IMP1 plays a protective role in LIN28B‐associated intestinal tumorigenesis by regulating ER stress and cell junction assembly

Abstract

IntroductionRNA binding proteins and miRNAs have emerged as crucial regulators of intestinal homeostasis by controlling the stability and translation of target mRNAs. LIN28B, an mRNA binding protein, plays a critical role in regulating growth and proliferation in the intestinal epithelium. Previous work in our lab revealed that LIN28B promotes growth and tumorigenesis of the intestinal epithelium via suppression of mature let‐7 miRNAs (Genes and Dev., 2013). LIN28B suppression of let‐7 promotes upregulation of let‐7 targets, including IMP1 (Insulin‐like growth factor II mRNA‐binding protein‐1). Previous studies from our lab have shown that transgenic mice expressing LIN28B from the mouse Vil1 promoter (Vil‐Lin28b mice) have an increase in IMP1 protein levels that is increased further with conditional knockout of let‐7. Mechanistically, Let‐7 isoforms have been known to physically and functionally interact with IMP1; however, the specific role of IMP1 in Lin28b‐let 7‐mediated tumorigenesis remains unknown.MethodsWe evaluated LIN28B and IMP1 expression and localization in colorectal cancer (CRC) patient samples using tissue microarrays with clinical outcomes. We used intestinal epithelial cell lines with LIN28B overexpression and CRISPR‐Cas9 mediated knockout of IMP1 to study the functional consequences on migration, invasion and proliferation. In parallel, we used RNA sequencing to understand the role of IMP1 deletion in LIN28B over‐expressing cell lines. Additionally, we used mice with intestinal epithelium specific LIN28B overexpression combined with IMP1 knockout to evaluate effect of IMP1 loss on tumor initiation and progression in an aging model as well as through AOM‐DSS induced tumorigenesis.ResultsLIN28B expression correlates positively with expression of IMP1 in CRC. Individually, LIN28B and IMP1 expression associated significantly with worse prognosis in stage II colon cancer that worsens when both were co‐expressed. Knockout of IMP1 in LIN28B overexpressing cells decreased migration of CRC cell lines and altered tumorigenesis in vivo. RNA‐seq revealed a potential role for IMP1 in ER stress and cell junction assembly proteins in the context of LIN28B overexpression.ConclusionsThese data suggest a requirement for IMP1 in LIN28B‐mediated colorectal tumor progression, potentially via ER stress modulation, and support an emerging paradigm for a critical and cooperative role of RNA‐binding proteins in intestinal homeostasis and cancer.Support or Funding InformationNIH R01DK056645 (AKR), NIH U01DK085551 (AKR), NIH K01DK100485 (KEH),NIH F32DK107052‐01 (SFA), NIH T32CA1152999 (SFA)