Oxygen-sensitive methylation of ULK1 is required for hypoxia-induced autophagy

Oxidative stress-induced CDO1 glutathionylation regulates cysteine metabolism and sustains redox homeostasis under ionizing radiation

Oxidative stress serves as a fundamental mechanism contributing to ionizing radiation-induced damage, which has significant implications for tissue injury. Cysteine dioxygenase type 1 (CDO1) catalyzes the rate-limiting step for cysteine oxidation pathway, thereby playing a crucial role in regulating cellular cysteine availability. However, the regulation of CDO1 activity and cysteine oxidation under ionizing radiation, as well as their subsequent effects on cell viability, remains largely unexplored. In this study, we provide evidence that CDO1 activity and cysteine oxidation are inhibited following radiation exposure. Mechanistically, ionizing radiation-induced oxidative stress triggers glutathionylation of CDO1 at cysteine (C) 164, which impairs CDO1 enzymatic activity by disrupting its interaction with the substrate cysteine. Furthermore, glutathionylation at CDO1 C164 is essential for maintaining cellular redox homeostasis and supports cell viability under ionizing radiation. These findings reveal a novel mechanism through which redox modifications of CDO1 regulate cysteine metabolism and glutathione synthesis under oxidative stress, thereby underscoring its potential as a therapeutic target for addressing radiation-induced injuries.

CDO1 phosphorylation is required for IL-6-induced tumor cell proliferation through governing cysteine availability

Inflammatory pathways are often hijacked by cancer cells to favor their own proliferation and survival. Cysteine dioxygenase type 1 (CDO1), an iron-dependent thiol dioxygenase enzyme, catalyzes the rate-limiting step for cysteine oxidation, and so that functions as an important regulator of cellular cysteine availability. However, whether inflammatory environment affects CDO1 activity and cysteine oxidation and its potential impact on tumor growth remains substantially elusive. In the present study, we demonstrate that CDO1 activity and cysteine oxidation is inhibited upon IL-6 treatment, without noticeable alterations in CDO1 expression. Mechanistically, AKT1 phosphorylates CDO1 T89 under IL-6 treatment, which represses CDO1 enzymatic activity by disrupting iron incorporation. Further, AKT1-mediated CDO1 T89 phosphorylation is required for IL-6-elicited oral squamous cell carcinoma (OSCC) growth, and is associated with the progression of OSCC development. The present data discover a new mechanism by which AKT1-mediated CDO1 T89 phosphorylation governs cysteine oxidation to support OSCC growth, thereby highlighting its value as a potential anti-tumor target.

Exposure of Parental Zebrafish to Difenoconazole throughout Their Life Cycle May Lead to Developmental Toxicity in the F1 Generation through Epigenetic Changes in Gametes, Impaired Nutrient Supply from the Ovum, and Maternal Transfer of Difenoconazole

Difenoconazole is a widely used agricultural fungicide that has been frequently detected in aquatic environments. Given its stable presence in aquatic environments, long-term exposure of wild fish may pose a risk to offspring embryonic development. This study demonstrated that exposure of zebrafish to environmental concentrations of difenoconazole throughout their life cycle resulted in abnormal development of offspring embryos/larvae, including decreased heart rate, delayed hatching, increased malformation rate, shortened body length, and increased mortality. These changes were significantly correlated with the affected apoptosis, autophagy, energy metabolism and MAPK signaling pathways in F1 generation. This transgenerational toxic effect results from epigenetic alterations in gametes, impaired nutrient supply from the ovum, and maternal transfer of difenoconazole. After exposure to difenoconazole, the development of female fish offspring was affected more than that of male fish offspring, which was mainly caused by the impaired nutrient supply from the ovum and the maternal transfer of difenoconazole. Because this transgenerational developmental toxicity was observed at environmental levels, difenoconazole may pose a threat to the survival of wild larvae and therefore a risk to wild fish populations.

Unraveling the triad of hypoxia, cancer cell stemness, and drug resistance

In the domain of addressing cancer resistance, challenges such as limited effectiveness and treatment resistance remain persistent. Hypoxia is a key feature of solid tumors and is strongly associated with poor prognosis in cancer patients. Another significant portion of the development of acquired drug resistance is attributed to tumor stemness. Cancer stem cells (CSCs), a small tumor cell subset with self-renewal and proliferative abilities, are crucial for tumor initiation, metastasis, and intra-tumoral heterogeneity. Studies have shown a significant association between hypoxia and CSCs in the context of tumor resistance. Recent studies reveal a strong link between hypoxia and tumor stemness, which together promote tumor survival and progression during treatment. This review elucidates the interplay between hypoxia and CSCs, as well as their correlation with resistance to therapeutic drugs. Targeting pivotal genes associated with hypoxia and stemness holds promise for the development of novel therapeutics to combat tumor resistance.

Evolutionary Insights into Irisin/FNDC5: Roles in Aging and Disease from Drosophila to Mammals

The Irisin/FNDC5 protein family has emerged as a pivotal link between exercise and the prevention of age-associated diseases. Irisin is highly expressed during exercise from skeletal and cardiac muscle cells, playing a critical role in mediating systemic health benefits through its actions on various tissues. However, Irisin levels decline with age, correlating with a heightened incidence of diseases such as muscle weakness, cardiovascular disorders, and neurodegeneration. Notably, the administration of Irisin has shown significant potential in both preventing and treating these conditions. Recently, an Irisin/FNDC5 homolog was identified in an invertebrate Drosophila model, providing valuable insights into its conserved role in exercise physiology. Importantly, Irisin/FNDC5 has been demonstrated to regulate autophagy-a process essential for clearing excessive nutrients, toxic aggregates, and dysfunctional organelles-in both flies and mammals. Dysregulated autophagy is often implicated in age-related diseases, highlighting its relevance to Irisin/FNDC5's functions. These findings deepen our understanding of Irisin/FNDC5's roles and its potential as a therapeutic target for mitigating aging-related health decline. Further studies are needed to elucidate the precise mechanisms by which Irisin regulates autophagy and its broader impact on physiological aging and related diseases.

The Mechanism of Acupuncture Regulating Autophagy: Progress and Prospect

Autophagy plays a crucial role in the physiopathological mechanisms of diseases by regulating cellular functions and maintaining cellular homeostasis, which has garnered extensive attention from researchers worldwide. The holistic regulation and bidirectional regulation effects of acupuncture can modulate cellular autophagy, promoting or restoring the homeostasis of the body's internal environment to achieve therapeutic outcomes. This paper systematically reviews the research progress on the use of acupuncture for treating various diseases via the autophagy pathway, summarizes signal pathways related to acupuncture regulating autophagy, and analyzes the deficiencies present in the existing research. The review results indicate that the mechanism of action of acupuncture on autophagy dysfunction is reflected in the changes in LC3, Beclin1, p53, and autophagy-associated (ATG) protein expression, and regulates signaling pathways and key proteins or genes. The regulatory effect of acupuncture on autophagy capacity is bidirectional: it inhibits the abnormal activation of autophagy to prevent exacerbation of injury and reduce apoptosis, while also activating or enhancing autophagy to promote the elimination of inflammation and reduce oxidative stress. Further analysis suggests that the mechanisms of acupuncture regulating autophagy are insufficiently explored. Future research should prioritize the development of more appropriate animal models, analyzing the accuracy of relevant pathways and the specificity of indicators, exploring the synergistic effects among targets and signaling pathways, clarifying the regulatory mechanisms of acupuncture at various stages of autophagy, and evaluating the efficacy of acupuncture in autophagy modulating. This paper offers valuable insights into the regulation of autophagy by acupuncture.

