Significance: Cancer stem cells, capable of self-renewing and giving rise to progeny cells in the tumor, have attracted attention as potential therapeutic targets. In this study, using genetically engineered mouse models, we showed that IL17RB, a tuft cell marker in the intestine, does not mark normal stem cells but marks tumor stem cells of mouse intestinal adenomas. Furthermore, using CRISPR-Cas9–mediated IL17RB-CreERT2 knockin human organoids, we showed that IL17RB marks human colorectal cancer stem cells by lineage tracing, and that long-term targeting of IL17RB ⁺ cells strongly suppressed the tumor growth in vivo. This study identifies IL17RB ⁺ cancer stem cells and preclinically validates them as a cancer therapeutic target.

Chromatin remodeler Brahma related gene 1 (BRG1) is silenced in approximately 10% of human pancreatic ductal adenocarcinomas (PDAs). We previously showed that BRG1 inhibits the formation of intraductal pancreatic mucinous neoplasm (IPMN) and that IPMN-derived PDA originated from ductal cells. However, the role of BRG1 in pancreatic intraepithelial neoplasia–derived (PanIN-derived) PDA that originated from acinar cells remains elusive. Here, we found that exclusive elimination of Brg1 in acinar cells of Ptf1a-Cre^ER; Kras^G12D; Brg1^fl/fl mice impaired the formation of acinar-to-ductal metaplasia (ADM) and PanIN independently of p53 mutation, while PDA formation was inhibited in the presence of p53 mutation. BRG1 bound to regions of the Sox9 promoter to regulate its expression and was critical for recruitment of upstream regulators, including PDX1, to the Sox9 promoter and enhancer in acinar cells. SOX9 expression was downregulated in BRG1-depleted ADMs/PanINs. Notably, Sox9 overexpression canceled this PanIN-attenuated phenotype in KBC mice. Furthermore, Brg1 deletion in established PanIN by using a dual recombinase system resulted in regression of the lesions in mice. Finally, BRG1 expression correlated with SOX9 expression in human PDAs. In summary, BRG1 is critical for PanIN initiation and progression through positive regulation of SOX9. Thus, the BRG1/SOX9 axis is a potential target for PanIN-derived PDA.

Inactivating mutations ofArid1a, a subunit of the Switch/sucrose nonfermentable chromatin remodeling complex, have been reported in multiple human cancers. Intestinal deletion ofArid1ahas been reported to induce colorectal cancer in mice; however, its functional role in intestinal homeostasis remains unclear. We investigated the functional role of Arid1a in intestinal homeostasis in mice. We found that intestinal deletion ofArid1aresults in loss of intestinal stem cells (ISCs), decreased Paneth and goblet cells, disorganized crypt-villous structures, and increased apoptosis in adult mice. Spheroids did not develop from intestinal epithelial cells deficient forArid1a. Lineage-tracing experiments revealed thatArid1adeletion in Lgr5⁺ISCs leads to impaired self-renewal of Lgr5⁺ISCs but does not perturb intestinal homeostasis. The Wnt signaling pathway, including Wnt agonists, receptors, and target genes, was strikingly down-regulated inArid1a-deficient intestines. We found that Arid1a directly binds to theSox9promoter to support its expression. Remarkably, overexpression ofSox9in intestinal epithelial cells abrogated the above phenotypes, althoughSox9overexpression in intestinal epithelial cells did not restore the expression levels of Wnt agonist and receptor genes. Furthermore,Sox9overexpression permitted development of spheroids fromArid1a-deficient intestinal epithelial cells. In addition, deletion ofArid1aconcomitant withSox9overexpression in Lgr5⁺ISCs restores self-renewal inArid1a-deleted Lgr5⁺ISCs. These results indicate that Arid1a is indispensable for the maintenance of ISCs and intestinal homeostasis in mice. Mechanistically, this is mainly mediated by Sox9. Our data provide insights into the molecular mechanisms underlying maintenance of ISCs and intestinal homeostasis.

Background & Aims SETDB1, a histone methyltransferase that trimethylates histone H3 on lysine 9, promotes development of several tumor types. We investigated whether SETDB1 contributes to development of pancreatic ductal adenocarcinoma (PDAC). Methods We performed studies with Ptf1a^Cre; Kras^G12D; Setdb1^f/f , Ptf1a^Cre; Kras^G12D; Trp53^f/+; Setdb1^f/f, and Ptf1a^Cre; Kras^G12D; Trp53^f/f; Setdb1^f/f mice to investigate the effects of disruption of Setdb1 in mice with activated KRAS-induced pancreatic tumorigenesis, with heterozygous or homozygous disruption of Trp53. We performed microarray analyses of whole-pancreas tissues from Ptf1a^Cre; Kras^G12D; Setdb1^f/f, and Ptf1a^Cre; Kras^G12D mice and compared their gene expression patterns. Chromatin immunoprecipitation assays were performed using acinar cells isolated from pancreata with and without disruption of Setdb1. We used human PDAC cells for SETDB1 knockdown and inhibitor experiments. Results Loss of SETDB1 from pancreas accelerated formation of premalignant lesions in mice with pancreata that express activated KRAS. Microarray analysis revealed up-regulated expression of genes in the apoptotic pathway and genes regulated by p53 in SETDB1-deficient pancreata. Deletion of Setdb1 from pancreas prevented formation of PDACs, concomitant with increased apoptosis and up-regulated expression of Trp53 in mice heterozygous for disruption of Trp53. In contrast, pancreata of mice with homozygous disruption of Trp53 had no increased apoptosis, and PDACs developed. Chromatin immunoprecipitation revealed that SETDB1 bound to the Trp53 promoter to regulate its expression. Expression of an inactivated form of SETDB1 in human PDAC cells with wild-type TP53 resulted in TP53-induced apoptosis. Conclusions We found that the histone methyltransferase SETDB1 is required for development of PDACs, induced by activated KRAS, in mice. SETDB1 inhibits apoptosis by regulating expression of p53. SETDB1 might be a therapeutic target for PDACs that retain p53 function.

ATP‐dependent chromatin remodeling complexes are a group of epigenetic regulators that can alter the assembly of nucleosomes and regulate the accessibility of transcription factors to DNA in order to modulate gene expression. One of these complexes, the SWI/SNF chromatin remodeling complex is mutated in more than 20% of human cancers. We have investigated the roles of the SWI/SNF complex in pancreatic ductal adenocarcinoma (PDA), which is the most lethal type of cancer. Here, we reviewed the recent literature regarding the role of the SWI/SNF complex in pancreatic tumorigenesis and current knowledge about therapeutic strategies targeting the SWI/SNF complex in PDA. The subunits of the SWI/SNF complex are mutated in 14% of human PDA. Recent studies have shown that they have context‐dependent oncogenic or tumor‐suppressive roles in pancreatic carcinogenesis. To target its tumor‐suppressive properties, synthetic lethal strategies have recently been developed. In addition, their oncogenic properties could be novel therapeutic targets. The SWI/SNF subunits are potential therapeutic targets for PDA and further understanding of the precise role of the SWI/SNF complex subunits in PDA is required to further development of novel strategies targeting SWI/SNF subunits against PDA.