A genome-first approach to variants in MLXIPL and their association with hepatic steatosis and plasma lipids

BACKGROUND

Common variants of the max-like protein X (MLX)-interacting protein-like (MLXIPL) gene, encoding the transcription factor carbohydrate-responsive element-binding protein, have been shown to be associated with plasma triglyceride levels. However, the role of these variants in steatotic liver disease (SLD) is unclear.

METHODS

We used a genome-first approach to analyze a variety of metabolic phenotypes and clinical outcomes associated with a common missense variant in MLXIPL, Gln241His, in 2 large biobanks: the UK Biobank and the Penn Medicine Biobank.

RESULTS

Carriers of MLXIPL Gln241His were associated with significantly lower serum levels of triglycerides, apolipoprotein-B, gamma-glutamyl transferase, and alkaline phosphatase. Additionally, MLXIPL Gln241His carriers were associated with significantly higher serum levels of HDL cholesterol and alanine aminotransferase. Carriers homozygous for MLXIPL Gln241His showed a higher risk of SLD in 2 unrelated cohorts. Carriers of MLXIPL Gln241His were especially more likely to be diagnosed with SLD if they were female, obese, and/or also carried the PNPLA3 I148M variant. Furthermore, the heterozygous carriage of MLXIPL Gln241His was associated with significantly higher all-cause, liver-related, and cardiovascular mortality rates. Nuclear magnetic resonance metabolomics data indicated that carriage of MLXIPL Gln241His was significantly associated with lower serum levels of VLDL and increased serum levels of HDL cholesterol.

CONCLUSIONS

Analyses of the MLXIPL Gln241His polymorphism showed a significant association with a higher risk of SLD diagnosis and elevated serum alanine aminotransferase as well as significantly lower serum triglycerides and apolipoprotein-B levels. MLXIPL might, therefore, be a potential pharmacological target for the treatment of SLD and hyperlipidemia, notably for patients at risk. More mechanistic studies are needed to better understand the role of MLXIPL Gln241His on lipid metabolism and steatosis development.

Aspirin is associated with a reduced incidence of liver disease in men

BACKGROUND

The hepatoprotective effects of aspirin have been observed in individuals with viral hepatitis; however, its impact on the general population remains uncertain. Understanding the association between aspirin use and the development of liver diseases is crucial for optimizing preventive strategies.

METHODS

We identified individuals with aspirin use in the UK Biobank and the Penn Medicine Biobank, as well as propensity-score-matched controls. Outcome measures included new liver disease development, diagnosed by MRI or "International Classification of Diseases and Related Health Problems" coding, and incidences of gastrointestinal bleeding and ulcers.

RESULTS

In the UK Biobank cohort, regular aspirin use was associated with an 11.2% reduction in the risk of developing new liver diseases during the average 11.84 ± 2.01-year follow-up period (HR=0.888, 95% CI = 0.819-0.963; p = 4.1 × 10-3). Notably, the risk of metabolic dysfunction-associated steatotic liver disease (ICD-10 K76.0) and MRI-diagnosed steatosis was significantly lower among aspirin users (HR = 0.882-0.911), whereas no increased risk of gastrointestinal bleeding or ulcers was observed. These findings were replicated in the Penn Medicine Biobank cohort, in which the protective effect of aspirin appeared to be dependent on the duration of intake. The greatest risk reduction for new liver disease development was observed after at least 1 year of aspirin use (HR = 0.569, 95% CI = 0.425-0.762; p = 1.6 × 10-4). Intriguingly, when considering general risk factors, only men exhibited a lower risk of MRI-confirmed or ICD-coded steatosis with aspirin use (HRs = 0.806-0.906), while no significant protective effect of aspirin was observed in females.

CONCLUSION

This cohort study demonstrated that regular aspirin use was associated with a reduced risk of liver disease in men without an elevated risk of gastrointestinal bleeding or ulcers. Further investigation is warranted to elucidate potential sex-related differences in the effects of aspirin and to inform tailored preventive strategies for liver diseases.

