Loss of microRNA-21 leads to profound stromal remodeling and short survival in K-Ras-driven mouse models of pancreatic cancer.

: The microenvironment of pancreatic cancer adenocarcinoma (PDAC) is highly desmoplastic with distinct tumor-restraining and tumor-promoting fibroblast subpopulations. Re-education rather than indiscriminate elimination of these fibroblasts has emerged as a new strategy for combination therapy. Here, we studied the effects of global loss of pro-fibrotic non-coding regulatory microRNA-21 (miR-21) in K-Ras-driven p53-deleted genetically engineered mouse models of PDAC. Strikingly, loss of miR-21 accelerated tumor initiation via mucinous cystic neoplastic lesions and progression to locally advanced invasive carcinoma from which animals precipitously succumbed at an early age. The absence of tumor-restraining myofibroblasts and a massive infiltrate of immune cells were salient phenotypic features of global miR-21 loss. Stromal miR-21 activity was required for induction of tumor-restraining myofibroblasts in in-vivo isograft transplantation experiments. Low miR-21 expression negatively correlated with a fibroblast gene expression signature and positively with an immune cell gene expression signature in TCGA PDAC data set (n = 156) mirroring findings in the mouse models. Our results exposed an overall tumor suppressive function of miR-21 in in-vivo PDAC models. These results have important clinical implications for anti-miR-21-based inhibitory therapeutic approaches under consideration for PDAC and other cancer types. Mechanistic dissection of the cell-intrinsic role of miR-21 in cancer-associated fibroblasts and other cell types will be needed to inform best strategies for pharmacological modulation of miR-21 activity in order to remodel the tumor microenvironment and enhance treatment response in PDAC. This article is protected by copyright. All rights reserved.