Autophagic UVRAG Promotes UV-Induced Photolesion Repair by Activation of the CRL4(DDB2) E3 Ligase

Emerging dimensions of autophagy in melanoma

Macroautophagy/autophagy has previously been regarded as simply a way for cells to deal with nutrient emergency. But explosive work in the last 15 years has given increasingly new knowledge to our understanding of this process. Many of the functions of autophagy that are unveiled from recent studies, however, cannot be reconciled with this conventional view of cell survival but, instead, point to autophagy being integrally involved at a deeper level of cell biology, playing a critical role in maintaining homeostasis and promoting an integrated stress/immune response. The new appreciation of the role of autophagy in the evolutionary trajectory of cancer and cancer interaction with the immune system provides a mechanistic framework for understanding the clinical benefits of autophagy-based therapies. Here, we examine current knowledge of the mechanisms and functions of autophagy in highly plastic and aggressive melanoma as a model disease of human malignancy, while highlighting emerging dimensions indicating that autophagy is at play beyond its classical face.Abbreviation: AMBRA1: autophagy and beclin 1 regulator 1; AMPK: AMP-activated protein kinase; ATF4: activating transcription factor 4; ATG: autophagy related; BRAF: B-Raf proto-oncogene, serine/threonine kinase; CAFs: cancer-associated fibroblasts; CCL5: C-C motif chemokine ligand 5; CQ: chloroquine; CRISPR: clustered regularly interspaced short palindromic repeats; CTLA4: cytotoxic T-lymphocyte associated protein 4; CTL: cytotoxic T lymphocyte; DAMPs: danger/damage-associated molecular patterns; EGFR: epidermal growth factor receptor; EIF2A/eIF2α: eukaryotic translation initiation factor 2A; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; FITM2: fat storage inducing transmembrane protein 2; HCQ: hydroxychloroquine; ICB: immune checkpoint blockade; ICD: immunogenic cell death; LDH: lactate dehydrogenase; MAPK: mitogen-activated protein kinase; MTORC1: mechanistic target of rapamycin kinase complex 1; NDP52: nuclear dot protein 52; NFKB/NF-κ B: nuclear factor kappa B; NBR1: the neighbor of BRCA1; NK: natural killer; NRF1: nuclear respiratory factor 1; NSCLC: non-small-cell lung cancer; OPTN: optineurin; PDAC: pancreatic ductal adenocarcinoma; PDCD1/PD-1: programmed cell death 1; PPT1: palmitoyl-protein thioesterase 1; PTEN: phosphatase and tensin homolog; PTK2/FAK1: protein tyrosine kinase 2; RAS: rat sarcoma; SQSTM1/p62: sequestosome 1; STK11/LKB1: serine/threonine kinase 11; TAX1BP1: Tax1 binding protein 1; TFEB: transcription factor EB; TGFB/TGF-β: transforming growth factor beta; TMB: tumor mutational burden; TME: tumor microenvironment; TSC1: TSC complex subunit 1; TSC2: TSC complex subunit 2; ULK1: unc-51 like autophagy activating kinase 1; UVRAG: UV radiation resistance associated.

Circular RNA expression profile and functional analysis of circUvrag in light-induced photoreceptor degeneration

BACKGROUND

Circular RNAs (circRNAs) are implicated in retinal pathophysiology; however, their expression profiles and functions in photoreceptor apoptosis are largely unknown. We explored circRNA-expression profiles and circUvrag (host gene: Uvrag, ultraviolet radiation resistance associated gene) function in light-induced photoreceptor apoptosis.

METHODS

Sprague-Dawley rats and 661 W photoreceptor cells were exposed to blue light to establish light-induced photoreceptor degeneration. Differentially expressed circRNAs were identified using microarrays. Potential functions of dysregulated circRNAs were analysed using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses. CircUvrag expression and localization were evaluated using quantitative RT-PCR and fluorescence in situ hybridization, respectively. CircUvrag overexpression and knockdown were induced using a plasmid and a small interfering RNA, respectively, and retinal function and structure were assessed using scotopic electroretinography, haematoxylin-eosin staining, and TUNEL staining. Microglial migration was assessed using IBA1 immunostaining. The apoptosis ratio of photoreceptor cells in vitro was detected using flow cytometry.

