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SMAD4 is dispensable for execution of epithelial-mesenchymal transition downstream of SNAIL1 in colorectal cancer cells

ABSTRACT: Transforming growth factor beta (TGFβ) superfamily signaling is a prime inducer of epithelial-mesenchymal transitions (EMT) that foster cancer cell invasion and metastasis, a major cause of cancer-related deaths. Yet, TGFβ signaling is frequently inactivated in human tumor entities including colorectal cancer (CRC) and pancreatic adenocarcinoma (PAAD) with a high proportion of mutations incapacitating SMAD4, which codes for a transcription factor (TF) central to canonical TGFβ and bone morphogenetic protein (BMP) signaling. Beyond its role in initiating EMT, SMAD4 was reported to crucially contribute to subsequent gene regulatory events during EMT execution. It is therefore widely assumed that SMAD4-mutant (SMAD4mut) cancer cells are unable to undergo EMT. Here, we scrutinized this notion and probed for potential SMAD4-independent EMT execution using SMAD4mut CRC cell lines. We show that SMAD4mut cells exhibit morphological changes, become invasive, and regulate EMT marker genes upon induction of the EMT-TF SNAIL1. Furthermore, SNAIL1-induced EMT in SMAD4mut cells was found to be entirely independent of TGFβ/BMP receptor activity. Global assessment of the SNAIL1‑dependent transcriptome confirmed the manifestation of an EMT gene regulatory program in SMAD4mut cells highly related to established EMT signatures. Finally, analyses of human tumor transcriptomes showed that SMAD4 mutations are not underrepresented in mesenchymal tumor samples and that expression patterns of EMT‑associated genes are similar in SMAD4mut and SMAD4 wild-type cases. Altogether, our findings reveal considerable plasticity of gene regulatory networks operating in EMT execution and establish that EMT is not categorically precluded in SMAD4mut tumors, which is relevant for their diagnostic and therapeutic evaluation. To identify genes regulated during EMT execution in HT29 cells, two clonal HT29 cell populations (4F5 and 3C2) overexpressing Snail1-HA in a doxycycline (Dox)-inducible manner, as well as control cells were treated with Dox for different periods of time.

ORGANISM(S): Homo sapiens

PROVIDER: GSE169735 | GEO | 2021/11/29

REPOSITORIES: GEO

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Project description:The liver is the most common site for colorectal cancer (CRC) metastasis and new tissue culture models are needed to study hepatic metastasis from CRC as none of the current models mimic the biological, biochemical and structural characteristics of the metastatic microenvironment. Decellularization provides a novel approach for the study of cancer extracellular matrix (ECM) as decellularized scaffolds retained their tissue-specific features and biological properties. In the present study we created a 3D model of CRC and matched CRC liver metastasis (CRLM) using patient-derived decellularized ECM scaffolds seeded with HT-29 CRC cell line. Here we show increased HT-29 cell proliferation and migration capability when cultured in cancer-derived scaffolds compared to same-patient healthy colon and liver tissues. CRLM scaffolds also induced activation of epithelial-mesenchymal transition (EMT) with cancer cells showing loss of E-cadherin expression and increased Vimentin expression. EMT was confirmed by gene expression profiling, with the most represented biological processes in CRLM-seeded scaffolds involving demethylation, deacethylation, cellular response to stress metabolic processes, response to oxygen level and to starvation. The complex 3D culture environment reduced the HT-29 cell response to anti-CRC drug 5-FU when used at standard IC50 determined in 2D cultures. In conclusion, our 3D culture system with patient-derived tissue-specific decellularized ECM better recapitulates the metastatic microenvironment compared to conventional 2D culture conditions and represents a relevant approach for the study of liver CRC metastasis formation and progression. Transcriptomic analysis was performed comparing the global gene expression profiles of HT29 cells grown on CRLM and HL scaffolds. The transcriptomic profile of each 3D subtype was compared with HT29 cells grown in plastic. Hierarchical clustering analysis revealed that the gene expression signature of recellularized CRLM scaffolds was more comparable to recellularized HL scaffolds, than to HT29 cells grown in 2D. Gene set enrichment analysis (GSEA) of the differently expressed genes (DEG) up-regulated in recellularized CRLM scaffolds compared to HT29 grown in 2D revealed that genes involved in demethylation, deacethylation and metabolic process belong to the most enriched biological pathways in repopulated-CRLM scaffolds. Comparing the DEG between recellularized CRLM scaffolds vs HT29 grown in 2D with a series of a-priori defined gene-set, called Hallmark, we obtained concordant results with the “HYPOXIA” and “EPITHELIAL_MESENCHYMAL_TRANSITION” pathway, enriched in recellularized CRLM, supporting the idea that 3D culture models are the ability to re-create a complex environment in terms of oxygen tension, nutrients, and metabolic gradient, similarly to the in vivo environment.

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SMAD4 is dispensable for execution of epithelial-mesenchymal transition downstream of SNAIL1 in colorectal cancer cells

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