Biology subjects

Arafat, M.

Publications and source records attributed to Arafat, M..

5 recordsLinked to original sources

bioRxiv2026

Spliceosomal miR-99b Regulates SPACA6-AS1 Pre-mRNA Levels and Promotes Malignant Phenotypes in Breast Cancer

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression primarily in the cytoplasm. However, emerging evidence highlights their additional roles in the nucleus. In particular, spliceosomal miRNAs have been implicated in novel regulatory functions, including the modulation of gene expression. Here, we investigate the nuclear role of spliceosomal miR-99b in breast cancer cells, focusing on its interaction with the long non-coding RNA (lncRNA) SPACA6-AS1. Using non-tumorigenic (MCF-10A) and breast cancer cell lines (MCF-7 and MDA-MB-231), we demonstrate that spliceosomal miR-99b expression increases with malignancy and correlates with elevated SPACA6-AS1 pre-mRNA levels. Notably, miR-99b exhibits full complementarity to the 5-prime splice junction of SPACA6-AS1, suggesting a direct role in splicing regulation. Functional assays reveal that inhibition of miR-99b reduces SPACA6-AS1 pre-mRNA levels, whereas its overexpression enhances pre-mRNA accumulation, indicating that miR-99b promotes the formation or stabilization of the unspliced transcript. Furthermore, increased miR-99b expression is associated with altered ratios of SPACA6 isoforms, supporting a broader role in RNA-level regulation of gene expression. Phenotypically, miR-99b enhances breast cancer cell migration and is required for efficient invasion, particularly in highly aggressive cancerous cells. Our findings uncover a novel nuclear function of miR-99b in modulating lncRNA splicing and gene expression. This spliceosomal miR-99b-SPACA6-AS1 axis represents a previously unrecognized regulatory pathway that contributes to breast cancer progression and may provide a potential target for diagnostic and therapeutic strategies.

molecular biology↗

bioRxiv2026

An Epstein-Barr virus-encoded snoRNA directs 2'-O-methylation of human rRNAs to control translation and the viral lytic switch

Epstein-Barr virus (EBV) establishes life-long latency in human B-cells yet the molecular strategies that balance its persistence with lytic replication remain incompletely understood. Here, we identify the EBV-encoded small nucleolar RNA, v-snoRNA1, as a bona fide 2'-O-methylation guide that directs methylation of host ribosomal RNAs at 18S-C621 and 28S-U1760, two conserved residues in the ribosomal A-site. V-snoRNA1-mediated hypermethylation impairs 18S rRNA maturation and compromises translational fidelity and output, resulting in slower cellular proliferation. Infection with a v-snoRNA1 deleted virus ({Delta}v-snoRNA1) leads to enhanced protein synthesis and increased proliferation, together with extensive rewiring of host and viral gene expression. This rewiring includes suppression of immune and interferon pathways and alterations in transcription factor activities important for B-cell differentiation. Importantly, we find that v-snoRNA1 is required to facilitate viral production. Our findings reveal a molecular strategy by which EBV directly controls translation to promote infection.

molecular biology↗

bioRxiv2026

Integron-Mediated Convergence of Carbapenemase and Disinfectant Resistance in Acinetobacter spp. from Critical Care Units

Acinetobacter spp. represents critical opportunistic pathogens driving severe bloodstream infections (BSIs) in intensive care unit (ICU) and neonatal intensive care unit (NICU) settings. The convergence of carbapenem resistance and emerging biocide tolerance, often mediated by mobile genetic elements, has intensified concerns regarding co-selection and persistence in clinical environments. A total of 90 molecularly confirmed Acinetobacter isolates (ICU = 44; NICU = 46) from bloodstream infections were analyzed. Antimicrobial susceptibility was determined using the Kirby-Bauer disk diffusion method in accordance with CLSI M100 (2024) guidelines and extended-spectrum {beta}-lactamase production was assessed by combined disc diffusion. Polymerase chain reaction (PCR) was employed to detect carbapenemase genes (blaVIM, blaNDM, blaIMP, blaOXA-23, blaOXA-58), biocide resistance determinants (qacE, qac{Delta}E1), and the class 1 integron-integrase gene (intI1). Multidrug-resistant (MDR) and extensively drug-resistant (XDR) phenotypes were identified in 71.1% (64/90) and 22.2% (20/90) of isolates, respectively. High resistance (>71%) was observed against meropenem and cephalosporins, whereas colistin (58.8%, 53/90) and amikacin (47.8%, 43/90) showed moderate susceptibility. The most prevalent genotypes were qac{Delta}E1 (76.6%, 69/90) and blaVIM (56.6%, 51/90). Statistical and network analyses revealed significant correlations between biocide and carbapenemase genes, identifying IntI1 as a primary driver of co-resistance. The findings indicate a significant co-occurrence of carbapenemase genes, biocide resistance determinants, and class 1 integrons among Acinobacter spp. isolates. These associations suggest that mobile genetic elements may contribute to the dissemination of resistance traits.

