TGF-β-induced cell motility requires downregulation of ARHGAPs to sustain Rac1 activity

ARHGAP4 Inhibits Proliferation and Growth of SW620 Colon Cancer Cells by Cell Cycle and Differentiation Pathways

The aim of this study is to explore the mechanism by which ARHGAP4 regulates the proliferation and growth of colon cancer cells, and it relates to the metastasis of colorectal cancer (CRC). Various techniques including western blot, CCK8, qRT-PCR, RNA seq assay, plate cloning, subcutaneous tumorigenesis assays, and bioinformatics tools were employed to identify genes that were upregulated or downregulated upon ARHGAP4 knockdown and their involvement in tumor cell proliferation and growth. The expression of ARHGAP4 in T and M stages of CRC uses immunohistochemistry. The expression levels of ARHGAP4 were found to be high in SW620, SW480, and HCT116 cell lines, while they were being low in HT29, LoVo, and NCM460 cell lines. Depletion of ARHGAP4 resulted in inhibited proliferation and growth in SW620 cells and inhibited subcutaneous tumorigenesis in nude mice, whereas overexpression of ARHGAP4 promoted proliferation and growth in HT29 cells and promoted subcutaneous tumorigenesis in nude mice. A total of 318 upregulated genes and 637 downregulated genes were identified in SW620 cells upon ARHGAP4 knockdown. The downregulated genes were primarily associated with cell cycle pathways, while the upregulated genes were enriched in differentiation-related pathways. Notable upregulated genes involved in cell differentiation included KRT10, KRT13, KRT16, IVL, and CD24, while significant downregulation was observed in genes related to the cell cycle such as CCNA2, CDKN2C, CDKN3, CENPA, and CENPF. ARHGAP4 expression is markedly elevated in the M1 stage of CRC compared to the M0 stage, suggesting ARHGAP4 linked to the metastatic in CRC. ARHGAP4 regulates the proliferation and growth of colon cancer cells by up- and downregulated cell cycle and differentiation-related molecules, which may be related to the metastasis of CRC.

Regulation of Cellular-Signaling Pathways by Mammalian Proteins Containing Bacterial EPIYA or EPIYA-Like Motifs Predicted to be Phosphorylated

The effector proteins of several pathogenic bacteria contain the Glu-Pro-Ile-Tyr-Ala (EPIYA) motif or other similar motifs. The EPIYA motif is delivered into the host cells by type III and IV secretion systems, through which its tyrosine residue undergoes phosphorylation by host kinases. These motifs atypically interact with a wide range of Src homology 2 (SH2) domain-containing mammalian proteins through tyrosine phosphorylation, which leads to the perturbation of multiple signaling cascades, the spread of infection, and improved bacterial colonization. Interestingly, it has been reported that EPIYA (or EPIYA-like) motifs exist in mammalian proteomes and regulate mammalian cellular-signaling pathways, leading to homeostasis and disease pathophysiology. It is possible that pathogenic bacteria have exploited EPIYA (or EPIYA-like) motifs from mammalian proteins and that the mammalian EPIYA (or EPIYA-like) motifs have evolved to have highly specific interactions with SH2 domain-containing proteins. In this review, we focus on the regulation of mammalian cellular-signaling pathways by mammalian proteins containing these motifs.

The Snail signaling branch downstream of the TGF-β/Smad3 pathway mediates Rho activation and subsequent stress fiber formation

Cancer cells acquire malignant phenotypes through an epithelial-mesenchymal transition, which is induced by environmental factors or extracellular signaling molecules, including transforming growth factor-β (TGF-β). Among epithelial-mesenchymal transition-associated cell responses, cell morphological changes and cell motility are closely associated with remodeling of the actin stress fibers. Here, we examined the TGF-β signaling pathways leading to these cell responses. Through knockdown experiments in A549 lung adenocarcinoma cells, we found that Smad3-mediated induction of Snail, but not that of Slug, is indispensable for morphological changes, stress fiber formation, and enhanced motility in cells stimulated with TGF-β. Ectopic expression of Snail in SMAD3-knockout cells rescued the defect in morphological changes and stress fiber formation by TGF-β, indicating that the role of Smad3 in these responses is to upregulate Snail expression. Mechanistically, Snail is required for TGF-β-induced upregulation of Wnt5b, which in turn activates RhoA and subsequent stress fiber formation in cooperation with phosphoinositide 3-kinase. However, ectopic expression of Snail in SMAD3-knockout cells failed to rescue the defect in cell motility enhancement by TGF-β, indicating that activation of the Smad3/Snail/Wnt5b axis is indispensable but not sufficient for enhancing cell motility; a Smad3-dependent but Snail-independent pathway to activate Rac1 is additionally required. Therefore, the Smad3-dependent pathway leading to enhanced cell motility has two branches: a Snail-dependent branch to activate RhoA and a Snail-independent branch to activate Rac1. Coordinated activation of these branches, together with activation of non-Smad signaling pathways, mediates enhanced cell motility induced by TGF-β.

