Colorectal Cancer Screening Recommendations and Outcomes in Lynch Syndrome

Screening for colorectal cancer (CRC) in Lynch syndrome enables early detection and likely cancer prevention. CRC screening guidelines have evolved from universal to gene-specific recommendations based on lifetime neoplasia risks. Regular screening for Lynch syndrome reduces CRC-related mortality; however, high CRC incidence during regular colonoscopy screening suggests the possibility of nonpolypoid carcinogenesis. Colonoscopy is the primary modality for screening for Lynch syndrome with mixed and emerging data on quality metrics, chromoendoscopy, artificial intelligence, and nonendoscopic modalities. Screening adherence varies across studies. In this review, we present the current state of CRC screening recommendations, outcomes, and modalities in Lynch syndrome.

Upregulation of polycistronic microRNA-143 and microRNA-145 in colonocytes suppresses colitis and inflammation-associated colon cancer

Because ADAM17 promotes colonic tumorigenesis, we investigated potential miRNAs regulating ADAM17; and examined effects of diet and tumorigenesis on these miRNAs. We also examined pre-miRNA processing and tumour suppressor roles of several of these miRNAs in experimental colon cancer. Using TargetScan, miR-145, miR-148a, and miR-152 were predicted to regulate ADAM17. miR-143 was also investigated as miR-143 and miR-145 are co-transcribed and associated with decreased tumour growth. HCT116 colon cancer cells (CCC) were co-transfected with predicted ADAM17-regulating miRNAs and luciferase reporters controlled by ADAM17-3'UTR. Separately, pre-miR-143 processing by colonic cells was measured. miRNAs were quantified by RT-PCR. Tumours were induced with AOM/DSS in WT and transgenic mice (Tg) expressing pre-miR-143/miR-145 under villin promoter. HCT116 transfection with miR-145, -148a or -152, but not scrambled miRNA inhibited ADAM17 expression and luciferase activity. The latter was suppressed by mutations in ADAM17-3'UTR. Lysates from colonocytes, but not CCC, processed pre-miR-143 and mixing experiments suggested CCC lacked a competency factor. Colonic miR-143, miR-145, miR-148a, and miR-152 were downregulated in tumours and more moderately by feeding mice a Western diet. Tg mice were resistant to DSS colitis and had significantly lower cancer incidence and tumour multiplicity. Tg expression blocked up-regulation of putative targets of miR-143 and miR-145, including ADAM17, K-Ras, XPO5, and SET. miR-145, miR-148a, and miR-152 directly suppress colonocyte ADAM17 and are down-regulated in colon cancer. This is the first direct demonstration of tumour suppressor roles for miR-143 and miR-145 in an in vivo model of colonic tumorigenesis.

Underdiagnosis of Hereditary Colorectal Cancers Among Medicare Patients: Genetic Testing Criteria for Lynch Syndrome Miss the Mark

PURPOSE

Strict clinical criteria used by Medicare for germline testing for Lynch syndrome (LS) could lead to missed diagnoses of hereditary cancer syndromes given variable individual and family phenotypes. The aim of this study was to compare rates and spectrum of pathogenic or likely pathogenic (P/LP) variants in LS and other hereditary cancer genes on the basis of meeting Medicare LS testing criteria.

METHODS

Retrospective review of Medicare beneficiaries who had multigene panel testing with an indication of personal or family history of colorectal cancer (CRC) was performed. Ordering providers determined if Medicare LS criteria were met. The results of genetic testing were compared on the basis of whether or not Medicare testing criteria were met.

RESULTS

Among 639 Medicare beneficiaries, 495 (77.5%) met testing criteria. Overall rates of P/LP variant identification were similar between those meeting and not meeting testing criteria (18.4% v 11.8%; P = .06). LS was diagnosed more frequently among those meeting testing criteria (10.1% v 4.9%; P = .05). No statistical differences were found in rates of P/LP variant identification for non-LS CRC genes (5.3% v 5.6%; P = .89) or non-CRC genes (4.2% v 2.1%; P = .23). PMS2, MUTYH, and ATM P/LP variants were found at higher rates among those outside of criteria.