microbiology↗

bioRxiv2025

Dynamic Ribosomal RNA Methylation Regulates Translation in the Hematopoietic System and is Essential for Stem Cell Fitness

Self-renewal and differentiation are at the basis of hematopoiesis. While it is known that tight regulation of translation is vital for hematopoietic stem cells (HSCs) biology, the mechanisms underlying translation regulation across the hematopoietic system remain obscure. Here we reveal a novel mechanism of translation regulation in the hematopoietic hierarchy, which is mediated by ribosomal RNA (rRNA) methylation dynamics. Using ultra-low input ribosome-profiling, we characterized cell-type-specific translation capacity during erythroid differentiation. We found that translation efficiency changes progressively with differentiation and can distinguish between discrete cell populations as well as to define differentiation trajectories. To reveal the underlying mechanism, we performed comprehensive mapping of the most abundant rRNA modification - 2-O-methyl (2OMe). We found that, like translation efficiency, 2OMe dynamics followed a distinct trajectory during erythroid differentiation. Genetic perturbation of individual 2OMe sites demonstrated their distinct roles in modulating proliferation and differentiation. By combining CRISPR screening, molecular and functional analyses, we identified a specific methylation site, 28S-Gm4588, which is progressively lost during differentiation, as a key regulator of HSC self-renewal. We showed that low methylation at this site led to translational skewing, mediated mainly by codon frequency, which promoted differentiation. Functionally, HSCs with diminished 28S-Gm4588 methylation exhibited impaired self-renewal capacity ex-vivo, and loss of fitness in-vivo in bone marrow transplantations. Extending our findings beyond the hematopoietic system, we also found distinct dynamics of 2OMe profiles during differentiation of non-hematopoietic stem cells. Our findings reveal rRNA methylation dynamics as a general mechanism for cell-type-specific translation, required for cell function and differentiation. KEY POINTSO_LIHematopoietic differentiation is associated with rRNA methylation dynamics to control cell-type-specific translation. C_LIO_LITranslation efficiency can distinguish discrete cell types and define differentiation trajectories. C_LIO_LIHSC fitness is regulated by a single rRNA methylation. C_LI

molecular biology↗

bioRxiv2025

Identification of RNA binding proteins that mediate a quality control mechanism of splicing

Accurate splicing, which involves the controlled removal of non-coding sequences (introns) from precursor messenger RNAs (pre-mRNAs), is essential for producing correct mature mRNAs that encode functional proteins. Within pre-mRNAs, latent splice sites (LSSs) resemble proper splice sites but are usually not used because their activation can introduce in-frame STOP codons. The nuclear suppression of splicing (SOS) mechanism prevents the use of LSSs. Although the SOS mechanism is not fully understood, recent studies have identified initiator-tRNA and the NCL protein as key components. To discover additional regulators, we performed a genetic screen targeting RNA-binding proteins (RBPs) with an siRNA library and a luminescence reporter for latent splice site activation. This identified five RBPs -- ALYREF (THOC4), PPIE, DDX41, DHX38, and HNRNPA2B1 -- whose knockdown significantly increased LSS usage in the reporter. RNA-Seq analysis after knocking down each of these RBPs confirmed these results, showing widespread LSS activation in hundreds of mRNAs. Among these, we focused on ALYREF, a conserved protein involved in mRNA export and splicing. Using fPAR-CLIP, we found that U5 snRNA is ALYREFs main binding partner. Overexpressing ALYREF deletion mutants activated latent splicing, and affinity purification confirmed its interaction with U5 snRNA. These mutants exhibited different binding properties, highlighting the importance of specific structural elements within ALYREF in SOS regulation. Our findings reveal that nuclear RBPs play a key role in suppressing LSS activation and suggest that ALYREF has a novel role in maintaining splicing accuracy within the spliceosome, advancing our understanding of the SOS mechanism.

genomics↗