Tumor Progression Locus 2 Mediates Signal-Induced Increases in Cytoplasmic Calcium and Cell Migration

The mitogen-activated protein kinase kinase kinase (MAPKKK or MAP3K) tumor progression locus 2 (Tpl2) is required for the transduction of signals initiated by the thrombin-activated G protein-coupled receptor (GPCR) protease-activated receptor-1 (PAR1), which promote reorganization of the actin cytoskeleton and cell migration. Here, we show that Tpl2 is activated through G alpha(i2)-transduced GPCR signals. Activated Tpl2 promoted the phosphorylation and activation of phospholipase C-beta 3 (PLC beta(3)); consequently, Tpl2 was required for thrombin-dependent production of inositol 1,4,5-trisphosphate (IP3), IP3-mediated cytoplasmic calcium ion (Ca2+) signals, and the activation of classical and novel members of the protein kinase C (PKC) family. A PKC-mediated feedback loop facilitated extracellular signal-regulated kinase (ERK) activation in response to Tpl2 and contributed to the coordinate regulation of the ERK and Ca2+ signaling pathways. Pharmacological and genetic studies revealed that stimulation of cell migration by Tpl2 depends on both of these pathways. Tpl2 also promoted Ca2+ signals and cell migration from sphingosine 1-phosphate-responsive GPCRs, which also couple to G alpha(i), from Wnt5a, and from the interleukin-1 beta (IL-1 beta) receptor, a member of the Toll-IL-1R (TIR) domain family. Our data provide new insights into the role of Tpl2 in GPCR-mediated Ca2+ signaling and cell migration.