TGFβ-induced focal complex formation in epithelial cells is mediated by activated ERK and JNK MAP kinases and is independent of Smad4

Abstract

Advanced malignancies often exhibit increased concentrations of transforming growth factor-beta (TGF beta), which has been suggested to promote invasion and metastasis. While inhibition of epithelial cell proliferation in response to TGF beta is mainly mediated by the well-characterised Smad pathway, the molecular mechanism leading to TGF beta-induced invasiveness and metastasis are largely unknown. To elucidate these mechanisms, we compared TGF beta1 signalling in MCF-7 and the Smad4-negative MDA-MB-468 breast cancer cells. Both cell lines react to TGF beta1 treatment with decreased subcortical actin and increased numbers of focal contacts. TGF beta1-induced cell migration was strongly dependent on the activation of extracellular signal-regulated kinase (ERK) and Jun N-terminal kinase (JNK). These mitogen-activated protein kinases were phosphorylated in response to TGF beta and subsequently translocated into focal contacts. Inhibition of the TGF beta type I receptor ALK5 slightly reduced phosphorylation of ERK in MCF-7 cells, but neither inhibited phosphorylation of ERK in MDA-MB-468 cells nor TGF beta1-induced migration of both cell lines. In contrast, ALK5 inhibition effectively blocked Smad2 phosphorylation. In addition to ERK and JNK, the monomeric GTPase RhoA was activated by TGF beta1 and necessary for TGF beta-induced migration. Taken together, our study identifies a role of ERK and JNK activation and association of activated MAPKs with focal complexes in TGF beta1-induced cell migration in epithelial cells. These TGF beta-dependent processes were mediated independently of Smad4.

Activin receptor‐like kinase 1 inhibits human microvascular endothelial cell migration: Potential roles for JNK and ERK

“…These data suggest that JNK and ERK might be targets for the inhibitory effects of ALK1. Such a link between JNK, ERK, and TGFb-family members has been previously shown by several groups (Atfi et al, 1997;Reimann et al, 1997) and evidence indicates that these kinases could be regulated by TGFb family members in a Smad-independent manner (Imamichi et al, 2005;Zhang et al, 2005). In our previous work, we could demonstrate that ALK1ca-induced inhibition of endothelial cell migration was not due to a decrease in motility but rather to a defect in cell orientation that could be visualized by a decrease in the expression of the focal adhesion protein paxillin at the edge of the wound (Lamouille et al, 2002).…”

TGFβ-induced downregulation of E-cadherin-based cell-cell adhesion depends on PI3-kinase and PTEN

“…Although important cellular effects of TGF␤ 1 are transmitted by the Smad pathway, some Smad-independent effects have been described, such as activation of RhoA, Ras and ERK, p38 MAPK or PI3-kinase (Imamichi et al, 2005;Mulder, 2000;Bhowmick et al, 2001;Bakin et al, 2002). Whereas the phosphorylation of ␤-catenin is Smad4-independent in pancreatic cancer cells, our data show that invasion of a collagen matrix depends on Smad4.…”

TβRI/Alk5-independent TβRII signaling to ERK1/2 in human skin cells according to distinct levels of TβRII expression

“…Tyrosine-phosphorylated ShcA in turn recruits the Grb2/Sos complex that activates the Ras-Raf-Mek1-ERK1/2 cascade (Lee et al, 2007). By contrast, Imamichi and co-workers showed that the TbRI inhibitor SB431542 could not fully block TGFb-induced ERK1/2 activation, suggesting that TbRI is not involved in ERK1/2 activation (Imamichi et al, 2005). However, none of these studies specifically addressed the roles of TbRII and TbRI in TGFb signaling to ERK1/2.…”