciation to the receptor. This MCP-l-initiated phosphorylation and asso ciation to JAK2 is also observed in CCR2B-transfected HEK293 cells. In contrast, when a CCR2B Tyr(139)Phe mutant is expressed in HEK293 cell s, it is not phosphorylated in tyrosine and triggers neither JAK2/STAT 3 activation nor Ca2+ mobilization in response to MCP-I, These results implicate the tyrosine kinase pathway in early chemokine signaling, s uggesting a key role for this kinase in later events.