Beta-catenin expression is altered in dysplastic and nondysplastic aberrant crypt foci of human colon

LINC00689 participates in proliferation, chemoresistance and metastasis via miR-31-5p/YAP/β-catenin axis in colorectal cancer

As a kind of high-incidence malignant tumors in the digestive tract, colorectal cancer (CRC) has extremely morbidity and mortality in the population. LncRNAs have been proved to regulate the proliferation, chemoresistance and metastasis of tumors including CRC. LINC00689 and miR-31-5p in CRC were found misregulated in CRC by TCGA analysis. However, the mechanism of LINC00689 and miR-31-5p in regulating CRC remains unknown. The expression levels of LINC00689, miR-31-5p and LATS2 in CRC tissues and cell lines were examined by qRT-PCR assay. Cell proliferation, metastasis (including invasion and migration) were quantified by MTT assay, colony formation and Transwell assay, respectively. Western blotting assay was then performed to verify the levels of YAP/β-catenin and metastasis-related proteins. Dual-luciferase reporter assay and RIP assay were performed to evaluate the interaction between LINC00689 (LATS2) and miR-31-5p. Moreover, the function of LINC00689 and miR-31-5p were confirmed by CRC xenograft in nude mice. LINC00689 was decreased while miR-31-5p was increased in CRC. The overexpression of LINC00689 or the knockdown of miR-31-5p inhibited cell proliferation, chemoresistance and metastasis of CRC cells. Meanwhile, the up-regulated LATS2 suppressed the activity of YAP/β-catenin pathway to repress CRC occurrence. Silencing LATS2 reversed the inhibition effects of overexpression of LINC00689 or knockdown of miR-31-5p on proliferation, chemoresistance and metastasis of CRC cells. LINC00689 indeed acted as a miR-31-5p sponge to inhibit CRC proliferation, chemoresistance and metastasis through up-regulating LATS2 and repressing YAP/β-catenin signaling pathway.

Establishment of a multicomponent dietary bioactive human equivalent dose to delete damaged Lgr5+ stem cells using a mouse colon tumor initiation model

Multicomponent therapy has gained interest for its potential to synergize and subsequently lower the effective dose of each constituent required to reduce colon cancer risk. We have previously showed that rapidly cycling Lgr5 stem cells are exquisitely sensitive to extrinsic dietary factors that modulate colon cancer risk. In the present study, we quantified the dose-dependent synergistic properties of dietary n-3 polyunsaturated fatty acids (PUFA) and curcumin (Cur) to promote targeted apoptotic deletion of damaged colonic Lgr5 stem cells. For this purpose, both heterogeneous bulk colonocytes and Lgr5 stem cells were isolated from Lgr5-EGFP-IRES-CreER knock-in mice injected with azoxymethane (AOM). Isolated cells were analyzed for DNA damage (γH2AX), apoptosis (cleaved caspase-3), and targeted apoptosis (both γH2AX and cleaved caspase-3) at 12 h post-AOM injection. Comparison of the percentage of targeted apoptosis in Lgr5 stem cells (GFP) across a broad bioactive dose-range revealed an ED50 of 16.0 mg/day n-3 PUFA + 15.9 mg/day Cur. This corresponded to a human equivalent dose of 3.0 g n-3 PUFA + 3.0 g Cur. In summary, our results provide evidence that a low dose (n-3 PUFA + Cur) combination diet reduces AOM-induced DNA damage in Lgr5 stem cells and enhances targeted apoptosis of DNA-damaged cells, implying that a lower human equivalent dose can be utilized in future human clinical trials.

Assessment of beta-catenin expression by immunohistochemistry in colorectal neoplasms and its role as an additional prognostic marker in colorectal adenocarcinoma

BACKGROUND

Cancer is one of the world's biggest health care challenges, with colorectal cancer (CRC) being one of the three most frequently encountered malignancy worldwide. The main cause of mortality associated with CRC is tumour invasion and metastasis. Pathogenesis of CRC is a multistep process, during which different molecular pathways come into play. The cardinal genomic alteration that has been found universally present in CRC is a mutation in the adenomatous polyposis coli gene (APC). APC mutation causes unrestricted action of the Wnt signaling pathway which subsequently enhances the intracellular accumulation of a protein called beta-catenin, responsible for cell proliferation, differentiation and enhanced survival of colorectal epithelial cells.

AIM

This study was conducted to analyze beta-catenin expression in various colorectal neoplasms, and its change with respect to different grades and stage of colorectal adenocarcinoma.

STUDY DESIGN

This was a cross-sectional observational study.

