Project description:The TP53 c.359A>G mutation severely impairs expression of the major TP53 transcript variant encoding p53 K120R by creating a new splicing donor site. Antisense morpholino oligomer (AMO) targeting the mutation site restored normal splicing and expression of the major variant. Despite the recovery of mutant TP53 mRNA levels, the functional restoration as the tumor suppressor of p53 K120R was unclear. Given that p53 exerts its tumor suppressor function through regulation of target genes that mediate growth arrest or apoptosis, the p53 K120R mutant exhibits impaired transcriptional regulation of CDKN1A, a key target gene in growth arrest, while maintaining normal induction of the pro-apoptotic BBC3 gene. Consequently, the p53 K120R mutant protein demonstrates a phenotype characterized by defective cell growth arrest but retained apoptotic induction capacity, suggesting that the p53 K120R mutant protein may retain some tumor suppressor functionality. In addition, Lysine 120 provides a critical acetylation site linked to p53 activation. Although other studies of the oncogenic effects of p53 K120R highlight the relevance of acetylation for tumor suppression, our findings indicate that targeting mutant TP53 mRNA is a prerequisite for restoration of p53 function. In particular, despite the presence of mutations, it showed sufficient corrective effect to restore p53 functions, including apoptosis induction. In conclusion, this study highlights the potential of AMO-mediated splice correction as a therapeutic approach for TP53 mutations.
Project description:P53 inactivation occurs in about 50% of 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 cytoplasmically localized hnRNA0, which otherwise stabilizes p27 mRNA leading to cell cycle arrest at the G0/G1 phase. In response to DNA damage, LIMp27 is upregulated in both wild-type and p53-mutant COAD cells, whereas cytoplasmic hnRNPA0 is only increased in p53-mutant COAD cells due to translocation from the nucleus. Moreover, high LIMp27 expression is associated with poor survival of p53-mutant but not wild-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.
Project description:Advanced colorectal cancer (CRC) is an unresolved clinical problem. Epigenetic drugs belonging to the group of histone deacetylase inhibitors (HDACi) may combat CRC in rationally designed treatment schedules. Unfortunately, there is sparse evidence on molecular mechanisms and markers that determine cellular sensitivity to HDACi. Irinotecan is widely used to treat CRC and causes replication stress (RS) and DNA damage as topoisomerase-I inhibitor. We applied irinotecan and the class I HDACi entinostat (MS-275) to isogenic p53-positive and -negative CRC cells. Combinations of irinotecan and MS-275 evoke mitochondrial damage, caspase-mediated apoptosis, and RS-associated DNA damage synergistically and p53-dependently. Targeted mass spectrometry and immunoblot show that irinotecan induces phosphorylation, acetylation, and accumulation of p53 and its target genes. Addition of MS-275 augments the irinotecan-induced acetylation of C-terminal lysine residues of p53 but decreases its phosphorylation and p53 target gene induction. Furthermore, MS-275 increases the amount of acetylated p53 at mitochondria and dysregulates the expression of pro- and anti-apoptotic BCL2 proteins in irinotecan-treated cells. Regarding DNA repair, we see that MS-275 represses the homologous recombination (HR) filament protein RAD51, which limits DNA damage and pro-apoptotic effects of irinotecan. These data suggest that key class I HDAC-dependent functions of p53 in cells with RS are linked to mitochondrial damage and a breakdown of HR. Most importantly, combinations of irinotecan plus MS-275 also kill short-term primary CRC cell cultures and organoids from CRC patients but spare organoids of adjacent matched normal tissue. Thus, irinotecan/HDACi treatment is a promising new approach for the therapy of p53-proficient tumors with clinically tractable inhibitors.
Project description:The point mutation that substitutes lysine with arginine at position 120 of human p53 has been characterized as a missense mutation. The K120R mutation renders the p53 protein disabled for acetylation and, as a result, defective for apoptotic function, which provides a mechanistic link between the missense mutation and tumorigenesis. However, we noticed the failures of tumorigenesis in mice with the mutation, and of the related studies to notice that it has arbitrarily reflected in amino acid change through a sequence modification (AGA) of the original tumor mutation (AGG) by codon degeneracy. Unlike this modified version, we also discovered a novel splicing site the original mutation, TP53 c.359A>G, may induce. Using a human induced pluripotent stem cell line that was engineered to be homozygous for the original mutation, we here identified that the accidental splicing site generates a defective transcript variant with a frame-shifted premature termination codon which is subjected to nonsense-mediated mRNA decay. The authentic splicing still occurs but in extremely low amounts. Taken together, this mutation causes depletion of cellular p53 via defective mRNA, suggesting a new link to tumorigenesis.
Project description: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.