Metabolomics,Unknown,Transcriptomics,Genomics,Proteomics

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Breast Cancer Suppressor Role of RUNX1: Estrogen-dependent Regulation of AXIN1 and b-catenin

ABSTRACT: The transcription factor RUNX1 exhibits recurrent loss-of-function mutations in estrogen receptor-positive (ER+) breast cancer (BCa). Its knockdown in vitro decreased AXIN1 expression in estrogen-dependent manner. Consistently, RUNX1 and AXIN1 mRNA levels are strongly correlated in ER+, not ER- tumors. RUNX1 occupies AXIN1â??s second intron in living cells, abutting an ERa-binding site. Potentially promoting BCa progression, decreased AXIN1 expression after RUNX1 knockdown associated with upregulation of b-catenin, and this was preventable by AXIN stabilizers. Unlike in colon cancer, however, deregulation of b-catenin in BCa cells affect neither c-Myc, nor CCND1, nor G1/S cell cycle phase transition. Instead, cyclin B1 was decreased and the G2/M checkpoint was compromised as indicated by mitotic slippage in the presence of microtubule disruptors. Thus, combined analysis of the RUNX1 transcriptome, its cistrome, and differential mRNA expression in tumors with wild type versus mutant RUNX1, altogether highlight a role for the RUNX1/AXIN1/b-catenin axis in ER+ BCa. Significance: Three recent exome sequencing studies assigned to RUNX1 a BCa suppressor role. The present study begins to uncover the underlying molecular mechanisms, offers an explanation for the specificity to ER+ tumors, and marks AXIN1 as a therapeutic target for ER+/RUNX1- BCa. Examination of RUNX1 binding in MCF7 cells

ORGANISM(S): Homo sapiens

SUBMITTER: Dustin Schones

PROVIDER: E-GEOD-65313 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Activating mutations of PIK3CA are the most frequent genomic alterations in estrogen receptor (ER)-positive breast tumors and selective PI3Kα inhibitors are in clinical development. The activity of these agents, however, is not homogenous and only a fraction of patients bearing PIK3CA-mutant ER-positive tumors benefit from single agent administration. Searching for mechanisms of resistance, we observed that suppression of PI3K signaling with different agents results in induction of ER-dependent transcriptional activity as demonstrated by changes in expression in genes containing ER binding sites, enhanced ER transcription and increased occupancy by the ER of promoter regions of upregulated genes. Furthermore, expression of ESR1 mRNA and ER protein levels themselves were also increased upon PI3K inhibition. These changes in gene expression were confirmed in vivo in xenograft and patient derived models and in tumors from patients undergoing treatment with the PI3Kα inhibitor BYL719. The observed effects on transcription were enhanced by the addition of estradiol and suppressed by the anti-ER therapies fulvestrant and tamoxifen. Fulvestrant markedly sensitized ER-positive tumors to PI3Kα inhibition. We propose that increased ER transcriptional activity may be a compensatory mechanism that limits the activity of PI3K inhibitors and that combined PI3K and ER inhibition is a rational approach to target these tumors. The aim of our study was to explore the mechanism by which combination of PI3K pathway inhibitors and estrogen receptor function blockade results in superior antitumor activity. We aimed to evaluate whether changes in ER function were influencing the clinical response to anti-PI3K therapy in ER-positive breast tumors that harbor PI3K pathway activation. For this purpose, we planned to use various specific PI3K inhibitors, namely: BYL719 (p110α specific catalytic inhibitor), GDC0941 (pan-PI3K inhibitor), GDC0032 and BAY80-6946 (p110sparing PI3K inhibitors) in a panel of ER-positive breast cancer cell lines and xenografts that harbor PIK3CA activating mutations. We also used MK2206 (pan-AKT allosteric inhibitor) to inhibit the PI3K pathway in ER-positive cell lines which activate this pathway through PTEN loss. Finally, in order to evaluate the role of ER up-regulation as a pro-survival signal in our in vitro and in vivo models, we planned to use the selective ER modulator 4-hydroxy-tamoxifen (4-OHT) and degrader fulvestrant. For the in vivo experiments, the number of animals in each group was calculated to measure a 25% difference between the means of placebo and treatment groups with a power of 80% and a p value of 0.01. Host mice carrying xenografts were randomly and equally assigned to either control or treatment groups. Animal experiments were conducted in a controlled and non-blinded manner. Moreover, we evaluated by means of RNAseq gene expression changes breast cancer patients that underwent BYL719 based therapy to validate our in vitro findings in terms of ER expression. In vitro experiments were performed at least two times and at least in triplicate for each replica.

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Breast Cancer Suppressor Role of RUNX1: Estrogen-dependent Regulation of AXIN1 and b-catenin

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