METHODS

A total of 66 cases were enrolled in this study. Census method of sampling was used. Data was collected using a pre-designed, pretested semi-structured schedule on dependent variables like beta-catenin expression and independent variables like clinico-pathological profile including dietary history, macroscopic findings, histological type, histological grade, stage and other relevant parameters.An institution based cross sectional observational study was performed between February 2016 and July 2017. Representative sections taken from the specimens included in the study were subjected to histopathological examination followed by immunohistochemistry [IHC] for beta-catenin expression; the data obtained were analyzed by mean ± SD, Student t test, Chi-square/ Fisher Exact test using statistical software SPSS 18.0.

RESULTS

A statistically significant correlation (P = 0.004), of beta-catenin localization and IHC score was noted between the benign, premalignant and malignant neoplasms following a gradual transition from a membranous to a nuclear positivity; also, a significant (P<0.001) correlation between beta-catenin nuclear score and the corresponding American Joint Committee on Cancer (AJCC) stage of colorectal adenocarcinoma was also found in this study.

CONCLUSION

The purpose of this study was to determine the change in beta-catenin expression which demonstrates a gradual shift from a membranous to subsequent cytoplasmic and nuclear positivity from normal colorectal tissue to benign, premalignant and malignant neoplasms respectively. This property of beta-catenin can determine the malignant potential of various premalignant neoplasms of the large intestine, thus aiding in an early initiation of prophylactic treatment, which can prevent the development of an invasive disease. The membranous, cytoplasmic and nuclear scores show a linear progression with the advancing stages of colorectal carcinoma, making beta-catenin a prognostic marker in malignant colorectal neoplasms.

Rapidly cycling Lgr5+ stem cells are exquisitely sensitive to extrinsic dietary factors that modulate colon cancer risk

The majority of colon tumors are driven by aberrant Wnt signaling in intestinal stem cells, which mediates an efficient route toward initiating intestinal cancer. Natural lipophilic polyphenols and long-chain polyunsaturated fatty acids (PUFAs) generally suppress Wnt- and NF-κB- (nuclear factor-κ light-chain enhancer of activated B-cell) related pathways. However, the effects of these extrinsic agents on colonic leucine-rich repeat-containing G-protein-coupled receptor 5-positive (Lgr5⁺) stem cells, the cells of origin of colon cancer, have not been documented to date. Therefore, we examined the effect of n-3 PUFA and polyphenol (curcumin) combination on Lgr5⁺ stem cells during tumor initiation and progression in the colon compared with an n-6 PUFA-enriched control diet. Lgr5-EGFP-IRES-^creERT2 knock-in mice were fed diets containing n-6 PUFA (control), n-3 PUFA, n-6 PUFA+curcumin or n-3 PUFA+curcumin for 3 weeks, followed by 6 azoxymethane (AOM) injections, and terminated 17 weeks after the last injection. To further elucidate the effects of the dietary bioactives at the tumor initiation stage, Lgr5⁺ stem cells were also assessed at 12 and 24 h post AOM injection. Only n-3 PUFA+curcumin feeding reduced nuclear β-catenin in aberrant crypt foci (by threefold) compared with control at the progression time point. n-3 PUFA+curcumin synergistically increased targeted apoptosis in DNA-damaged Lgr5⁺ stem cells by 4.5-fold compared with control at 12 h and maximally reduced damaged Lgr5⁺ stem cells at 24 h, down to the level observed in saline-treated mice. Finally, RNAseq analysis indicated that p53 signaling in Lgr5⁺ stem cells from mice exposed to AOM was uniquely upregulated only following n-3 PUFA+curcumin cotreatment. These novel findings demonstrate that Lgr5⁺ stem cells are uniquely responsive to external dietary cues following the induction of DNA damage, providing a therapeutic strategy for eliminating damaged Lgr5⁺ stem cells to reduce colon cancer initiation.