CONCLUSION

Among Medicare beneficiaries undergoing genetic testing for suspected LS, rates of P/LP variants in actionable cancer genes were similar regardless of whether testing criteria were met. Current testing criteria fail to identify individuals with P/LP variants in PMS2 and other actionable cancer genes. Relaxing LS testing criteria could improve identification of individuals with hereditary cancer syndromes among Medicare beneficiaries.

Metachronous Advanced Neoplasia on Surveillance Colonoscopy in Patients With Young- vs Older-onset of Colorectal Cancer

The incidence of colorectal cancer (CRC) and cancer-related mortality has increased in patients <55 years old.¹ Consensus on optimal intervals for post-CRC surveillance colonoscopy in young patients is lacking. The primary endpoint of this study was comparison of rates of metachronous advanced neoplasia (AN) in patients diagnosed with CRC at <50 and 50-75 years. The secondary aim was to evaluate risk factors of metachronous AN.

Collaborative Group of the Americas on Inherited Gastrointestinal Cancer Position statement on multigene panel testing for patients with colorectal cancer and/or polyposis

Multigene panel tests for hereditary cancer syndromes are increasingly utilized in the care of colorectal cancer (CRC) and polyposis patients. However, widespread availability of panels raises a number of questions including which patients should undergo testing, which genes should be included on panels, and the settings in which panels should be ordered and interpreted. To address this knowledge gap, key questions regarding the major issues encountered in clinical evaluation of hereditary CRC and polyposis were designed by the Collaborative Group of the Americas on Inherited Gastrointestinal Cancer Position Statement Committee and leadership. A literature search was conducted to address these questions. Recommendations were based on the best available evidence and expert opinion. This position statement addresses which genes should be included on a multigene panel for a patient with a suspected hereditary CRC or polyposis syndrome, proposes updated genetic testing criteria, discusses testing approaches for patients with mismatch repair proficient or deficient CRC, and outlines the essential elements for ordering and disclosing multigene panel test results. We acknowledge that critical gaps in access, insurance coverage, resources, and education remain barriers to high-quality, equitable care for individuals and their families at increased risk of hereditary CRC.

Genomic and epigenomic active vitamin D responses in human colonic organoids

Active vitamin D, 1α,25(OH)₂D₃, is a nuclear hormone with roles in colonic homeostasis and carcinogenesis; yet, mechanisms underlying these effects are incompletely understood. Human organoids are an ideal system to study genomic and epigenomic host-environment interactions. Here, we use human colonic organoids to measure 1α,25(OH)₂D₃ responses on genome-wide gene expression and chromatin accessibility over time. Human colonic organoids were cultured and treated in triplicate with 100 nM 1α,25(OH)₂D₃ or vehicle control for 4 h and 18 h for chromatin accessibility, and 6 h and 24 h for gene expression. ATAC- and RNA-sequencing were performed. Differentially accessible peaks were analyzed using DiffBind and edgeR; differentially expressed genes were analyzed using DESeq2. Motif enrichment was determined using HOMER. At 6 h and 24 h, 2,870 and 2,721 differentially expressed genes, respectively (false discovery rate, FDR < 5%), were identified with overall stronger responses with 1α,25(OH)₂D₃. Similarly, 1α,25(OH)₂D₃ treatment led to stronger chromatin accessibility especially at 4 h. The vitamin D receptor (VDR) motif was strongly enriched among accessible chromatin peaks with 1α,25(OH)₂D₃ treatment accounting for 30.5% and 11% of target sequences at 4 h and 18 h, respectively (FDR < 1%). A number of genes such as CYP24A1, FGF19, MYC, FOS, and TGFBR2 showed significant transcriptional and chromatin accessibility responses to 1α,25(OH)₂D₃ treatment with accessible chromatin located distant from promoters for some gene regions. Assessment of chromatin accessibility and transcriptional responses to 1α,25(OH)₂D₃ yielded new observations about vitamin D genome-wide effects in the colon facilitated by application of human colonic organoids. This framework can be applied to study host-environment interactions between individuals and populations in the future.