Regulation of autophagy and cellular signaling through non-histone protein methylation

Autophagy is a highly conserved catabolic pathway that is precisely regulated and plays a significant role in maintaining cellular metabolic balance and intracellular homeostasis. Abnormal autophagy is directly linked to the development of various diseases, particularly immune disorders, neurodegenerative conditions, and tumors. The precise regulation of proteins is crucial for proper cellular function, and post-translational modifications (PTMs) are key epigenetic mechanisms in the regulation of numerous biological processes. Multiple proteins undergo PTMs that influence autophagy regulation. Methylation modifications on non-histone lysine and arginine residues have been identified as common PTMs critical to various life processes. This paper focused on the regulatory effects of non-histone methylation modifications on autophagy, summarizing related research on signaling pathways involved in autophagy-related non-histone methylation, and discussing current challenges and clinical significance. Our review concludes that non-histone methylation plays a pivotal role in the regulation of autophagy and its associated signaling pathways. Targeting non-histone methylation offers a promising strategy for therapeutic interventions in diseases related to autophagy dysfunction, such as cancer and neurodegenerative disorders. These findings provide a theoretical basis for the development of non-histone-methylation-targeted drugs for clinical use.

Histone demethylases in autophagy and inflammation

Autophagy dysfunction is associated with changes in autophagy-related genes. Various factors are connected to autophagy, and the mechanism regulating autophagy is highly complicated. Epigenetic changes, such as aberrant expression of histone demethylase, are actively associated not only with oncogenesis but also with inflammatory responses. Among post-translational modifications, histone lysine methylation holds significant importance. There are over 30 members of histone lysine demethylases (KDMs), which act as epigenetic regulators in physiological processes and diseases. Importantly, KDMs are abnormally expressed in the regulation of cellular autophagy and inflammation, representing a crucial mechanism affecting inflammation-related diseases. This article reviewed the function of KDMs proteins in autophagy and inflammation. Specifically, It focused on the specific regulatory mechanisms underlying the activation or inhibition of autophagy, as well as their abnormal expression in inflammatory responses. By analyzing each KDM in epigenetic modification, this review provides a reliable theoretical basis for clinical decision marking regarding autophagy abnormalities and inflammatory diseases.

Lysine and arginine methylation of transcription factors

Post-translational modifications (PTMs) are implicated in many biological processes including receptor activation, signal transduction, transcriptional regulation and protein turnover. Lysine's side chain is particularly notable, as it can undergo methylation, acetylation, SUMOylation and ubiquitination. Methylation affects not only lysine but also arginine residues, both of which are implicated in epigenetic regulation. Beyond histone-tails as substrates, dynamic methylation of transcription factors has been described. The focus of this review is on these non-histone substrates providing a detailed discussion of what is currently known about methylation of hypoxia-inducible factor (HIF), P53, nuclear receptors (NRs) and RELA. The role of methylation in regulating protein stability and function by acting as docking sites for methyl-reader proteins and via their crosstalk with other PTMs is explored.

Hypoxia reconstructed colorectal tumor microenvironment weakening anti-tumor immunity: construction of a new prognosis predicting model through transcriptome analysis

Background

Hypoxia in the tumor microenvironment (TME) plays a pivotal role in the progression and prognosis of colorectal cancer (CRC). However, effective methods for assessing TME hypoxia remain lacking. This study aims to develop a novel hypoxia-related prognostic score (HPS) based on hypoxia-associated genes to improve CRC prognostication and inform treatment strategies.

Methods

Transcriptomic data from CRC patients were analyzed using Lasso regression to identify hypoxia-associated genes with the strongest prognostic significance. The identified genes were validated in vitro by assessing their expression under normoxic and hypoxic conditions in normal intestinal epithelial cells and CRC tumor cell lines. Functional relevance was explored through differential gene expression analysis, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, and protein-protein interaction (PPI) network construction. The association of HPS with extracellular matrix (ECM) composition, immune cell infiltration, and immune suppression was also investigated.

Results

Seven hypoxia-associated signature genes were identified, each demonstrating a strong correlation with CRC prognosis. The hypoxia-related prognostic score (HPS), derived from these genes, was significantly linked to changes in the TME. Specifically, HPS values were associated with alterations in ECM composition and distinct immune cell infiltration patterns. Higher HPS values corresponded to increased infiltration of immune-suppressive cells and reduced presence of anti-tumor immune cells. This imbalance promoted an immune-suppressive TME, facilitating tumor progression and immune evasion.

Conclusions

The hypoxia-related prognostic score (HPS) captures the regulatory influence of TME hypoxia on immune responses, offering valuable insights into its role in tumor progression. HPS holds promise as a prognostic tool and a guide for developing personalized treatment strategies in CRC.

Protein arginine methyltransferase 5 confers the resistance of triple-negative breast cancer to nanoparticle albumin-bound paclitaxel by enhancing autophagy through the dimethylation of ULK1

Chemotherapy remains the major strategy for treating triple-negative breast cancer (TNBC); however, frequently acquired chemoresistance greatly limits the treatment outcomes. Protein arginine methyltransferase 5 (PRMT5), which modulates arginine methylation, is important in chemoresistance acquisition across various cancers. The function of PRMT5 in the development of chemoresistance in TNBC is still not well understood. This work focused on defining PRMT5's function in contributing to the chemoresistance in TNBC and demonstrating the possible mechanisms involved. Two TNBC cell lines resistant to nanoparticle albumin-bound paclitaxel (Nab-PTX), designated MDA-MB-231/R and MDA-MB-468/R, were developed. The expression of PRMT5 was markedly elevated in the cytoplasm of Nab-PTX-resistant cells accompanied with enhanced autophagy. The depletion of PRMT5 rendered these cells sensitive to Nab-PTX-evoked cytotoxicity. The autophagic flux was upregulated in Nab-PTX-resistant cells, which was markedly repressed by PRMT5 depletion. The dimethylation of ULK1 was markedly elevated in Nab-PTX-resistant cells, which was decreased by silencing PRMT5. Re-expression of PRMT5 in PRMT5-depleted cells restored the dimethylation and activation of ULK1 as well as the autophagic flux, while the catalytically-dead PRMT5 (R368A) mutant showed no significant effects. The depletion of PRMT5 rendered the subcutaneous tumors formed by Nab-PTX-resistant TNBC cells sensitive to Nab-PTX. The findings of this work illustrate that PRMT5 confers chemoresistance of TNBC by enhancing autophagy through dimethylation and the activation of ULK1, revealing a novel mechanism for understanding the acquisition of chemoresistance in TNBC. Targeting PRMT5 could be a viable approach for overcoming chemoresistance in the treatment of TNBC.

