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Hippo Inactivation in the Mammary Epithelium Drives the Evolution of a Tumor-Associated Niche

ABSTRACT: Basal-like breast cancers exhibit distinct intratumor cell heterogeneity that contributes to disease pathology. In this study we use a genetic mouse model of basal-like breast cancer driven by epithelial-specific inactivation of the Hippo pathway-regulating Lats1 and Lats2 kinases to elucidate epithelial-stromal interactions in the basal-like tumor niche. We demonstrate that basal-like carcinoma initiation is accompanied by the accumulation of distinct cancer-associated fibroblasts, tumor-associated macrophage recruitment, and dramatic extracellular matrix remodeling, phenocopying the stromal diversity observed in human triple-negative breast tumors.Epithelial-stromal signaling dysregulation was observed, including increased TGF-β, PDGF, and CSF intercellular communication. Autonomous activation of the transcriptional effector TAZ was observed in Lats1/2-deleted cells along with non-autonomous activation within the evolving tumor niche. We further demonstrate that small molecule inhibition of the YAP/TAZ-associated TEAD family of transcription factors can block the development of the carcinomas and tumor-associated microenvironment. These observations demonstrate that carcinomas resulting from Hippo pathway dysregulation in the mammary epithelium are sufficient to drive cellular events that promote a basal-like tumor-associated niche and suggest that targeting dysregulated YAP/TAZ-TEAD activity provides an opportunity for therapeutic intervention of basal-like mammary tumors.

ORGANISM(S): Mus musculus

PROVIDER: GSE267351 | GEO | 2025/01/21

REPOSITORIES: GEO

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Project description:Background: Post-transcriptional modification of tumor-associated factors plays a pivotal role in breast cancer progression. However, the underlying mechanism remains unknown. Modifications to m6A are dynamic and reversible in cancer cells and have been found to impact tumor initiation and progression through various mechanisms. In this study, we explored the regulatory mechanism of m6A methylation in the Hippo pathway, a key pathway involved in cell proliferation and metabolism. Methods: First, a combination of MeRIP-seq, RNA-seq and metabolomics-seq was utilized to reveal the map of m6A modifications in breast cancer tissues and cells. Secondly, we identified the relationship between m6A proteins and LATS1 in m6A regulation in breast cancer cells by performing RNA pull-down assays, RIP-qPCR, MeRIP-qPCR, and RNA stability analysis. The expression and biological functions of METTL3 and YTHDF2 were confirmed in breast cancer cell lines in vitro and in vivo. Furthermore, we investigated the phosphorylation levels and localization of YAP/TAZ to reveal that the activity of the Hippo pathway could be affected by m6A regulation of LATS1 in breast cancer cells. Results: We demonstrated that m6A regulation plays an important role in proliferation and glycolytic metabolism in breast cancer through the Hippo pathway factor, LATS1. METTL3 was identified as the m6A writer, with YTHDF2 as the reader protein of LATS1 mRNA, which plays a positive role in promoting both tumorigenesis and glycolysis in breast cancer. High levels of m6A modification were induced by METTL3 in LATS1 mRNA. YTHDF2 identified m6A sites in LATS1 mRNA and reduced its stability. Knockout of the protein expression of METTL3 or YTHDF2 increased the expression of LATS1 mRNA and suppressed breast cancer tumorigenesis by activating YAP/TAZ in the Hippo pathway. Conclusions: In summary, we discovered that the METTL3-LATS1-YTHDF2 pathway plays an important role in the progression of breast cancer by activating YAP/TAZ in the Hippo pathway.

Project description:Uncontrolled Transforming growth factor-beta (TGFβ) signaling promotes aggressive metastatic properties in late-stage breast cancers. However, how TGFβ-mediated cues are directed to induce late-stage tumorigenic events is poorly understood, particularly given that TGFβ has clear tumor suppressing activity in other contexts. Here we demonstrate that the transcriptional regulators TAZ and YAP (TAZ/YAP), key effectors of the Hippo pathway, are necessary to promote and maintain TGFβ-induced tumorigenic phenotypes in breast cancer cells. Interactions between TAZ/YAP, TGFβ-activated SMAD2/3, and TEAD transcription factors reveal convergent roles for these factors in the nucleus. Genome-wide expression analyses indicate that TAZ/YAP, TEADs and TGFβ-induced signals coordinate a specific pro-tumorigenic transcriptional program. Importantly, genes cooperatively regulated by TAZ/YAP, TEAD, and TGFβ, such as the novel targets NEGR1 and UCA1, are necessary for maintaining tumorigenic activity in metastatic breast cancer cells. Nuclear TAZ/YAP also cooperate with TGFβ signaling to promote phenotypic and transcriptional changes in non-tumorigenic cells to overcome TGFβ repressive effects. Our work thus identifies crosstalk between nuclear TAZ/YAP and TGFβ signaling in breast cancer cells, revealing novel insight into late-stage disease-driving mechanisms. Expression profiling was conducted following the repression of the transcriptional regulators TAZ and YAP (TAZ/YAP), the TEAD family of transcription factors (TEAD1/2/3/4), or the TGFb signaling pathway (with SB-431542, an inhibitor of the TBRI recpeptor) in human MDA-MB-231-LM2 breast cancer cells treated with TGFβ1. Human MDA-MB-231-LM2-4 breast cancer cells were transfected with control siRNA, or siRNAs targeting TAZ/YAP or all four TEADs and were treated 24 hours later with 500pM TGFβ1 or 5mM SB-431542 for an additional 24 hours. Total RNA was isolated and twelve microarrays in total were performed, with each condition carried out three times on separate days. The Boston University Microarray Core generated the data using the Affymetrix Human Gene 1.0 St Array.

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Hippo Inactivation in the Mammary Epithelium Drives the Evolution of a Tumor-Associated Niche

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