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Results for “MutL Protein Homolog 1”

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PubMed2024

Surviving without BRCA2: MLH1 gets R-looped in to curtail genomic instability.

While breast cancer 2 (BRCA2) loss of heterozygosity (LOH) promotes cancer initiation, it can also induce death in nontransformed cells. In contrast, mismatch repair gene mutL homolog 1 (MLH1) is a tumor-suppressor gene that protects cells from cancer development through repairing mismatched base pairs during DNA mismatch repair (MMR). Sengodan et al., in this issue of the JCI, reveal an interplay between the 2 genes: MLH1 promoted the survival of BRCA2-deficient cells independently of its MMR function. MLH1 protected replication forks from degradation, while also resolving R-loops, thereby reducing genomic instability. Moreover, MLH1 expression was regulated directly by estrogen, shedding light into the hormone-responsive nature of many BRCA2 mutant breast cancers. These results provide important insight into the genetics that drive the initiation of BRCA2-mutated breast cancers.

Humans↗
PubMed2026

Clinical and genetic characterization of constitutional MLH1 promoter hypermethylation: Implications for Lynch syndrome diagnosis.

PURPOSE: Constitutional MLH1 promoter hypermethylation (CMPH) is a relatively rare cause of Lynch syndrome. While most cases appear to be sporadic, some result from secondary epimutations, mainly caused by germline variants in the MLH1 promoter region. This study describes the clinical phenotype and genetic etiology of CMPH in the largest clinical cohort to date. METHODS: A retrospective analysis was conducted for 422 individuals who underwent clinical CMPH testing. Promoter sequencing was used to identify the underlying variants. Long-read sequencing further characterized MLH1 promoter methylation. RESULTS: CMPH was identified in 15.6% of the study cohort participants. Of these, 63 exhibited clinical features consistent with Lynch syndrome. The most common associated cancers were colorectal cancer, followed by endometrial cancer, breast cancer, and sebaceous neoplasms. Mendelian inheritance of CMPH was observed in 5 families in the study cohort, indicating secondary epimutations. Promoter sequencing identified 8 unique germline variants, including 3 novel variants. Methylation analysis by long-read sequencing revealed mutant allele-specific promoter methylation for these variants. CONCLUSION: Our findings provide the most comprehensive review of the clinical phenotype associated with CMPH and highlight the significant contribution of promoter variants to its etiology. These results underscore the need to include the assessment of constitutional MLH1 promoter methylation for Lynch syndrome diagnosis.

Humans↗
PubMed2026

Suppression of transcription-replication conflicts by sequence-coordinated actions of TRDMT1 and MutLα.

TRDMT1 is an RNA methyltransferase that catalyzes 5-methylcytosine (m5C) formation in R-loops to promote transcription-coupled homologous recombination (TC-HR). Although TRDMT1 inhibition selectively kills BRCA1-deficient cancer cells, broader cancer dependencies on TRDMT1 remain unclear. Here, a TRDMT1 inhibitor (TRDMT1i) sensitivity screen across a large panel of cancer cell lines identifies loss of MLH1 or PMS2, two components of the MutLα mismatch repair (MMR) complex frequently inactivated in tumors, as key determinants of TRDMT1 dependency. In contrast, MutLβ and MutSα/β are dispensable for TRDMT1i resistance, revealing a unique MMR-independent function of MutLα. Mechanistically, TRDMT1 and MutLα independently recognize DNA-RNA hybrids and cooperatively suppress co-transcriptional R-loops genome-wide in undamaged cells, with m5C directing pathway choice. Furthermore, MutLα suppresses R-loops through its ATPase and endonuclease activities and through recruitment of EXO1. Combined loss of TRDMT1 and MLH1 causes extensive R-loop accumulation and transcription replication conflicts (TRCs), impairing replication fork progression, inducing DNA damage, and driving apoptosis-mediated synthetic lethality. Importantly, TRDMT1i suppresses growth of MLH1-deficient tumors by inducing TRCs in vivo, suggesting a potential therapeutic strategy for targeting MutLα-deficient tumors. These studies not only expand our understanding of cancer dependency on TRDMT1, but also identify a promising strategy to exploit TRCs in cancer therapy.

Humans↗
PubMed2026

Mismatch repair protein MLH1 controls testis development by regulating the Hippo-YAP signaling pathway.

