The mitophagy receptor NIX induces vIRF-1 oligomerization and interaction with GABARAPL1 for the promotion of HHV-8 reactivation-induced mitophagy

Poly-l-arginine promotes ferroptosis in asthmatic airway epithelial cells by modulating PBX1/GABARAPL1 axis

Eosinophils play a featured role among inflammatory cells participating in the onset and development of asthma. Activated eosinophils release several cytotoxic granular proteins, such as major basic protein (MBP), posing a significant threat to airway epithelium. Ferroptosis, a novel form of cell death, is gaining recognition for its involvement in asthma pathogenesis, though the specific mechanisms remain largely unknown. Herein, we revealed that poly-l-arginine (PLA), an MBP mimic, induced ferroptosis in airway epithelium by downregulating γ-aminobutyric acid receptor-associated protein-like 1 (GABARAPL1). Reduced GABARAPL1 expression was further confirmed in ovalbumin (OVA)-induced asthma mice and PLA-treated human airway organoids (hAOs). Mechanistically, PLA activated mechanistic target of rapamycin complex 1 (mTORC1) signaling, inhibiting pre-B-cell leukemia transcription factor 1 (PBX1), which in turn leads to transcriptional downregulation of GABARAPL1. Furthermore, MBP extracted from eosinophils, similar to PLA, induced ferroptosis in airway epithelial cells, as well as modulating mTORC1/PBX1/GABARAPL1 pathway. Finally, Ferrostatin-1 treatment or GABARAPL1 overexpression alleviated ferroptosis and airway inflammation in asthmatic mice. Overall, our findings highlight the cell communication between eosinophils and airway epithelial cells. MBP modulates the mTORC1/PBX1/GABARAPL1 axis, thereby serving as a significant contributor to ferroptosis in airway epithelium and airway inflammation. This suggests that suppressing ferroptosis in airway epithelium or targeting eosinophils and MBP could lead to novel therapeutic strategies for asthma management.

Lactylation of NAT10 promotes N4-acetylcytidine modification on tRNASer-CGA-1-1 to boost oncogenic DNA virus KSHV reactivation

N4-acetylcytidine (ac4C), a conserved but recently rediscovered RNA modification on tRNAs, rRNAs and mRNAs, is catalyzed by N-acetyltransferase 10 (NAT10). Lysine acylation is a ubiquitous protein modification that controls protein functions. Our latest study demonstrates a NAT10-dependent ac4C modification, which occurs on the polyadenylated nuclear RNA (PAN) encoded by oncogenic DNA virus Kaposi's sarcoma-associated herpesvirus (KSHV), can induce KSHV reactivation from latency and activate inflammasome. However, it remains unclear whether a novel lysine acylation occurs in NAT10 during KSHV reactivation and how this acylation of NAT10 regulates tRNAs ac4C modification. Here, we showed that NAT10 was lactylated by α-tubulin acetyltransferase 1 (ATAT1), as a writer at the critical domain, to exert RNA acetyltransferase function and thus increase the ac4C level of tRNASer-CGA-1-1. Mutagenesis at the ac4C site in tRNASer-CGA-1-1 inhibited its ac4C modifications, translation efficiency of viral lytic genes, and virion production. Mechanistically, KSHV PAN orchestrated NAT10 and ATAT1 to enhance NAT10 lactylation, resulting in tRNASer-CGA-1-1 ac4C modification, eventually boosting KSHV reactivation. Our findings reveal a novel post-translational modification in NAT10, as well as expand the understanding about tRNA-related ac4C modification during KSHV replication, which may be exploited to design therapeutic strategies for KSHV-related diseases.

Dysfunction of astrocytic glycophagy exacerbates reperfusion injury in ischemic stroke

Glycophagy has evolved from an alternative glycogen degradation pathway into a multifaceted pivot to regulate cellular metabolic hemostasis in peripheral tissues. However, the pattern of glycophagy in the brain and its potential therapeutic impact on ischemic stroke remain unknown. Here, we observed that the dysfunction of astrocytic glycophagy was caused by the downregulation of the GABA type A receptor-associated protein like 1 (GABARAPL1) during reperfusion in ischemic stroke patients and mice. PI3K-Akt pathway activation is involved in driving GABARAPL1 downregulation during cerebral reperfusion. Moreover, glycophagy dysfunction-induced glucosamine deficiency suppresses the nuclear translocation of specificity protein 1 and TATA binding protein, the transcription factors for GABARAPL1, by decreasing their O-GlcNAcylation levels, and accordingly feedback inhibits GABARAPL1 in astrocytes during reperfusion. Restoring astrocytic glycophagy by overexpressing GABARAPL1 decreases DNA damage and oxidative injury in astrocytes and improves the survival of surrounding neurons during reperfusion. In addition, a hypocaloric diet in the acute phase after cerebral reperfusion can enhance astrocytic glycophagic flux and accelerate neurological recovery. In summary, glycophagy in the brain links autophagy, metabolism, and epigenetics together, and glycophagy dysfunction exacerbates reperfusion injury after ischemic stroke.

