Molecular and Cellular Biology最新文献

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by neuronal cell death, brain atrophy, and cognitive decline. Aggregation of Tau protein in neurons is a critical factor in the pathogenesis of AD. Tau aggregates increase as the disease progresses and contribute to neuronal cell death. This study investigated the role of ubiquitin-specific protease 10 (USP10) in Tau pathology and neuronal viability in AD. We found that the expression of USP10 was reduced in the brains of late-stage AD patients with severe Tau aggregate accumulation, which correlated with increased neuronal apoptosis. Mechanistically, our results suggest that USP10 downregulation in late-stage AD may be due to its degradation by the accumulation of p62, an inducer of selective autophagy. Brain-specific Usp10 knockout mice show increased neuronal apoptosis during embryonic development and postnatal brain atrophy. In the P301S-Tau transgenic mice, heterozygous Usp10 knockout lowered Tau levels and slightly improved early survival, suggesting USP10 has stage-dependent effects: its reduction lessens Tau burden early but worsens neuronal loss in late stage. This study identifies USP10 as a key regulator of Tau pathology and neuronal survival in AD.

During genotoxic stress, mammalian cells adapt to resume transcription after repair of damaged DNA. However, mechanisms of these adaptations leading to optimal transcriptional restart are poorly known. In this study, we show critical role of EAF1-mediated enhanced phase separation of elongation factor ELL in its interaction with DNA repair factors for efficient repair of damaged DNA and subsequent transcriptional restart. ELL protein has intrinsic ability to phase separate and form liquid condensates both in vitro and in vivo within mammalian cells. Upon association with EAF1, intrinsic phase separation ability of ELL is enhanced resulting in changes in material property of ELL●EAF1 condensates. Physiologically, upon exposure to genotoxic stress, ATM-mediated phosphorylation-dependent increased EAF1 binding leads to enhanced phase separation and changes the material property of ELL. This, in turn, causes its increased interaction with DNA-PKc and associated Ku complex components. This increased interaction is important for their optimal recruitment on chromatin and corresponding repair of damaged DNA and transcriptional restart. An EAF1 knockdown or ELL mutant that fails to show its enhanced interaction with EAF1 during DNA damage, also fails to show efficient DNA damage repair, transcriptional restart and cell survival after exposure to genotoxic stress.

Shc family adaptor proteins are involved in diverse signaling pathways that regulate critical cellular functions, including proliferation, differentiation, migration, and survival. ShcD is the most recently isolated member and while previous studies have identified its prominent expression in the brain, specifically within the olfactory bulb, its physiological functions remain largely unknown. Here we report initial characterization of ShcD knockout (ShcD^KO) mice and identify structural, behavioral, and biochemical deficits associated with ShcD deletion. Specifically, ShcD^KO mice have decreased olfactory bulb weight with a corresponding reduced granule cell layer compared to controls, and defects in olfactory performance. Intriguingly, ShcD^KO mice display increased proliferation in the subventricular zone, which serves as the reservoir for neural progenitors migrating into the olfactory bulb. Supporting these cellular changes, we noted Erk2 hyperactivation in the olfactory bulb of ShcD^KO mice, and using a cultured neuron model, we also detected altered signaling of Erk5, a MAPK protein associated with neural stem cell differentiation, as well as increased p66ShcA expression, indicating a potential compensatory mechanism within the Shc family. These results uncover a possible physiological role for ShcD in neurogenesis and imply its involvement in signaling pathways that regulate stem cell maintenance and/or differentiation.

Mitochondria rely on the coordinated function of over 1000 proteins, most of which are nuclear-encoded, synthesized in the cytosol, and imported into distinct mitochondrial sub-compartments. Thirteen additional proteins are synthesized within the organelle itself, forming core components of the oxidative phosphorylation (OXPHOS) system. Once inside, mitochondrial precursors undergo precise maturation, folding, and assembly, supported by specialized factors that ensure their function. These processes are safeguarded by an intricate network of chaperones, proteases, and disaggregases that maintain proteome integrity. Protein biogenesis and quality control are deeply interconnected, operating continuously to preserve mitochondrial function. Disruption at any stage, whether in import, folding, assembly, or degradation, can lead to proteotoxic stress and mitochondrial dysfunction, underlying a wide spectrum of mitochondrial diseases. Despite progress in characterizing many of these pathways in human cells, large gaps in knowledge remain. A complete understanding of protein biogenesis and surveillance mechanisms is essential to uncover how their dysregulation drives disease. This knowledge will be foundational for interpreting pathogenic mutations, predicting disease mechanisms, and ultimately guiding therapeutic strategies aimed at restoring mitochondrial proteostasis and health.

Rho GTPases are Ras-like proteins that contribute to many aspects of human cancer. However, unlike Ras, Rho proteins are not often mutagenically activated in cancers, but require activation by upstream proteins known as Rho GDP exchange factors (RhoGEFs). The neuroepithelial transforming gene 1 (Net1) is a RhoA/RhoB-specific GEF that is overexpressed in many cancers, and high levels of Net1 protein expression often correlate with reduced disease-free and overall survival. Net1 promotes multiple phenotypes in cancer cells, including cell motility, invasion, and proliferation. It does so by regulating diverse signaling pathways that ultimately control actin cytoskeletal organization, transcription, DNA damage signaling, and mitosis. In tumors, Net1 is required for tumor cell proliferation, tumor angiogenesis, and distant metastasis. In this review we will delineate the evidence supporting a role for Net1 in tumor progression, and describe mechanisms that regulate Net1 expression and cellular activity.

