Project description:In colorectal cancer, p53 is commonly inactivated, associated with chemo-resistance, and marks the transition from non-invasive to invasive disease. Cancers, including colorectal cancer, are thought to be diseases of aberrant stem cell populations, as stem cells are able to self-renew, making them long-lived enough to acquire mutations necessary to manifest the disease. We have shown that extracts from sweet sorghum stalk components eliminate colon cancer stem cells (CCSC) in a partial p53-dependent fashion. However, the underlying mechanisms are unknown. In the present study, CCSC were transfected with short hairpin-RNA against p53 (CCSC p53 shRNA) and treated with sweet sorghum phenolics extracted from different plant components (dermal layer, leaf, seed head and whole plant). While all components demonstrated anti-proliferative and pro-apoptotic effects in CCSC, phenolics extracted from the dermal layer and seed head were more potent in eliminating CCSC by elevating caspases 3/7 activity, PARP cleavage, and DNA fragmentation in a p53-dependent and p53-independent fashion, respectively. Further investigations revealed that the anti-proliferative and pro-apoptotic effects were associated with decreases in beta-catenin protein levels, and beta-catenin targets cyclin D1, cMyc, and survivin. These results suggest that the anti-proliferative and pro-apoptotic effects of sweet sorghum extracts against human colon cancer stem cells are via suppression of Wnt/beta-catenin pro-survival signaling in a p53-dependent (dermal layer) and partial p53-independent (seed head) fashion. LCMS used to identify phenolic compounds associated with extract activity
Project description:We determined the effect of p53 activation on de novo protein synthesis using quantitative proteomics of newly synthesized proteins (pulsed stable isotope labeling with amino acids in cell culture, pSILAC) in combination with mRNA and non-coding RNA expression analyses by next generation sequencing (RNA-, miR-Seq) in the colorectal cancer (CRC) cell line SW480. Furthermore, genome-wide DNA binding of p53 was analyzed by chromatin-immunoprecipitation (ChIP-Seq). Thereby, we identified differentially regulated mRNAs (1258 up, 415 down), miRNAs (111 up, 95 down), lncRNAs (270 up, 123 down) and proteins (542 up, 569 down). Changes in mRNA and protein expression levels showed a positive correlation (r = 0.50, p < 0.0001). More transcriptionally induced genes displayed occupied p53 binding sites (4.3% mRNAs, 7.2% miRNAs, 6.3% lncRNAs, 5.9% proteins) than repressed genes (2.4% mRNAs, 3.2% miRNAs, 0.8% lncRNAs, 1.9% proteins), suggesting indirect mechanisms of repression. Around 50% of the downregulated proteins displayed seed-matching sequences of p53-induced miRNAs in the corresponding 3â??-UTRs. Moreover, proteins repressed by p53 significantly overlapped with those previously shown to be repressed by miR-34a. We confirmed upregulation of the novel direct p53 target genes LINC01021, MDFI, ST14 and miR-486 and showed that ectopic LINC01021 expression inhibited proliferation in SW480 cells. Furthermore, HMGB1, KLF12 and CIT mRNAs were confirmed as direct targets of the p53-induced miR-34a, miR-205 and miR-486-5p, respectively. In line with the loss of p53 function during tumor progression, elevated expression of HMGB1, KLF12 and CIT was detected in advanced stages of cancer. This study provides new insights and a comprehensive catalogue of p53-mediated regulations and p53 DNA binding in CRC cells.
Project description:We mapped the genomic binding sites of the tumor suppressor protein p53 in the human colorectal cancer cell line HCT116 and report here that the binding patterns of endogenous wild type p53 differed significantly between the genomes of the cancer cell line HCT116 and the normal human IMR90 fibroblasts (GSE31558) under the same experimental conditions (6 hr treatment with 5-fluorouracil). p53 binding differences affect promoter regions, CpG islands and major families of human repeat elements such as LTR, LINE and SINE. While p53 genomic binding sites residing in repeats have been reported before, we show here that the fraction of the p53 genomic binding sites residing in different repeat families differs between the normal and cancer human cell lines. We confirm that the p53 genomic binding sites in HCT116 cells are excluded from CpG islands, an observation we made previously based on analysis of data reported by others. While the p53 ability to elicit stress-specific and cell-type-specific responses is well documented, how this specificity is established, at the level of binding to the genome and/or during post-binding events, represents an open question. Our data indicate that p53 binding to the human genome is cell line-specific and highly selective. The differences in the p53 genome-wide binding patterns between the cancer cell line HCT116 and the normal cell line IMR90, namely exclusion from CpG islands and enrichment at repeats in HCT116, likely reflect cancer-associated epigenetic changes in the chromatin. Identification of genomic p53 binding sites in HCT116 cells by ChIP-seq.