A phenotypic approach to obesity treatment

Obesity is a chronic disease that increases morbidity and mortality and adversely affects quality of life. The rapid rise of obesity has outpaced the development and deployment of effective therapeutic interventions, thereby creating a global health crisis. The presentation, complications, and response to obesity treatments vary, yet lifestyle modification, which is the foundational therapeutic intervention for obesity, is often "one size fits all." The concept of personalized medicine uses genetic and phenotypic information as a guide for disease prevention, diagnosis, and treatment and has been successfully applied in diseases such as cancer, but not in obesity. As we gain insight into the pathophysiologic mechanisms of obesity and its phenotypic expression, specific pathways can be targeted to yield a greater, more sustained therapeutic impact in an individual patient with obesity. A phenotype-based pharmacologic treatment approach utilizing objective measures to classify patients into predominant obesity mechanism groups resulted in greater weight loss (compared with a non-phenotype-based approach) in a recent study by Acosta and colleagues. In this review, we discuss the application of lifestyle modifications, behavior therapy and pharmacotherapy using the obesity phenotype-based approach as a framework.

Large-scale identification of undiagnosed hepatic steatosis using natural language processing

Background

Nonalcoholic fatty liver disease (NAFLD) is a major cause of liver-related morbidity in people with and without diabetes, but it is underdiagnosed, posing challenges for research and clinical management. Here, we determine if natural language processing (NLP) of data in the electronic health record (EHR) could identify undiagnosed patients with hepatic steatosis based on pathology and radiology reports.

Methods

A rule-based NLP algorithm was built using a Linguamatics literature text mining tool to search 2.15 million pathology report and 2.7 million imaging reports in the Penn Medicine EHR from November 2014, through December 2020, for evidence of hepatic steatosis. For quality control, two independent physicians manually reviewed randomly chosen biopsy and imaging reports (n = 353, PPV 99.7%).

Findings

After exclusion of individuals with other causes of hepatic steatosis, 3007 patients with biopsy-proven NAFLD and 42,083 patients with imaging-proven NAFLD were identified. Interestingly, elevated ALT was not a sensitive predictor of the presence of steatosis, and only half of the biopsied patients with steatosis ever received an ICD diagnosis code for the presence of NAFLD/NASH. There was a robust association for PNPLA3 and TM6SF2 risk alleles and steatosis identified by NLP. We identified 234 disorders that were significantly over- or underrepresented in all subjects with steatosis and identified changes in serum markers (e.g., GGT) associated with presence of steatosis.

Interpretation

This study demonstrates clear feasibility of NLP-based approaches to identify patients whose steatosis was indicated in imaging and pathology reports within a large healthcare system and uncovers undercoding of NAFLD in the general population. Identification of patients at risk could link them to improved care and outcomes.

Funding

The study was funded by US and German funding sources that did provide financial support only and had no influence or control over the research process.

Association of Statin Use With Risk of Liver Disease, Hepatocellular Carcinoma, and Liver-Related Mortality

Importance

Given the burden of chronic liver disease on the health care system, more information on the hepatoprotective association of statins in the general population is needed.

Objective

To examine whether regular statin use is associated with a reduction in liver disease, particularly hepatocellular carcinoma (HCC) and liver-related deaths, in the general population.

Design, Setting, and Participants

This cohort study used data from the UK Biobank (UKB) (individuals aged 37-73 years) collected from baseline (2006-2010) to the end of follow-up in May 2021, from the TriNetX cohort (individuals aged 18-90 years) enrolled from baseline (2011-2020) until end of follow-up in September 2022, and from the Penn Medicine Biobank (PMBB) (individuals aged 18-102 years) with ongoing enrollment starting in 2013 to the end of follow-up in December 2020. Individuals were matched using propensity score matching according to the following criteria: age, sex, body mass index, ethnicity, diabetes with or without insulin or biguanide use, hypertension, ischemic heart disease, dyslipidemia, aspirin use, and number of medications taken (UKB only). Data analysis was performed from April 2021 to April 2023.

Exposure

Regular statin use.

Main Outcomes and Measures

Primary outcomes were liver disease and HCC development as well as liver-associated death.