Physiological functions of ULK1/2

UNC-51-like kinases 1 and 2 (ULK1/2) are serine/threonine kinases that are best known for their evolutionarily conserved role in the autophagy pathway. Upon sensing the nutrient status of a cell, ULK1/2 integrate signals from upstream cellular energy sensors such as mTOR and AMPK and relay them to the downstream components of the autophagy machinery. ULK1/2 also play indispensable roles in the selective autophagy pathway, removing damaged mitochondria, invading pathogens, and toxic protein aggregates. Additional functions of ULK1/2 have emerged beyond autophagy, including roles in protein trafficking, RNP granule dynamics, and signaling events impacting innate immunity, axon guidance, cellular homeostasis, and cell fate. Therefore, it is no surprise that alterations in ULK1/2 expression and activity have been linked with pathophysiological processes, including cancer, neurological disorders, and cardiovascular diseases. Growing evidence suggests that ULK1/2 function as biological rheostats, tuning cellular functions to intra and extra-cellular cues. Given their broad physiological relevance, ULK1/2 are candidate targets for small molecule activators or inhibitors that may pave the way for the development of therapeutics for the treatment of diseases in humans.

Streptococcus pneumoniae extracellular vesicles aggravate alveolar epithelial barrier disruption via autophagic degradation of OCLN (occludin)

Streptococcus pneumoniae (S. pneumoniae) represents a major human bacterial pathogen leading to high morbidity and mortality in children and the elderly. Recent research emphasizes the role of extracellular vesicles (EVs) in bacterial pathogenicity. However, the contribution of S. pneumoniae EVs (pEVs) to host-microbe interactions has remained unclear. Here, we observed that S. pneumoniae infections in mice led to severe lung injuries and alveolar epithelial barrier (AEB) dysfunction. Infections of S. pneumoniae reduced the protein expression of tight junction protein OCLN (occludin) and activated macroautophagy/autophagy in lung tissues of mice and A549 cells. Mechanically, S. pneumoniae induced autophagosomal degradation of OCLN leading to AEB impairment in the A549 monolayer. S. pneumoniae released the pEVs that could be internalized by alveolar epithelial cells. Through proteomics, we profiled the cargo proteins inside pEVs and found that these pEVs contained many virulence factors, among which we identified a eukaryotic-like serine-threonine kinase protein StkP. The internalized StkP could induce the phosphorylation of BECN1 (beclin 1) at Ser93 and Ser96 sites, initiating autophagy and resulting in autophagy-dependent OCLN degradation and AEB dysfunction. Finally, the deletion of stkP in S. pneumoniae completely protected infected mice from death, significantly alleviated OCLN degradation in vivo, and largely abolished the AEB disruption caused by pEVs in vitro. Overall, our results suggested that pEVs played a crucial role in the spread of S. pneumoniae virulence factors. The cargo protein StkP in pEVs could communicate with host target proteins and even hijack the BECN1 autophagy initiation pathway, contributing to AEB disruption and bacterial pathogenicity.Abbreviations: AEB: alveolarepithelial barrier; AECs: alveolar epithelial cells; ATG16L1: autophagy related 16 like 1; ATP:adenosine 5'-triphosphate; BafA1: bafilomycin A1; BBB: blood-brain barrier; CFU: colony-forming unit; co-IP: co-immunoprecipitation; CQ:chloroquine; CTRL: control; DiO: 3,3'-dioctadecylox-acarbocyanineperchlorate; DOX: doxycycline; DTT: dithiothreitol; ECIS: electricalcell-substrate impedance sensing; eGFP: enhanced green fluorescentprotein; ermR: erythromycin-resistance expression cassette; Ery: erythromycin; eSTKs: eukaryotic-like serine-threoninekinases; EVs: extracellular vesicles; HA: hemagglutinin; H&E: hematoxylin and eosin; HsLC3B: human LC3B; hpi: hours post-infection; IP: immunoprecipitation; KD: knockdown; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LC/MS: liquid chromatography-mass spectrometry; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MVs: membranevesicles; NC:negative control; NETs:neutrophil extracellular traps; OD: optical density; OMVs: outer membrane vesicles; PBS: phosphate-buffered saline; pEVs: S.pneumoniaeextracellular vesicles; protK: proteinase K; Rapa: rapamycin; RNAi: RNA interference; S.aureus: Staphylococcusaureus; SNF:supernatant fluid; sgRNA: single guide RNA; S.pneumoniae: Streptococcuspneumoniae; S.suis: Streptococcussuis; TEER: trans-epithelium electrical resistance; moi: multiplicity ofinfection; TEM:transmission electron microscope; TJproteins: tight junction proteins; TJP1/ZO-1: tight junction protein1; TSA: tryptic soy agar; WB: western blot; WT: wild-type.

Mechanistic insights into cisplatin response in breast tumors: Molecular determinants and drug/nanotechnology-based therapeutic opportunities

Breast cancer continues to be a major global health challenge, driving the need for effective therapeutic strategies. Cisplatin, a powerful chemotherapeutic agent, is widely used in breast cancer treatment. However, its effectiveness is often limited by systemic toxicity and the development of drug resistance. This review examines the molecular factors that influence cisplatin response and resistance, offering crucial insights for the scientific community. It highlights the significance of understanding cisplatin resistance's genetic and epigenetic contributors, which could lead to more personalized treatment approaches. Additionally, the review explores innovative strategies to counteract cisplatin resistance, including combination therapies, nanoparticle-based drug delivery systems, and targeted therapies. These approaches are under intensive investigation and promise to enhance breast cancer treatment outcomes. This comprehensive discussion is a valuable resource to advance breast cancer therapeutics and address the challenge of cisplatin resistance.

Oxidative stress induces extracellular vesicle release by upregulation of HEXB to facilitate tumour growth in experimental hepatocellular carcinoma

Extracellular vesicles (EVs) play a crucial role in triggering tumour-aggressive behaviours. However, the energetic process by which tumour cells produce EVs remains poorly understood. Here, we demonstrate the involvement of β-hexosaminidase B (HEXB) in mediating EV release in response to oxidative stress, thereby promoting the development of hepatocellular carcinoma (HCC). Mechanistically, reactive oxygen species (ROS) stimulate the nuclear translocation of transcription factor EB (TFEB), leading to the upregulation of both HEXB and its antisense lncRNA HEXB-AS. HEXB-AS can bind HEXB to form a protein/RNA complex, which elevates the protein stability of HEXB. The stabilized HEXB interacts with lysosome-associated membrane glycoprotein 1 (LAMP1), disrupting lysosome-multivesicular body (MVB) fusion, which protects EVs from degradation. Knockdown of HEXB efficiently inhibits EV release and curbs HCC growth both in vitro and in vivo. Moreover, targeting HEXB by M-31850 significantly inhibits HCC growth, especially when combined with GW4869, an inhibitor of exosome release. Our results underscore the critical role of HEXB as a modulator that promotes EV release during HCC development.

Relationship between arginine methylation and vascular calcification

In patients on maintenance hemodialysis (MHD), vascular calcification (VC) is an independent predictor of cardiovascular disease (CVD), which is the primary cause of death in chronic kidney disease (CKD). The main component of VC in CKD is the vascular smooth muscle cells (VSMCs). VC is an ordered, dynamic activity. Under the stresses of oxidative stress and calcium-‑phosphorus imbalance, VSMCs undergo osteogenic phenotypic transdifferentiation, which promotes the formation of VC. In addition to traditional epigenetics like RNA and DNA control, post-translational modifications have been discovered to be involved in the regulation of VC in recent years. It has been reported that the process of osteoblast differentiation is impacted by catalytic histone or non-histone arginine methylation. Its function in the osteogenic process is comparable to that of VC. Thus, we propose that arginine methylation regulates VC via many signaling pathways, including as NF-B, WNT, AKT/PI3K, TGF-/BMP/SMAD, and IL-6/STAT3. It might also regulate the VC-related calcification regulatory factors, oxidative stress, and endoplasmic reticulum stress. Consequently, we propose that arginine methylation regulates the calcification of the arteries and outline the regulatory mechanisms involved.

