Project description:FOXA1 is recurrently altered in hormone-driven malignancies, with activating hotspot mutations detected in 10-40% of primary prostate cancers based on ethnicity. Yet, the tumorigenic potential and pathobiology of FOXA1 remain unexplored in vivo. Here, we generated and characterized knock-in mouse models harboring FOXA1 mutant transgenes that represent distinct classes of activating mutations. Our findings reveal that FOXA1 class 1 mutations (i.e., wing 2 alterations) in a Trp53-null background, drive high-grade, invasive luminal adenocarcinoma with full penetrance by 40 weeks of age. These hyperproliferative lesions retain luminal characteristics, gain expression of NSD2, and regress upon androgen withdrawal—mirroring features of primary human prostate adenocarcinomas. Mechanistically, class 1 mutants aberrantly activate mTORC1/2 signaling and reprogram androgen receptor (AR) activity by expanding the enhancer landscape at non-canonical chimeric AR-half elements enriched in patient tumors. In contrast, FOXA1 class 2 mutations (i.e., C-terminal truncations) do not drive transformation but induce intra-luminal plasticity in androgen-intact normal tissues, which is otherwise triggered in response to castration. Class 2 mutants lead to a 10- to 20-fold expansion of Ar+/Ck8+ luminal epithelia expressing stem/progenitor markers such as Trop2, Ck4, and Psca. Mechanistically, class 2 mutants maintain AR activity while de-compacting over 40,000 new cis-regulatory elements bound by Klf5 and AP-1 transcription factors to activate stemness and WNT gene programs. Class 2-mutant-expressing prostate epithelial cells resist castration-induced atrophy, remain proliferative in androgen-deprived conditions, and form organoids and allografts at higher frequencies. Additionally, metastatic prostate tumors from patients harboring class 2 mutations show elevated KLF5 expression and stemness signatures. Collectively, our data establish FOXA1 as a critical oncogene in both primary and advanced AR-dependent prostate cancers, revealing its functional versatility in driving either tumor initiation or therapy resistance depending on the mutation class.

Project description:Breast cancer is a heterogeneous disease comprised of at least five major subtypes. Luminal subtype tumors confer a more favourable patient prognosis, which is in part, attributed to the Estrogen Receptor-alpha (ER) positivity and anti-hormone responsiveness of these tumors. Expression of the forkhead box transcription factor, FOXA1, also correlates with the luminal subtype and patient survival, but is present in a subset of ER-negative tumors. Similarly, FOXA1 is consistently expressed in luminal breast cancer cell lines even in the absence of ER. In contrast, basal breast cancer cell lines do not express FOXA1, and loss of FOXA1 in luminal cells increases migration and invasion, characteristics of the basal subtype. To delineate an ER-independent role for FOXA1 in maintaining the luminal phenotype, and hence a more favourable prognosis, we performed cDNA microarray analyses on luminal FOXA1-positive, ER-positive (MCF7, T47D) and FOXA1-positive, ER-negative (MDA-MB-453, SKBR3) cell lines in the presence or absence of transient FOXA1 silencing. This resulted in three FOXA1 transcriptomes: (1) a luminal-signature (consistent across cell lines), (2) an ER-positive signature (restricted to MCF7 and T47D) and (3) an ER-negative signature (restricted to MDA-MB-453 and SKBR3). Use of Gene Set Enrichment Analyses (GSEA) as a phenotyping tool revealed that FOXA1 silencing resulted in a transcriptome shift from luminal to basal gene expression signatures. FOXA1 binds to both luminal and basal genes within luminal breast cancer cells, suggesting that it not only transactivates luminal genes, but also represses basal-associated genes. From these results we conclude that FOXA1 controls plasticity between basal and luminal cells, playing a dominant role in repressing the basal phenotype, and thus tumor aggressiveness, in luminal breast cancer cells. Although it has been proposed that FOXA1-targeting agents may be useful for treating luminal tumors, these data suggest that this approach may promote transitions toward a more aggressive cancer. FOXA1 siRNA treated breast cell lines compared directly to nonspecific siRNA treated cell lines using Agilent 4X44 microarrays.

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Divergently evolved FOXA1 mutations drive prostate tumorigenesis or therapy-resistant intra-luminal plasticity

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