Results

A total of 1 785 491 individuals were evaluated after matching (aged 55 to 61 years on average, up to 56% men, and up to 49% women). A total of 581 cases of liver-associated death, 472 cases of incident HCC, and 98 497 new liver diseases were registered during the follow-up period. Individuals were aged 55-61 years on average, with a slightly higher proportion of men (up to 56%). In UKB individuals (n = 205 057) without previously diagnosed liver disease, statin users (n = 56 109) had a 15% lower hazard ratio (HR) for the association of developing a new liver disease (HR, 0.85; 95% CI, 0.78-0.92; P < .001). In addition, statin users demonstrated a 28% lower HR for the association with liver-related death (HR, 0.72; 95% CI, 0.59-0.88; P = .001) and a 42% lower HR for the development of HCC (HR, 0.58; 95% CI, 0.35-0.96; P = .04). In TriNetX individuals (n = 1 568 794), the HR for the association of HCC was reduced even further for statin users (HR, 0.26; 95% CI, 0.22-0.31; P = .003). The hepatoprotective association of statins was time and dose dependent, with a significant association in PMBB individuals (n = 11 640) for incident liver diseases after 1 year of statin use (HR, 0.76; 95% CI, 0.59-0.98; P = .03). Taking statins was particularly beneficial in men, individuals with diabetes, and individuals with a high Fibrosis-4 index at baseline. Carriers of the heterozygous minor allele of PNPLA3 rs738409 benefited from statin use and had a 69% lower HR for the association with HCC (UKB HR, 0.31; 95% CI, 0.11-0.85; P = .02).

Conclusions and Relevance

This cohort study indicates substantial preventive associations of statins against liver disease, with an association with duration and dose of intake.

A coding variant in the microsomal triglyceride transfer protein reduces both hepatic steatosis and plasma lipids

BACKGROUND AND AIMS

Genetic inactivation and pharmacologic inhibition of the microsomal triglyceride transfer protein (MTP; gene name MTTP) inhibits hepatic secretion of VLDL, thereby reducing serum lipids and apoB at the expense of increasing hepatic steatosis. Little is known about the effects of missense variants in MTTP on hepatic and circulating lipids.

METHODS

We analysed the association of MTTP missense variants with metabolic, hepatic and clinical phenotypes in the Penn Medicine Biobank (PMBB; n = 37,960) and the UKBiobank (UKB; n = 451,444).

RESULTS

We analysed 24 missense variants in MTTP in PMBB for association with biopsy-proven hepatic steatosis and found that an isoleucine 128 to threonine variant (I128T: rs3816873-A, frequency 26%) was associated with reduced steatosis (p < 0.001). PMBB subjects with imaging-proven steatosis also revealed significantly fewer carriers of MTTP I128T compared to controls. Analysis in UKB also showed that MTTP I128T was associated with reduced risk of hepatic steatosis. Unexpectedly, MTTP I128T was found to be associated with reduced plasma levels of LDL-cholesterol and apoB (all p < 0.001). Functional studies indicated that MTTP I128T is neither a classic loss nor gain of function allele.

CONCLUSIONS

MTTP I128T is associated with reduced hepatic steatosis as well as reduced plasma lipids and apoB. This paradoxical profile is not consistent with a simple gain or loss of function in MTP activity and suggests a more complex effect on MTP function. Further investigation of MTTP I128T will provide insight into the structure-function of MTP and potentially new approaches to modulate MTP activity that could both reduce hepatic and circulating lipids.

Dietary Vitamin E Intake Is Associated With a Reduced Risk of Developing Digestive Diseases and Nonalcoholic Fatty Liver Disease

INTRODUCTION

Vitamin E supplementation is recommended for the treatment of nonalcoholic fatty liver disease (NAFLD) for nondiabetic patients, but its preventative effects are unclear.

METHODS

We assessed dietary vitamin E intake with disease phenotypes and evaluated vitamin E levels with the development of NAFLD.

RESULTS

Data from >210,000 participants demonstrate that increased dietary vitamin E associates with reduced rates of several gastrointestinal diseases and reduced overall mortality. Diabetic and overweight subjects with increased vitamin E intake have fewer NAFLD diagnoses.

DISCUSSION

Our findings reveal the relevance of vitamin E consumption for several gastrointestinal diseases and warrant further mechanistic and therapeutic investigations.

Systematic Review and Meta-Analysis: Efficacy of Vancomycin Taper and Pulse Regimens in Clostridioides difficile Infection

BACKGROUND

Vancomycin is the drug of choice for treating Clostridioides difficile infection (CDI). We compare CDI resolution with vancomycin taper, pulse, and taper-and-pulse regimens.

METHODS

We searched for Medline, Embase, Cochrane, and Scopus through October 9^th, 2020. Taper regimen was defined as dose reduction over time; pulse was a regimen less frequent than daily. Studies assessing CDI resolution rates were included. Meta-analyses for resolution rates were performed using weighted proportion ratios (WPR).

