Effects of OsMSH6 Mutations on Microsatellite Stability and Homeologous Recombination in Rice

Rectal cancer is a heterogeneous disease at the genetic and molecular levels, both aspects having major repercussions on the tumor immune contexture. Whilst microsatellite status and tumor mutational load have been associated with response to immunotherapy, presence of tumor-infiltrating lymphocytes is one of the most powerful prognostic and predictive biomarkers. Yet, the majority of rectal cancers are characterized by microsatellite stability, low tumor mutational burden and poor T cell infiltration. Consequently, these tumors do not respond to immunotherapy and treatment largely relies on radiotherapy alone or in combination with chemotherapy followed by radical surgery. Importantly, pre-clinical and clinical studies suggest that radiotherapy can induce a complete reprograming of the tumor microenvironment, potentially sensitizing it for immune checkpoint inhibition. Nonetheless, growing evidence suggest that this synergistic effect strongly depends on radiotherapy dosing, fractionation and timing. Despite ongoing work, information about the radiotherapy regimen required to yield optimal clinical outcome when combined to checkpoint blockade remains largely unavailable. In this review, we describe the molecular and immune heterogeneity of rectal cancer and outline its prognostic value. In addition, we discuss the effect of radiotherapy on the tumor microenvironment, focusing on the mechanisms and benefits of its combination with immune checkpoint inhibitors.

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Regulation of Mitotic Homeologous Recombination in Yeast: Functions of Mismatch Repair and Nucleotide Excision Repair Genes

Genetics ◽

10.1093/genetics/154.1.133 ◽

2000 ◽

Vol 154 (1) ◽

pp. 133-146 ◽

Cited By ~ 1

Author(s):

Ainsley Nicholson ◽

Miyono Hendrix ◽

Sue Jinks-Robertson ◽

Gray F Crouse

Keyword(s):

Saccharomyces Cerevisiae ◽

Mismatch Repair ◽

Nucleotide Excision Repair ◽

Excision Repair ◽

Mitotic Recombination ◽

Inverted Repeats ◽

Replication Errors ◽

Nucleotide Excision ◽

Homeologous Recombination ◽

Repair Genes

Abstract The Saccharomyces cerevisiae homologs of the bacterial mismatch repair proteins MutS and MutL correct replication errors and prevent recombination between homeologous (nonidentical) sequences. Previously, we demonstrated that Msh2p, Msh3p, and Pms1p regulate recombination between 91% identical inverted repeats, and here use the same substrates to show that Mlh1p and Msh6p have important antirecombination roles. In addition, substrates containing defined types of mismatches (base-base mismatches; 1-, 4-, or 12-nt insertion/deletion loops; or 18-nt palindromes) were used to examine recognition of these mismatches in mitotic recombination intermediates. Msh2p was required for recognition of all types of mismatches, whereas Msh6p recognized only base-base mismatches and 1-nt insertion/deletion loops. Msh3p was involved in recognition of the palindrome and all loops, but also had an unexpected antirecombination role when the potential heteroduplex contained only base-base mismatches. In contrast to their similar antimutator roles, Pms1p consistently inhibited recombination to a lesser degree than did Msh2p. In addition to the yeast MutS and MutL homologs, the exonuclease Exo1p and the nucleotide excision repair proteins Rad1p and Rad10p were found to have roles in inhibiting recombination between mismatched substrates.

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Mechanisms of Recombination between Diverged Sequences in Wild-Type and BLM-Deficient Mouse and Human Cells

Molecular and Cellular Biology ◽

10.1128/mcb.01553-09 ◽

2010 ◽

Vol 30 (8) ◽

pp. 1887-1897 ◽

Cited By ~ 40

Author(s):

Jeannine R. LaRocque ◽

Maria Jasin

Keyword(s):

Gene Conversion ◽

Mammalian Cells ◽

Sequence Divergence ◽

Dna Lesions ◽

Human Cells ◽

Deficient Mouse ◽

Wild Type ◽

Strand Breaks ◽

Major Mechanism ◽

Homeologous Recombination

ABSTRACT Double-strand breaks (DSBs) are particularly deleterious DNA lesions for which cells have developed multiple mechanisms of repair. One major mechanism of DSB repair in mammalian cells is homologous recombination (HR), whereby a homologous donor sequence is used as a template for repair. For this reason, HR repair of DSBs is also being exploited for gene modification in possible therapeutic approaches. HR is sensitive to sequence divergence, such that the cell has developed ways to suppress recombination between diverged (“homeologous”) sequences. In this report, we have examined several aspects of HR between homeologous sequences in mouse and human cells. We found that gene conversion tracts are similar for mouse and human cells and are generally ≤100 bp, even in Msh2 − / − cells which fail to suppress homeologous recombination. Gene conversion tracts are mostly unidirectional, with no observed mutations. Additionally, no alterations were observed in the donor sequences. While both mouse and human cells suppress homeologous recombination, the suppression is substantially less in the transformed human cells, despite similarities in the gene conversion tracts. BLM-deficient mouse and human cells suppress homeologous recombination to a similar extent as wild-type cells, unlike Sgs1-deficient Saccharomyces cerevisiae.

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Genetic Heterogeneity of Variable Number Tandem Repeats in Thymidylate Synthase Gene in Colorectal Cancer Patients

The International Journal of Biological Markers ◽

10.1177/172460080401900413 ◽

2004 ◽

Vol 19 (4) ◽

pp. 332-336 ◽

Cited By ~ 4

Author(s):

M. Agostini ◽

S. Pucciarelli ◽

P. Calandra ◽

F. Villani ◽

M. Lise ◽

...