Smad2Δexon3 and Smad3 have distinct properties in signal transmission leading to TGF-β-induced cell motility

In mammalian cells, Smad2 and Smad3, two receptor-regulated Smad proteins, play crucial roles in the signal transmission of transforming growth factor-β (TGF-β) and are involved in various cell regulatory processes, including epithelial-mesenchymal transition-associated cell responses, that is, cell morphological changes, E-cadherin downregulation, stress fiber formation, and cell motility enhancement. Smad2 contains an additional exon encoding 30 amino acid residues compared with Smad3, leading to distinct Smad2 and Smad3 functional properties. Intriguingly, Smad2 also has an alternatively spliced isoform termed Smad2Δexon3 (also known as Smad2β) lacking the additional exon and behaving similarly to Smad3. However, Smad2Δexon3 and Smad3 signaling properties have not yet been compared in detail. In this study, we reveal that Smad2Δexon3 rescues multiple TGF-β-induced in vitro cellular responses that would become defective upon SMAD3 KO but does not rescue cell motility enhancement. Using Smad2Δexon3/Smad3 chimeric proteins, we identified that residues Arg-104 and Asn-210 in Smad3, which are not conserved in Smad2Δexon3, are key for TGF-β-enhanced cell motility. Moreover, we discovered that Smad2Δexon3 fails to rescue the enhanced cell motility as it does not mediate TGF-β signals to downregulate transcription of ARHGAP24, a GTPase-activating protein that targets Rac1. This study reports for the first time distinct signaling properties of Smad2Δexon3 and Smad3.

Analysis of ARHGAP4 Expression With Colorectal Cancer Clinical Characteristics and Prognosis

Background

This study aims to analyze the correlation between ARHGAP4 in the expression and clinical characteristics of colorectal cancer (CRC), and the influence of ARHGAP4 expression on the prognosis of CRC, and to evaluate whether ARHGAP4 is a potential prognostic oncotarget for CRC.

Methods

ARHGAP4 was identified using the Gene Expression Omnibus database through weighted gene coexpression network analysis. Using the Gene Expression Profiling Interactive Analysis to perform and analyze the expression and prognosis of ARHGAP4 in CRC. The expression of AGRGAP4 and immune cells was analyzed by the Tumor IMmune Estimation Resource online database. Finally, immunohistochemistry was used to analyze the expression difference and prognosis of ARHGAP4 in CRC and adjacent normal tissues, as well as the relationship between AGRGAP4 expression and clinical features of CRC.

Results

We identified ARHGAP4 that is related to the recurrence of CRC from GSE97781 data. ARHGAP4 has not been reported in CRC. The high expression of ARHGAP4 in select colon adenocarcinoma indicates a poor prognosis by database analysis. In our clinical data results, ARHGAP4 is highly expressed in CRC and lowly expressed in normal tissues adjacent to cancer. Compared with the low-expression group, the high-expression group has a significantly poorer prognosis. In colon cancer, the B-cell, macrophage, neutrophil, and dendritic-cell levels are downregulated after ARHGAP4 gene knockout; the levels of CD8⁺ and CD4⁺ T cells, neutrophils, and dendritic cells are upregulated after the amplification of the ARHGAP4 gene. In addition, ARHGAP4 expression is related to N,M staging and clinical staging.

Conclusion

ARHGAP4 is highly expressed in CRC, and the high expression of ARHGAP4 has a poor prognosis. The expression of ARHGAP4 in CRC is related to the immune cells such as B cells, CD8⁺ and CD4⁺ T cells, macrophages, neutrophils, and dendritic cells. ARHGAP4 is correlated with N,M staging and clinical staging in CRC. ARHGAP4 may be a potential biomarker for the prognosis of CRC.

Pretreatment with valproic acid alleviates pulmonary fibrosis through epithelial-mesenchymal transition inhibition in vitro and in vivo

Epithelial-mesenchymal transition (EMT) plays a crucial role in the development of pulmonary fibrosis. This study aims to investigate the effects of valproic acid (VPA) on EMT in vitro and in vivo. In vitro, EMT was induced by the administration of transforming growth factor-β1 (TGF-β1) in a human alveolar epithelial cell line (A549). The dose effects of VPA (0.1-3 mM) on EMT were subsequently evaluated at different timepoints. VPA (1 mM) was applied prior to the administration of TGF-β1 and the expression of E-cadherin, vimentin, p-Smad2/3 and p-Akt was assessed. In addition, the effects of a TGF-β type I receptor inhibitor (A8301) and PI3K-Akt inhibitor (LY294002) on EMT were evaluated. In vivo, the effects of VPA on bleomycin-induced lung fibrosis were evaluated by assessing variables such as survival rate, body weight and histopathological changes, whilst the expression of E-cadherin and vimentin in lung tissue was also evaluated. A8301 and LY294002 were used to ascertain the cellular signaling pathways involved in this model. The administration of VPA prior to TGF-β1 in A549 cells prevented EMT in both a time- and concentration-dependent manner. Pretreatment with VPA downregulated the expression of both p-Smad2/3 and p-Akt. A8301 administration increased the expression of E-cadherin and reduced the expression of vimentin. LY294002 inhibited Akt phosphorylation induced by TGF-β1 but failed to prevent EMT. Pretreatment with VPA both increased the survival rate and prevented the loss of body weight in mice with pulmonary fibrosis. Interestingly, both VPA and A8301 prevented EMT and facilitated an improvement in lung structure. Overall, pretreatment with VPA attenuated the development of pulmonary fibrosis by inhibiting EMT in mice, which was associated with Smad2/3 deactivation but without Akt cellular signal involvement.