RESULTS

Ten studies with 675 patients treated with vancomycin regimens were included. Resolution rates were 83% (212/266, 95% CI 69-94%, I² = 85%) for taper-and-pulse, 68% (264/383, 95% CI 57-78%, I² = 72%) for taper alone, and 54% (11/26 95% CI 0-100%, I² = 86%) for pulse alone regimens. Taper-and-pulse was superior to taper alone (WPR 83% vs 68%, p < 0.0001) and pulse alone (WPR 83% vs 54%, p < 0.0004), no significant difference between taper alone or pulse alone (WPR 68% vs 54%, p = 0.1).

CONCLUSIONS

Limitations of our analysis are a small number of included studies and heterogeneity. Vancomycin taper-and-pulse seems superior to pulse alone or taper alone for recurrent CDI. A randomized controlled trial comparing vancomycin taper-and-pulse to fidaxomicin and microbiome restoration is needed.

A genome-first approach to mortality and metabolic phenotypes in MTARC1 p.Ala165Thr (rs2642438) heterozygotes and homozygotes

BACKGROUND

A coding variant in MTARC1 (rs2642438; p.Ala165Thr) was recently associated with protection from cirrhosis in European individuals. However, its impact on overall and cause-specific mortality remained elusive.

METHODS

Using a genome-first approach, we explored a range of metabolic phenotypes and outcomes associated with MTARC1 p.Ala165Thr in the UKBiobank and the Penn-Medicine BioBank.

FINDINGS

MTARC1 p.Ala165Thr was significantly associated with higher triglycerides, lower total cholesterol, lower LDL-C, lower ApoB, lower HDL-C, lower ApoA-I and higher IGF-1. Per each minor allele, the risk of NAFLD was reduced by ~15%. The ALT-lowering and NAFLD-protective effect of MTARC1 p.Ala165Thr was amplified by obesity, diabetes mellitus and presence of PNPLA3 rs738409:G. In African-American and Black-British individuals, the allele frequency of MTARC1 p.Ala165Thr was lower, but carriers showed the same distinctive lipid phenotype. Importantly, MTARC1 p.Ala165Thr carriers did not show higher cardiovascular disease burden as evidenced by cardiac MRI and carotid ultrasound. In prospective analyses, the homozygous minor allele was associated with up to 39% lower rates of liver-related mortality, while no risk of increased overall or cardiovascular death could be observed. Strikingly, liver-related mortality was more than 50% reduced in diabetic participants or carriers of PNPLA3 rs738409:G.

CONCLUSIONS

Together these data highlight MTARC1 as an important liver disease modifier that influences plasma lipids in an allele-dose-dependent manner without increasing cardiovascular outcomes. Our results point toward potential mechanisms and reveal a remarkable association with liver-related mortality calling for future studies exploring its therapeutic potential.

FUNDING

This study was funded by the German Research Foundation (DFG).

Physical activity is associated with reduced risk of liver disease in the prospective UK Biobank cohort

Background & Aims

Previous studies have identified physical activity as an important lifestyle factor in the pathogenesis of chronic liver diseases (CLD). However, most studies were short in follow-up, and based on self-reported activity. Moreover, it is unknown whether physical activity affects the risk of liver disease development in the general population. Herein, we aimed to clarify the association between physical activity and CLD by examining the risk of liver disease and progression in relation to accelerometer-based physical activity in a large subset of prospectively recruited participants in the UK Biobank.

Methods

We analysed data from 96,688 participants that recorded their physical activity through the use of a wrist accelerometer. Relative risks for development of liver diseases were calculated using multivariable-adjusted Cox regression models. In a subgroup of participants without any previously diagnosed liver disease (n = 95,974), a total of 374 liver disease cases were diagnosed during follow-up (mean = 5.5 years).

Results

Participants in the top compared with the bottom quartile of physical activity had a reduced risk of both overall CLD (hazard ratio [HR]: 0.41 [0.29-0.59]) and NAFLD (HR: 0.39 [0.21-0.70]). An activity increase of an additional 2,500 steps per day, was associated with a 38% reduction in CLD and a 47% reduction in NAFLD development, independent of adiposity. In the subgroup of participants with previously diagnosed liver disease (n = 714), participants in the top compared with the bottom quartile of physical activity had a striking 89% risk reduction in liver-related death (HR: 0.11 [0.02-0.86]), and 85% risk reduction in all-cause mortality (adjusted HR: 0.15 [0.05-0.44]). Walking an additional 2,500 steps per day was associated with 44% reduction in liver disease progression.

