LncRNA LIMp27 regulates the DNA damage response through p27 in p53-defective cancer cells

P53 inactivation occurs in about 50% human cancers, where p53-driven p21 activity is devoid and p27 becomes essential for the establishment of the G1/S checkpoint upon DNA damage. Here, we show that the E2F1-responsive lncRNA LIMp27 selectively represses p27 expression and contributes to proliferation, tumorigenicity, and treatment resistance in p53-defective colon adenocarcinoma (COAD) cells. LIMp27 competes with p27 mRNA for binding to cytoplasm-localized hnRNA0, which otherwise stabilizes p27 mRNA leading to cell cycle arrest at G0/G1 phase. In response to DNA-damage, LIMp27 is upregulated in both wild-type and p53-muant COAD cells, whereas cytoplasmic hnRNPA0 is only increased due to translocation from the nucleus in p53-mutant COAD cells. High LIMp27 expression is associated with poor survival of p53-mutant but not wide-type p53 COAD patients. These results uncover a lncRNA mechanism that promotes p53-defective cancer pathogenesis and suggest that LIMp27 may constitute a target for the treatment of such cancers. Overall design: To dissect the mechanism through which LIMp27 promotes p53-mutant COAD cell proliferation, we compared the transcriptomes of WiDr cells with and without LIMp27 knockdown using two different siRNAs for 24 hours.