The molecular origin of the MMR-dependent apoptosis pathway from dynamics analysis of MutSα-DNA complexes

Genomic and Epigenomic Biomarkers of Immune Checkpoint Immunotherapy Response in Melanoma: Current and Future Perspectives

Immune checkpoint inhibitors (ICIs) demonstrate durable responses, long-term survival benefits, and improved outcomes in cancer patients compared to chemotherapy. However, the majority of cancer patients do not respond to ICIs, and a high proportion of those patients who do respond to ICI therapy develop innate or acquired resistance to ICIs, limiting their clinical utility. The most studied predictive tissue biomarkers for ICI response are PD-L1 immunohistochemical expression, DNA mismatch repair deficiency, and tumour mutation burden, although these are weak predictors of ICI response. The identification of better predictive biomarkers remains an important goal to improve the identification of patients who would benefit from ICIs. Here, we review established and emerging biomarkers of ICI response, focusing on epigenomic and genomic alterations in cancer patients, which have the potential to help guide single-agent ICI immunotherapy or ICI immunotherapy in combination with other ICI immunotherapies or agents. We briefly review the current status of ICI response biomarkers, including investigational biomarkers, and we present insights into several emerging and promising epigenomic biomarker candidates, including current knowledge gaps in the context of ICI immunotherapy response in melanoma patients.

Target-Based Small Molecule Drug Discovery for Colorectal Cancer: A Review of Molecular Pathways and In Silico Studies

Colorectal cancer is one of the most prevalent cancer types. Although there have been breakthroughs in its treatments, a better understanding of the molecular mechanisms and genetic involvement in colorectal cancer will have a substantial role in producing novel and targeted treatments with better safety profiles. In this review, the main molecular pathways and driver genes that are responsible for initiating and propagating the cascade of signaling molecules reaching carcinoma and the aggressive metastatic stages of colorectal cancer were presented. Protein kinases involved in colorectal cancer, as much as other cancers, have seen much focus and committed efforts due to their crucial role in subsidizing, inhibiting, or changing the disease course. Moreover, notable improvements in colorectal cancer treatments with in silico studies and the enhanced selectivity on specific macromolecular targets were discussed. Besides, the selective multi-target agents have been made easier by employing in silico methods in molecular de novo synthesis or target identification and drug repurposing.

Loss of mismatch repair signaling impairs the WNT-bone morphogenetic protein crosstalk and the colonic homeostasis

The fine balance between proliferation, differentiation, and apoptosis in the colonic epithelium is tightly controlled by the interplay between WNT, Notch, and bone morphogenetic protein (BMP) signaling. How these complex networks coordinate the colonic homeostasis, especially if cancer predisposing mutations such as mutations in the DNA mismatch repair (MMR) are present, is unclear. Inactivation of the MMR system has long been linked to colorectal cancer; however, little is known about its role in the regulation of the colonic homeostasis. It has been shown that loss of MMR promotes the proliferation of colon epithelial cells that renders them highly susceptible to transformation. The mechanism through which MMR mediates this effect, yet, remains to be determined. Using an MMR-deficient mouse model, we show that increased methylation of Dickkopf1 impacts its expression, and consequently, the ability to negatively regulate WNT signaling. As a result, excessive levels of active β-catenin promote strong crypt progenitor-like phenotype and abnormal proliferation. Under these settings, the development and function of the goblet cells are affected. MMR-deficient mice have fewer goblet cells with enlarged mucin-loaded vesicles. We further show that MMR inactivation impacts the WNT–BMP signaling crosstalk.

Bovine Leukemia Virus Infection Affects Host Gene Expression Associated with DNA Mismatch Repair

Bovine leukemia virus (BLV) causes enzootic bovine leukosis, a malignant form of B-cell lymphoma, and is closely related to human T-cell leukemia viruses. We investigated whether BLV infection affects host genes associated with DNA mismatch repair (MMR). Next-generation sequencing of blood samples from five calves experimentally infected with BLV revealed the highest expression levels of seven MMR genes (EXO1, UNG, PCNA, MSH2, MSH3, MSH6, and PMS2) at the point of peak proviral loads (PVLs). Furthermore, MMR gene expression was only upregulated in cattle with higher PVLs. In particular, the expression levels of MSH2, MSH3, and UNG positively correlated with PVL in vivo. The expression levels of all seven MMR genes in pig kidney-15 cells and the levels of PMS2 and EXO1 in HeLa cells also increased tendencies after transient transfection with a BLV infectious clone. Moreover, MMR gene expression levels were significantly higher in BLV-expressing cell lines compared with those in the respective parental cell lines. Expression levels of MSH2 and EXO1 in BLV-infected cattle with lymphoma were significantly lower and higher, respectively, compared with those in infected cattle in vivo. These results reveal that BLV infection affects MMR gene expression, offering new candidate markers for lymphoma diagnosis.