Autophagy is the main driver of radioresistance of HNSCC cells in mild hypoxia

Hypoxia poses a significant challenge to the effectiveness of radiotherapy in head and neck squamous cell carcinoma (HNSCC) patients, and it is imperative to discover novel approaches to overcome this. In this study, we investigated the underlying mechanisms contributing to x-ray radioresistance in HPV-negative HNSCC cells under mild hypoxic conditions (1% oxygen) and explored the potential for autophagy modulation as a promising therapeutic strategy. Our findings show that HNSCC cells exposed to mild hypoxic conditions exhibit increased radioresistance, which is largely mediated by the hypoxia-inducible factor (HIF) pathway. We demonstrate that siRNA knockdown of HIF-1α and HIF-1β leads to increased radiosensitivity in HNSCC cells under hypoxia. Hypoxia-induced radioresistance was not attributed to differences in DNA double strand break repair kinetics, as these remain largely unchanged under normoxic and hypoxic conditions. Rather, we identify autophagy as a critical protective mechanism in HNSCC cells following irradiation under mild hypoxia conditions. Targeting key autophagy genes, such as BECLIN1 and BNIP3/3L, using siRNA sensitizes these cells to irradiation. Whilst autophagy's role in hypoxic radioresistance remains controversial, this study highlights the importance of autophagy modulation as a potential therapeutic approach to enhance the effectiveness of radiotherapy in HNSCC.

CK1δ/ε inhibition induces ULK1-mediated autophagy in tumorigenesis

INTRODUCTION

Autophagy is an important mechanism of cell homeostasis maintenance. As essential serine/threonine-protein kinases, casein kinase I family members affect tumorigenesis by regulating a variety of cellular progression. However, the mechanism by which they regulate autophagy remains unclear.

MATERIALS AND METHODS

We silenced CK1δ/ε in cancer cells and observed cell morphology, the expression of autophagy-related genes, and its impact on cancer cell growth and viability. By inhibiting CK1δ/ε-induced upregulation of autophagy genes, we profiled the regulatory mechanism of CK1δ/ε on autophagy and cancer cell growth. The impact of CK1δ/ε inhibition on tumor cell growth was also assessed in vivo.

RESULTS

Here, we found that CK1δ/ε played an important role in ULK1-mediated autophagy regulation in both lung cancer and melanoma cells. Mechanically, silencing CK1δ/ε increased ULK1 expression with enhanced autophagic flux and suppressed cancer cell proliferation, while ULK1 knockdown blocked the activation of autophagy caused by CK1δ/ε inhibition. By silencing CK1δ/ε in syngeneic mouse model bearing LLC1 murine lung cancer cells in vivo, we observed tumor growth suppression mediated by CK1δ/ε inhibition.

CONCLUSION

Our results provide evidence for the role of CK1δ/ε in the regulation of tumorigenesis via the ULK1-mediated autophagy, and also suggest the impact of CK1δ/ε inhibition on tumor growth and its significance as a potential therapeutic target.

Hypoxic microenvironment promotes dermal fibroblast migration and proliferation via a BNIP3-autophagy pathway

Upon injury, nearby cells, including fibroblasts at the wound edge, are often found in a hypoxic microenvironment. Nevertheless, the influence of hypoxia on skin fibroblasts is poorly understood. Using previously established mouse full-thickness wounds, we show that Bcl-2 and adenovirus E1B 19-kDa interacting protein 3 (BNIP3) expression was significantly elevated at the wound edge, and hypoxia treatment enhanced BNIP3 expression in fibroblasts. Interestingly, BNIP3 promoted the migration and proliferation, as well as the activation of autophagy, in fibroblasts under hypoxia. The hypoxia-induced autophagy was found to induce the migration and proliferation of fibroblasts, a process that could be reversed by knocking down the autophagy-related gene for autophagy protein 5, ATG5. Furthermore, hypoxia-inducible factor 1 subunit alpha (HIF-1α) was significantly upregulated in fibroblasts under hypoxia treatment, and HIF-1α knockdown attenuated the hypoxia-induced expression of BNIP3 and the migration and proliferation of fibroblasts. Altogether, our results establish the hypoxia-BNIP3-autophagy signaling axis as a newly identified regulatory mechanism of skin fibroblast migration and proliferation upon wounding. Autophagy intervening might thus represent a promising therapeutic strategy for patients with chronic refractory wounds.

Oxygen-regulated post-translation modifications as master signalling pathway in cells

Oxygen is essential for viability in mammalian organisms. However, cells are often exposed to changes in oxygen availability, due to either increased demand or reduced oxygen supply, herein called hypoxia. To be able to survive and/or adapt to hypoxia, cells activate a variety of signalling cascades resulting in changes to chromatin, gene expression, metabolism and viability. Cellular signalling is often mediated via post-translational modifications (PTMs), and this is no different in response to hypoxia. Many enzymes require oxygen for their activity and oxygen can directly influence several PTMS. Here, we review the direct impact of changes in oxygen availability on PTMs such as proline, asparagine, histidine and lysine hydroxylation, lysine and arginine methylation and cysteine dioxygenation, with a focus on mammalian systems. In addition, indirect hypoxia-dependent effects on phosphorylation, ubiquitination and sumoylation will also be discussed. Direct and indirect oxygen-regulated changes to PTMs are coordinated to achieve the cell's ultimate response to hypoxia. However, specific oxygen sensitivity and the functional relevance of some of the identified PTMs still require significant research.

Exosomal circHIPK3 derived from umbilical cord-derived mesenchymal stem cells enhances skin fibroblast autophagy by blocking miR-20b-5p/ULK1/Atg13 axis

BACKGROUND

Umbilical cord-derived mesenchymal stem cells (UCMSCs) could alleviate diabetes-induced injury. Hence, this investigation aimed to explore the role and mechanism of UCMSCs-derived exosomal circHIPK3 (exo-circHIPK3) in diabetes mellitus (DM).

METHODS

HFF-1 cells were cultured in high glucose (HG) medium or normal medium, and treated with UCMSCs-derived exo-circHIPK3 or miR-20b-5p mimics or Unc-51-like autophagy activating kinase 1 (ULK1) overexpression vector. The surface markers of UCMSCs were analyzed using a flow cytometer. The differentiation potential of UCMSCs was evaluated using oil red O staining, alizarin red staining and alkaline phosphatase (ALP) staining. Cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The miRNA expressions were analyzed by reverse transcription-quantitative polymerase chain reaction (qRT-PCR). Protein levels were quantified by western blot. An immunofluorescence staining was used for observing LC3 expression. The interaction between miR-20b-5p and circHIPK3, and between miR-20b-5b and ULK1 were identified by a RNA immunoprecipitation (RIP) assay and a luciferase reporter assay.