Keyword(s):

Thymidylate Synthase ◽

Tandem Repeats ◽

Colorectal Adenocarcinoma ◽

Variable Number ◽

Mismatch Repair Genes ◽

Pcr Product ◽

Group A ◽

Microsatellite Stability ◽

Group B ◽

Repair Genes

Purpose To analyze the genetic variability in a variable number of tandem repeats (VNTR) in the thymidylate synthase (TS) enhancer promoter region and assess the influence of functional alterations in mismatch repair genes by analyzing constitutional and tumoral DNA from patients with colorectal adenocarcinoma with a high microsatellite instability (MSI-H) or microsatellite stability (MSS) status. Patients and methods Patients who underwent surgery for colorectal adenocarcinoma were selected from the colorectal database of our institute and, on the basis of MSI status, assigned to a study group and a control group: group A, MSI-H; group B, MSS. Microsatellite status was investigated using the Bethesda recommended panel (BAT-26, BAT-25, D2S123, D5S346, D17S250). In MSI-H patients an additional analysis was made of the microsatellite loci D18S61 and D18S58, both mapping in the region containing the TS gene (18p11.2–11.32). Based on the number of altered microsatellites (≥2, 1, or 0), tumors were considered as having high (MSI-H) or low (MSI-L) instability or microsatellite stability (MSS), respectively. Genotyping for thymidylate synthase promoter polymorphism was carried out on constitutional and tumor DNA of each patient by PCR amplification of the polymorphic region. Results MSI-H was found in 55 patients (group A) and MSS in 50 patients (group B). In none of the MSI-H patients was microsatellite instability found in the additional D18S61 and D18S58 loci. In five group A and ten group B cases the analysis was not performed because constitutional DNA and/or tumoral DNA were not amplifiable. Homozygotes for the triple repeat variant (3R/3R) displayed only the large PCR product, homozygotes for the double repeat variant (2R/2R) displayed only the smaller PCR product, while heterozygotes (2R/3R) displayed both the larger and smaller PCR products. In 3/50 (6%) group A patients and 5/40 (12%) group B patients repeat variations were found in tumoral DNA. Conclusion Our findings demonstrate that there is genetic homogeneity between constitutional and tumoral DNA but do not support the hypothesis that mismatch repair genes are involved in VNTR recombinant events in TS gene variability.

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Potential Mechanism of Immune Evasion Associated with the Master Regulator ASCL2 in Microsatellite Stability in Colorectal Cancer

Journal of Immunology Research ◽

10.1155/2021/5964752 ◽

2021 ◽

Vol 2021 ◽

pp. 1-12

Author(s):

Qian Yang ◽

Guowei Huang ◽

Liyan Li ◽

Enmin Li ◽

Liyan Xu

Keyword(s):

Colorectal Cancer ◽

Immune Evasion ◽

Enrichment Analysis ◽

Gene Set Enrichment Analysis ◽

Novel Treatments ◽

T Cell Infiltration ◽

Immune Resistance ◽

Unbiased Gene ◽

Ifn Γ ◽

Microsatellite Stability

Colorectal cancer (CRC) has two major subtypes, microsatellite instability (MSI) and microsatellite stability (MSS) based on the genomic instability. In this study, using computational programs, we identified 9 master transcription factors (TFs) based on epigenomic profiling in MSS CRC samples. Notably, unbiased gene set enrichment analysis (GSEA) showed that several master TFs were strongly associated with immune-related functions in TCGA MSS CRC tissues, such as interferon gamma (IFN-γ) and interferon alpha (IFN-α) responses. Focusing to the top candidate, ASCL2, we found that CD8+ T cell infiltration was low in ASCL2 overexpressed MSS CRC samples. Compared with other gastrointestinal (GI) cancers (gastric cancer, MSI CRC, and esophageal cancer), ASCL2 is specifically upregulated in MSS CRC. Moreover, we identified 28 candidate genes in IFN-γ and IFN-α response pathways which were negatively correlated with ASCL2. Together, these results link transcriptional dysregulation with the immune evasion in MSS CRC, which may advance the understanding of immune resistance and contribute to developing novel treatments of MSS CRC.

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Unbiased homeologous recombination during pneumococcal transformation allows for multiple chromosomal integration events

eLife ◽

10.7554/elife.58771 ◽

2020 ◽

Vol 9 ◽

Cited By ~ 1

Author(s):

Jun Kurushima ◽

Nathalie Campo ◽

Renske van Raaphorst ◽

Guillaume Cerckel ◽

Patrice Polard ◽

...

Keyword(s):

Transformation Efficiency ◽

Integration Site ◽

Cell Level ◽

Exogenous Dna ◽

Recombination Efficiency ◽

Safe Strategy ◽

Original Genome ◽

Homeologous Recombination ◽

Fail Safe ◽

Lagging Strand

The spread of antimicrobial resistance and vaccine escape in the human pathogen Streptococcus pneumoniae can be largely attributed to competence-induced transformation. Here, we studied this process at the single-cell level. We show that within isogenic populations, all cells become naturally competent and bind exogenous DNA. We find that transformation is highly efficient and that the chromosomal location of the integration site or whether the transformed gene is encoded on the leading or lagging strand has limited influence on recombination efficiency. Indeed, we have observed multiple recombination events in single recipients in real-time. However, because of saturation and because a single-stranded donor DNA replaces the original allele, transformation efficiency has an upper threshold of approximately 50% of the population. The fixed mechanism of transformation results in a fail-safe strategy for the population as half of the population generally keeps an intact copy of the original genome.

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