Existing and Emerging Biomarkers for Immune Checkpoint Immunotherapy in Solid Tumors

In the last few years, immunotherapy has transformed the way we treat solid tumors, including melanoma, lung, head neck, breast, renal, and bladder cancers. Durable responses and long-term survival benefit has been experienced by many cancer patients, with favorable toxicity profiles of immunotherapeutic agents relative to chemotherapy. Cures have become possible in some patients with metastatic disease. Additional approvals of immunotherapy drugs and in combination with other agents are anticipated in the near future. Multiple additional immunotherapy drugs are in earlier stages of clinical development, and their testing in additional tumor types is under way. Despite considerable early success and relatively fewer side effects, the majority of cancer patients do not respond to checkpoint inhibitors. Additionally, while the drugs are generally well tolerated, there is still the potential for significant, unpredictable and even fatal toxicity with these agents. Improved biomarkers may help to better select patients who are more likely to respond to these drugs. Two key biologically important predictive tissue biomarkers, specifically, PD-L1 and mismatch repair deficiency, have been FDA-approved in conjunction with the checkpoint inhibitor, pembrolizumab. Tumor mutation burden, another promising biomarker, is emerging in several tumor types, and may also soon receive approval. Finally, several other tissue and liquid biomarkers are emerging that could help guide single-agent immunotherapy and in combination with other agents. Of these, one promising investigational biomarker is alteration or deficiency in DNA damage response (DDR) pathways, with altered DDR observed in a broad spectrum of tumors. Here, we provide a critical overview of current, emerging, and investigational biomarkers in the context of response to immunotherapy in solid tumors.

Mismatch repair protein loss in breast cancer: clinicopathological associations in a large British Columbia cohort

Purpose

Alterations to mismatch repair (MMR) pathways are a known cause of cancer, particularly colorectal and endometrial carcinomas. Recently, checkpoint inhibitors have been approved for use in MMR-deficient cancers of any type (Prasad et al. in JAMA Oncol 4:157–158, 2018). Functional studies in breast cancer have shown associations between MMR loss, resistance to aromatase inhibitors and sensitivity to palbociclib (Haricharan et al. in Cancer Discov 7:1168–1183, 2017). Herein, we investigate the clinical meaning of MMR deficiency in breast cancer by immunohistochemical assessment of MSH2, MSH6, MLH1 and PMS2 on a large series of breast cancers linked to detailed biomarker and long-term outcome data.

Methods

Cases were classified as MMR intact when all four markers expressed nuclear reactivity, but MMR-deficient when at least one of the four biomarkers displayed loss of nuclear staining in the presence of positive internal stromal controls on the tissue microarray core.

Results

Among the 1635 cases with interpretable staining, we identified 31 (1.9%) as MMR-deficient. In our cohort, MMR deficiency was present across all major breast cancer subtypes, and was associated with high-grade, low-progesterone receptor expression and high tumor-infiltrating lymphocyte counts. MMR deficiency is significantly associated with inferior overall (HR 2.29, 95% CI 1.02–5.17, p = 0.040) and disease-specific survival (HR 2.71, 95% CI 1.00–7.35, p = 0.042) in the 431 estrogen receptor-positive patients who were uniformly treated with tamoxifen as their sole adjuvant systemic therapy.

Conclusion

Overall, this study supports the concept that breast cancer patients with MMR deficiency as assessed by immunohistochemistry may be good candidates for alternative treatment approaches such as immune checkpoint or CDK4 inhibitors.

Electronic supplementary material

The online version of this article (10.1007/s10549-019-05438-y) contains supplementary material, which is available to authorized users.

