Serine phosphorylation of paxillin by heregulin-β1: role of p38 mitogen activated protein kinase

Abstract

The mechanisms through which heregulin (HRG) regulates the progression of breast cancer cells to a more invasive phenotype are currently unknown. Recently we have shown that HRG treatment of breast cancer cells leads to the formation of lamellipodia/ ®lopodia, and increased cell migration and invasiveness through the phosphatidylinositol 3-kinase (PI-3 kinase).Since the process of cell migration must involve changes in adhesion, we explored the potential HRG regulation of paxillin, a major cytoskeletal phosphoprotein of focal adhesion. We report that HRG stimulation of noninvasive breast cancer cells resulted in stimulation of p38 mitogen-activated protein kinase (p38 MAPK ), extracellular signal-regulated kinases (ERK) and PI-3K, and a concurrent unexpected increase in the level of paxillin phosphorylation on serine residue which was sensitive to protein-phosphatase 2b but not to protein tyrosine phosphatase 1. In addition, HRG triggered a rapid redistribution of paxillin to the perinuclear regions from the tyrosine-phosphorylated focal adhesions, and increased cell scattering. There was no e ect of HRG on the state of phosphorylation and localization of focal adhesion kinase. The HRG-induced increase in serine phosphorylation of paxillin and cell scattering were selectively inhibited by a speci®c inhibitor of p38 MAPK or a dominant-negative p38 MAPK mutant, but not by inhibitors of p42/44 MAPK or PI-3 kinase pathways. For the ®rst time our results have shown that HRG, a potent migratory growth factor stimulates serine phosphorylation of paxillin. These ®ndings suggest a role of p38 MAPKdependent signal transduction pathway(s) in serine phosphorylation and disassembly of the paxillin from the focal complexes during HRG-induced cell shape alterations and motility.

SLK-mediated phosphorylation of paxillin is required for focal adhesion turnover and cell migration

“…Additionally, cells expressing this mutant paxillin exhibit a defect in spreading and protrusive abilities and migrate more actively [66,85,86,117]. Collectively, this would suggest that paxillin serine phosphorylation regulates the degradation status of the protein, which in turn, is important in the modulation of paxillin-dependent membrane dynamics affecting cell motility.…”

“…Whereas tyrosine phosphorylation of paxillin by FAK/Src is well documented, much less is known of the consequences of paxillin serine phosphorylation or the kinases that are involved [32,47,66,86,117]. Like tyrosine phosphorylation, paxillin serine/threonine phosphorylation is induced by a variety of stimuli: for example, cellular activation via integrin ligation has been documented to result in phosphorylation of S188/190 [47].…”

“…Paxillin serine/threonine phosphorylation has also been shown to be stimulated by growth factors such as angiotensin II, activin A, TGF-β, EGF, heregulin and interleukin [47,117,118].…”

TGFβ pathobiology in the eye

“…[30][31][32] Although Smad2/3 signaling is relatively specific to the binding of ligands of the TGFb/activin family to cell surface receptors, investigators are discovering that MAPKs (p42/p44 Erk1/2, JNK, or p38MAPK) phosphorylate specific sites in the middle linker region of Smad2/3, sites that are distinct from the C-terminus that is phosphorylated by the TGFb II receptor (Figure 2). [33][34][35][36] Thus, ligands capable of activating MAPKs potentially modulate Smad signaling induced by TGFb. It has recently been demonstrated that p38MAPK activate phosphorylation of Smad3 in the middle linker region, which enhances Smad3/4 complex formation and nuclear translocation, 37 consistent with our finding of diminished Smad3/4 reporter gene activity in the presence of a p38MAPK inhibitor.…”

Expression profiling of gastric adenocarcinoma using cDNA array

“…16 The p38 MAP kinase-dependent signal transduction pathway(s) plays a role in serine phosphorylation and disassembly of paxillin. 17 Expression of VEGF, a multifunctional cytokine, is crucial in angiogenesis during the development of cancer and correlates with disease recurrence in patients with early gastric carcinoma. 18 p38 MAP kinase activation by VEGF mediates actin reorganization and cell migration in human endothelial cells.…”