Cellular senescence has a dual role in both tumor suppression and the promotion of age-related diseases. This paradox suggests the existence of functionally distinct "beneficial" and "detrimental" senescent states, yet the molecular basis that governs their fate has remained elusive. Here, we reveal that the dynamic exchange of histone H2AX on chromatin functions as an essential quality control mechanism that dictates the quality of senescence. We demonstrate that the histone acetyltransferase TIP60, in complex with the chaperone FACT, acetylates H2AX at lysine 5 (K5), which in turn drives its dynamic exchange. This histone exchange is indispensable for promoting the degradation of the DNA damage response mediator MDC1, a process we uncover is mediated by a novel DNA-PKcs-p97 signaling axis. Disruption of this TIP60-FACT-H2AX exchange pathway leads to the hyperaccumulation of MDC1 and a shift toward error-prone nonhomologous end joining (NHEJ), inducing a pathological senescent state with oncogenic potential. Our study redefines histone exchange from a passive chromatin event to an active regulatory hub that determines the fate of aging cells. These findings provide a molecular basis for the heterogeneity of senescence and establish a rationale for developing "senomorphic" therapies aimed at improving the quality of aging.

Regulation of gene expression at the messenger RNA (mRNA) level is crucial for organisms to rapidly respond to changing environmental conditions, especially harmful toxins. The highly conserved nonsense-mediated mRNA decay (NMD) pathway is a translation dependent messenger RNA (mRNA) degradation pathway. Although NMD is well known for targeting mRNAs with premature termination codons (PTCs), it is now recognized as a pathway with additional essential regulatory functions. Notably, NMD precisely regulates protein coding natural mRNAs, hence controlling gene expression within several physiologically significant pathways. Pathways controlled by NMD include essential bio-metal homeostasis and metal ion detoxification, and the crosstalk between them. Here, we discuss the relationships between NMD and various metal ion detoxification pathways. We review the role that the NMD pathway plays in cadmium, arsenic, and lithium detoxification.

Transposable elements (TEs) are indispensable components of eukaryotic genomes, mechanistically linked to carcinogenesis, aging and other degenerative diseases. The ability of TEs to self-propagate and cause deletions, inversions or insertions within the genome poses a real threat to the fidelity of genomic integrity. This review discusses the fundamental properties of TEs, with a focus on cellular interactions associated with mechanisms involved in recombination, replication, and DNA repair. Since mobilization of TEs induces double-strand breaks (DSBs), faulty repair mechanisms could lead to cellular dysfunction, pathology and death. The TE-induced DNA DSB repair cascade follows either homologous recombination (HR) or non-homologous end-joining (NHEJ) pathways. Importantly, epigenetic regulatory mechanisms including DNA methylation and histone acetylation provide additional control in ensuring accurate DNA repair and could prove to be key targets for therapeutic intervention.

Cholesterol trafficking from the endoplasmic reticulum (ER) through the mitochondria-associated ER membrane (MAM) and finally to mitochondria is essential for mammalian survival. ER lipid raft-associated protein 2 (ERLIN2) scaffolds raft-like microdomains in the trans-Golgi network, endosomes, and plasma membrane. We found that ERLIN2 assists in rolling cholesterol trafficking-associated lipid vesicles by facilitating the intermediate folding of cholesterol trafficker steroidogenic acute regulatory protein (StAR) from the ER to MAM prior to delivery to the outer mitochondrial membrane. Each ERLIN2-StAR interaction is short. The absence of ERLIN2 ablates mitochondrial cholesterol transport. Over time, StAR association with ERLIN2 increases from the ER to MAM, thereby enhancing mitochondrial cholesterol transport. Thus, ERLIN2 is central for regulating mitochondrial cholesterol trafficking required for mitochondrial steroid metabolism.

The concentration of cellular labile pool of copper must be strictly regulated because disruption in copper homeostasis results in diseases. In Saccharomyces cerevisiae, elevated levels of labile copper impair cell viability by inhibiting Sec61-mediated protein translocation into the endoplasmic reticulum. We investigated how metabolic pathways, specifically mitochondrial respiration and autophagy, contribute to copper homeostasis and the translocation of secretory proteins. We show that copper selectively inhibits protein translocation in yeast cells grown in minimal medium but not in a rich medium, highlighting a critical role of nutrients in modulating copper toxicity. Supplementation of specific amino acids suppresses the copper-induced defects in protein translocation and cell death, identifying amino acids as suppressors of the copper toxicity. Using a panel of gene deletion mutants affecting mitochondrial functions, autophagy, peroxisomes, and lipid droplets, we demonstrate that metabolic pathways regulate subcellular concentration of copper and translocation of secretory proteins. Further, disruption of redox and pH homeostasis, and pharmacological inhibition of respiration, reveals that correct subcellular concentration of copper is essential to prevent inhibitory effects on protein translocation. Together, our findings provide mechanistic insights into how metabolic status influences cellular copper homeostasis and the secretory pathway of proteins, with broader implications for understanding diseases of copper metabolism.