Morphologic and molecular analysis of early-onset gastric cancer

BACKGROUND

Evidence suggests that early-onset gastric cancers are distinct from traditional gastric cancers; however, detailed genomic and morphologic characterization of these cancers has not been performed.

METHODS

Genomic analysis was performed for 81 patients with gastric cancer who were 50 years old or younger; pathology slides were available for 53 of these patients, and they were re-reviewed to perform a morphologic-molecular correlation analysis. The results were compared with corresponding cBioPortal data and The Cancer Genome Atlas (TCGA) analysis, which represent traditional gastric cancers. The TP53 molecular signature was established to determine the pattern of somatic mutational damage. Variants of potential germline origin were also identified from next-generation sequencing data.

RESULTS

A higher rate of CDH1 mutations (22.2% of early-onset gastric cancers vs 11.4% of traditional gastric cancers; P = .0042) but a similar rate of TP53 mutations (63% of early-onset gastric cancers vs 56.6% of traditional gastric cancers; P = .2674) were seen in early-onset cancers in comparison with traditional gastric cancers. The diffuse/mixed types correlated with the TCGA genomically stable type, and the remaining Lauren types correlated with the TCGA chromosomal instability type. Diffuse and indeterminate histologic types (overall survival, 26.25 months for the intestinal type, 20.5 months for the mixed type, 12.62 months for the diffuse type, and 9 months for the indeterminate type; P = .027) and the presence of a CDH1 gene mutation (overall survival, 9 months for mutant CDH1 and 22 months for wild-type CDH1; P = .013) significantly correlated with worse survival. The TP53 gene frequently showed transition mutations (65.5%) involving the CpG sites (49%). Variants of potential germline origin were seen in high-penetrance genes (CDH1 and APC) and moderate-penetrance genes (ATM, NBN, and MUTYH) in 9.9% of cancers.

CONCLUSIONS

Early-onset gastric cancer has distinct genomic alterations, such as CDH1 mutations, but shares with traditional gastric cancers a high frequency of TP53 mutations and the TP53 mutagenic signature. Diffuse and indeterminate histologic types and the presence of a CDH1 mutation are associated with worse overall survival. Endogenous factors leading to cytosine deamination and potential germline alterations in moderate-penetrance cancer susceptibility genes may be implicated in the pathogenesis of these cancers.

No Evidence of Increased Risk of Breast Cancer in Women With Lynch Syndrome Identified by Multigene Panel Testing

PURPOSE

Prior estimates of breast cancer risk in women with Lynch syndrome (LS) range from population risk to 18-fold increased risk with reported differences by gene. Here, breast cancer rates were determined in a large cohort of women with pathogenic variants (PVs) in a mismatch repair (MMR) gene detected through multigene panel testing and compared with rates in the US population and women undergoing panel testing.

METHODS

MMR gene PV carriers were identified among women tested for suspicion of LS or hereditary breast and ovarian cancer (HBOC) who met inclusion criteria. Standardized incidence ratios (SIRs) and 95% CIs of breast cancer were calculated compared with age-matched incidence in the general US female population and with women negative for PVs stratified by the test indication.

RESULTS

In total, 0.8% of women (30,362 of 441,966 women) carried MMR gene PVs. PVs in PMS2 (37.5%) and MSH6 (29.3%) were more common than in MLH1 (13.7%) and MSH2/EPCAM (19.4%). Women with PVs in PMS2 and MSH6 were tested more frequently for HBOC, whereas those with PVs in MLH1 and MSH2/EPCAM were tested more frequently for LS. Breast cancer rates in women with LS were lower than those in the general female population (SIR, 0.88; 95% CI, 0.81 to 0.96) and did not differ compared with women with negative panel testing for HBOC (SIR, 0.90; 95% CI, 0.82 to 0.99) or LS (SIR, 1.02; 95% CI, 0.78 to 1.30).