RESULTS

Up-regulation of circHIPK3 was found in UCMSCs-derived exosomes. Exo-circHIPK3 decreased the miR-20b-5p level while increasing the contents of ULK1 and autophagy-related gene 13 (Atg13) in HG-induced fibroblasts. In addition, exo-circHIPK3 activated HG-induced fibroblast autophagy and proliferation. Overexpressed miR-20b-5p promoted fibroblast injury by inhibiting cell autophagy via the ULK1/Atg13 axis in HG conditions of high glucose. Moreover, exo-circHIPK3 enhanced autophagy and cell viability in HG-induced fibroblasts through the miR-20b-5p/ULK1/Atg13 axis.

CONCLUSION

UCMSCs-derived exosomal circHIPK3 promoted cell autophagy and proliferation and accelerated the fibroblast injury repair by the miR-20b-5p/ULK1/Atg13 axis.

IL-6/JAK2-dependent G6PD phosphorylation promotes nucleotide synthesis and supports tumor growth

OBJECTIVE

Tumor cells hijack inflammatory mechanisms to promote their own growth. IL-6 is one of the major cytokines, and is frequently upregulated in tumors. The pentose phosphate pathway (PPP) generates the indispensable building blocks to produce various nucleotides. Here we aimed to determine whether and how PPP is timely tuned in response to IL-6 to support tumor growth.

METHODS

Protein expression was examined by immunoblot. Protein interaction was examined by immunoprecipitation. Tumor cell proliferation in in vitro culture was examined by BrdU assay and colony formation assay. Tumor cell proliferation in mouse xenograft model was examined by Ki-67 staining.

RESULTS

Here we show that the metabolic flux of PPP and enzymatic activity of glucose-6-phosphate dehydrogenase (G6PD) is rapidly induced under IL-6 treatment, without obvious changes in G6PD expression level. Mechanistically, Janus kinase 2 (JAK2) phosphorylates G6PD Y437 under IL-6 treatment, which accentuates G6PD enzymatic activity by promoting G6PD binding with its substrate G6P. Further, JAK2-dependent G6PD Y437 phosphorylation is required for IL-6-induced nucleotide biosynthesis and tumor cell proliferation, and is associated with the progression of oral squamous cell carcinoma.

CONCLUSIONS

Our findings report a new mechanism implicated in the crosstalk between tumor cells and inflammatory microenvironment, by which JAK2-dependent activation of G6PD governs nucleotide synthesis to support tumor cell proliferation, thereby highlighting its value as a potential anti-tumor target.

The role of autophagy in hypoxia-induced radioresistance

Radiotherapy is a widely used treatment modality against cancer, and although survival rates are increasing, radioresistant properties of tumours remain a significant barrier for curative treatment. Tumour hypoxia is one of the main contributors to radioresistance and is common in most solid tumours. Hypoxia is responsible for many molecular changes within the cell which helps tumours to survive under such challenging conditions. These hypoxia-induced molecular changes are predominantly coordinated by the hypoxia inducible factor (HIF) and have been linked with the ability to confer resistance to radiation-induced cell death. To overcome this obstacle research has been directed towards autophagy, a cellular process involved in self degradation and recycling of macromolecules, as HIF plays a large role in its coordination under hypoxic conditions. The role that autophagy has following radiotherapy treatment is conflicted with evidence of both cytoprotective and cytotoxic effects. This literature review aims to explore the intricate relationship between radiotherapy, hypoxia, and autophagy in the context of cancer treatment. It provides valuable insights into the potential of targeting autophagy as a therapeutic strategy to improve the response of hypoxic tumours to radiotherapy.

Desialylation of ATG5 by sialidase (NEU1) promotes macrophages autophagy and exacerbates inflammation under hypoxia

During the process of atherosclerosis (AS), hypoxia induces plaque macrophage inflammation, promoting lipid accumulation. Autophagy is a cell homeostasis process that increases tolerance to stressors like oxidative stress and hypoxia. However, the specific mechanism by which hypoxia initiates autophagy and the inflammation of macrophages remains to be elucidated. Here, we found that hypoxia-induced macrophage inflammation was mediated by autophagy. Then, the effect of hypoxia on autophagy was investigated in terms of post-translational modifications of proteins. The results showed that desialylation of the autophagy protein ATG5 under hypoxic conditions enhanced protein stability by affecting its charge effect and promoted the formation of the ATG5-ATG12-ATG16L complex, further increasing autophagosome formation. And NEU1, a key enzyme in sialic acid metabolism, was significantly up-regulated under hypoxic conditions and was identified as an interacting protein of ATG5, affecting the sialylation of ATG5. In addition, the knockdown or inhibition of NEU1 reversed hypoxia-induced autophagy and inflammatory responses. In conclusion, our data reveal a key mechanism of autophagy regulation under hypoxia involving ATG5 sialylation and NEU1, suggesting that NEU1 may be a potential target for the prevention and treatment of atherosclerosis.

Activation of ULK1 to trigger FUNDC1-mediated mitophagy in heart failure: Effect of Ginsenoside Rg3 intervention

BACKGROUND

Although the development of therapies for heart failure (HF) continues apace, clinical outcomes are often far from ideal. Unc51-like-kinase 1 (ULK1)-mediated mitophagy prevents pathological cardiac remodeling and heart failure (HF). Molecularly ULK1-targeted agent to enhance mitophagy is scanty.

HYPOTHESIS/PURPOSE

This study aimed to investigate whether Ginsenoside Rg3 (Rg3) can activate ULK1 to trigger FUNDC1-mediated mitophagy for protecting heart failure.

METHODS

Molecular docking and surface plasmon resonance were used to detect the ULK1 binding behavior of Rg3. Established HF model in rats and transcriptome sequencing were used to evaluate the therapeutic effect and regulatory mechanism of Rg3. Loss-of-function approaches in vivo and in vitro were performed to determine the role of ULK1 in Rg3-elicited myocardial protection against HF. FUNDC1 recombinant plasmid of site mutation was applied to elucidate more in-depth mechanisms.

RESULTS

Structurally, a good binding mode was unveiled between ULK1 and Rg3. In vivo, Rg3 improved cardiac dysfunction, adverse remodeling, and mitochondrial damage in HF rats. Furthermore, Rg3 promoted Ulk1-triggered mitophagy both in vivo and in vitro, manifested by the impetus of downstream Fundc1-Lc3 interaction. Of note, the protective effects conferred by Rg3 against mitophagy defects, pathological remodeling, and cardiac dysfunction were compromised by Ulk1 gene silencing both in vivo and in vitro. Mechanistically, Rg3 activated mitophagy by inducing ULK1-mediated phosphorylation of FUNDC1 at the Ser17 site, not the Ser13 site.

CONCLUSION

Together these observations demonstrated that Rg3 acts as a ULK1 activator for the precise treatment of HF, which binds to ULK1 to activate FUNDC1-mediated mitophagy.

