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GATA3

GATA3, a transcription factor that regulates T lymphocyte differentiation and maturation, is exclusively expressed in early stage well differentiated breast cancers but not in advanced invasive cancers. However, little is understood regarding its activity and the mechanisms underlying this differential expression in cancers. Here, we employed GATA3-positive, non-invasive (MCF-7) and GATA3-negative, invasive (MDA-MB-231) breast cancer cells to define its role in the transformation between these two distinct phenotypes. Ectopic expression of GATA3 in MDA-MB-231 cells led to a cuboidal-like epithelial phenotype and reduced cell invasive activity. These cells also increased E-cadherin expression but decreased levels of vimentin, N-cadherin, and MMP-9. Further, MDA-MB-231 cells expressing GATA3 grew smaller primary tumors without metastasis compared with larger metastatic tumors derived from control MDA-MB-231 cells in xenografted mice. GATA3 was found to induce E-cadherin expression through binding GATA-like motifs located in the E-cadherin promoter. Blockade of GATA3 using small interfering RNA gene knockdown in MCF-7 cells triggered fibroblastic transformation and cell invasion, resulting in distant metastasis. Studies of human breast cancer showed that GATA3 expression correlated with elevated E-cadherin levels, ER expression, and long disease-free survival. These data suggest that GATA3 drives invasive breast cancer cells to undergo the reversal of epithelial-mesenchymal transition, leading to the suppression of cancer metastasis.

The transcription factor GATA3 is known as a breast tumor suppressor as well as a urothelial marker, and its loss is often seen in high-grade invasive bladder cancer. Nonetheless, GATA3 functions in bladder cancer cells remain largely unknown. In this study, we assessed the effects of GATA3 silencing via RNA interference on cell migration, invasion, and proliferation of bladder cancer. GATA3 expression was downregulated in all four bladder cancer lines examined, compared with a non-neoplastic urothelial line SVHUC. Knockdown of GATA3 in the bladder cancer lines (5637, TCC-SUP, J82) resulted in promotion of cell migration and invasion as well as increases in the expression of their related molecules, such as vascular endothelial growth factor, matrix metalloproteinase (MMP)-2, and MMP-9, and the activity of MMP-2 and MMP-9. GATA3 loss was also associated with an increasing level of a mesenchymal marker N-cadherin and a decreasing level of an epithelial marker beta-catenin. Consistent with these findings, enforced expression of GATA3 in UMUC3 inhibited cell migration and invasion. However, GATA3 showed marginal effects on bladder cancer cell viability and the expression of cell cycle- or apoptosis-related molecules. Additionally, in contrast to bladder cancer lines, no significant effects of GATA3 silencing on cell migration were seen in SVHUC. These findings suggest that GATA3 plays an important role in the prevention of bladder cancer progression and metastasis by inhibiting cell migration and invasion as well as epithelial-to-mesenchymal transition.

p38gamma is a member of p38 MAPK family which contains four isoforms p38alpha, p38beta, p38gamma, and p38delta. p38gamma MAPK has unique function and is less investigated. Recent studies revealed that p38gamma MAPK may be involved in tumorigenesis and cancer aggressiveness. However, the underlying cellular/molecular mechanisms remain unclear. epithelial-mesenchymal transition (EMT) is a process that epithelial cancer cells transform to facilitate the loss of epithelial features and gain of mesenchymal phenotype. EMT promotes cancer cell progression and metastasis, and is involved in the regulation of cancer stem cells (CSCs) which have self-renewal capacity and are resistant to chemotherapy and target therapy. We showed that p38gamma MAPK significantly increased EMT in breast cancer cells; over-expression of p38gamma MAPK enhanced EMT while its down-regulation inhibited EMT. Meanwhile, p38gamma MAPK augmented CSC population while knock down of p38gamma MAPK decreased CSC ratio in breast cancer cells. MicroRNA-200b (miR-200b) was down-stream of p38gamma MAPK and inhibited by p38gamma MAPK; miR-200b mimics blocked p38gamma MAPK-induced EMT while miR-200b inhibitors promoted EMT. p38gamma MAPK regulated miR-200b through inhibiting GATA3. p38gamma MAPK induced GATA3 ubiquitination, leading to its proteasome-dependent degradation. Suz12, a Polycomb group protein, was down-stream of miR-200b and involved in miR-200b regulation of EMT. Thus, our study established an important role of p38gamma MAPK in EMT and identified a novel signaling pathway for p38gamma MAPK-mediated tumor promotion.CI - Copyright (c) 2018 Elsevier B.V. All rights reserved.

Paclitaxel is a firstline chemotherapeutic agent for gastric cancer; however, resistance limits its effectiveness. Investigation into the underlying mechanisms of paclitaxel resistance is urgently required. In the present study, a paclitaxelresistant gastric cancer cell line (MGC803R) was generated with a morphological phenotype of epithelialtomesenchymal transition (EMT) and increased expression levels of microRNA (miR)1555p. MGC803R cellderived exosomes were effectively taken up by paclitaxelsensitive MGC803S cells, which exhibited EMT and chemoresistance phenotypes. miR1555p was enriched in MGC803Rexosomes and could be delivered into MGC803S cells. miR1555p overexpression in MGC803S cells via transfection with mimics resulted in similar phenotypic effects as treatment with MGC803R exosome and increased miR1555p content in MGC803S exosomes, which then capable of inducing the malignant phenotype in the sensitive cells. GATA binding protein 3 (GATA3) and tumor protein p53inducible nuclear protein 1 (TP53INP1) were identified as targets of miR1555p. Exosomal miR1555p inhibited these targets by directly targeting their 3' untranslated regions. Knockdown of miR1555p was observed to reverse the EMT and chemoresistant phenotypes of MGC803R cells, potentially via GATA3 and TP53INP1 upregulation, which inhibited MGC803Rexosomes from inducing the malignant phenotype. These results demonstrated that exosomal delivery of miR1555p may induce EMT and chemoresistant phenotypes from paclitaxelresistant gastric cancer cells to the sensitive cells, which may be mediated by GATA3 and TP53INP1 suppression. Targeting miR1555p may thus be a promising strategy to overcome paclitaxel resistance in gastric cancer.