Mitochondrial outer membrane permeabilisation (MOMP) is often essential for apoptosis, by enabling cytochrome c release that leads to caspase activation and rapid cell death. Recently, MOMP has been shown to be inherently pro-inflammatory with emerging cellular roles, including its ability to elicit anti-tumour immunity. Nonetheless, how MOMP triggers inflammation and how the cell regulates this remains poorly defined. We find that upon MOMP, many proteins localised either to inner or outer mitochondrial membranes are ubiquitylated in a promiscuous manner. This extensive ubiquitylation serves to recruit the essential adaptor molecule NEMO, leading to the activation of pro-inflammatory NF-κB signalling. We show that disruption of mitochondrial outer membrane integrity through different means leads to the engagement of a similar pro-inflammatory signalling platform. Therefore, mitochondrial integrity directly controls inflammation, such that permeabilised mitochondria initiate NF-κB signalling.
© 2024. The Author(s).

Medulloblastoma is the most common malignant paediatric brain tumour, representing 20% of all paediatric intercranial tumours. Current aggressive treatment protocols and the use of radiation therapy in particular are associated with high levels of toxicity and significant adverse effects, and long-term sequelae can be severe. Therefore, improving chemotherapy efficacy could reduce the current reliance on radiation therapy. Here, we demonstrated that systems-level analysis of basal apoptosis protein expression and their signalling interactions can differentiate between medulloblastoma cell lines that undergo apoptosis in response to chemotherapy, and those that do not. Combining computational predictions with experimental BH3 profiling, we identified a therapeutically-exploitable dependence of medulloblastoma cells on BCL-XL, and experimentally validated that BCL-XL targeting, and not targeting of BCL-2 or MCL-1, can potentiate cisplatin-induced cytotoxicity in medulloblastoma cell lines with low sensitivity to cisplatin treatment. Finally, we identified MCL-1 as an anti-apoptotic mediator whose targeting is required for BCL-XL inhibitor-induced apoptosis. Collectively, our study identifies that BCL-XL and MCL-1 are the key anti-apoptotic proteins in medulloblastoma, which mediate distinct protective roles. While BCL-XL has a first-line role in protecting cells from apoptosis basally, MCL-1 represents a second line of defence that compensates for BCL-XL upon its inhibition. We provide rationale for the further evaluation of BCL-XL and MCL-1 inhibitors in the treatment of medulloblastoma, and together with current efforts to improve the cancer-specificity of BCL-2 family inhibitors, these novel treatment strategies have the potential to improve the future clinical management of medulloblastoma.
© 2023. The Author(s).

Mitochondria are often essential for apoptosis through mitochondrial outer membrane permeabilization (MOMP). This central event enables cytochrome c release leading to caspase activation and rapid cell death. Recently, MOMP has been shown to be inherently pro-inflammatory, for instance, by enabling mitochondrial DNA-dependent activation of cGAS-STING signalling. Alongside having emerging functions in health and disease, MOMP associated inflammation can also elicit anti-tumour immunity. Nonetheless, how MOMP triggers inflammation and how the cell counteracts this remains poorly defined. We find that upon MOMP, mitochondria are ubiquitylated in a promiscuous manner targeting proteins localised to both inner and outer mitochondrial membranes. Mitochondrial ubiquitylation serves to recruit the essential adaptor molecule, NEMO, leading to activation of pro-inflammatory NF-κB signalling. We find that disruption of mitochondrial outer membrane integrity through different means leads to engagement of a similar pro-inflammatory signalling platform. Thus, mitochondrial integrity directly controls inflammation, such that permeabilised mitochondria initiate NF-κB signalling. This event may be important for the various pathophysiological functions of MOMP-associated inflammation.

The prognosis of patients with advanced renal cell carcinoma (RCC) has improved with newer therapies, including molecular-targeted therapies and immuno-oncology agents. Despite these therapeutic advances, many patients with metastatic disease remain uncured. Inhibition of glycogen synthase kinase-3β (GSK-3β) is a promising new therapeutic strategy for RCC; however, the precise regulatory mechanism has not yet been fully elucidated. MicroRNAs (miRNAs) act as post-translational regulators of target genes, and we investigated the potential regulation of miRNAs on GSK-3β in RCC. We selected nine candidate miRNAs from three databases that could potentially regulate GSK-3β. Among these, hsa-miR-4465 (miR-4465) was downregulated in RCC cell lines and renal cancer tissues. Furthermore, luciferase assays revealed that miR-4465 directly interacted with the 3' untranslated region of GSK-3β, and Western blot analysis showed that overexpression of miR-4465 significantly decreased GSK-3β protein expression. Functional assays showed that miR-4465 overexpression significantly suppressed cell invasion of A498 and Caki-1 cells; however, cell proliferation and migration were suppressed only in Caki-1 and A498 cells, respectively, with no effect on cell cycle and apoptosis. In conclusion, miR-4465 regulates GSK-3β expression but does not consistently affect RCC cell function as a single molecule. Further comprehensive investigation of regulatory networks is required in this field.

Obesity has been reported to promote disordered folliculogenesis, but the exact molecular mechanisms are still not fully understood. In this study, we find that miR-133a is involved in obesity-induced follicular development disorder. After feeding with a high-fat diet (HFD) and fructose water for nine weeks, the mouse body weight is significantly increased, accompanied by an inflammatory state and increased expression of miR-133a in the adipose tissues and ovaries as well as accelerated follicle depletion. Although miR-133a is increased in the fat and ovaries of HFD mice, the increased miR-133a in the HFD ovaries is not derived from exosome transferred from obese adipose tissues but is synthesized by ovarian follicular cells in response to HFD-induced inflammation. In vivo experiments show that intrabursal injection of miR-133a agomir induces a decrease in primordial follicles and an increase in antral follicles and atretic follicles, which is similar to HFD-induced abnormal folliculogenesis. Overexpression of miR-133a modestly promotes granulosa cell apoptosis by balancing the expression of anti-apoptotic proteins such as C1QL1 and XIAP and pro-apoptotic proteins such as PTEN. Overall, this study reveals the function of miR-133a in obesity-induced ovarian folliculogenesis dysfunction and sheds light on the etiology of female reproductive disorders.