ERK2 but Not ERK1 Induces Epithelial-to-Mesenchymal Transformation via DEF Motif-Dependent Signaling Events

Abstract

Summary Hyperactivation of Ras-ERK1/2 signaling is critical to the development of many human malignancies but little is known regarding the specific contribution of ERK1 or ERK2 to oncogenic processes. We demonstrate that ERK2 but not ERK1 signaling is necessary for Ras-induced epithelial-to-mesenchymal transformation (EMT). Further, ERK2 but not ERK1 overexpression is sufficient to induce EMT. Many ERK1/2 interacting proteins contain amino acid motifs, e.g. DEF or D-motifs, which regulate docking with ERK1/2. Remarkably, ERK2 signaling to DEF motif-containing targets is required to induce EMT and correlates with increased migration, invasion and survival. Importantly, the late response gene product Fra1 is necessary for Ras- and ERK2-induced EMT through up-regulation of ZEB1/2 proteins. Thus, an apparent critical role for ERK2 DEF motif signaling during tumorigenesis is the regulation of Fra1, and the subsequent induction of ZEB1/2, suggesting a potential therapeutic target for Ras-regulated tumorigenesis.

Fra-1/AP-1 induces EMT in mammary epithelial cells by modulating Zeb1/2 and TGFβ expression

“…Several reports have connected Fra-1/AP-1 in human breast cancer to increased expression of the EMT-TFs Zeb1 and Zeb2 and to a lesser extent Slug. [12][13][14][15]17 We investigated whether Fra-1/AP-1 and the EMT-TFs also correlated in mouse mammary EMT. Expression of Fra-1 in EpH4 cells induced EMT and increased proliferation, migration and invasiveness.…”

“…Our findings are consistent with reports that Fra-1 affects the proliferation and motility of human breast cancer cell lines 17,42 and that Fra-1 is a critical EMT effector downstream of Ras signalling. 13,14 Ras and TGFβ cooperate to induce and stabilize a mesenchymal switch in EpH4 cells. 21,22,40 Unlike human breast cancer cells where upstream signalling kinases activation is required, 14,16 ectopic Fra-1 expression was sufficient for EMT and tumorigenesis in EpH4 cells.…”

“…13,14 Ras and TGFβ cooperate to induce and stabilize a mesenchymal switch in EpH4 cells. 21,22,40 Unlike human breast cancer cells where upstream signalling kinases activation is required, 14,16 ectopic Fra-1 expression was sufficient for EMT and tumorigenesis in EpH4 cells. Moreover, Fra-1 increased TGFβ expression and production, similarly to c-Fos and unlike oncogenic Ras, 43 thus TGFβ treatment was not necessary for EMT in EpFra1 cells.…”

“…We demonstrated that Fra-1 binds to two regions in the murine tgfb1 promoter containing several AP-1-binding elements. As autocrine TGFβ production has also been observed in human breast cancer cells, where extracellular signal-regulated kinase 2 (ERK2)-induced EMT depends on Fra-1 14 and as Fra-1 binds the human TGFB2 gene in colorectal cancer cells, 44 it is tempting to speculate that Fra-1/AP-1 modulates the transcription of TGFB genes in the context of EMT. However, inhibition of TGFβ signalling in EpFra1 cells only partially restored epithelial markers expression, similarly to the situation during Fos-or ERK2-induced EMT.…”

“…10,11 Strikingly, suppression of Fra-1 restores epithelial characteristics, including E-cadherin expression, and abrogates the invasive potential of human breast cancer cell lines. 12,13 Furthermore, Fra-1 has been implicated in human breast cancer EMT through increased expression of the Snai2/Slug, Zinc finger E-box-binding homeobox 1 (Zeb1) and Zeb2 EMT-TFs, [13][14][15][16][17] although the mechanisms how Fra-1 modulates EMT-TFs expression are not fully understood.…”