XPA tumor variant leads to defects in NER that sensitize cells to cisplatin

Nucleotide excision repair (NER) reduces efficacy of treatment with platinum (Pt)-based chemotherapy by removing Pt lesions from DNA. Previous study has identified that missense mutation or loss of the NER genes Excision Repair Cross Complementation Group 1 and 2 (ERCC1 and ERCC2) leads to improved patient outcomes after treatment with Pt-based chemotherapies. Although most NER gene alterations found in patient tumors are missense mutations, the impact of mutations in the remaining nearly 20 NER genes is unknown. Towards this goal, we previously developed a machine learning strategy to predict genetic variants in an essential NER protein, Xeroderma Pigmentosum Complementation Group A (XPA), that disrupt repair. In this study, we report in-depth analyses of a subset of the predicted variants, including in vitro analyses of purified recombinant protein and cell-based assays to test Pt agent sensitivity in cells and determine mechanisms of NER dysfunction. The most NER deficient variant Y148D had reduced protein stability, weaker DNA binding, disrupted recruitment to damage, and degradation. Our findings demonstrate that tumor mutations in XPA impact cell survival after cisplatin treatment and provide valuable mechanistic insights to improve variant effect prediction. Broadly, these findings suggest XPA tumor variants should be considered when predicting chemotherapy response.

An evaluation of the effectiveness of a lipid clinic in identifying people with familial hypercholesterolaemia and reducing their risk of cardiovascular disease

Introduction

The NHS Long Term Plan aims to ‘prevent up to 150,000 heart attacks, strokes and dementia cases over the next 10 years’.1 People with Familial Hypercholesterolaemia (FH) are considered to be at high-risk of heart attack, stroke and dementia but an estimated 90% remain undiagnosed.1 The Chesterfield and Dronfield Primary Care Network were commissioned to set-up a 12-month pharmacist-led clinic across 9 practices to identify, treat and refer FH patients. Patients with suspected FH benefit from referral to specialist services.2

Aim

This study aimed to evaluate the number of FH patients identified and any unintended benefits of the Lipid Clinic.

Methods

Ethical approval was not required for this service evaluation. Informed consent was sought prior to data collection and the dataset was anonymised. Searches of practice patient records identified patients with a previously raised lipid level (total Cholesterol >7.5mmol/L and/or non-HDL-C > 5.9mmol/L)2 for review in the Lipid Clinic. Patients reviewed in the Lipid Clinic were initiated/optimised on lipid lowering medication as appropriate.2 Data were collected for patients invited for review in the Lipid Clinic between May-July 2022. Patients’ attendance as well as decline/non-response to the Clinic was recorded. The data collected included family history, QRISK score (where applicable), lipid lowering treatment the patient was taking (if any) and blood tests results (serum lipids, HBA1c and thyroid function tests). If bloods were deranged it was documented whether or not it was a new finding. The data was analysed by categorising patients into potential FH, primary/secondary prevention of cardiovascular disease and whether they needed referral to secondary care.

Results

Out of the 260 patients invited for review, 219 attended the clinic. Of these, 30 (13.7%) were provided with lifestyle advice as they did not meet the criteria for treatment. Twenty-three patients (10.5%) met the Simon-Broom criteria for possible FH. A further 3 patients identified were known to have FH but had not undergone genetic cascade testing. These 26 patients (11.8%) were referred to secondary care for genetic testing and specialist input. Newly raised HbA1c indicative of either diabetes or non-diabetic hyperglycaemia was incidentally found in 39 patients (17.8%). Lipid-lowering medication was initiated/titrated in 189 patients (86.3%).

Discussion/Conclusion

The significant proportion of patients requiring follow up in secondary care (11.8%) suggesting targeted searches are effective in identifying patients with possible FH. Identifying FH patients, testing and treating their family members appropriately reduces their risk of cardiovascular events.2 The Lipid Clinic has identifying that nearly a fifth of patients were previously undiagnosed with either diabetes or non-diabetic hyperglycaemia (17.8%) suggests that this is also an opportunity to identify and treat these patients earlier than they would otherwise have been identified. The results highlight the need for primary care staff education on the new AAC NHS Guidelines2 relating to managing lipid results. One limitation of the study is although the Lipid Clinic has received good informal feedback, formal feedback is yet to be collected from patients and stake holders. In addition, the clinic is still ongoing, and more data is being collected.

References

1. NHS Long Term Plan. Chapter 3: Further progress on care quality and outcomes. Better care for major health conditions. Cardiovascular Disease. 2019. Available from: https://www.longtermplan.nhs.uk/online-version/chapter-3-further-progress-on-care-quality-and-outcomes/better-care-for-major-health-conditions/cardiovascular-disease/

2. Khatib R, Neely D, on behalf of the AAC Clinical Subgroup. Summary of National Guidance for Lipid Management for Primary and Secondary Prevention of CVD, AAC NHS Guidelines, Nov 2021. Review date: Nov 2022. NICE endorsed Dec 2021.

3. National Institution for Health and Care Excellence (NICE). Cardiovascular disease: risk assessment and reduction, including lipid modification, Clinical guideline [CG181] Published: 18 July 2014 Last updated: 27 September 2016.

Two interaction surfaces between XPA and RPA organize the preincision complex in nucleotide excision repair

The xeroderma pigmentosum protein A (XPA) and replication protein A (RPA) proteins fulfill essential roles in the assembly of the preincision complex in the nucleotide excision repair (NER) pathway. We have previously characterized the two interaction sites, one between the XPA N-terminal (XPA-N) disordered domain and the RPA32 C-terminal domain (RPA32C), and the other with the XPA DNA binding domain (DBD) and the RPA70AB DBDs. Here, we show that XPA mutations that inhibit the physical interaction in either site reduce NER activity in biochemical and cellular systems. Combining mutations in the two sites leads to an additive inhibition of NER, implying that they fulfill distinct roles. Our data suggest a model in which the interaction between XPA-N and RPA32C is important for the initial association of XPA with NER complexes, while the interaction between XPA DBD and RPA70AB is needed for structural organization of the complex to license the dual incision reaction. Integrative structural models of complexes of XPA and RPA bound to single-stranded/double-stranded DNA (ss/dsDNA) junction substrates that mimic the NER bubble reveal key features of the architecture of XPA and RPA in the preincision complex. Most critical among these is that the shape of the NER bubble is far from colinear as depicted in current models, but rather the two strands of unwound DNA must assume a U-shape with the two ss/dsDNA junctions localized in close proximity. Our data suggest that the interaction between XPA and RPA70 is key for the organization of the NER preincision complex.

Kemp Eliminases of the AlleyCat Family Possess High Substrate Promiscuity

Minimalist enzymes designed to catalyze model reactions provide useful starting points for creating catalysts for practically important chemical transformations. We have shown that Kemp eliminases of the AlleyCat family facilitate conversion of leflunomide (an immunosupressor pro-drug) to its active form teriflunomide with outstanding rate enhancement (nearly four orders of magnitude) and catalytic proficiency (more than seven orders of magnitude) without any additional optimization. This remarkable activity is achieved by properly positioning the substrate in close proximity to the catalytic glutamate with very high pKa.