RESULTS

We identified 764 differentially expressed circRNAs, which were potentially related with the development of retinal structures, including neurons, dendrites, and synapses, and might participate in nervous-system pathophysiology. Light exposure enriched circUvrag in the cytoplasm of photoreceptors in the outer nuclear layer (ONL). CircUvrag knockdown decreased photoreceptor apoptosis and microglial migration to the ONL after light exposure, preserving ONL thickness and a-wave amplitude. In vitro, circUvrag knockdown inhibited photoreceptor apoptosis, although circUvrag overexpression slightly promoted photoreceptor apoptosis.

CONCLUSIONS

CircUvrag knockdown attenuated light-induced photoreceptor apoptosis, and might be a potential target in retinal degeneration.

DDB2 promotes melanoma cell growth by transcriptionally regulating the expression of KMT2A and predicts a poor prognosis

Identification of potential key targets of melanoma, a fatal skin malignancy, is critical to the development of new cancer therapies. Lysine methyltransferase 2A (KMT2A) promotes melanoma growth by activating the human telomerase reverse transcriptase (hTERT) signaling pathway; however, the exact mechanism remains elusive. This study aimed to reveal new molecular targets that regulate KMT2A expression and melanoma growth. Using biotin-streptavidin-agarose pull-down and proteomics, we identified Damage-specific DNA-binding protein 2 (DDB2) as a KMT2A promoter-binding protein in melanoma cells and validated its role as a regulator of KMT2A/hTERT signaling. DDB2 knockdown inhibited the expression of KMT2A and hTERT and inhibited the growth of melanoma cells in vitro. Conversely, overexpression of DDB2 activated the expression of KMT2A and promoted the growth of melanoma cells. Additionally, we demonstrated that DDB2 expression was higher in tumor tissues of patients with melanoma than in corresponding normal tissues and was positively correlated with KMT2A expression. Kaplan-Meier analysis showed a poor prognosis in patients with high levels of DDB2 and KMT2A. Overall, our data suggest that DDB2 promotes melanoma cell growth through the transcriptional regulation of KMT2A expression and predicts poor prognosis. Therefore, targeting DDB2 may regulate the effects of KMT2A on melanoma growth and progression, providing a new potential therapeutic strategy for melanoma.

Beyond self‑eating: Emerging autophagy‑independent functions for the autophagy molecules in cancer (Review)

Autophagy is a conserved catabolic process that controls organelle quality, removes misfolded or abnormally aggregated proteins and is part of the defense mechanisms against intracellular pathogens. Autophagy contributes to the suppression of tumor initiation by promoting genome stability, cellular integrity, redox balance and proteostasis. On the other hand, once a tumor is established, autophagy can support cancer cell survival and promote epithelial‑to‑mesenchymal transition. A growing number of molecules involved in autophagy have been identified. In addition to their key canonical activity, several of these molecules, such as ATG5, ATG12 and Beclin‑1, also exert autophagy‑independent functions in a variety of biological processes. The present review aimed to summarize autophagy‑independent functions of molecules of the autophagy machinery and how the activity of these molecules can influence signaling pathways that are deregulated in cancer progression.

Targeting WDxR motif reprograms immune microenvironment and inhibits hepatocellular carcinoma progression

The WD-repeat (WDR) family affects carcinogenesis, but its role in the immune microenvironment is poorly characterized. Although functional loss or gain of WDR6 does not markedly change in vitro proliferative and invasive capacity of HCC cells, its deficiency in hepa1-6 cells drastically inhibits the growth and lung metastasis of orthotopically implanted tumors in immune-competent C57BL/6J mice. Mechanistically, WDR6 targets tumor suppressor UVRAG to the CUL4A-DDB1-ROC1 E3 ubiquitin ligase complex through a unique WDxR motif and promotes its degradation. This upregulates chromatin accessibility at the TNFα locus by blocking autophagic degradation of p65, elevates intratumoral myeloid-derived suppressor cell (MDSC) number, and reduces CD8⁺ T cell infiltration, thereby promoting HCC progression. These immunosuppressive effects are reversed by TNFα blockade. TNFα recruits NF-κB to activate the transcription of WDR6, establishing a WDR6-TNFα loop. Clinically, the WDR6/UVRAG/NF-κB pathway is hyperactivated in HCC, predicting a poor prognosis. Importantly, a WDxR-like peptide disrupts the WDR6/UVRAG complex and enhances the efficiency of anti-PD-L1 against HCC with WDR6 dysregulation.