CONCLUSION

In this large cohort of women with LS identified through panel testing, there was no evidence for increased risk of breast cancer compared with the general US population or women undergoing panel testing. These findings support average-risk breast cancer screening in women with LS.

Hereditary diffuse gastric cancer: updated clinical practice guidelines

Hereditary diffuse gastric cancer (HDGC) is an autosomal dominant cancer syndrome that is characterised by a high prevalence of diffuse gastric cancer and lobular breast cancer. It is largely caused by inactivating germline mutations in the tumour suppressor gene CDH1, although pathogenic variants in CTNNA1 occur in a minority of families with HDGC. In this Policy Review, we present updated clinical practice guidelines for HDGC from the International Gastric Cancer Linkage Consortium (IGCLC), which recognise the emerging evidence of variability in gastric cancer risk between families with HDGC, the growing capability of endoscopic and histological surveillance in HDGC, and increased experience of managing long-term sequelae of total gastrectomy in young patients. To redress the balance between the accessibility, cost, and acceptance of genetic testing and the increased identification of pathogenic variant carriers, the HDGC genetic testing criteria have been relaxed, mainly through less restrictive age limits. Prophylactic total gastrectomy remains the recommended option for gastric cancer risk management in pathogenic CDH1 variant carriers. However, there is increasing confidence from the IGCLC that endoscopic surveillance in expert centres can be safely offered to patients who wish to postpone surgery, or to those whose risk of developing gastric cancer is not well defined.

Implication of DNA repair genes in Lynch-like syndrome

Many colorectal cancers (CRCs) that exhibit microsatellite instability (MSI) are not explained by MLH1 promoter methylation or germline mutations in mismatch repair (MMR) genes, which cause Lynch syndrome (LS). Instead, these Lynch-like syndrome (LLS) patients have somatic mutations in MMR genes. However, many of these patients are young and have relatives with cancer, suggesting a hereditary entity. We performed germline sequence analysis in LLS patients and determined their tumor's mutational profiles using FFPE DNA. Six hundred and fifty-four consecutive CRC patients were screened for suspected LS using MSI and absence of MLH1 methylation. Suspected LS cases were exome sequenced to identify germline and somatic mutations. Single nucleotide variants were used to characterize mutational signatures. We identified 23 suspected LS cases. Germline sequence analysis of 16 available samples identified five cases with LS mutations and 11 cases without LS mutations, LLS. Most LLS tumors had a combination of somatic MMR gene mutation and loss of heterozygosity. LLS patients were relatively young and had excess first-degree relatives with cancer. Four of the 11 LLS patients had rare likely pathogenic variants in genes that maintain genome integrity. Moreover, tumors from this group had a distinct mutational signature compared to tumors from LLS patients lacking germline mutations in these genes. In summary, more than a third of the LLS patients studied had germline mutations in genes that maintain genome integrity and their tumors had a distinct mutational signature. The possibility of hereditary factors in LLS warrants further studies so counseling can be properly informed.

Risk Assessment and Genetic Testing for Inherited Gastrointestinal Syndromes

A number of inherited syndromes affect the gastrointestinal tract, including Lynch syndrome and other hereditary colorectal cancers, hereditary polyposis, hereditary gastric cancer, hereditary pancreatic cancer, and hereditary pancreatitis. Recognition and diagnosis of these syndromes are paramount because affected individuals and family members can be offered life-saving screening, risk-reducing surgeries, and other therapies. Genetic counseling and testing are critical components of risk assessment and diagnosis of inherited syndromes. With the advent of next-generation sequencing, multigene panels have significantly changed the practice of genetic counseling and testing. Gastroenterology providers interface with patients who are at risk for inherited gastrointestinal syndromes; thus, providers should learn to recognize these syndromes and know when to refer their patients. Additionally, gastroenterology providers should have an understanding of genetic counseling and be able to interpret multigene panel test results. This article provides an overview of and practical tips for the assessment and diagnosis of hereditary gastrointestinal cancer syndromes and pancreatitis.