Molecular Mechanisms of DNA Replication and Repair Machinery: Insights from Microscopic Simulations

Reproduction, the hallmark of biological activity, requires making an accurate copy of the genetic material to allow the progeny to inherit parental traits. In all living cells, the process of DNA replication is carried out by a concerted action of multiple protein species forming a loose protein-nucleic acid complex, the replisome. Proofreading and error correction generally accompany replication but also occur independently, safeguarding genetic information through all phases of the cell cycle. Advances in biochemical characterization of intracellular processes, proteomics and the advent of single-molecule biophysics have brought about a treasure trove of information awaiting to be assembled into an accurate mechanistic model of the DNA replication process. In this review, we describe recent efforts to model elements of DNA replication and repair processes using computer simulations, an approach that has gained immense popularity in many areas of molecular biophysics but has yet to become mainstream in the DNA metabolism community. We highlight the use of diverse computational methods to address specific problems of the fields and discuss unexplored possibilities that lie ahead for the computational approaches in these areas.

Investigation of the probable homo-dimer model of the Xeroderma pigmentosum complementation group A (XPA) protein to represent the DNA-binding core

The Xeroderma pigmentosum complementation group A (XPA) protein functions as a primary damage verifier and as a scaffold protein in nucleotide excision repair (NER) in all higher organisms. New evidence of XPA's existence as a dimer and the redefinition of its DNA-binding domain (DBD) raises new questions regarding the stability and functional position of XPA in NER. Here, we have investigated XPA's dimeric status with respect to its previously defined DBD (XPA_98-219) as well as with its redefined DBD (XPA_98-239). We studied the stability of XPA_98-210 and XPA_98-239 homo-dimer systems using all-atom molecular dynamics simulation, and we have also characterized the protein-protein interactions (PPI) of these two homo-dimeric forms of XPA. After conducting the root mean square deviation (RMSD) analyses, it was observed that the XPA_98-239 homo-dimer has better stability than XPA_98-210. It was also found that XPA_98-239 has a larger number of hydrogen bonds, salt bridges, and hydrophobic interactions than the XPA_98-210 homo-dimer. We further found that Lys, Glu, Gln, Asn, and Arg residues shared the major contribution toward the intermolecular interactions in XPA homo-dimers. The binding free energy (BFE) analysis, which used the molecular mechanics Poisson-Boltzmann method (MM-PBSA) and the generalized Born and surface area continuum solvation model (GBSA) for both XPA homo-dimers, also substantiated the positive result in favor of the stability of the XPA_98-239 homo-dimer. Communicated by Ramaswamy H. Sarma.

Visualizing correlated motion with HDBSCAN clustering

Correlated motion analysis provides a method for understanding communication between and dynamic similarities of biopolymer residues and domains. The typical equal-time correlation matrices-frequently visualized with pseudo-colorings or heat maps-quickly convey large regions of highly correlated motion but hide more subtle similarities of motion. Here we propose a complementary method for visualizing correlations within proteins (or general biopolymers) that quickly conveys intuition about which residues have a similar dynamic behavior. For grouping residues, we use the recently developed non-parametric clustering algorithm HDBSCAN. Although the method we propose here can be used to group residues using correlation as a similarity matrix-the most straightforward and intuitive method-it can also be used to more generally determine groups of residues which have similar dynamic properties. We term these latter groups "Dynamic Domains", as they are based not on spatial closeness but rather closeness in the column space of a correlation matrix. We provide examples of this method across three human proteins of varying size and function-the Nf-Kappa-Beta essential modulator, the clotting promoter Thrombin and the mismatch repair protein (dimer) complex MutS-alpha. Although the examples presented here are from all-atom molecular dynamics simulations, this visualization technique can also be used on correlations matrices built from any ensembles of conformations from experiment or computation.

MutSα's Multi-Domain Allosteric Response to Three DNA Damage Types Revealed by Machine Learning

