BAP1 and HMGB1 alterations are implicated in the pathogenesis of mesothelioma, an aggressive cancer of the membranes covering the thoracic and abdominal cavities. Genetic inactivating mutations of BAP1 cause cancer in ~100% of carriers. The mechanism/s that regulate BAP1 expression were unknown. We discovered that HMGB1 directly modulates BAP1 expression. Studying our Hmgb1 knock-out mouse mesothelioma models, primary fibroblasts obtained from carriers of pathogenic heterozygous germline BAP1 mutations, and mesothelioma cell lines, we discovered that HMGB1 loss caused a significant reduction in BAP1 expression and protein levels, whereas HMGB1 overexpression increased BAP1 mRNA and protein levels. We demonstrated that HMGB1 binds to the BAP1 promoter and activates its transcription, leading to BAP1 overexpression, which in turn promoted the proliferation, migration, and invasion of mesothelioma cells. These findings were confirmed in lung, colon, and cholangiocarcinoma cell lines. These findings indicate that while BAP1 inactivating mutations promote cancer development, cancer cells that do not express BAP1 are less aggressive, pointing to the HMGB1-BAP1 axis as a novel attractive target for therapy. Furthermore, our discovery that HMGB1-driven BAP1 overexpression supports cancer growth provides a mechanistic rationale for the improved survival observed in mesothelioma patients with somatic BAP1 inactivating mutations.
Ferroptosis contributes to osteoarthritis (OA), but the upstream mechanisms connecting cytoskeletal stress, mitochondrial quality control, and antioxidant defense remain unclear. We investigated whether four-and-a-half LIM domain protein 2 (Fhl2) couples microtubule remodeling to chondrocyte ferroptosis. Public bulk and single-cell transcriptomes were integrated with RNA sequencing (RNA-seq) from RSL3-treated chondrocytes to nominate ferroptosis regulators in OA. Fhl2 was validated in human cartilage, destabilization of the medial meniscus (DMM) mouse cartilage, and interleukin-1 beta (IL-1β)- or RSL3-treated primary murine chondrocytes. Lentiviral Fhl2 knockdown, microtubule imaging, mitochondria-lysosome co-localization, mitophagy marker analysis, paclitaxel/nocodazole perturbation, intra-articular sh-Fhl2 delivery, and cartilage-specific nuclear factor erythroid 2-related factor 2 (Nrf2) conditional knockout were used to define mechanism and in vivo relevance. Fhl2 emerged as a shared hub across OA bulk signatures, chondrocyte states prone to ferroptosis, and the RSL3-induced ferroptosis program, and was elevated in human OA cartilage, DMM cartilage, and stressed chondrocytes. Fhl2 upregulation accompanied microtubule disorganization, impaired mitophagic flux, translocase of outer mitochondrial membrane 20 (TOMM20)/p62/microtubule-associated protein 1 light chain 3 beta (LC3B) accumulation, mitochondrial retention, reactive oxygen species (ROS) production, and lipid peroxidation. Fhl2 knockdown preserved microtubules, improved mitochondria-lysosome coupling, reduced ferroptotic injury, attenuated cartilage degeneration after DMM, improved gait parameters, and restored Nrf2/glutathione peroxidase 4 (GPX4) signaling. Nrf2 deficiency was associated with matrix catabolism and a ferroptosis-prone cartilage phenotype after DMM. Fhl2 promotes chondrocyte ferroptosis in OA by linking impaired microtubule-dependent mitophagic flux to mitochondrial retention and antioxidant failure. Targeting the link between Fhl2, cytoskeletal integrity, and mitochondrial quality control may help limit cartilage degeneration driven by ferroptosis.