Identification of host proteins that interact with African swine fever virus pE301R

African swine fever virus (ASFV) infection poses enormous threats and challenges to the global pig industry; however, no effective vaccine is available against ASFV, attributing to the huge viral genome (approximately189 kb) and numerous encoding products (>150 genes) due to the limited understanding on the molecular mechanisms of viral pathogenesis. Elucidating the host-factor/viral-protein interaction network will reveal new targets for developing novel antiviral therapies. Using proteomic analysis, we identified 255 cellular proteins that interact with the ASFV-encoded pE301R protein when transiently expressed in HEK293T cells. Gene ontology (GO) annotation, Kyoto Encyclopedia of Genes and Genomes (KEGG) database enrichment, and protein-protein interaction (PPI) network analyses revealed that pE301R-interacting host proteins are potentially involved in various biological processes, including protein translation and folding, response to stimulation, and mitochondrial transmembrane transport. The interactions of two putative cellular proteins (apoptosis inducing factor mitochondria associated 1 (AIFM1) and vimentin (VIM)) with pE301R-apoptosis inducing factor have been verified by co-immunoprecipitation. Our study revealed the inhibitory role of pE301R in interferon (IFN) induction that involves VIM sequestration by pE301R, identified interactions between ASFV pE301R and cellular proteins, and predicted the potential function of pE301R and its associated biological processes, providing valuable information to enhance our understanding of viral protein function, pathogenesis, and potential candidates for the prevention and control of ASFV infection.

TUFM in health and disease: exploring its multifaceted roles

The nuclear-encoded mitochondrial protein Tu translation elongation factor, mitochondrial (TUFM) is well-known for its role in mitochondrial protein translation. Originally discovered in yeast, TUFM demonstrates significant evolutionary conservation from prokaryotes to eukaryotes. Dysregulation of TUFM has been associated with mitochondrial disorders. Although early hypothesis suggests that TUFM is localized within mitochondria, recent studies identify its presence in the cytoplasm, with this subcellular distribution being linked to distinct functions of TUFM. Significantly, in addition to its established function in mitochondrial protein quality control, recent research indicates a broader involvement of TUFM in the regulation of programmed cell death processes (e.g., autophagy, apoptosis, necroptosis, and pyroptosis) and its diverse roles in viral infection, cancer, and other disease conditions. This review seeks to offer a current summary of TUFM's biological functions and its complex regulatory mechanisms in human health and disease. Insight into these intricate pathways controlled by TUFM may lead to the potential development of targeted therapies for a range of human diseases.

Herpesvirus lytic infection-induced mitophagy via viral interferon regulatory factor 1

Viral control of mitochondria via mitophagy has a dampening effect on mitochondrion-mediated innate immune responses. We previously found that human herpesvirus 8 (HHV-8) could activate mitophagy via its lytic gene product vIRF-1 (viral interferon regulatory factor 1). Mechanistically, we previously demonstrated that vIRF-1 interacts with the mitophagic proteins BNIP3L (BCL2 interacting protein 3 like) and TUFM (Tu translation elongation factor, mitochondrial). Despite these significant findings, however, the precise molecular mechanisms underlying vIRF-1-activated mitophagy, particularly with core components of the autophagy machinery, remained to be fully elucidated. We recently reported that vIRF-1 binds preferentially and directly to GABARAPL1 (GABA type A receptor associated protein like 1) in a noncanonical manner, and this interaction is essential for virus-productive replication. Furthermore, we found that BNIP3L is a crucial factor that promotes vIRF-1 oligomerization and associated mitophagy activation, including GABARAPL1 interaction with vIRF-1 and TUFM dimerization. Together, our findings deepen our understanding of lytic infection-induced mitophagy and provide the key protein-protein interactions involved in vIRF-1-mediated mitophagy.

NAT10-dependent N4-acetylcytidine modification mediates PAN RNA stability, KSHV reactivation, and IFI16-related inflammasome activation

N-acetyltransferase 10 (NAT10) is an N4-acetylcytidine (ac4C) writer that catalyzes RNA acetylation at cytidine N4 position on tRNAs, rRNAs and mRNAs. Recently, NAT10 and the associated ac4C have been reported to increase the stability of HIV-1 transcripts. Here, we show that NAT10 catalyzes ac4C addition to the polyadenylated nuclear RNA (PAN), a long non-coding RNA encoded by the oncogenic DNA virus Kaposi's sarcoma-associated herpesvirus (KSHV), triggering viral lytic reactivation from latency. Mutagenesis of ac4C sites in PAN RNA in the context of KSHV infection abolishes PAN ac4C modifications, downregulates the expression of viral lytic genes and reduces virion production. NAT10 knockdown or mutagenesis erases ac4C modifications of PAN RNA and increases its instability, and prevents KSHV reactivation. Furthermore, PAN ac4C modification promotes NAT10 recruitment of IFN-γ-inducible protein-16 (IFI16) mRNA, resulting in its ac4C acetylation, mRNA stability and translation, and eventual inflammasome activation. These results reveal a novel mechanism of viral and host ac4C modifications and the associated complexes as a critical switch of KSHV replication and antiviral immunity.