MutSα is a key component in the mismatch repair (MMR) pathway. This protein is responsible for initiating the signaling pathways for DNA repair or cell death. Herein we investigate this heterodimer's post-recognition, post-binding response to three types of DNA damage involving cytotoxic, anti-cancer agents-carboplatin, cisplatin, and FdU. Through a combination of supervised and unsupervised machine learning techniques along with more traditional structural and kinetic analysis applied to all-atom molecular dynamics (MD) calculations, we predict that MutSα has a distinct response to each of the three damage types. Via a binary classification tree (a supervised machine learning technique), we identify key hydrogen bond motifs unique to each type of damage and suggest residues for experimental mutation studies. Through a combination of a recently developed clustering (unsupervised learning) algorithm, RMSF calculations, PCA, and correlated motions we predict that each type of damage causes MutSα to explore a specific region of conformation space. Detailed analysis suggests a short range effect for carboplatin-primarily altering the structures and kinetics of residues within 10 angstroms of the damaged DNA-and distinct longer-range effects for cisplatin and FdU. In our simulations, we also observe that a key phenylalanine residue-known to stack with a mismatched or unmatched bases in MMR-stacks with the base complementary to the damaged base in 88.61% of MD frames containing carboplatinated DNA. Similarly, this Phe71 stacks with the base complementary to damage in 91.73% of frames with cisplatinated DNA. This residue, however, stacks with the damaged base itself in 62.18% of trajectory frames with FdU-substituted DNA and has no stacking interaction at all in 30.72% of these frames. Each drug investigated here induces a unique perturbation in the MutSα complex, indicating the possibility of a distinct signaling event and specific repair or death pathway (or set of pathways) for a given type of damage.

Uncovering Large-Scale Conformational Change in Molecular Dynamics without Prior Knowledge

As the length of molecular dynamics (MD) trajectories grows with increasing computational power, so does the importance of clustering methods for partitioning trajectories into conformational bins. Of the methods available, the vast majority require users to either have some a priori knowledge about the system to be clustered or to tune clustering parameters through trial and error. Here we present non-parametric uses of two modern clustering techniques suitable for first-pass investigation of an MD trajectory. Being non-parametric, these methods require neither prior knowledge nor parameter tuning. The first method, HDBSCAN, is fast-relative to other popular clustering methods-and is able to group unstructured or intrinsically disordered systems (such as intrinsically disordered proteins, or IDPs) into bins that represent global conformational shifts. HDBSCAN is also useful for determining the overall stability of a system-as it tends to group stable systems into one or two bins-and identifying transition events between metastable states. The second method, iMWK-Means, with explicit rescaling followed by K-Means, while slower than HDBSCAN, performs well with stable, structured systems such as folded proteins and is able to identify higher resolution details such as changes in relative position of secondary structural elements. Used in conjunction, these clustering methods allow a user to discern quickly and without prior knowledge the stability of a simulated system and identify both local and global conformational changes.

Long-Range Signaling in MutS and MSH Homologs via Switching of Dynamic Communication Pathways

Allostery is conformation regulation by propagating a signal from one site to another distal site. This study focuses on the long-range communication in DNA mismatch repair proteins MutS and its homologs where intramolecular signaling has to travel over 70 Å to couple lesion detection to ATPase activity and eventual downstream repair. Using dynamic network analysis based on extensive molecular dynamics simulations, multiple preserved communication pathways were identified that would allow such long-range signaling. The pathways appear to depend on the nucleotides bound to the ATPase domain as well as the type of DNA substrate consistent with previously proposed functional cycles of mismatch recognition and repair initiation by MutS and homologs. A mechanism is proposed where pathways are switched without major conformational rearrangements allowing for efficient long-range signaling and allostery.

Recapturing the Correlated Motions of Protein Using Coarse- Grained Models

Long-range interactions and allostery are important for many biological processes. Increasing numbers of studies, both experimental and computational, show that internal dynamics may play an important role in such behaviors. Investigating the dynamical effects of proteins, how- ever, is a challenging problem using all-atom molecular dynamics because of the length-scales and timescales involved. As a result, coarse-grained models are often implemented. Herein, we use three well-defined coarse-grained models: Go, Martini and Cafemol, and a small model protein Eglin C, which is readily studied via all-atom molecular dynamics, to examine if these coarse grained models can explore the dynamics of Eglin C accurately as well as to see how these models respond to mutations. We found that all three models can recapture the dynamics of Eglin C to a significant extent - where we focus on root-mean square fluctuations and correlated motions as dynamical measures - but that the Cafemol and Go models are superior. The best agreement with all-atom simulations is for structured regions of Eglin C.

