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Identification of a plastid-targeted RecQ-like helicase in the red alga Cyanidioschyzon merolae.

Plastids retain their own genomic DNA (plastid DNA, ptDNA) which must be faithfully maintained for proper organelle function. However, the molecular mechanisms responsible for ptDNA maintenance remain poorly understood, particularly in red algae. Here, we identified a plastid-targeted RecQ-like helicase (ptRECQ) in the unicellular red alga Cyanidioschyzon merolae. Biochemical assays demonstrated that ptRECQ possesses ATP-dependent helicase activity and preferentially unwinds splayed DNA substrates that mimic replication fork structures. ptrecQ mutant cells were hypersensitive to nalidixic acid, a ptDNA gyrase inhibitor that induces replication stress, indicating a role for ptRECQ in plastid genome maintenance under replication stress. Phylogenetic analyses showed that ptRECQ is broadly conserved in red algae, absent from green algae and land plants, and phylogenetically distinct from cyanobacterial RecQ proteins. These results suggest that red algae employ a ptDNA maintenance system that differs from that of the green lineage.

Rhodophyta

Discordant neoplasms in monozygotic twins with a germline RECQL5 variant.

RECQL5 is a member of the RecQ helicase family involved in DNA replication, homologous recombination, and maintenance of genomic stability. While germline pathogenic variants in other RecQ helicases cause established cancer predisposition syndromes, the role of RECQL5 in human cancer susceptibility remains uncertain. We report monozygotic adolescent twins with distinct tumors: dysembryoplastic neuroepithelial tumor in one twin and Burkitt lymphoma in the other. Clinical genome sequencing was initially nondiagnostic, but reanalysis identified a rare heterozygous nonsense variant in RECQL5 (NM_004259.7:c.2698C>T, p.(Gln900Ter)), present in both twins and their unaffected mother. The variant is predicted to undergo nonsense-mediated mRNA decay or produce a truncated protein lacking the C-terminal SRI (Set2-Rpb1 interacting) domain, which mediates interaction with RNA polymerase II. However, tumor sequencing data were not available to evaluate loss of heterozygosity or second somatic events. Given the unaffected carrier parent, lack of tumor molecular confirmation, and the biological heterogeneity of the tumors, a causal relationship for this variant cannot be established. This case highlights the challenges of interpreting rare germline variants in genes with emerging but incompletely characterized disease associations. Although the available evidence is insufficient to establish a definitive causal relationship, the identification of a shared loss-of-function RECQL5 variant in monozygotic twins with distinct tumors is noteworthy and adds to the limited clinical evidence suggesting a potential role for RECQL5 in cancer susceptibility. Additional functional studies, tumor-based analyses and the accumulation of well-characterized clinical cases will be essential to determine whether RECQL5 contributes to hereditary cancer predisposition.

Adolescent

Engineering bubble structures as Cas12a activators for highly sensitive monitoring of WRN helicase function.

The Werner syndrome helicase (WRN) is a critical synthetic lethal target in microsatellite instability cancers, essential for resolving complex genomic structures like replication bubbles and R-loops. However, strategies to simultaneously discriminate WRN activity on DNA versus DNA-RNA substrates in living cells are lacking. Here, we developed a structure-specific CRISPR/Cas12a biosensing strategy to visualize WRN functional activity by engineering bubble-structure probes. These probes were rationally designed to structurally mimic DNA replication bubbles and R-loop associated DNA-RNA hybrids. Upon specific unwinding by WRN, the probes release a sequestered activator strand that triggers Cas12a trans-cleavage, effectively converting the unwinding event into an amplified fluorescent signal. This assay achieves low picomolar sensitivity (LODs: 5.6-6.0 pM) and exceptional selectivity against homologous RecQ helicases. Uniquely, this strategy enables the parallel quantification of WRN activity on both substrate types, providing insights into distinct WRN-mediated pathways for resolving genomic stress. We further demonstrated the strategy's utility by visualizing endogenous WRN dynamics in living cells and profiling the efficacy of small-molecule inhibitors. This work offers a powerful molecular toolkit for dissecting WRN biology and facilitating high-throughput drug screening in targeted cancer therapy.

Werner Syndrome Helicase

RECQL correlates with immune infiltration and serves as a prognostic biomarker and therapeutic predictor in gastric cancer.

