Mitofusin-2 (MFN2) is a dynamin-like GTPase that plays a central role in regulating mitochondrial fusion and cell metabolism. Mutations in MFN2 cause the neurodegenerative disease Charcot-Marie-Tooth type 2A (CMT2A). The molecular basis underlying the physiological and pathological relevance of MFN2 is unclear. Here, we present crystal structures of truncated human MFN2 in different nucleotide-loading states. Unlike other dynamin superfamily members including MFN1, MFN2 forms sustained dimers even after GTP hydrolysis via the GTPase domain (G) interface, which accounts for its high membrane-tethering efficiency. The biochemical discrepancy between human MFN2 and MFN1 largely derives from a primate-only single amino acid variance. MFN2 and MFN1 can form heterodimers via the G interface in a nucleotide-dependent manner. CMT2A-related mutations, mapping to different functional zones of MFN2, lead to changes in GTP hydrolysis and homo/hetero-association ability. Our study provides fundamental insight into how mitofusins mediate mitochondrial fusion and the ways their disruptions cause disease.

This protocol is described in detail in Supplemental Experimental Procedures. RNA Sequencing (RNA-Seq) and Analysis This protocol is described in detail in Supplemental Experimental Procedures. The RNA-seq data have been deposited in the NCBI Gene Expression Omnibus (GEO) under the Accession Code GSE110523. Real-Time RT-qPCR and Immunoblotting This protocol is described in detail in Supplemental Experimental Procedures.

Inactive von Hippel-Lindau (VHL) is linked to metabolic reprogramming and plays pivotal roles in the pathogenesis of clear cell renal cell carcinoma (ccRCC). Here, we identify a previously unknown oncogenic role for inactive VHL in actively triggering histone lactylation to promote ccRCC progression. In patients with ccRCC, inactive VHL positively correlates with the presence of histone lactylation, and high levels of histone lactylation indicates poor patient prognosis. Inactive VHL-triggered histone lactylation contributes to ccRCC progression by activating the transcription of platelet-derived growth factor receptor β (PDGFRβ). In turn, PDGFRβ signaling is shown to stimulate histone lactylation, thereby forming an oncogenic positive feedback loop in ccRCC. Target correction of aberrant histone lactylation represses the growth and metastasis of ccRCC in vivo. More importantly, the combined inhibition of histone lactylation and PDGFRβ significantly reinforces the therapeutic efficacy. This work underscores the importance of histone lactylation in facilitating ccRCC progression and suggests targeting the positive feedback loop between histone lactylation and PDGFRβ signaling might provide a promising therapeutic strategy for ccRCC patients.

Systematic analysis of tumor‐infiltrating lymphocytes is essential for the development of new cancer treatments and the prediction of clinical responses to immunotherapy. Immunomodulatory drugs are used for the treatment of oral squamous cell carcinoma (OSCC), depending on immune infiltration profiles of the tumor microenvironment. In this study, we isolated 11,866 single T cells from tumors and paired adjacent normal tissues of three patients with OSCC. Using single‐cell RNA sequencing, we identified 14 distinct T‐cell subpopulations within the tumors and 5 T‐cell subpopulations in the adjacent normal tissues and delineated their developmental trajectories. Exhausted CD8+ T cells and regulatory CD4+ T cells (CD4+ Tregs) were enriched in OSCC tumors, potentially linked to tumor immunosuppression. Programmed death protein 1 (PD‐1) and cytotoxic T lymphocyte‐associated protein 4 (CTLA4) were identified as marker genes in exhausted CD8+ T cells, whereas forkhead box P3 (FOXP3) and CTLA4 were identified as markers of CD4+ Tregs. Furthermore, our data revealed that thymocyte selection‐associated high‐mobility group box (TOX) may be a key regulator of T‐cell dysfunction in the OSCC microenvironment. Overexpression of TOX upregulated expression of genes related to T‐cell dysfunction. In vitro experiments demonstrated that cytotoxic activity and proliferation efficiency of CD8+ T cells overexpressing PD‐1 or TOX were reduced. Notable, the transcription factor PRDM1 was found to transactivate TOX expression via a binding motif in the TOX promoter. Our findings provide valuable insight into the functional states and heterogeneity of T‐cell populations in OSCC that could advance the development of novel therapeutic strategies.

Background Clear cell renal cell carcinoma (ccRCC) is the most lethal renal cancer. An overwhelming increase of patients experience tumor progression and unfavorable prognosis. However, the molecular events underlying ccRCC tumorigenesis and metastasis remain unclear. Therefore, uncovering the underlying mechanisms will pave the way for developing novel therapeutic targets for ccRCC. In this study, we sought to investigate the role of mitofusin‐2 (MFN2) in supressing ccRCC tumorigenesis and metastasis. Methods The expression pattern and clinical significance of MFN2 in ccRCC were analyzed by using the Cancer Genome Atlas datasets and samples from our independent ccRCC cohort. Both in vitro and in vivo experiments, including cell proliferation, xenograft mouse models and transgenic mouse model, were used to determine the role of MFN2 in regulating the malignant behaviors of ccRCC. RNA‐sequencing, mass spectrum analysis, co‐immunoprecipitation, bio‐layer interferometry and immunofluorescence were employed to elucidate the molecular mechanisms for the tumor‐supressing role of MFN2. Results we reported a tumor‐suppressing pathway in ccRCC, characterized by mitochondria‐dependent inactivation of epidermal growth factor receptor (EGFR) signaling. This process was mediated by the outer mitochondrial membrane (OMM) protein MFN2. MFN2 was down‐regulated in ccRCC and associated with favorable prognosis of ccRCC patients. in vivo and in vitro assays demonstrated that MFN2 inhibited ccRCC tumor growth and metastasis by suppressing the EGFR signaling pathway. In a kidney‐specific knockout mouse model, loss of MFN2 led to EGFR pathway activation and malignant lesions in kidney. Mechanistically, MFN2 preferably binded small GTPase Rab21 in its GTP‐loading form, which was colocalized with endocytosed EGFR in ccRCC cells. Through this EGFR‐Rab21‐MFN2 interaction, endocytosed EGFR was docked to mitochondria and subsequently dephosphorylated by the OMM‐residing tyrosine‐protein phosphatase receptor type J (PTPRJ). Conclusions Our findings uncover an important non‐canonical mitochondria‐dependent pathway regulating EGFR signaling by the Rab21‐MFN2‐PTPRJ axis, which contributes to the development of novel therapeutic strategies for ccRCC.