The PRMT5 inhibitor C9 mitigates hypoxia-induced carboplatin resistance in lung cancer by inducing autophagy

Hypoxia, a common feature of solid tumors, can promote chemoresistance in cancer cells. PRMT5 mediates various cellular processes involved in cancer development and progression. However, the role of PRMT5 in hypoxia-induced chemoresistance is unclear. In this study, hypoxia upregulated PRMT5 expression in lung cancer cells. Additionally, PRMT5 overexpression promoted cancer cell resistance to carboplatin. In carboplatin-resistant cancer cells, PRMT5 overexpression promoted the methylation of ULK1, a critical regulator of autophagy. ULK1 hypermethylation leads to the upregulation of autophagy, which can improve the survival of cancer cells under hypoxic conditions. Furthermore, this study demonstrated that the PRMT5 inhibitor C9 significantly enhanced the sensitivity of lung cancer cells to carboplatin. These findings suggest that targeting PRMT5-mediated autophagy with C9 can overcome hypoxia-induced carboplatin resistance and improve the efficacy of chemotherapy in patients with cancer.

Rapid phosphorylation of glucose-6-phosphate dehydrogenase by casein kinase 2 sustains redox homeostasis under ionizing radiation

Exposure to ionizing radiation leads to oxidative damages in living cells. NADPH provides the indispensable reducing power to regenerate the reduced glutathione to maintain cellular redox equilibria. In mammalian cells, pentose phosphate pathway (PPP) is the major route to produce NADPH by using glycolytic intermediates, and the rate-limiting step of PPP is controlled by glucose-6-phosphate dehydrogenase (G6PD). Nevertheless, whether G6PD is timely co-opted under ionizing radiation to cope with oxidative stress remains elusive. Here we show that cellular G6PD activity is induced 30 min after ionizing radiation, while its protein expression is mostly unchanged. Mechanistically, casein kinase 2 (CK2) phosphorylates G6PD T145 under ionizing radiation, which consolidates the enzymatic activity of G6PD by facilitating G6PD binding with its substrate NADP+. Further, CK2-dependent G6PD T145 phosphorylation promotes NADPH production, decreases ROS level and supports cell proliferation under ionizing radiation. Our findings report a new anti-oxidative signaling route under ionizing radiation, by which CK2-mediated rapid activation of G6PD orchestrates NADPH synthesis to maintain redox homeostasis, thereby highlighting its potential value in the early treatment of ionizing radiation-induced injuries.

Methylation across the central dogma in health and diseases: new therapeutic strategies

The proper transfer of genetic information from DNA to RNA to protein is essential for cell-fate control, development, and health. Methylation of DNA, RNAs, histones, and non-histone proteins is a reversible post-synthesis modification that finetunes gene expression and function in diverse physiological processes. Aberrant methylation caused by genetic mutations or environmental stimuli promotes various diseases and accelerates aging, necessitating the development of therapies to correct the disease-driver methylation imbalance. In this Review, we summarize the operating system of methylation across the central dogma, which includes writers, erasers, readers, and reader-independent outputs. We then discuss how dysregulation of the system contributes to neurological disorders, cancer, and aging. Current small-molecule compounds that target the modifiers show modest success in certain cancers. The methylome-wide action and lack of specificity lead to undesirable biological effects and cytotoxicity, limiting their therapeutic application, especially for diseases with a monogenic cause or different directions of methylation changes. Emerging tools capable of site-specific methylation manipulation hold great promise to solve this dilemma. With the refinement of delivery vehicles, these new tools are well positioned to advance the basic research and clinical translation of the methylation field.

Role of Mitochondria-ER Contact Sites in Mitophagy

Mitochondria are often referred to as the "powerhouse" of the cell. However, this organelle has many more functions than simply satisfying the cells' metabolic needs. Mitochondria are involved in calcium homeostasis and lipid metabolism, and they also regulate apoptotic processes. Many of these functions require contact with the ER, which is mediated by several tether proteins located on the respective organellar surfaces, enabling the formation of mitochondria-ER contact sites (MERCS). Upon damage, mitochondria produce reactive oxygen species (ROS) that can harm the surrounding cell. To circumvent toxicity and to maintain a functional pool of healthy organelles, damaged and excess mitochondria can be targeted for degradation via mitophagy, a form of selective autophagy. Defects in mitochondria-ER tethers and the accumulation of damaged mitochondria are found in several neurodegenerative diseases, including Parkinson's disease and amyotrophic lateral sclerosis, which argues that the interplay between the two organelles is vital for neuronal health. This review provides an overview of the different mechanisms of mitochondrial quality control that are implicated with the different mitochondria-ER tether proteins, and also provides a novel perspective on how MERCS are involved in mediating mitophagy upon mitochondrial damage.

Searching for molecular hypoxia sensors among oxygen-dependent enzymes

The ability to sense and respond to changes in cellular oxygen levels is critical for aerobic organisms and requires a molecular oxygen sensor. The prototypical sensor is the oxygen-dependent enzyme PHD: hypoxia inhibits its ability to hydroxylate the transcription factor HIF, causing HIF to accumulate and trigger the classic HIF-dependent hypoxia response. A small handful of other oxygen sensors are known, all of which are oxygen-dependent enzymes. However, hundreds of oxygen-dependent enzymes exist among aerobic organisms, raising the possibility that additional sensors remain to be discovered. This review summarizes known and potential hypoxia sensors among human O2-dependent enzymes and highlights their possible roles in hypoxia-related adaptation and diseases.

Autophagy dictates sensitivity to PRMT5 inhibitor in breast cancer

Protein arginine methyltransferase 5 (PRMT5) catalyzes mono-methylation and symmetric di-methylation on arginine residues and has emerged as a potential antitumor target with inhibitors being tested in clinical trials. However, it remains unknown how the efficacy of PRMT5 inhibitors is regulated. Here we report that autophagy blockage enhances cellular sensitivity to PRMT5 inhibitor in triple negative breast cancer cells. Genetic ablation or pharmacological inhibition of PRMT5 triggers cytoprotective autophagy. Mechanistically, PRMT5 catalyzes monomethylation of ULK1 at R532 to suppress ULK1 activation, leading to attenuation of autophagy. As a result, ULK1 inhibition blocks PRMT5 deficiency-induced autophagy and sensitizes cells to PRMT5 inhibitor. Our study not only identifies autophagy as an inducible factor that dictates cellular sensitivity to PRMT5 inhibitor, but also unearths a critical molecular mechanism by which PRMT5 regulates autophagy through methylating ULK1, providing a rationale for the combination of PRMT5 and autophagy inhibitors in cancer therapy.

Effectors and effects of arginine methylation

Arginine methylation is a ubiquitous and relatively stable post-translational modification (PTM) that occurs in three types: monomethylarginine (MMA), asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA). Methylarginine marks are catalyzed by members of the protein arginine methyltransferases (PRMTs) family of enzymes. Substrates for arginine methylation are found in most cellular compartments, with RNA-binding proteins forming the majority of PRMT targets. Arginine methylation often occurs in intrinsically disordered regions of proteins, which impacts biological processes like protein-protein interactions and phase separation, to modulate gene transcription, mRNA splicing and signal transduction. With regards to protein-protein interactions, the major 'readers' of methylarginine marks are Tudor domain-containing proteins, although additional domain types and unique protein folds have also recently been identified as methylarginine readers. Here, we will assess the current 'state-of-the-art' in the arginine methylation reader field. We will focus on the biological functions of the Tudor domain-containing methylarginine readers and address other domains and complexes that sense methylarginine marks.

