Bi-directional Regulation of Ser-985 Phosphorylation of c-Met via Protein Kinase C and Protein Phosphatase 2A Involves c-Met Activation and Cellular Responsiveness to Hepatocyte Growth Factor

Abstract

Hepatocyte growth factor (HGF), 1 originally identified and cloned as a mitogenic protein for hepatocytes (1-3), evokes multiple cellular responses, including mitogenesis, morphogenesis, migration, and anti-apoptosis (4 -6). These biological activities of HGF are triggered by tyrosine phosphorylation of c-Met, a specific receptor tyrosine kinase for HGF (7). Biological activities of HGF support tissue organization during development and regeneration of organs, including the liver, kidney, placenta, and skeletal muscle (4 -6), but unregulated and/or constitutive activation of the c-Met receptor endows tumor cells with invasive and metastatic characteristics (8, 9).The c-Met receptor is a heterodimeric protein composed of extracellular ␣-chain and membrane-spanning ␤-chain, which contains an intracellular tyrosine kinase domain. Specific binding of HGF to the c-Met receptor activates tyrosine kinase activity, thereby facilitating phosphorylation of C-terminal tyrosine residues, so-called multifunctional docking sites (10, 11). In addition to the catalytic tyrosine kinase domain, the ␤-chain contains a juxtamembrane domain of 47 amino acid residues, which is highly conserved in distinct species (12). Previous studies indicated that a serine residue at position 985, which resides in the juxtamembrane domain of c-Met, is phosphorylated by treatment of cells with 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator for protein kinase C (PKC). Most interesting, Ser-985 phosphorylation was associated with decreased tyrosine phosphorylation of the c-Met receptor (13); however, neither regulatory mechanisms nor the biological significance of the Ser-985 phosphorylation of c-Met has been elucidated.In the present study, we found that the phosphorylation status of juxtamembrane Ser-985 of the c-Met receptor is bidirectionally regulated through reverse activities of PKC␦/⑀ and protein phosphatase 2A (PP2A), a serine/threonine protein phosphatase. Likewise, oxidative stress in cells induced PKCmediated Ser-985 phosphorylation, and this was associated with inhibition of c-Met tyrosine phosphorylation and subsequent biological responses upon HGF stimulus. Our observations mean that the Ser-985 phosphorylation of c-Met mediated via PKCs and PP2A provides a unique mechanism, which confers cellular responsiveness/unresponsiveness to HGF, depending on the extracellular environment and conditions.

Lysophosphatidic acid modulates c-Met redistribution and hepatocyte growth factor/c-Met signaling in human bronchial epithelial cells through PKC δ and E-cadherin

“…Here we present evidence that LPA-induced c-Met serine phosphorylation and redistribution to plasma membrane is dependent on activation of PKC δ in HBEpCs. These results are consistent with the study in A549 cells, in which PKC δ regulates ser-985 phosphorylation of c-Met [37]. In conclusion, PKC isoforms play a bi-directional regulatory role of c-Met intracellular traffic: PKC α regulates "traffic in", and PKC δ regulates "traffic out".…”

“…Recently, serine phosphorylation of c-Met by PKC has been associated with decreased tyrosine phosphorylation of c-Met and has been shown to negatively regulate HGF / c-Met biological function [36,37]. Unlike LPA-mediated tyrosine phosphorylation of PDGF-Rβ and EGF-R [20,21] …”

“…In contrast, Gandino et al showed that PKC activation inhibited tyrosine phosphorylation of c-Met in the gastric carcinoma cell line GTL-16 [36]. Recently, Hashigasako et al demonstrated that HGF-dependent tyrosine phosphorylation of c-Met was largely suppressed with a reciprocal relationship to Ser-985 phosphorylation by PKC δ in A549 cell line [37]. Similar to c-Met, insulin receptors were phosphorylated at serine residues and tyrosine kinase activity was decreased by PKC [38,39].…”

“…Nath et al reported that shedding of c-Met was regulated by LPA-mediated EGF-R transactivation and TIMP-3 sensitive metalloproteinase in A549 cells [37]. The role of LPA in regulating the HGF / c-Met pathways is still not clear.…”

Le récepteur Met fête ses 30 ans

“…La mutation de la Y1003 induit l'activation du récepteur et augmente ses capacités de transformation cellulaire, soulignant l'importance de cette modification (Figure 3). D'autres sites de régulation siègent au niveau du domaine juxtamembranaire de Met, comme la sérine 983, dont la phosphorylation par les PKC (protéine kinase C) réprime son activité [21]. Ce domaine est également la cible de protéases.…”