Phosphorylated nuclear DICER1 promotes open chromatin state and gastric cell fate in lung adenocarcinomas [ATAC-seq]

DICER1 canonically regulates micro(mi)RNA-mediated epithelial-to-mesenchymal transition (EMT) in lung adenocarcinomas (LUADs). We discovered that KRAS/ERK pathway phosphorylates DICER1 causing its nuclear translocation; phosphomimetic Dicer1 contributes to tumorigenesis in mice. Mechanisms through which phospho-DICER1 regulates tumor progression remain undefined. Here, we show that phospho-DICER1 is expressed in invasive human LUADs and promotes late-stage tumor progression in mice with oncogenic Kras, independent of miRNAs and EMT. Strikingly, in mice, we observed that the AT2 tumor cells with phospho-DICER1 express endodermal (gastric) genes and display an open chromatin state such that there are sub-populations of tumors cells with alveolar-endodermal or only endodermal identity. Importantly, we also observed expression of gastric genes in human LUADs with phospho-DICER1. Mechanistically, we identify a chromatin-DICER1 nuclear complex comprised of Mediator complex subunit 12, CBX1, MACROH2A.1 and transcriptional regulators. Together, we propose that phosphorylated-nuclear DICER1 leads to lineage reprogramming of AT2 tumor cells to mediate lung cancer progression. Overall design: Chromatin accessibility across the genome of KrasLA1/+;Dicer1S2D/+ lung tumors was determined by ATAC sequencing.