Abstract
Epithelial tumor cells often acquire malignant properties, such as invasion/metastasis and uncontrolled cell growth, by undergoing epithelial–mesenchymal transition (EMT). However, the mechanisms by which EMT contributes to malignant progression remain elusive. Here we show that the Rho guanine nucleotide exchange factor (GEF) ARHGEF5 promotes tumor malignancy in a manner dependent on EMT status. We previously identified ARHGEF5, a member of the Dbl family of GEFs, as a multifunctional mediator of Src-induced cell invasion and tumor growth. In the present study, ARHGEF5 was upregulated during tumor growth factor-β-induced EMT in human epithelial MCF10A cells, and promoted cell migration by activating the Rho-ROCK pathway. ARHGEF5 was necessary for the invasive and in vivo metastatic activity of human colorectal cancer HCT116 cells. These findings underscore the crucial role of ARHGEF5 in cell migration and invasion/metastasis. An in vivo tumorigenesis assay revealed that ARHGEF5 had the potential to promote tumor growth via the phosphatidylinositol 3-kinase (PI3K) pathway. However, ARHGEF5 was not required for tumor growth in epithelial-like human colorectal cancer HCT116 and HT29 cells, whereas the growth of mesenchymal-like SW480 and SW620 cells depended on ARHGEF5. Induction of EMT by tumor necrosis factor-α or Slug in HCT116 cells resulted in the dependence of tumor growth on ARHGEF5. In these mesenchymal-like cells, Akt was activated via ARHGEF5 and its activity was required for tumor growth. Analysis of a transcriptome data set revealed that the combination of ARHGEF5 upregulation and E-cadherin downregulation or Snail upregulation was significantly correlated with poor prognosis in patients with colorectal cancers. Taken together, our findings suggest that EMT-induced ARHGEF5 activation contributes to the progression of tumor malignancy. ARHGEF5 may serve as a potential therapeutic target in a subset of malignant tumors that have undergone EMT.
Highlights
The malignant progression of tumor cells is associated with acquisition of invasive and metastatic properties and uncontrolled cell growth.[1,2] Over the course of this process, epithelial tumor cells often undergo epithelial–mesenchymal transition (EMT),[3,4,5,6] a reversible phenotypic change that takes place during embryonic development, wound healing, and malignant progression
As tumor growth factor-β (TGF-β) signaling is basally activated in MCF10A cells via the autocrine action of TGF-β,32 blockade of TGF-β signaling with the TGF-β receptor inhibitor SD208 downregulated ARHGEF5 expression (Figure 1c)
ARHGEF5-dependent activation of Akt was required for tumor growth from mesenchymal-like colorectal cancer cells. These results suggest that the EMT-mediated assembly of the ARHGEF5 axis at cell adhesion sites have a crucial role in promoting both cell invasion/metastasis and tumor growth in mesenchymal-like cancer cells (Supplementary Figure S5)
Summary
The malignant progression of tumor cells is associated with acquisition of invasive and metastatic properties and uncontrolled cell growth.[1,2] Over the course of this process, epithelial tumor cells often undergo epithelial–mesenchymal transition (EMT),[3,4,5,6] a reversible phenotypic change that takes place during embryonic development, wound healing, and malignant progression. During EMT, epithelial cells lose cell–cell junctions and apicobasal polarity, and acquire invasive phenotypes that are essential for metastatic spread. These directional shifts in gene expression are regulated by several transcription factors, including Snail, Slug and ZEB1/2; these are induced by cell signaling activated by cytokines and growth factors such as tumor growth factor-β (TGF-β),[7] tumor necrosis factor-α (TNF-α),[8,9] epidermal growth factor[10] and hepatocyte growth factor.[10]. These observations indicate that an aberrant EMT process leads to poor clinical outcomes.[13,14] suppression of EMT can increase sensitivity to anticancer drugs.[15,16] the identification of EMT characteristics and inhibitors of EMT-related molecules could potentially contribute to the treatment of cancer
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