The catalytic domains of all human KDM5 JmjC demethylases catalyse N-methyl arginine demethylation

The demethylation of Nε -methyllysine residues on histones by Jumonji-C lysine demethylases (JmjC-KDMs) has been established. A subset of JmjC-KDMs has also been reported to have Nω -methylarginine residue demethylase (RDM) activity. Here, we describe biochemical screening studies, showing that the catalytic domains of all human KDM5s (KDM5A-KDM5D), KDM4E and, to a lesser extent, KDM4A/D, have both KDM and RDM activities with histone peptides. Ras GTPase-activating protein-binding protein 1 peptides were shown to be RDM substrates for KDM5C/D. No RDM activity was observed with KDM1A and the other JmjC-KDMs tested. The results highlight the potential of JmjC-KDMs to catalyse reactions other than Nε -methyllysine demethylation. Although our study is limited to peptide fragments, the results should help guide biological studies investigating JmjC functions.

PRMT5 Facilitates Infectious Bursal Disease Virus Replication through Arginine Methylation of VP1

The infectious bursal diseases virus (IBDV) polymerase, VP1 protein, is responsible for transcription, initial translation and viral genomic replication. Knowledge about the new kind of post-translational modification of VP1 supports identification of novel drugs against the virus. Because the arginine residue is known to be methylated by protein arginine methyltransferase (PRMT) enzyme, we investigated whether IBDV VP1 is a substrate for known PRMTs. In this study, we show that VP1 is specifically associated with and methylated by PRMT5 at the arginine 426 (R426) residue. IBDV infection causes the accumulation of PRMT5 in the cytoplasm, which colocalizes with VP1 as a punctate structure. In addition, ectopic expression of PRMT5 significantly enhances the viral replication. In the presence of PMRT5, enzyme inhibitor and knockout of PRMT5 remarkably decreased viral replication. The polymerase activity of VP1 was severely damaged when R426 mutated to alanine, resulting in impaired viral replication. Our study reports a novel form of post-translational modification of VP1, which supports its polymerase function to facilitate the viral replication. IMPORTANCE Post-translational modification of infectious bursal disease virus (IBDV) VP1 is important for the regulation of its polymerase activity. Investigation of the significance of specific modification of VP1 can lead to better understanding of viral replication and can probably also help in identifying novel targets for antiviral compounds. Our work demonstrates the molecular mechanism of VP1 methylation mediated by PRMT5, which is critical for viral polymerase activity, as well as viral replication. Our study expands a novel insight into the function of arginine methylation of VP1, which might be useful for limiting the replication of IBDV.

Effects of hypoxia on bronchial and alveolar epithelial cells linked to pathogenesis in chronic lung disorders

Introduction: Chronic lung disorders involve pathological alterations in the lung tissue with hypoxia as a consequence. Hypoxia may influence the release of inflammatory mediators and growth factors including vascular endothelial growth factor (VEGF) and prostaglandin (PG)E2. The aim of this work was to investigate how hypoxia affects human lung epithelial cells in combination with profibrotic stimuli and its correlation to pathogenesis.

Methods: Human bronchial (BEAS-2B) and alveolar (hAELVi) epithelial cells were exposed to either hypoxia (1% O2) or normoxia (21% O2) during 24 h, with or without transforming growth factor (TGF)-β1. mRNA expression of genes and proteins related to disease pathology were analysed with qPCR, ELISA or immunocytochemistry. Alterations in cell viability and metabolic activity were determined.

Results: In BEAS-2B and hAELVi, hypoxia significantly dowregulated genes related to fibrosis, mitochondrial stress, oxidative stress, apoptosis and inflammation whereas VEGF receptor 2 increased. Hypoxia increased the expression of Tenascin-C, whereas both hypoxia and TGF-β1 stimuli increased the release of VEGF, IL-6, IL-8 and MCP-1 in BEAS-2B. In hAELVi, hypoxia reduced the release of fibroblast growth factor, epidermal growth factor, PGE2, IL-6 and IL-8, whereas TGF-β1 stimulus significantly increased the release of PGE2 and IL-6. TGF-β1 stimulated BEAS-2B cells showed a decreased release of VEGF-A and IL-8, while TGF-β1 stimulated hAELVi cells showed a decreased release of PGE2 and IL-8 during hypoxia compared to normoxia. Metabolic activity was significantly increased by hypoxia in both epithelial cell types.

Discussion: In conclusion, our data indicate that bronchial and alveolar epithelial cells respond differently to hypoxia and profibrotic stimuli. The bronchial epithelium appears more responsive to changes in oxygen levels and remodelling processes compared to the alveoli, suggesting that hypoxia may be a driver of pathogenesis in chronic lung disorders.

Targeting PSAT1 to mitigate metastasis in tumors with p53-72Pro variant

The single-nucleotide polymorphism (SNP) of p53, in particular the codon 72 variants, has recently been implicated as a critical regulator in tumor progression. However, the underlying mechanism remains elusive. Here we found that cancer cells carrying codon 72-Pro variant of p53 showed impaired metastatic potential upon serine supplementation. Proteome-wide mapping of p53-interacting proteins uncovered a specific interaction of the codon 72 proline variant (but not p53^72R) with phosphoserine aminotransferase 1 (PSAT1). Interestingly, p53^72P-PSAT1 interaction resulted in dissociation of peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) that otherwise bound to p53^72P, leading to subsequent nuclear translocation of PGC-1α and activation of oxidative phosphorylation (OXPHOS) and tricarboxylic acid (TCA) cycle. Depletion of PSAT1 restored p53^72P-PGC-1α interaction and impeded the OXPHOS and TCA function, resulting in mitochondrial dysfunction and metastasis suppression. Notably, pharmacological targeting the PSAT1-p53^72P interaction by aminooxyacetic acid (AOA) crippled the growth of liver cancer cells carrying the p53^72P variant in both in vitro and patient-derived xenograft models. Moreover, AOA plus regorafenib, an FDA-proved drug for hepatocellular carcinoma and colorectal cancer, achieved a better anti-tumor effect on tumors carrying the p53^72P variant. Therefore, our findings identified a gain of function of the p53^72P variant on mitochondrial function and provided a promising precision strategy to treat tumors vulnerable to p53^72P-PSAT1 perturbation.

Hypoxia signaling in cancer: Implications for therapeutic interventions

Hypoxia is a persistent physiological feature of many different solid tumors and a key driver of malignancy, and in recent years, it has been recognized as an important target for cancer therapy. Hypoxia occurs in the majority of solid tumors due to a poor vascular oxygen supply that is not sufficient to meet the needs of rapidly proliferating cancer cells. A hypoxic tumor microenvironment (TME) can reduce the effectiveness of other tumor therapies, such as radiotherapy, chemotherapy, and immunotherapy. In this review, we discuss the critical role of hypoxia in tumor development, including tumor metabolism, tumor immunity, and tumor angiogenesis. The treatment methods for hypoxic TME are summarized, including hypoxia-targeted therapy and improving oxygenation by alleviating tumor hypoxia itself. Hyperoxia therapy can be used to improve tissue oxygen partial pressure and relieve tumor hypoxia. We focus on the underlying mechanisms of hyperoxia and their impact on current cancer therapies and discuss the prospects of hyperoxia therapy in cancer treatment.