A randomized clinical trial of the effects of supplemental calcium and vitamin D3 on the APC/β-catenin pathway in the normal mucosa of colorectal adenoma patients

APC/β-catenin pathway perturbation is a common early event in colorectal carcinogenesis and is affected by calcium and vitamin D in basic science studies. To assess the effects of calcium and vitamin D on adenomatous polyposis coli (APC), β-catenin, and E-cadherin expression in the normal appearing colorectal mucosa of sporadic colorectal adenoma patients, we conducted a randomized, double-blinded, placebo-controlled 2 × 2 factorial clinical trial. Pathology-confirmed colorectal adenoma cases were treated with 2 g/day elemental calcium and/or 800 IU/day vitamin D(3) versus placebo over 6 months (N = 92; 23/group). Overall APC, β-catenin, and E-cadherin expression and distributions in colon crypts in normal-appearing rectal mucosa biopsies were detected by standardized automated immunohistochemistry and quantified by image analysis. In the vitamin D(3)-supplemented group relative to placebo, the proportion of APC in the upper 40% of crypts (Φh APC) increased 21% (P = 0.01), β-catenin decreased 12% (P = 0.18), E-cadherin increased 72% (P = 0.03), and the Φh APC/β-catenin ratio (APC/β-catenin score) increased 31% (P = 0.02). In the calcium-supplemented group Φh APC increased 10% (P = 0.12), β-catenin decreased 15% (P = 0.08), and the APC/β-catenin score increased 41% (P = 0.01). In the calcium/vitamin D(3)-supplemented group, β-catenin decreased 11% (P = 0.20), E-cadherin increased 51% (P = 0.08), and the APC/β-catenin score increased 16% (P = 0.26). These results support (i) that calcium and vitamin D modify APC, β-catenin, and E-cadherin expression in humans in directions hypothesized to reduce risk for colorectal neoplasms, (ii) calcium and vitamin D as potential chemopreventive agents against colorectal neoplasms, and (iii) the potential of APC, β-catenin, and E-cadherin expression as modifiable, preneoplastic risk biomarkers for colorectal neoplasms.

N-methylpurine DNA glycosylase inhibits p53-mediated cell cycle arrest and coordinates with p53 to determine sensitivity to alkylating agents

Alkylating agents induce genome-wide base damage, which is repaired mainly by N-methylpurine DNA glycosylase (MPG). An elevated expression of MPG in certain types of tumor cells confers higher sensitivity to alkylation agents because MPG-induced apurinic/apyrimidic (AP) sites trigger more strand breaks. However, the determinant of drug sensitivity or insensitivity still remains unclear. Here, we report that the p53 status coordinates with MPG to play a pivotal role in such process. MPG expression is positive in breast, lung and colon cancers (38.7%, 43.4% and 25.3%, respectively) but negative in all adjacent normal tissues. MPG directly binds to the tumor suppressor p53 and represses p53 activity in unstressed cells. The overexpression of MPG reduced, whereas depletion of MPG increased, the expression levels of pro-arrest gene downstream of p53 including p21, 14-3-3σ and Gadd45 but not proapoptotic ones. The N-terminal region of MPG was specifically required for the interaction with the DNA binding domain of p53. Upon DNA alkylation stress, in p53 wild-type tumor cells, p53 dissociated from MPG and induced cell growth arrest. Then, AP sites were repaired efficiently, which led to insensitivity to alkylating agents. By contrast, in p53-mutated cells, the AP sites were repaired with low efficacy. To our knowledge, this is the first direct evidence to show that a DNA repair enzyme functions as a selective regulator of p53, and these findings provide new insights into the functional linkage between MPG and p53 in cancer therapy.

Biology and diagnosis of aberrant crypt foci

AIM

Aberrant crypt foci (ACFs) are clusters of colonic crypts that can be identified after staining and that have a different behaviour than the surrounding crypts. They have been hypothesized to be the potential precursors of colonic neoplastic lesions. Since they are detectable in vivo with endoscopic stains, they have been proposed as early biomarkers for colonic carcinogenesis. Our aim was to examine the literature regarding the role of ACFs in the pathogenesis of colorectal cancer (CRC).

METHOD

An intensive PubMed search was performed with the following terms: aberrant crypt foci, colorectal cancer, biomarker, carcinogenesis.

RESULTS

  Aberrant crypt foci have a variable prevalence and little is known about their natural history. They can be classified as hyperplastic or dysplastic. There is evidence that supports their role as preneoplastic lesions and features detectable by chromoendoscopy have been related to CRC risk. Moreover, ACFs have been shown to harbour genetic and epigenetic alterations common in adenomas and CRC. However, contradictory results have been obtained and difficulties in endoscopic detection and characterization have been described in large-scale studies.

CONCLUSION

  Despite the inconsistencies in ACF detection and characterization, several genetic and epigenetic changes common in both ACFs and CRC have been verified throughout the studies. This evidence is increasingly strong and it grows along with progress in the knowledge of carcinogenesis molecular pathways. Clinical application of ACFs as an intermediate endpoint for colorectal carcinogenesis is under development and a deeper knowledge of cancer mechanisms is needed before it can be applied or discarded.