Distinct Phenotypes Caused by Mutation of MSH2 in Trypanosome Insect and Mammalian Life Cycle Forms Are Associated with Parasite Adaptation to Oxidative Stress

Background

DNA repair mechanisms are crucial for maintenance of the genome in all organisms, including parasites where successful infection is dependent both on genomic stability and sequence variation. MSH2 is an early acting, central component of the Mismatch Repair (MMR) pathway, which is responsible for the recognition and correction of base mismatches that occur during DNA replication and recombination. In addition, recent evidence suggests that MSH2 might also play an important, but poorly understood, role in responding to oxidative damage in both African and American trypanosomes.

Methodology/Principal Findings

To investigate the involvement of MMR in the oxidative stress response, null mutants of MSH2 were generated in Trypanosoma brucei procyclic forms and in Trypanosoma cruzi epimastigote forms. Unexpectedly, the MSH2 null mutants showed increased resistance to H₂O₂ exposure when compared with wild type cells, a phenotype distinct from the previously observed increased sensitivity of T. brucei bloodstream forms MSH2 mutants. Complementation studies indicated that the increased oxidative resistance of procyclic T. brucei was due to adaptation to MSH2 loss. In both parasites, loss of MSH2 was shown to result in increased tolerance to alkylation by MNNG and increased accumulation of 8-oxo-guanine in the nuclear and mitochondrial genomes, indicating impaired MMR. In T. cruzi, loss of MSH2 also increases the parasite capacity to survive within host macrophages.

Conclusions/Significance

Taken together, these results indicate MSH2 displays conserved, dual roles in MMR and in the response to oxidative stress. Loss of the latter function results in life cycle dependent differences in phenotypic outcomes in T. brucei MSH2 mutants, most likely because of the greater burden of oxidative stress in the insect stage of the parasite.

Trypanosoma brucei and Trypanosoma cruzi are protozoa parasites that cause sleeping sickness and Chagas disease, respectively, two neglected tropical diseases endemic in sub-Saharan Africa and Latin America. The high genetic diversity found in the T. cruzi population and the highly diverse repertoire of surface glycoprotein genes found in T. brucei are crucial factors that ensure a successful infection in their hosts. Besides responding to host immune responses, these parasites must deal with various sources of oxidative stress that can cause DNA damage. Thus, by determining the right balance between genomic stability and genetic variation, DNA repair pathways have a big impact in the ability of these parasites to maintain infection. This study is focused on the role of a DNA mismatch repair (MMR) protein named MSH2 in protecting these parasites’ DNA against oxidative assault. Using knock-out mutants, we showed that, besides acting in the MMR pathway as a key protein that recognizes and repairs base mismatches, insertions or deletions that can occur after DNA replication, MSH2 has an additional role in the oxidative stress response. Importantly, this extra role of MSH2 seems to be independent of other MMR components and dependent on the parasite developmental stage.

Importance of long-time simulations for rare event sampling in zinc finger proteins

Molecular dynamics (MD) simulation methods have seen significant improvement since their inception in the late 1950s. Constraints of simulation size and duration that once impeded the field have lessened with the advent of better algorithms, faster processors, and parallel computing. With newer techniques and hardware available, MD simulations of more biologically relevant timescales can now sample a broader range of conformational and dynamical changes including rare events. One concern in the literature has been under which circumstances it is sufficient to perform many shorter timescale simulations and under which circumstances fewer longer simulations are necessary. Herein, our simulations of the zinc finger NEMO (2JVX) using multiple simulations of length 15, 30, 1000, and 3000 ns are analyzed to provide clarity on this point.

Destabilization of the MutSα's protein-protein interface due to binding to the DNA adduct induced by anticancer agent carboplatin via molecular dynamics simulations

DNA mismatch repair (MMR) proteins maintain genetic integrity in all organisms by recognizing and repairing DNA errors. Such alteration of hereditary information can lead to various diseases, including cancer. Besides their role in DNA repair, MMR proteins detect and initiate cellular responses to certain type of DNA damage. Its response to the damaged DNA has made the human MMR pathway a useful target for anticancer agents such as carboplatin. This study indicates that strong, specific interactions at the interface of MutSα in response to the mismatched DNA recognition are replaced by weak, non-specific interactions in response to the damaged DNA recognition. Data suggest a severe impairment of the dimerization of MutSα in response to the damaged DNA recognition. While the core of MutSα is preserved in response to the damaged DNA recognition, the loss of contact surface and the rearrangement of contacts at the protein interface suggest a different packing in response to the damaged DNA recognition. Coupled in response to the mismatched DNA recognition, interaction energies, hydrogen bonds, salt bridges, and solvent accessible surface areas at the interface of MutSα and within the subunits are uncoupled or asynchronously coupled in response to the damaged DNA recognition. These pieces of evidence suggest that the loss of a synchronous mode of response in the MutSα's surveillance for DNA errors would possibly be one of the mechanism(s) of signaling the MMR-dependent programed cell death much wanted in anticancer therapies. The analysis was drawn from dynamics simulations.