DNA mismatch repair (MMR) maintains genomic stability, and defects in MMR genes such as MLH1 and MSH2 predispose to cancer. Unlike other MMR components, MLH1 has unexplained roles in development, as Mlh1-deficient male mice exhibit severe testicular hypoplasia and sterility. Here, we uncover that MLH1 regulates testis development through the Hippo-Yes-associated protein (YAP) pathway. MLH1 directly binds YAP via its C-terminal domain and the WW domains of YAP, competitively inhibiting LATS1-mediated YAP phosphorylation. This interaction stabilizes YAP by suppressing ubiquitination and promotes its nuclear translocation dependent on MLH1's nuclear localization signal. Additionally, MLH1 facilitates YAP-TEAD complex formation, enabling expression of testicular development genes, including Wt1, Sox9, and Ctgf. These functions are independent of the MMR activity of MLH1. Mlh1-deficient mice show elevated YAP phosphorylation, reduced target gene expression, and impaired proliferation in developing testes. Pharmacological inhibition of the Hippo pathway kinases MST1/2 partially rescues testis hypoplasia in Mlh1-/- mice. These findings establish MLH1 as a Hippo pathway regulator and resolve its long-standing role in male gonad development.

Male↗
PubMed2025

Integrating network pharmacology and experimental validation to uncover the synergistic effects of Huangqi ()-Ezhu () with 5-fluorouracil in colorectal cancer models.

OBJECTIVE: To evaluate the effects of Huangqi (Radix Astragali Mongolici)-Ezhu (Rhizoma Curcumae Phaeocaulis) (HQEZ) on colorectal cancer therapies and to elucidate the potential mechanisms of HQEZ, especially in combination with 5-Fluorouracil (5-FU). METHODS: The anti-tumor effects of HQEZ were evaluated in colorectal cancer models both in vivo and in vitro. The network pharmacological assay was used to investigate potential mechanisms of HQEZ. Potential target genes were selected by Gene Ontology (GO) enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, protein-protein interaction network (PPI) and molecular docking. Within key targets, potential targets related to drug sensitivity, especially the sensitivity to 5-FU, were evaluated in HCT116 in vitro by immunofluorescence, quantitative real-time polymerase chain reaction (qPCR) and Western-blot. Then, changes in potential targets were assessed in tumors from tumor-bearing mice and the expression of these targets was also evaluated in colorectal cancer (COAD) patients from the Cancer Genome Atlas Program (TCGA) database. RESULTS: HQEZ significantly enhanced the anti-tumor activity of 5-FU in vivo and inhibit the growth of HCT116 in vitro. By network pharmacological analysis, key targets, such as protein kinase B (AKT1), epidermal growth factor receptor (EGFR), adenosine triphosphate (ATP) binding cassette subfamily B member 1 (ABCB1, also named multidrug resistance protein 1, MDR1), ATP binding cassette subfamily G member 2 (ABCG2), thymidylate synthetase (TYMS, also named TS), prostaglandin-endoperoxide synthase 2 (PTGS2), matrix metallopeptidase 2 (MMP2), MMP9, toll like receptor 4 (TLR4), TLR9 and dihydropyrimidine dehydrogenase (DPYD), were identified. Additionally, 4 potential core active ingredients (Folate, Curcumin, quercetin and kaempferol) were identified to be important for the treatment of colorectal cancer with HQEZ. In key targets, chemoresistance related targets were validated to be affected by HQEZ. Furthermore, 5-FU sensitivity related targets, including MDR1, TS, EGFR, ribonucleotide reductase catalytic subunit M1, Breast and Ovarian Cancer Susceptibility Protein 1 (BRCA1) and mutl homolog 1 were also significantly reduced by HQEZ both in vitro and in vivo. Finally, these validated key targets and 5-FU sensitivity related targets were demonstrated to be up-regulated in COAD patients based on TCGA database. CONCLUSION: HQEZ has synergistic effects on the anti-tumor activity of 5-FU in the treatment of colorectal cancer both in vivo and in vitro. The beneficial effect of HQEZ results from the inhibition of the drug sensitivity targets associated with 5-FU. The combination therapy of HQEZ with 5-FU or other chemotherapeutic drugs will also improve the anti-tumor efficacy of chemotherapy.

Humans↗