Conclusions

Greater physical activity is associated with a dose-dependent reduction in liver disease, which appears to be independent of adiposity.

Lay summary

In this study, we aimed to clarify the association between accelerometer-measured physical activity and chronic liver disease by examining risk of overall and specific liver diseases and their progression in relation to accelerometer-based physical activity in 96,688 participants in the UK Biobank. Our results show a clear, dose-dependent protective association between accelerometer-measured physical activity and liver disease development and progression. The linkage of device-measured activity could therefore create a framework for using wearables for personalised prevention of liver diseases.

Ileo-colonic delivery of conjugated bile acids improves glucose homeostasis via colonic GLP-1-producing enteroendocrine cells in human obesity and diabetes

Background

The bile acid (BA) pathway plays a role in regulation of food intake and glucose metabolism, based mainly on findings in animal models. Our aim was to determine whether the BA pathway is altered and correctable in human obesity and diabetes.

Methods

We conducted 3 investigations: 1) BA receptor pathways were studied in NCI-H716 enteroendocrine cell (EEC) line, whole human colonic mucosal tissue and in human colonic EEC isolated by Fluorescence-activated Cell Sorting (ex vivo) from endoscopically-obtained biopsies colon mucosa; 2) We characterized the BA pathway in 307 participants by measuring during fasting and postprandial levels of FGF19, 7αC4 and serum BA; 3) In a placebo-controlled, double-blind, randomised, 28-day trial, we studied the effect of ileo-colonic delivery of conjugated BAs (IC-CBAS) on glucose metabolism, incretins, and lipids, in participants with obesity and diabetes.

Findings

Human colonic GLP-1-producing EECs express TGR5, and upon treatment with bile acids in vitro, human EEC differentially expressed GLP-1 at the protein and mRNA level. In Ussing Chamber, GLP-1 release was stimulated by Taurocholic acid in either the apical or basolateral compartment. FGF19 was decreased in obesity and diabetes compared to controls. When compared to placebo, IC-CBAS significantly decreased postprandial glucose, fructosamine, fasting insulin, fasting LDL, and postprandial FGF19 and increased postprandial GLP-1 and C-peptide. Increase in faecal BA was associated with weight loss and with decreased fructosamine.

Interpretations

In humans, BA signalling machinery is expressed in colonic EECs, deficient in obesity and diabetes, and when stimulated with IC-CBAS, improved glucose homeostasis. ClinicalTrials.gov number, NCT02871882, NCT02033876.

Funding

Research support and drug was provided by Satiogen Pharmaceuticals (San Diego, CA). AA, MC, and NFL report grants (AA- C-Sig P30DK84567, K23 DK114460; MC- NIH R01 DK67071; NFL- R01 DK057993) from the NIH. JR was supported by an Early Career Grant from Society for Endocrinology.

Cell-free DNA testing: future applications in gastroenterology and hepatology

The application of next-generation sequencing in clinical practice is increasing as accuracy and interpretation have improved and the cost continues to decline rapidly. Cell-free DNA is a unique source for next-generation sequencing that could change routine clinical practice in gastroenterology and hepatology. Testing of cell-free DNA in blood and fecal samples is an easy, rapid, and noninvasive method to assess for premalignant, malignant, metabolic, infectious, inflammatory, and autoimmune gastrointestinal and liver diseases. In this review, we describe cell-free DNA technologies, current applications of cell-free DNA testing, and proposed cell-free DNA targets for gastrointestinal and hepatic diseases, with a specific focus on malignancy. In addition, we provide commentary on how cell-free DNA can be integrated into clinical practice and help guide diagnosis, prognosis, disease management, and therapeutic response.

Rho GTPases: Anti- or pro-neoplastic targets?

Rho GTPases are critical signal transducers of multiple pathways. They have been proposed to be useful anti-neoplastic targets for over two decades, especially in Ras-driven cancers. Until recently, however, few in vivo studies had been carried out to test this premise. Several recent mouse model studies have verified that Rac1, RhoA, and some of their effector proteins such as PAK and ROCK, are likely anti-cancer targets for treating K-Ras-driven tumors. Other seemingly contradictory studies have suggested that at least in certain instances inhibition of individual Rho GTPases may paradoxically result in pro-neoplastic effects. Significantly, both RhoA GTPase gain- and loss-of-function mutations have been discovered in primary leukemia/lymphoma and gastric cancer by human cancer genome sequencing efforts, suggesting both pro- and anti-neoplastic roles. In this review we summarize and integrate these unexpected findings and discuss the mechanistic implications in the design and application of Rho GTPase targeting strategies in future cancer therapies.