Project description:We determined the effect of p53 activation on de novo protein synthesis using quantitative proteomics of newly synthesized proteins (pulsed stable isotope labeling with amino acids in cell culture, pSILAC) in combination with mRNA and non-coding RNA expression analyses by next generation sequencing (RNA-, miR-Seq) in the colorectal cancer (CRC) cell line SW480. Furthermore, genome-wide DNA binding of p53 was analyzed by chromatin-immunoprecipitation (ChIP-Seq). Thereby, we identified differentially regulated mRNAs (1258 up, 415 down), miRNAs (111 up, 95 down), lncRNAs (270 up, 123 down) and proteins (542 up, 569 down). Changes in mRNA and protein expression levels showed a positive correlation (r = 0.50, p < 0.0001). More transcriptionally induced genes displayed occupied p53 binding sites (4.3% mRNAs, 7.2% miRNAs, 6.3% lncRNAs, 5.9% proteins) than repressed genes (2.4% mRNAs, 3.2% miRNAs, 0.8% lncRNAs, 1.9% proteins), suggesting indirect mechanisms of repression. Around 50% of the downregulated proteins displayed seed-matching sequences of p53-induced miRNAs in the corresponding 3’-UTRs. Moreover, proteins repressed by p53 significantly overlapped with those previously shown to be repressed by miR-34a. We confirmed upregulation of the novel direct p53 target genes LINC01021, MDFI, ST14 and miR-486 and showed that ectopic LINC01021 expression inhibited proliferation in SW480 cells. Furthermore, HMGB1, KLF12 and CIT mRNAs were confirmed as direct targets of the p53-induced miR-34a, miR-205 and miR-486-5p, respectively. In line with the loss of p53 function during tumor progression, elevated expression of HMGB1, KLF12 and CIT was detected in advanced stages of cancer. This study provides new insights and a comprehensive catalogue of p53-mediated regulations and p53 DNA binding in CRC cells.
Project description:We experimentally demonstrated that CHD7 promotes the growth of colorectal cancer cells in vitro and in vivo. Mechanistically, RNA-seq and ATAC-seq approaches together with ChIP assays indicated that CHD7 can bind to the promoters of target genes to maintain chromatin accessibility and facilitate transcription. We found that CHD7 knockdown downregulates AK4 expression and activates AMPK phosphorylation, thereby promoting the phosphorylation and stability of p53 and leading to the inhibition of the colorectal cancer growth. Our genomic analyses of ATPCRs across large-scale cancer specimens identified potential therapeutic targets and our experimental studies revealed a novel CHD7-AK4-AMPK-p53 axis that plays an oncogenic role in colorectal cancer.
Project description:p53 mutation is common and highly related to radiotherapy resistance in rectal cancer. APR-246, as a small molecule, can restore the tumor-suppressor function to mutant p53. There is no study on combining APR-246 with radiation in rectal cancer; therefore, we examined whether APR-246 sensitized colorectal cancer cells with different p53 status to radiation. The combination treatment had synergistic effects on HCT116p53-R248W/-(p53Mut) cells, followed by HCT116p53+/+(p53WT) cells, and exhibited an additive effect on HCT116p53-/-(p53Null) cells through inhibiting proliferation, enhancing reactive oxygen species, and apoptosis. The results were confirmed in zebrafish xenografts. Comparison of the transcriptome in colorectal cancer cells with different p53 status 72hrs post-treatment with APR-246, irradiation, or the combination of APR-246 with irradiation was carried out. p53Mut and p53WT cells shared more activated pathways and differentially expressed genes following the combination treatment, compared to p53Null cells, although the combination treatment regulated individual pathways in the different cell lines. APR-246 mediated radio-sensitization effects through p53-dependent and -independent ways.