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TRIM28 regulates the G2/M transition via histone modification and DNA damage repair during mouse oocyte meiosis.

TRIM28, a member of the tripartite motif (TRIM) family, functions as a transcriptional coregulator involved in maintaining genome stability during mitosis. In this study, we explored the role of TRIM28 in mouse oocyte meiotic maturation, where transcriptional activity is barely detectable. We found that TRIM28 was constitutively expressed during the early stages of oocyte meiotic maturation, with predominant nuclear localization in germinal vesicle (GV)-stage oocytes. TRIM28 depletion caused defective germinal vesicle breakdown (GVBD), but oocytes that successfully underwent GVBD displayed unimpaired first polar body (PB1) extrusion. TRIM28 depletion impaired CDK1 activity and reduced cyclin B1 levels, leading to a delay in the G2/M transition. This delay might be caused by altered levels of HDAC2-mediated H4K12ac and H3K4me2-modulated H3K9me2 in nonsurrounded nucleolus (NSN)-type GV oocytes, which decreased transcription activity. Additionally, TRIM28-depleted oocytes exhibited elevated γ-H2A.X expression, accompanied by aberrant expression of CHK1 and CHK2, as well as dysregulated expression of RAD51, which collectively contributed to GVBD failure in mouse oocytes. In conclusion, our findings indicate that TRIM28 participates in the regulation of the G2/M transition during mouse oocyte meiotic maturation, acting through the modulation of histone modifications and DNA damage repair.

Animals

A tumor suppressor role of the miR-15b/16-2 cluster in T-cell acute lymphoblastic leukemia.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy arising from the neoplastic transformation of immature T cells during their development in the thymus. Deciphering the developmental programs whose dysregulation drives T-ALL pathogenesis is critical for the development of novel targeted therapies, which remain an urgent unmet need for the treatment of this disease. MicroRNAs (miRNAs) have emerged as key posttranscriptional regulators of numerous physiological processes, including cancer. However, the specific role of miRNAs in human T-cell development and T-ALL pathogenesis remains largely unexplored. In this study, we comprehensively evaluated miRNA expression profiles across human T-cell development using microarray analysis and identified a dynamic expression pattern of miR-16-2, which is upregulated during early pre-T-cell proliferative stages up to the resting stage of immature thymocytes immediately preceding T-cell receptor αβ expression and is subsequently downregulated. We also confirmed the coordinated regulation of miR-15b expression, consistent with the reported clustered genomic location of both miRNAs. Notably, functional studies identified the miR-15b/16-2 cluster as a negative regulator of early thymocyte proliferation and demonstrated that overexpression of miR-15b/16-2 in T-ALL cells impaired leukemic growth in vitro and tumor progression in patient-derived xenotransplantation assays. Mechanistically, miR-15b/16-2 represses the expression of the genes encoding BCL-2 and cyclin D3, thereby promoting apoptosis and cell cycle dysregulation in T-ALL cells, characterized by an accumulation of G0-phase cells and a defective transition to the G2/M phase. Overall, these findings support a novel tumor-suppressive function for miR-15b/16-2 in T-ALL and highlight its potential as a promising therapeutic target.

MicroRNAs

IRAK4 constrains cellular plasticity during chemically-induced cell fate reprogramming into multiple lineages.

Chemical reprogramming holds transformative potential for regenerative medicine. However, the regulatory mechanisms governing cell fate transitions are not well understood. Here, we identify Interleukin-1 Receptor-Associated Kinase 4 (IRAK4) as a barrier to multi-lineage reprogramming. Pharmacological inhibition of IRAK4 enhances the reprogramming of mouse embryonic fibroblasts (MEFs) through a chemically activated multi-lineage priming (CaMP) state and extraembryonic endoderm (XEN)-like intermediates, increasing colony formation, and the expression of core XEN regulators (Sox17, Gata4, Sall4, and Foxa2). Genetic knockdown of Irak4 similarly accelerates reprogramming, whereas its overexpression blocks cell fate transitions. IRAK4 inhibition enhances chromatin accessibility and reshapes cell cycle dynamics, characterized by G0/G1 shortening and G2/M lengthening, potentially contributing to multi-lineage state establishment. Furthermore, IRAK4 suppression enhances the direct conversion of MEFs to neuron-like and hepatocyte-like cells, which exhibit enhanced functional maturity, including increased glycogen storage and improved detoxification capacity. Our findings establish IRAK4 as a regulator that constrains cellular plasticity potentially by coordinating chromatin accessibility and cell cycle dynamics.

Animals

B-MYB (MYBL2): from cell cycle regulator to an oncogenic player.

B-MYB (MYBL2) is a transcription factor of the MYB family that plays critical roles in cell cycle progression, proliferation, and survival. Through the DREAM-MMB-FOXM1 network, B-MYB coordinates the expression of genes required for mitosis and cytokinesis (G2/M genes), while genes required for DNA replication during S phase are regulated by E2F-DP complexes. Initially identified as a regulator of normal cell cycle processes, B-MYB has emerged as a key oncogenic driver across multiple cancer types. This review addresses the physiological roles of B-MYB, the mechanisms underlying its oncogenic activation, and its contributions to tumorigenesis and clinical relevance as a prognostic biomarker and potential therapeutic target. Aberrant activation of B-MYB, driven by gene amplification, transcriptional upregulation, or post-translational modification, is reported as a recurrent feature of aggressive cancers. The consequences of B-MYB overexpression, including uncontrolled proliferation, genomic instability, apoptosis evasion, epithelial-to-mesenchymal transition, therapy resistance and metabolic reprogramming, further underscore B-MYB as a central oncogenic driver. Clinically, B-MYB overexpression correlates with poor prognosis, advanced disease and chemoresistance across multiple malignancies. Thus, we aim to emphasise the biological roles of B-MYB in physiological and cancer mechanisms, alongside the growing evidence establishing it as both a biomarker of disease and a potential therapeutic target. While previous reviews have addressed isolated aspects of B-MYB biology, this review provides a comprehensive and updated integration of recent mechanistic advances (A-MYB/B-MYB functional redundancy and YAP/TAZ-TEAD crosstalk) and the therapeutic potential of non-canonical DNA structures at the B-MYB promoter. We further review current trends and methodologies for targeting B-MYB and outline new perspectives for future therapeutic research.

Humans