BACKGROUND: RecQ-like helicase (RECQL), a member of the RecQ-like DNA helicase family, plays a crucial role in maintaining genomic stability. However, its relevance in gastric cancer (GC) has not been fully investigated. This study aimed to explore the clinical significance, biological functions, and potential role of RECQL in the tumor immune microenvironment of GC through comprehensive bioinformatics analyses and in vitro experiments. METHODS: Weighted gene co-expression network analysis (WGCNA), differential expression analysis, and least absolute shrinkage and selection operator (LASSO) regression were performed using public datasets [The Cancer Genome Atlas Stomach Adenocarcinoma (TCGA-STAD), GSE150290] to identify key genes associated with GC progression. Subsequently, key pathways were identified through functional enrichment analysis, while immune infiltration and spatial transcriptomic analyses were conducted to characterize RECQL expression and its association with the tumor immune microenvironment. Finally, the effects of RECQL knockdown on the biological function of GC cells were assessed through Cell Counting Kit-8 (CCK-8), colony formation, scratch, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays. RESULTS: RECQL was significantly upregulated in GC tissues and correlated with advanced clinical stage and poor prognosis. Gene set enrichment analysis (GSEA) revealed a strong association between high RECQL expression and DNA repair pathway. Immune infiltration analysis indicated significant enrichment of M2 macrophages in the high-RECQL group, along with upregulation of immune checkpoint molecules including PDCD1, CTLA4, and CD274. Spatial transcriptomics further demonstrated co-localization of RECQL with myeloid cell-enriched regions in tumor parenchymal areas. Furthermore, in vitro experimental results indicated that RECQL was highly expressed in GC cell lines, and its knockdown effectively inhibited the viability, proliferation, and migration capabilities of HGC-27 cells, while enhancing their apoptosis. CONCLUSIONS: RECQL serves as a promising biomarker and potential therapeutic target in GC.

DNA repair

Targeting RECQL4 in hepatocellular carcinoma: from prognosis to therapeutic potential.

OBJECTIVE: The aim of this study is to assess the clinical utility of RecQ Like Helicase 4 (RECQL4) as a prognostic marker in hepatocellular carcinoma (HCC) and investigate its associations with various biological processes, angiogenesis-related factors, immune cell infiltration, immune checkpoints, and drug sensitivity. METHODS: RECQL4 expression was analyzed across a range of cancer types utilizing data from the TCGA database. Disparities in RECQL4 expression levels between normal and malignant tissues were evaluated, alongside an analysis of progression-free interval (PFI), disease-specific survival (DSS), and overall survival (OS) curves. Exploration of pertinent pathways, immune cell infiltration, single-cell RNA-seq data, and drug sensitivity was conducted employing The Cancer Genome Atlas (TCGA) and Tumor Immune Single-Cell Hub (TISCH) databases. Furthermore, validation of in-silico results was validated through qPCR, Western blotting, CCK-8 assay, EdU assay, clonogenic assay, wound-healing assay, and transwell assay. RESULTS: In HCC, RECQL4 was highly expressed and associated with poorer prognosis (p&#x2009;<&#x2009;0.05). It positively correlated with pathways related to MYC targets, DNA replication, PI3K/AKT/mTOR signaling, DNA repair mechanisms, and the G2/M checkpoint (R&#x2009;>&#x2009;0.24, p&#x2009;<&#x2009;0.001). RECQL4 also showed significant correlations with angiogenesis-related genes, including PTK2 (R&#x2009;>&#x2009;0.4, p&#x2009;<&#x2009;0.05), suggesting a potential role in angiogenesis regulation. Immune analysis indicated that RECQL4 was associated with immune cell types such as T helper 2 cells, NK CD56bright cells, and follicular helper T cells, suggesting a positive relationship with their infiltration. High RECQL4 expression was also linked to increased sensitivity to drugs including Sorafenib, 5-Fluorouracil, Cisplatin, and Doxorubicin. Cellular experiments showed that RECQL4 expression at the mRNA and protein levels were significantly higher in HCC cell lines Hep3B and Huh7 compared to the normal liver cell line MHA. Moreover, RECQL4 knockdown resulted in reduced proliferation and migration in HCC cell lines (p&#x2009;<&#x2009;0.05). CONCLUSIONS: RECQL4 shows promise as a biomarker for predicting recurrence and survival in HCC and may affect angiogenesis regulation. Its expression also appears to impact sensitivity to drugs such as Sorafenib, 5-Fluorouracil, Cisplatin, and Doxorubicin. Furthermore, silencing RECQL4 significantly inhibits HCC cell line proliferation and migration.

Humans