Lack of APC somatic mutation is associated with early-onset colorectal cancer in African Americans

African Americans (AAs) have higher incidence and mortality rates of colorectal cancer (CRC) compared with other US populations. They present with more right-sided, microsatellite stable disease and are diagnosed at earlier ages compared with non-Hispanic Whites (NHWs). To gain insight into these trends, we conducted exome sequencing (n = 45), copy number (n = 33) and methylation analysis (n = 11) of microsatellite stable AA CRCs. Results were compared with data from The Cancer Genome Atlas (TCGA). Two of the 45 tumors contained POLE mutations. In the remaining 43 tumors, only 27 (63%) contained loss-of-function mutations in APC compared with 80% of TCGA NHW CRCs. APC-mutation-negative CRCs were associated with an earlier onset of CRC (P = 0.01). They were also associated with lower overall mutation burden, fewer copy number variants and a DNA methylation signature that was distinct from the CpG island methylator phenotype characterized in microsatellite unstable disease. Three of the APC-mutation-negative CRCs had loss-of-function mutations in BCL9L. Mutations in driver genes identified by TCGA exome analysis were less frequent in AA CRC cases than TCGA NHWs. Genes that regulate the WNT signaling pathway, including SOX9, GATA6, TET1, GLIS1 and FAT1, were differentially hypermethylated in APC-mutation-negative CRCs, suggesting a novel mechanism for cancer development in these tumors. In summary, we have identified a subtype of CRC that is associated with younger age of diagnosis, lack of APC mutation, microsatellite and chromosome stability, lower mutation burden and distinctive methylation changes.

Risk factors for small bowel bleeding in an overt gastrointestinal bleeding presentation after negative upper and lower endoscopy

INTRODUCTION

A small bowel source is suspected when evaluation of overt gastrointestinal (GI) bleeding with upper and lower endoscopy is negative. Video capsule endoscopy (VCE) is the recommended next diagnostic test for small bowel bleeding sources. However, clinical or endoscopic predictive factors for small bowel bleeding in the setting of an overt bleeding presentation are unknown. We aimed to define predictive factors for positive VCE among individuals presenting with overt bleeding and a suspected small bowel source.

METHODS

We included consecutive inpatient VCE performed between September 1, 2012 to September 1, 2015 for melena or hematochezia at two tertiary centers. All patients had EGD and colonoscopy performed prior to VCE. Patient demographics, medication use, and endoscopic findings were retrospectively recorded. VCE findings were graded based on the P0-P2 grading system. The primary outcome of interest was a positive (P2) VCE. The secondary outcome of interest was the performance of a therapeutic intervention. Data were analyzed with the Fisher exact test for dichotomous variables and logistic regression.

RESULTS

Two hundred forty-three VCE were reviewed, and 117 were included in the final analysis. A positive VCE (P2) was identified in 35 (29.9%) cases. In univariate analysis, a positive VCE was inversely associated with presence of diverticula on preceding colonoscopy (OR: 0.44, 95% CI: 0.2-0.99), while identification of blood on terminal ileal examination was associated with a positive VCE (OR: 5.18, 95% CI: 1.51-17.76). In multivariate analysis, only blood identified on terminal ileal examination remained a significant risk factor for positive VCE (OR: 6.13, 95% CI: 1.57-23.81). Blood on terminal ileal examination was also predictive of therapeutic intervention in both univariate (OR: 4.46, 95% CI: 1.3-15.2) and multivariate analysis (OR: 5.04, 95% CI: 1.25-20.32).

