Background/Objectives: Long non-coding RNAs (lncRNAs) are integral to the regulation of viral tumorigenesis. We have previously identified that the chicken lncRNA-803, which responds to Marek’s disease virus (MDV), inhibits apoptosis in the chicken embryonic fibroblast cell line DF-1, accompanied by changes in the expression of the p53 protein. Nonetheless, the molecular mechanism of lncRNA-803 in apoptosis has yet to be elucidated. Methods: In this study, through lentivirus-mediated overexpression and knockdown experiments, we determined that the overexpression of lncRNA-803 induces elevated expression levels of murine double minute 2 (MDM2), murine double minute 4 (MDM4), tumor protein p53 (p53), and tumor protein p53 binding protein 1 (TP53BP1) within the p53 signaling pathway. Results: This modulation subsequently leads to an upregulation of B-cell lymphoma-2 (Bcl-2) expression, while concurrently resulting in the downregulation of cysteinyl aspartate specific proteinase 8 (Caspase-8), cysteinyl aspartate specific proteinase 9 (Caspase-9), Bcl-2 associated protein X (Bax), and cysteinyl aspartate specific proteinase 9 (Caspase-3) in the apoptosis pathway. In terms of its mechanism, lncRNA-803 functions as a molecular sponge for miR-6555-3p. lncRNA-803 engages in competitive binding with miR-6555-3p, thereby diminishing its inhibitory effect on MDM4. Conclusions: These results elucidate that lncRNA-803 modulates apoptosis in DF-1 cells through a novel competing endogenous RNA mechanism involving the miR-6555-3p/MDM4/p53 axis. These findings provide new insights into the molecular pathogenesis of MDV.

The oncogenic Marek’s disease virus (MDV) triggers Marek’s disease (MD), which is a substantial threat to poultry as it transforms infected T cells into tumors. Our research identified that long non-coding RNA 9802 (lncRNA-9802) exhibits increased expression in the chicken spleen following MDV infection, with its expression being strongly associated with the expression of tumor p53-binding protein 1 (TP53BP1). The function of lncRNA-9802 in T cells transformed by MDV remains unclear. Consequently, the expression levels of lncRNA-9802 were either over-expressed or knocked down in MDV-transformed T cells, MDCC-MSB1, through lentivirus-mediated over-expression and knock down experiments. Our findings demonstrate that lncRNA-9802 induces proliferation disturbances in MDCC-MSB1 cells by causing arrest in the S phase, which is accompanied by increased expression levels of TP53BP1, p53, and p21. Activation of the p53 pathway results in elevated levels of Cyclin E and Cyclin-dependent kinase 2 (CDK2), thereby facilitating the entry of MDCC-MSB1 cells into the S phase. Concurrently, the reduced levels of Cyclin A inhibit the exit of MDCC-MSB1 cells from the S phase. By modulating the TP53BP1/p53/p21 pathway, lncRNA-9802 induces S phase arrest in MDCC-MSB1 cells, characterized by upregulation of Cyclin E and CDK2 and downregulation of Cyclin A. This research enhances the understanding of the pathogenic mechanisms of MDV and provides a foundation for identifying potential targets for antiviral drug development.

Germline loss-of-function mutations in BRCA1 and BRCA2 markedly increase susceptibility to breast, ovarian, and other cancers. Mechanistically, BRCA2 facilitates RAD51 recruitment to sites of DNA damage, whereas BRCA1 regulates homologous recombination repair (HRR) through double-strand break resection and broader DNA damage response signaling. These insights underpin targeted therapies such as poly (ADP-ribose) polymerase inhibitors (PARPis), which induce synthetic lethality in homologous recombination-deficient tumors. Clinically, PARPis have demonstrated significant benefit in BRCA1/2-mutated breast, ovarian, pancreatic, and prostate cancers. However, resistance remains a major obstacle, with secondary intragenic BRCA1/2 mutations restoring partial protein function representing a prominent mechanism. Despite therapeutic advances, critical gaps persist in understanding how specific BRCA1/2 domains and residual protein activities contribute to tumorigenesis and treatment response. In this review, we summarize the structural and functional domains of BRCA1/2, their pathogenic mutation profiles, and therapeutic strategies targeting BRCA1/2-deficient cancers. Despite therapeutic advances, critical gaps persist in understanding how specific BRCA1/2 domains and residual protein activities contribute to tumorigenesis and treatment response. This review emphasizes the need for functional studies of BRCA1/2 variants to refine risk prediction and develop mutation-tailored therapies.