Autophagy Paradox: Strategizing Treatment Modality in Melanoma

OPINION STATEMENT

The primordial autophagy process, originally identified as a starvation response in baker's yeast, has since been shown to have a wide spectrum of functions other than survival. In many cases, it is accepted that autophagy operates as a key tumor suppressor mechanism that protects cells from adverse environmental cues by enforcing homeostasis and maintaining the functional and structural integrity of organelles. Paradoxically, heightened states of autophagy are also seen in some cancers, leading to the prevailing view that the pro-survival aspect of autophagy might be hijacked by some tumors to promote their fitness and pathogenesis. Notably, recent studies have revealed a broad range of cell-autonomous autophagy in reshaping tumor microenvironment and maintaining lineage integrity and immune homeostasis, calling for a renewed understanding of autophagy beyond its classical roles in cell survival. Here, we evaluate the increasing body of literature that argues the "double-edged" consequences of autophagy manipulation in cancer therapy, with a particular focus on highly plastic and mutagenic melanoma. We also discuss the caveats that must be considered when evaluating whether autophagy blockade is the effector mechanism of some anti-cancer therapy particularly associated with lysosomotropic agents. If autophagy proteins are to be properly exploited as targets for anticancer drugs, their diverse and complex roles should also be considered.

Photoprotective Effects of Cannabidiol against Ultraviolet-B-Induced DNA Damage and Autophagy in Human Keratinocyte Cells and Mouse Skin Tissue

Cannabidiol (CBD) has emerged as a phytocannabinoid with various beneficial effects for the skin, including anti-photoaging effects, but its mechanisms of action are not fully elucidated. The study assessed CBD’s photoprotective effects against acute ultraviolet B (UVB)-induced damage in HaCaT human keratinocyte cells and murine skin tissue. CBD (8 μM) alleviated UVB-induced cytotoxicity, apoptosis, and G2/M cell cycle arrest in HaCaT cells. The contents of γH2AX and cyclobutane pyrimidine dimers were decreased after CBD treatment. CBD reduced the production of reactive oxygen species and modulated the expression of antioxidant-related proteins such as nuclear factor erythroid 2-related factor 2 in UVB-stimulated HaCaT cells. Furthermore, CBD mitigated the UVB-induced cytotoxicity by activating autophagy. In addition, a cream containing 5% CBD showed effectiveness against UVB-induced photodamage in a murine model. The CBD cream improved the skin’s condition by lowering the photodamage scores, reducing abnormal skin proliferation, and decreasing expression of the inflammation-related protein cyclooxygenase-2 in UVB-irradiated skin tissue. These findings indicate that CBD might be beneficial in alleviating UVB-induced skin damage in humans. The photoprotective effects of CBD might be attributed to its modulatory effects on redox homeostasis and autophagy.

Nrf2 Pathway and Autophagy Crosstalk: New Insights into Therapeutic Strategies for Ischemic Cerebral Vascular Diseases

Cerebrovascular disease is highly prevalent and has a complex etiology and variable pathophysiological activities. It thus poses a serious threat to human life and health. Currently, pathophysiological research on cerebrovascular diseases is gradually improving, and oxidative stress and autophagy have been identified as important pathophysiological activities that are gradually attracting increasing attention. Many studies have found some effects of oxidative stress and autophagy on cerebrovascular diseases, and studies on the crosstalk between the two in cerebrovascular diseases have made modest progress. However, further, more detailed studies are needed to determine the specific mechanisms. This review discusses nuclear factor erythroid 2-related factor 2 (Nrf2) molecules, which are closely associated with oxidative stress and autophagy, and the crosstalk between them, with the aim of providing clues for studying the two important pathophysiological changes and their crosstalk in cerebrovascular diseases as well as exploring new target treatments.

