Mammary stem/progenitor cells (MaSCs) maintain self-renewal of the mammary epithelium during puberty and pregnancy. DNA methylation provides a potential epigenetic mechanism for maintaining cellular memory during self-renewal. Although DNA methyltransferases (DNMTs) are dispensable for embryonic stem cell maintenance, their role in maintaining MaSCs and cancer stem cells (CSCs) in constantly replenishing mammary epithelium is unclear. Here we show that DNMT1 is indispensable for MaSC maintenance. Furthermore, we find that DNMT1 expression is elevated in mammary tumors, and mammary gland-specific DNMT1 deletion protects mice from mammary tumorigenesis by limiting the CSC pool. Through genome-scale methylation studies, we identify ISL1 as a direct DNMT1 target, hypermethylated and downregulated in mammary tumors and CSCs. DNMT inhibition or ISL1 expression in breast cancer cells limits CSC population. Altogether, our studies uncover an essential role for DNMT1 in MaSC and CSC maintenance and identify DNMT1-ISL1 axis as a potential therapeutic target for breast cancer treatment.

CD73, an ecto-5′-nucleotidase (NT5E), serves as an immune checkpoint by generating adenosine (ADO), which suppresses immune activation through the A 2A receptor. Elevated CD73 levels in tumor tissues correlate with poor clinical outcomes. However, the crucial source of CD73 activity within the tumor microenvironment remains unspecified. Here, we demonstrate that cancer-associated fibroblasts (CAFs) constitute the prominent CD73 hi population in human colorectal cancers (CRCs) and two CD73 − murine tumor models, including a modified CRC. Clinically, high CAF abundancy in CRC tissues correlates strongly with elevated CD73 activity and poor prognosis. Mechanistically, CAF-CD73 expression is enhanced via an ADO-A 2B receptor-mediated feedforward circuit triggered by tumor cell death, which enforces the CD73-checkpoint. Simultaneous inhibition of A 2A and A 2B pathways with CD73-neutralization synergistically enhances antitumor immunity in CAF-rich tumors. Therefore, the strategic and effective targeting of both the A 2B-mediated ADO-CAF-CD73 feedforward circuit and A 2A-mediated immune suppression is crucial for improving therapeutic outcomes.

MicroRNAs have pathogenic roles in the development of a variety of leukemias. Here we identify miRNAs that have important roles in the development of B-lymphomas resulting from the expression of the chimeric BCR-FGFR1 kinase. The miR-17/92 cluster was particularly implicated and forced expression resulted in increased cell proliferation, while inhibiting its function using microRNA sponges reduced cell growth and induced apoptosis. Cells treated with the potent BGJ389 FGFR1 inhibitor led to miR-17/92 downregulation suggesting regulation by FGFR1. Transient luciferase reporter assays and qRT-PCR detection of endogenous miR-17/92 expression in stable transduced cell lines demonstrated that BCR-FGFR1 can regulate miR-17/92 expression. This positive association of miR-17/92 with BCR-FGFR1 was also confirmed in primary mouse SCLL tissues and primary human CLL samples. miR-17/92 promotes cell proliferation and survival by targeting CDKN1A and PTEN in B-lymphoma cell lines and primary tumors. An inverse correlation in expression levels was seen between miR-17/92 and both CDKN1A and PTEN in two cohorts of CLL patients. Finally, in vivo engraftment studies demonstrated that manipulation of miR-17/92 was sufficient to affect BCR-FGFR1 driven leukemogenesis. Overall, our results define miR-17/92 as a downstream effector of FGFR1 in BCR-FGFR1 driven B cell lymphoblastic leukemia.

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