Loss of RhoA Exacerbates, Rather Than Dampens, Oncogenic K-Ras Induced Lung Adenoma Formation in Mice

Numerous cellular studies have indicated that RhoA signaling is required for oncogenic Ras-induced transformation, suggesting that RhoA is a useful target in Ras induced neoplasia. However, to date very limited data exist to genetically attribute RhoA function to Ras-mediated tumorigenesis in mammalian models. In order to assess whether RhoA is required for K-Ras-induced lung cancer initiation, we utilized the K-RasG12D Lox-Stop-Lox murine lung cancer model in combination with a conditional RhoAflox/flox and RhoC-/- knockout mouse models. Deletion of the floxed Rhoa gene and expression of K-RasG12D was achieved by either CCSP-Cre or adenoviral Cre, resulting in simultaneous expression of K-RasG12D and deletion of RhoA from the murine lung. We found that deletion of RhoA, RhoC or both did not adversely affect normal lung development. Moreover, we found that deletion of either RhoA or RhoC alone did not suppress K-RasG12D induced lung adenoma initiation. Rather, deletion of RhoA alone exacerbated lung adenoma formation, whereas dual deletion of RhoA and RhoC together significantly reduced K-RasG12D induced adenoma formation. Deletion of RhoA appears to induce a compensatory mechanism that exacerbates adenoma formation. The compensatory mechanism is at least partly mediated by RhoC. This study suggests that targeting of RhoA alone may allow for compensation and a paradoxical exacerbation of neoplasia, while simultaneous targeting of both RhoA and RhoC is likely to lead to more favorable outcomes.

Abstract 4445: RhoA is required for lung adenocarcinoma progression but is dispensable for K-Ras-induced tumor initiation

K-Ras is a prolific driver of lung tumorigenesis, yet it has eluded direct pharmaceutical inhibition to date. Here we test an alternative inhibition strategy by targeting RhoA, the prototypic member of the Rho family of GTPases and a downstream functional mediator of K-Ras signaling. Rho GTPases are signal transduction proteins that control cell shape, motility and proliferation. Given these roles, it is unsurprising that Rho proteins have been implicated in multiple stages of cancer progression. In fact, RhoA protein and activity levels are increased in lung, gastric, pancreatic and colon cancers. In vitro studies by us and others have found that K-Ras-driven lung adenocarcinoma cells are exquisitely sensitive to shRNA mediated RhoA inhibition, and demonstrate decreased proliferation, migration, invasion and anchorage-independent growth. Despite these findings, no genetic studies demonstrating RhoA involvement in tumorigenesis have been carried out to date. Thus, we generated a murine lung cancer model by crossing the widely used Lox-Stop-Lox KRasG12D transgenic mouse with RhoAflox/flox mice. Simultaneous deletion of RhoA and activation of K-Ras is achieved by either endotracheal administration of Adeno-Cre virus or by transgenic expression of CCSP-Cre; a lung specific Clara cell secretory protein promoter driven Cre. We found that Adeno-Cre administration to RhoAflox/flox mice not only led to the growth of RhoA-null tumors, but that surprisingly these mice had more and larger tumors as compared to wild type controls. These results indicate that RhoA is not essential for K-Ras-driven tumor formation. However, RhoAflox/flox RhoC-/- mice administered Adeno-Cre virus displayed fewer and smaller tumors, suggesting that K-Ras-driven tumorigenesis requires either RhoA or RhoC signaling. In contrast, CCSP-Cre driven tumors grow unabated regardless of RhoA status. Given the stark contrast between our in vivo and in vitro studies, we are testing the hypothesis that during the natural course of lung adenocarcinoma progression, cells grow reliant on RhoA signaling and may be susceptible to pharmaceutical RhoA inhibition. On the other hand, murine tumors initiated in the absence of RhoA may upregulate compensatory pathways downstream of K-Ras, paradoxically increasing tumor growth. While RhoA represents a valid target for suppressing K-Ras driven tumor cell proliferation and invasion, neither RhoA nor RhoC is essential for K-Ras-driven tumorigenesis. Moreover, our findings suggest that there is selective pressure within tumors after RhoA loss resulting not only in compensation between Rho-family members but also complex compensatory signaling leading to a paradoxical increase in tumor formation.