Non-specificity and synergy at the binding site of the carboplatin-induced DNA adduct via molecular dynamics simulations of the MutSα-DNA recognition complex

MutSα is the most abundant mismatch-binding factor of human DNA mismatch repair (MMR) proteins. MMR maintains genetic stability by recognizing and repairing DNA defects. Failure to accomplish their function may lead to cancer. In addition, MutSα recognizes at least some types of DNA damage making it a target for anticancer agents. Here, complementing scarce experimental data, we report unique hydrogen-bonding motifs associated with the recognition of the carboplatin induced DNA damage by MutSα. These data predict that carboplatin and cisplatin induced damaging DNA adducts are recognized by MutSα in a similar manner. Our simulations also indicate that loss of base pairing at the damage site results in (1) non-specific binding and (2) changes in the atomic flexibility at the lesion site and beyond. To further quantify alterations at MutSα-DNA interface in response to damage recognition, non-bonding interactions and salt bridges were investigated. These data indicate (1) possible different packing and (2) disruption of the salt bridges at the MutSα-DNA interface in the damaged complex. These findings (1) underscore the general observation of disruptions at the MutSα-DNA interface and (2) highlight the nature of the anticancer effect of the carboplatin agent. The analysis was carried out from atomistic simulations.

Transcription pattern of p53-targeted DNA repair genes in the hypoxia-tolerant subterranean mole rat Spalax

The tumor suppressor gene p53 induces growth arrest and/or apoptosis in response to DNA damage/hypoxia. Inactivation of p53 confers a selective advantage to tumor cells under a hypoxic microenvironment during tumor progression. The subterranean blind mole rat, Spalax, spends its life underground at low-oxygen tensions, hence developing a wide range of respiratory/molecular adaptations to hypoxic stress, including critical changes in p53 structure and signaling pathway. The highly conserved p53 Arg(R)-172 is substituted by lysine (K) in Spalax, identical with a tumor-associated mutation. Functionality assays revealed that Spalax p53 is unable to activate apoptotic target genes but is still capable of activating cell cycle arrest genes. Furthermore, we have shown that the transcription patterns of representative p53-induced genes (Apaf1 and Mdm2) in Spalax are influenced by hypoxia. Cell cycle arrest allows the cells to repair DNA damage via different DNA repair genes. We tested the transcription pattern of three p53-related DNA repair genes (p53R2, Mlh1, and Msh2) under normoxia and short-acute hypoxia in Spalax, C57BL/6 wild-type mice, and two strains of mutant C57BL/6 mice, each carrying a different mutation at the R172 position. Our results show that while wild-type/mutant mice exhibit strong hypoxia-induced reductions of repair gene transcript levels, no such inhibition is found in Spalax under hypoxia. Moreover, unlike mouse p53R2, Spalax p53R2 transcript levels are strongly elevated under hypoxia. These results suggest that critical repair functions, which are known to be inhibited under hypoxia in mice, remain active in Spalax, as part of its unique hypoxia tolerance mechanisms.

DNA mismatch repair system: repercussions in cellular homeostasis and relationship with aging

The mechanisms that concern DNA repair have been studied in the last years due to their consequences in cellular homeostasis. The diverse and damaging stimuli that affect DNA integrity, such as changes in the genetic sequence and modifications in gene expression, can disrupt the steady state of the cell and have serious repercussions to pathways that regulate apoptosis, senescence, and cancer. These altered pathways not only modify cellular and organism longevity, but quality of life (“health-span”). The DNA mismatch repair system (MMR) is highly conserved between species; its role is paramount in the preservation of DNA integrity, placing it as a necessary focal point in the study of pathways that prolong lifespan, aging, and disease. Here, we review different insights concerning the malfunction or absence of the DNA-MMR and its impact on cellular homeostasis. In particular, we will focus on DNA-MMR mechanisms regulated by known repair proteins MSH2, MSH6, PMS2, and MHL1, among others.