Pharmacological Activation of Autophagy Restores Cellular Homeostasis in Ultraviolet-(B)-Induced Skin Photodamage

Ultraviolet (UV) exposure to the skin causes photo-damage and acts as the primary etiological agent in photo-carcinogenesis. UV-B exposure induces cellular damage and is the major factor challenging skin homeostasis. Autophagy allows the fundamental adaptation of cells to metabolic and oxidative stress. Cellular dysfunction has been observed in aged tissues and in toxic insults to cells undergoing stress. Conversely, promising anti-aging strategies aimed at inhibiting the mTOR pathway have been found to significantly improve the aging-related disorders. Recently, autophagy has been found to positively regulate skin homeostasis by enhancing DNA damage recognition. Here, we investigated the geno-protective roles of autophagy in UV-B-exposed primary human dermal fibroblasts (HDFs). We found that UV-B irradiation to HDFs impairs the autophagy response in a time- and intensity-independent manner. However, improving autophagy levels in HDFs with pharmacological activators regulates the UV-B-induced cellular stress by decreasing the induction of DNA photo-adducts, promoting the DNA repair process, alleviating oxidative and ER stress responses, and regulating the expression levels of key cell cycle regulatory proteins. Autophagy also prevents HDFs from UV-B-induced nuclear damage as is evident in TUNEL assay and Acridine Orange/Ethidium Bromide co-staining. Salubrinal (an eIF2α phosphatase inhibitor) relieves ER stress response in cells and also significantly alleviates DNA damage and promotes the repair process in UV-B-exposed HDFs. P62-silenced HDFs show enhanced DNA damage response and also disturb the tumor suppressor PTEN/pAKT signaling axis in UV-B-exposed HDFs whereas Atg7-silenced HDFs reveal an unexpected consequence by decreasing the UV-B-induced DNA damage. Taken together, these results suggest that interventional autophagy offers significant protection against UV-B radiation-induced photo-damage and holds great promise in devising it as a suitable therapeutic strategy against skin pathological disorders.

Genome-wide signatures of mammalian skin covering evolution

Animal body coverings provide protection and allow for adaptation to environmental pressures such as heat, ultraviolet radiation, water loss, and mechanical forces. Here, using a comparative genomics analysis of 39 mammal species spanning three skin covering types (hairless, scaly and spiny), we found some genes (e.g., UVRAG, POLH, and XPC) involved in skin inflammation, skin innate immunity, and ultraviolet radiation damage repair were under selection in hairless ocean mammals (e.g., whales and manatees). These signatures might be associated with a high risk of skin diseases from pathogens and ultraviolet radiation. Moreover, the genomes from three spiny mammal species shared convergent genomic regions (EPHB2, EPHA4, and NIN) and unique positively selected genes (FZD6, INVS, and CDC42) involved in skin cell polarity, which might be related to the development of spines. In scaly mammals, the shared convergent genomic regions (e.g., FREM2) were associated with the integrity of the skin epithelium and epidermal adhesion. This study identifies potential convergent genomic features among distantly related mammals with the same skin covering type.

CRL4ADTL degrades DNA-PKcs to modulate NHEJ repair and induce genomic instability and subsequent malignant transformation

Genomic instability induced by DNA damage and improper DNA damage repair is one of the main causes of malignant transformation and tumorigenesis. DNA double strand breaks (DSBs) are the most detrimental form of DNA damage, and nonhomologous end-joining (NHEJ) mechanisms play dominant and priority roles in initiating DSB repair. A well-studied oncogene, the ubiquitin ligase Cullin 4A (CUL4A), is reported to be recruited to DSB sites in genomic DNA, but whether it regulates NHEJ mechanisms of DSB repair is unclear. Here, we discovered that the CUL4A-DTL ligase complex targeted the DNA-PKcs protein in the NHEJ repair pathway for nuclear degradation. Overexpression of either CUL4A or DTL reduced NHEJ repair efficiency and subsequently increased the accumulation of DSBs. Moreover, we demonstrated that overexpression of either CUL4A or DTL in normal cells led to genomic instability and malignant proliferation. Consistent with the in vitro findings, in human precancerous lesions, CUL4A expression gradually increased with increasing malignant tendency and was negatively correlated with DNA-PKcs and positively correlated with γ-H2AX expression. Collectively, this study provided strong evidence that the CUL4A-DTL axis increases genomic instability and enhances the subsequent malignant transformation of normal cells by inhibiting NHEJ repair. These results also suggested that CUL4A may be a prognostic marker of precancerous lesions and a potential therapeutic target in cancer.