CONCLUSION

Among patients presenting with overt bleeding but negative upper and lower endoscopy, the presence of blood on examination of the terminal ileum is strongly associated with a small bowel bleeding source as well as with small bowel therapeutic intervention. Presence of diverticula on colonoscopy is inversely associated with a positive VCE and therapeutic intervention in univariate analysis.

Low Referral Rate for Genetic Testing in Racially and Ethnically Diverse Patients Despite Universal Colorectal Cancer Screening

BACKGROUND & AIMS

Guidelines recommend that all colorectal tumors be assessed for mismatch repair deficiency, which could increase identification of patients with Lynch syndrome. This is of particular importance for minority populations, in whom hereditary syndromes are under diagnosed. We compared rates and outcomes of testing all tumor samples (universal testing) collected from a racially and ethnically diverse population for features of Lynch syndrome.

METHODS

We performed a retrospective analysis of colorectal tumors tested from 2012 through 2016 at 4 academic centers. Tumor samples were collected from 767 patients with colorectal cancer (52% non-Hispanic white [NHW], 26% African American, and 17% Hispanic patients). We assessed rates of tumor testing, recommendations for genetic evaluation, rates of attending a genetic evaluation, and performance of germline testing overall and by race/ethnicity. We performed univariate and multivariate regression analyses.

RESULTS

Overall, 92% of colorectal tumors were analyzed for mismatch repair deficiency without significant differences among races/ethnicities. However, minority patients were significantly less likely to be referred for genetic evaluation (21.2% for NHW patients vs 16.9% for African American patients and 10.9% for Hispanic patients; P = .02). Rates of genetic testing were also lower among minority patients (10.7% for NHW patients vs 6.0% for AA patients and 3.1% for Hispanic patients; P < .01). On multivariate analysis, African American race, older age, and medical center were independently associated with lack of referral for genetic evaluation and genetic testing.

CONCLUSION

In a retrospective analysis, we found that despite similar rates of colorectal tumor analysis, minority patients are less likely to be recommended for genetic evaluation or to undergo germline testing for Lynch syndrome. Improvements in institutional practices in follow up after tumor testing could reduce barriers to diagnosis of Lynch diagnosis in minorities.

Adherence to postresection colorectal cancer surveillance at National Cancer Institute-designated Comprehensive Cancer Centers

Guidelines recommend surveillance after resection of colorectal cancer (CRC), but rates of adherence to surveillance are variable and have not been studied at National Cancer Institute (NCI)‐designated Comprehensive Cancer Centers. The aim of this study was to determine rates of adherence to standard postresection CRC surveillance recommendations including physician visits, carcinoembryonic antigen (CEA), computed tomography (CT), and colonoscopy after CRC resection at three NCI‐designated centers.

Data on patients with resected CRC from 2010 to 2017 were reviewed. Adherence to physician visits was defined as having at least two visits within 14 months after surgical resection. CEA adherence was defined as having at least four CEA levels drawn within 14 months. CT and colonoscopy adherence were defined as completing each between 10 and 14 months from surgical resection. Chi‐square test and logistic regression analyses were performed for overall adherence and adherence to individual components.

A total of 241 CRC patients were included. Overall adherence was 23%. While adherence to physician visits was over 98%, adherence to CEA levels, CT, and colonoscopy were each less than 50%. Center was an independent predictor of adherence to CEA, CT, and/or colonoscopy. Stage III disease predicted CT adherence, while distance traveled of 40 miles or less predicted colonoscopy adherence.

Overall adherence to postresection CRC guideline‐recommended care is low at NCI‐designated centers. Adherence rates to surveillance vary by center, stage, and distance traveled for care. Understanding factors associated with adherence is critical to ensure CRC patients benefit from postresection surveillance.

