Autocrine motility factor (neuroleukin, phosphohexose isomerase) induces cell movement through 12-lipoxygenase-dependent tyrosine phosphorylation andserine dephosphorylation events

Autocrine motility factor (AMF) is one of the motility cytokines regulating tumor cell migration, therefore identification of the signaling pathway co upled with it has critical importance. Previous studies revealed several el ements of this pathway predominated by lipoxygenase-PKC activations but the role for tyrosine kinases remained questionable. Motility cytokines freque ntly have mitogenic effect as well, producing activation of overlapping sig naling pathways therefore we have used B16a melanoma cells as models where AMF has exclusive motility effect. Our studies revealed that in B16a cells AMF initiated rapid (1-5 min) activation of the protein tyrosine kinase (PT K) cascade inducing phosphorylation of 179, 125, 95 and 40/37 kD proteins w hich was mediated by upstream cyclo- and lipoxygenases. The phosphorylated proteins were localized to the cortical actin-stress fiber attachment zones in situ by confocal microscopy. On the other hand, AMF receptor activation induced significant decrease in overall serine-phosphorylation level of ce llular proteins accompanied by serine phosphorylation of 200, 90, 78 and 65 kd proteins. The decrease in serine phosphorylation was independent of PTK s, PKC as well as cyclo- and lipoxygenases. However, AMF induced robust tra nslocation of PKC alpha to the stress fibers and cortical actin suggesting a critical role for this kinase in the generation of the motility signal. B ased on the significant decrease in serine phosphorylation after AMF stimul us in B16a cells we postulated the involvement of putative serine/threonine phosphatase(s) upstream lipoxygenase and activation of the protein tyrosin e kinase cascade downstream cyclo- and lipoxygenase(s) in the previously id entified autocrine motility signal.