Cisplatin-based chemotherapy remains a standard treatment for advanced bladder cancer (BCa), however, the development of chemoresistance substantially compromises its clinical efficacy and patient prognosis. In this study, we investigated the functional role of NEK8 in cisplatin resistance in BCa and elucidated its underlying molecular mechanisms. We found that NEK8 was significantly upregulated in cisplatin-resistant BCa and was associated with unfavorable prognosis. Functional studies demonstrated that NEK8 promoted cisplatin resistance and tumor progression both in vitro and in vivo. Mechanistically, NEK8 directly interacted with ALYREF and promoted its phosphorylation and subsequent nuclear translocation. Nuclear ALYREF recognized m5C-modified CDK18 mRNA and enhanced its stability, resulting in increased CDK18 expression. Elevated CDK18 facilitated DNA damage repair, ultimately driving cisplatin resistance in BCa. Collectively, we identified a NEK8-mediated mechanism in which ALYREF phosphorylation and nuclear translocation enhance CDK18 mRNA stability and DNA damage repair, thereby driving cisplatin resistance in BCa.
Resistance to next-generation androgen receptor antagonists represents a major clinical challenge in prostate cancer (PCa), underscoring the need to define its underlying mechanisms. Here, through an integrated analysis of multiple cohorts, we identify PABPC1 as an RNA-binding protein upregulated in therapy-resistant tumors, whose expression correlates with adverse clinicopathological features. Elevated PABPC1 confers enzalutamide (Enz) resistance by suppressing tumor-cell ferroptosis and CD8+ T-cell cytotoxicity. Mechanistically, PABPC1 promotes the cytoplasmic colocalization of EIF4A1 with ATF4 mRNA and enhances EIF4A1-associated translation of ATF4 mRNA. Subsequently, ATF4 binds the BCAT1 promoter and transcriptionally upregulates BCAT1, thereby promoting branched-chain amino acid (BCAA) metabolic remodeling and ferroptosis resistance, with leucine emerging as a major functional contributor to both ferroptosis regulation and CD8+ T-cell effector responses. In preclinical models, ixazomib restores ferroptotic vulnerability, reinvigorates T-cell activity, and synergizes with Enz, without overt histopathological abnormalities in major organs. These results identify the PABPC1-ATF4-BCAT1 axis as a key regulatory pathway linking RNA regulation with metabolic and immune reprogramming to facilitate treatment resistance in PCa.
Premortem exposure of calreticulin (CALR) on stressed cancer cells is a cardinal damage-associated molecular pattern that licenses anticancer immunity, yet its immunological sufficiency has remained difficult to define because it normally coincides with cellular stress and cell death. Here, we engineered a chemical-genetic system enabling the conditional, biotin-driven translocation of a membrane-anchored CALR chimera from the endoplasmic reticulum to the plasma membrane, thereby uncoupling CALR exposure from cytotoxicity and other hallmarks of immunogenic cell death. This reductionist approach revealed that isolated CALR surface presentation is sufficient to promote CD91/LRP1-dependent engulfment of tumor cells by conventional dendritic cells, particularly cDC1 and cDC2, leading to enhanced dendritic cell activation, cytotoxic lymphocyte responses, and immunological memory. Across multiple syngeneic tumor models, enforced CALR exposure exerted modest standalone antitumor activity but robustly sensitized poorly immunogenic cancers to cisplatin and PD-1 blockade, culminating in T cell-dependent tumor eradication and durable protective immunity. Remarkably, concurrent inhibition of the CD47–SIRPα axis facilitated complete tumor eradication in all treated animals, highlighting the functional cooperation between eat-me and don’t-eat-me signals in orchestrating antigen presentation and adaptive immune priming. These findings further suggest that maximizing the therapeutic activity of CD47 blockade may require concomitant reinforcement of pro-phagocytic signals such as CALR exposure, providing a conceptual framework for the rational design of next-generation combination immunotherapies. Collectively, these findings establish surface-exposed CALR as a cell-autonomous immunogenic signal with instructive activity for dendritic cell-mediated cross-priming and provide a tractable platform to mechanistically deconvolute immunogenic stress responses, with immediate implications for the rational design of combinatorial chemo- and immunotherapeutic regimens in preclinical and potentially clinical oncology.