Clinical interpretation of pathogenic ATM and CHEK2 variants on multigene panel tests: navigating moderate risk

Comprehensive genomic cancer risk assessment (GCRA) helps patients, family members, and providers make informed choices about cancer screening, surgical and chemotherapeutic risk reduction, and genetically targeted cancer therapies. The increasing availability of multigene panel tests for clinical applications allows testing of well-defined high-risk genes, as well as moderate-risk genes, for which the penetrance and spectrum of cancer risk are less well characterized. Moderate-risk genes are defined as genes that, when altered by a pathogenic variant, confer a 2 to fivefold relative risk of cancer. Two such genes included on many comprehensive cancer panels are the DNA repair genes ATM and CHEK2, best known for moderately increased risk of breast cancer development. However, the impact of screening and preventative interventions and spectrum of cancer risk beyond breast cancer associated with ATM and/or CHEK2 variants remain less well characterized. We convened a large, multidisciplinary, cross-sectional panel of GCRA clinicians to review challenging, peer-submitted cases of patients identified with ATM or CHEK2 variants. This paper summarizes the inter-professional case discussion and recommendations generated during the session, the level of concordance with respect to recommendations between the academic and community clinician participants for each case, and potential barriers to implementing recommended care in various practice settings.

Vitamin D Regulation of the Uridine Phosphorylase 1 Gene and Uridine-Induced DNA Damage in Colon in African Americans and European Americans

BACKGROUND & AIMS

African Americans have the greatest colorectal cancer (CRC) burden in the United States; interethnic differences in protective effects of vitamin D might contribute to disparities. 1α,25(OH)₂D₃ vitamin D (the active form of vitamin D) induces transcription of the uridine phosphorylase gene (UPP1) in colon tissues of European Americans but to a lesser extent in colon tissues of African Americans. UPP1-knockout mice have increased intestinal concentrations of uridine and Deoxyuridine triphosphate (dUTP), have increased uridine-induced DNA damage, and develop colon tumors. We studied 1α,25(OH)₂D₃ regulation of UPP1 and uridine-induced DNA damage in the colon and differences in these processes between African and European Americans.

METHODS

We quantified expression and activity of UPP1 in response to 1α,25(OH)₂D₃ in young adult mouse colonic cells, human CRC cells (LS174T), and organoids (derived from rectosigmoid biopsy samples of healthy individuals undergoing colonoscopies) using quantitative polymerase chain reaction, immunoblot, and immunocytochemistry assays. Binding of the vitamin D receptor to UPP1 was tested by chromatin immunoprecipitation. Uridine-induced DNA damage was measured by fragment-length analysis in repair enzyme assays. Allele-specific 1α,25(OH)₂D₃ responses were tested using luciferase assays.

RESULTS

Vitamin D increased levels of UPP1 mRNA, protein, and enzymatic activity and increased vitamin D receptor binding to the UPP1 promoter in young adult mouse colonic cells, LS174T cells, and organoids. 1α,25(OH)₂D₃ significantly reduced levels of uridine and uridine-induced DNA damage in these cells, which required UPP1 expression. Organoids derived from colon tissues of African Americans expressed lower levels of UPP1 after exposure to 1α,25(OH)₂D₃ and had increased uridine-induced DNA damage compared with organoids derived from tissues of European Americans. Luciferase assays with the T allele of single nucleotide polymorphism rs28605337 near UPP1, which is found more frequently in African Americans than European Americans, expressed lower levels of UPP1 after exposure to 1α,25(OH)₂D₃ than assays without this variant.

CONCLUSIONS

We found vitamin D to increase expression of UPP1, leading to reduce uridine-induced DNA damage, in colon cells and organoids. A polymorphism in UPP1 found more frequently in African Americans than European Americans reduced UPP1 expression upon cell exposure to 1α,25(OH)₂D₃. Differences in expression of UPP1 in response to vitamin D could contribute to the increased risk of CRC in African Americans.