Protein degradation: expanding the toolbox to restrain cancer drug resistance

Despite significant progress in clinical management, drug resistance remains a major obstacle. Recent research based on protein degradation to restrain drug resistance has attracted wide attention, and several therapeutic strategies such as inhibition of proteasome with bortezomib and proteolysis-targeting chimeric have been developed. Compared with intervention at the transcriptional level, targeting the degradation process seems to be a more rapid and direct strategy. Proteasomal proteolysis and lysosomal proteolysis are the most critical quality control systems responsible for the degradation of proteins or organelles. Although proteasomal and lysosomal inhibitors (e.g., bortezomib and chloroquine) have achieved certain improvements in some clinical application scenarios, their routine application in practice is still a long way off, which is due to the lack of precise targeting capabilities and inevitable side effects. In-depth studies on the regulatory mechanism of critical protein degradation regulators, including E3 ubiquitin ligases, deubiquitylating enzymes (DUBs), and chaperones, are expected to provide precise clues for developing targeting strategies and reducing side effects. Here, we discuss the underlying mechanisms of protein degradation in regulating drug efflux, drug metabolism, DNA repair, drug target alteration, downstream bypass signaling, sustaining of stemness, and tumor microenvironment remodeling to delineate the functional roles of protein degradation in drug resistance. We also highlight specific E3 ligases, DUBs, and chaperones, discussing possible strategies modulating protein degradation to target cancer drug resistance. A systematic summary of the molecular basis by which protein degradation regulates tumor drug resistance will help facilitate the development of appropriate clinical strategies.

Function and regulation of ULK1: From physiology to pathology

The expression of ULK1, a core protein of autophagy, is closely related to autophagic activity. Numerous studies have shown that pathological abnormal expression of ULK1 is associated with various human diseases such as neurological disorders, infections, cardiovascular diseases, liver diseases and cancers. In addition, new advances in the regulation of ULK1 have been identified. Furthermore, targeting ULK1 as a therapeutic strategy for diseases is gaining attention as new corresponding activators or inhibitors are being developed. In this review, we describe the structure and regulation of ULK1 as well as the current targeted activators and inhibitors. Moreover, we highlight the pathological disorders of ULK1 expression and its critical role in human diseases.

A "short-cut" response of autophagy to oxidative stress: oxygen-dependent activity of a lysine demethylase guides the activity of ULK1 during hypoxia

Hypoxia is a type of stress caused by an insufficient supply of oxygen. Macroautophagy/autophagy, a well-conserved pathway, is induced during hypoxia; however, the exact mechanism by which autophagy is regulated in a hypoxic environment remains to be elucidated. A recent study by Li et al. shed light on how hypoxia can regulate early steps of autophagy induction. In this study, the authors discovered a novel symmetrical dimethylation of ULK1 at arginine 170 (R170me2s) that accumulates during hypoxia and increases ULK1 kinase activity by promoting autophosphorylation of ULK1 at T180. The authors identified PRMT5 and KDM5C as the primary methyltransferase and demethylase regulating ULK1 R170me2s and show that the lack of oxygen directly leads to reduced activity of KDM5C, which is likely the cause of accumulation of ULK1 R170me2s during hypoxia. Furthermore, the authors showed that ULK1 R170me2s promotes mitochondrial turnover and maintains cell viability in response to hypoxia stress. Together these data provide a new perspective on how the oxygen level regulates autophagy induction and show the physiological role of ULK1 R170me2s.

Life and Death Decisions-The Many Faces of Autophagy in Cell Survival and Cell Death

Autophagy is a process conserved from yeast to humans. Since the discovery of autophagy, its physiological role in cell survival and cell death has been intensively investigated. The inherent ability of the autophagy machinery to sequester, deliver, and degrade cytoplasmic components enables autophagy to participate in cell survival and cell death in multiple ways. The primary role of autophagy is to send cytoplasmic components to the vacuole or lysosomes for degradation. By fine-tuning autophagy, the cell regulates the removal and recycling of cytoplasmic components in response to various stress or signals. Recent research has shown the implications of the autophagy machinery in other pathways independent of lysosomal degradation, expanding the pro-survival role of autophagy. Autophagy also facilitates certain forms of regulated cell death. In addition, there is complex crosstalk between autophagy and regulated cell death pathways, with a number of genes shared between them, further suggesting a deeper connection between autophagy and cell death. Finally, the mitochondrion presents an example where the cell utilizes autophagy to strike a balance between cell survival and cell death. In this review, we consider the current knowledge on the physiological role of autophagy as well as its regulation and discuss the multiple functions of autophagy in cell survival and cell death.

Hippo pathway monomerizes STAT3 to regulate prostate cancer growth

Prostate cancer ranks among the most commonly diagnosed malignancies for men, and has become a non-negligible threat for public health. Interplay between inflammatory factors and cancer cells renders inflammatory tissue environment as a predisposing condition for cancer development. The Hippo pathway is a conserved signaling pathway across multiple species during evolution that regulates tissue homeostasis and organ development. Nevertheless, whether Hippo pathway regulates cancer-related inflammatory factors remain elusive. Here we show that high cell density-mediated activation of Hippo pathway blunts STAT3 activity in prostate cancer cells. Hippo pathway component MST2 kinase phosphorylates STAT3 at T622, which is located in the SH2 domain of STAT3. This phosphorylation blocks SH2 domain in one STAT3 molecule to bind with the phosphorylated Y705 site in another STAT3 molecule, which further counteracts IL6-induced STAT3 dimerization and activation. Expression of a non-phosphoryable STAT3 T622A mutant enhances STAT3 activity and IL6 expression at high cell density, and promotes tumor growth in mice xenograft model. Our findings demonstrate that STAT3 is a novel phosphorylation substrate for MST2, and thereby highlight a regulatory cascade underlying the crosstalk between inflammation and Hippo pathway in prostate cancer cells.

Autophagy and beyond: Unraveling the complexity of UNC-51-like kinase 1 (ULK1) from biological functions to therapeutic implications

UNC-51-like kinase 1 (ULK1), as a serine/threonine kinase, is an autophagic initiator in mammals and a homologous protein of autophagy related protein (Atg) 1 in yeast and of UNC-51 in Caenorhabditis elegans. ULK1 is well-known for autophagy activation, which is evolutionarily conserved in protein transport and indispensable to maintain cell homeostasis. As the direct target of energy and nutrition-sensing kinase, ULK1 may contribute to the distribution and utilization of cellular resources in response to metabolism and is closely associated with multiple pathophysiological processes. Moreover, ULK1 has been widely reported to play a crucial role in human diseases, including cancer, neurodegenerative diseases, cardiovascular disease, and infections, and subsequently targeted small-molecule inhibitors or activators are also demonstrated. Interestingly, the non-autophagy function of ULK1 has been emerging, indicating that non-autophagy-relevant ULK1 signaling network is also linked with diseases under some specific contexts. Therefore, in this review, we summarized the structure and functions of ULK1 as an autophagic initiator, with a focus on some new approaches, and further elucidated the key roles of ULK1 in autophagy and non-autophagy. Additionally, we also discussed the relationships between ULK1 and human diseases, as well as illustrated a rapid progress for better understanding of the discovery of more candidate small-molecule drugs targeting ULK1, which will provide a clue on novel ULK1-targeted therapeutics in the future.