Citation Format: Inuk Zandvakili, Yi Zheng. RhoA is required for lung adenocarcinoma progression but is dispensable for K-Ras-induced tumor initiation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4445. doi:10.1158/1538-7445.AM2014-4445

The prevalence of BRCA1 mutations among young women with triple-negative breast cancer

Background

Molecular screening for BRCA1 and BRCA2 mutations is now an established component of risk evaluation and management of familial breast cancer. Features of hereditary breast cancer include an early age-of-onset and over-representation of the 'triple-negative' phenotype (negative for estrogen-receptor, progesterone-receptor and HER2). The decision to offer genetic testing to a breast cancer patient is usually based on her family history, but in the absence of a family history of cancer, some women may qualify for testing based on the age-of-onset and/or the pathologic features of the breast cancer.

Methods

We studied 54 women who were diagnosed with high-grade, triple-negative invasive breast cancer at or before age 40. These women were selected for study because they had little or no family history of breast or ovarian cancer and they did not qualify for genetic testing using conventional family history criteria. BRCA1 screening was performed using a combination of fluorescent multiplexed-PCR analysis, BRCA1 exon-13 6 kb duplication screening, the protein truncation test (PTT) and fluorescent multiplexed denaturing gradient gel electrophoresis (DGGE). All coding exons of BRCA1 were screened. The two large exons of BRCA2 were also screened using PTT. All mutations were confirmed with direct sequencing.

Results

Five deleterious BRCA1 mutations and one deleterious BRCA2 mutation were identified in the 54 patients with early-onset, triple-negative breast cancer (11%).

Conclusion

Women with early-onset triple-negative breast cancer are candidates for genetic testing for BRCA1, even in the absence of a family history of breast or ovarian cancer.

Germline RAP80 mutations and susceptibility to breast cancer

Most of the breast cancer susceptibility genes identified to date are involved in DNA repair, including BRCA1, BRCA2, PALB2, CHEK2 and BRIP1. RAP80 works upstream of BRCA1 and is essential for the localization of BRCA1 to the site of damaged DNA. To investigate whether or not RAP80 is also a breast cancer susceptibility gene, we sequenced the entire exonic regions of RAP80 in the germline DNA of 152 women with familial breast cancer, who were previously found to be negative for BRCA1 and BRCA2 mutations. No truncating mutation was identified. Eleven potentially deleterious RAP80 variants were identified; these 11 variants were genotyped in 424 more familial cases and in 726 healthy controls. Three novel p.Ala342Thr, p.Met353Thr and p.Tyr575Asp rare missense variants and a novel haplotype composed of two variants in the CpG island (c.-24149G > T and c.-24001A > G) and a variant in the 5'UTR (c.-8A > G) and a variant in the 3'UTR (c.*27A > C) were detected in 26 of 571 (4.6%) individuals with familial breast cancer, compared to 14 of 725 (1.9%) controls (P = 0.01; OR = 2.4, 95% CI = 1.2-5.1). In summary, we did not find truncating mutations of the RAP80 gene to be a cause of familial breast cancer. A novel RAP80 haplotype or rare missense mutations may be associated with a modest increased risk of breast cancer, but this observation needs to be confirmed by additional studies.

Germline BRCA2 mutations and the risk of esophageal squamous cell carcinoma

The incidence of esophageal squamous cell carcinoma (ESCC) is very high among the Turkmen population of Iran. Family studies suggest a genetic component to the disease. Turkmen are ethnically homogenous and are well suited for genetic studies. A previous study from China suggested that BRCA2 might play a role in the etiology of ESCC. We screened for mutations in the coding region of the BRCA2 gene in the germline DNA of 197 Turkmen patients with ESCC. A nonsense variant, K3326X, was identified in 9 of 197 cases (4.6%) vs 2 of 254 controls (0.8%) (OR=6.0, 95% CI=1.3-28; P=0.01). This mutation leads to the loss of the C-terminal domain of the BRCA2 protein, a part of the region of interaction with the FANCD2 protein. We observed nine other BRCA2 variants in single cases only, including two deletions, and seven missense mutations. Six of these were judged to be pathogenic. In total, a suspicious deleterious BRCA2 variant was identified in 15 of 197 ESCC cases (7.6%).