Suppressing UVRAG Induces Radiosensitivity by Triggering Lysosomal Membrane Permeabilization in Hypopharyngeal Squamous Cell Carcinoma

Introduction

Radiotherapy is one of the most important methods in the treatment of patients with hypopharyngeal squamous cell carcinoma (HSCC). However, radioresistance will be developed after repeated irradiation. Among many key factors contributing to radioresistance, enhanced autophagy is recognized as one of the most important. The ultraviolent irradiation resistance-associated gene (UVRAG) is reported to be a crucial gene involved in the process of autophagy. Here, we test whether UVRAG has effect on the radioresistance of HSCC.

Methods

HSCC cell line Fadu cells were treated with irradiation to test levels of autophagy. Tumor tissues from primary and recurrent HSCC patients were tested by immunohistochemistry. Then, we knocked down UVRAG to test its role in cell growth and the malignant behaviors. Response of cells to treatment was examined using LDH release assay, immunofluorescence, Western blot analysis and colony formation.

Results

We found that irradiation induced autophagy in Fadu cells. Immunohistochemistry of primary and irradiated HSCC tumor tissues showed that UVRAG was upregulated after irradiation treatment. Inhibiting UVRAG with siRNA interfered cell growth, cell cycle, malignant behaviors and autophagic flux in Fadu cells. Knocking down UVRAG increased DNA damage and cell death induced by irradiation. Finally, we found that inhibiting UVRAG induced lysosomal membrane permeabilization, which contributed to radiosensitization of Fadu cells.

Conclusion

Our findings supported the oncogenic properties of UVRAG in HSCC and inhibiting UVRAG increased radiosensitivity in HSCC by triggering lysosomal membrane permeabilization. Therefore, UVRAG might be a promising target in the treatment of HSCC.

Integrating DNA damage response and autophagy signalling axis in ultraviolet-B induced skin photo-damage: a positive association in protecting cells against genotoxic stress

The skin acts as both physical as well as an immunological barrier against hazardous agents from the outside environment and protects the internal organs against damage. Skin ageing is a dynamic process caused by the influence of various external factors, including damage from ultraviolet (UV-B) radiation, which is known as photo-ageing, and due to internal chronological mechanisms. A normal ageing process requires several orchestrated defense mechanisms to diverse types of stress responses, the concomitant renewal of cellular characteristics, and the homeostasis of different cell types that directly or indirectly protect the integrity of skin. Cumulative oxidative and endoplasmic reticulum (ER) stress responses and their adverse impact on biological systems in the skin are a common mechanism of the ageing process, negatively impacting DNA by causing mutations that lead to many physiological, functional, and aesthetic changes in the skin, culminating in the development of many diseases, including photo-damage and photo-carcinogenesis. Exposure of the skin to ultraviolet-(B) elicits the activation of signal transduction pathways, including DNA damage response, autophagy, and checkpoint signal adaptations associated with clearing radiation-induced DNA damage. Recent experimental reports suggest that autophagy is involved in maintaining skin homeostasis upon encountering different stresses, notably genotoxic stress. It has also been revealed that autophagy positively regulates the recognition of DNA damage by nucleotide excision repair and that skin ageing is associated with defects in the autophagy process. Moreover, autophagy is constitutively active in the skin epithelium, imparting protection to skin cells against a diverse range of outside insults, thus increasing resistance to environmental stressors. It has also been found that the stress-induced suppression of the autophagy response in experimental settings leads to enhanced apoptosis during photo-ageing upon UV-B exposure and that the maintenance of homeostasis depends on cellular autophagy levels. More recent reports in this domain claim that relieving the oxidative-stress-mediated induction of the ER stress response upon UV-B irradiation protects skin cells from photo-damage effects. The integration of autophagy and the DNA damage response under genotoxic stress is being considered as a meaningful partnership for finding novel molecular targets and devising suitable therapeutic strategies against photo-ageing disorders. Here, we summarize and review the current understanding of the mechanisms governing the intricate interplay between autophagy and the DNA damage response and its regulation by UV-B, the roles of autophagy in regulating the cellular response to UV-B-induced photodamage, and the implications of the modulation of autophagy as a meaningful partnership in the treatment and prevention of photoaging disorders.

Autophagy-Independent Functions of the Autophagy Machinery

Macroautophagy (herein referred to as autophagy) is an evolutionary ancient mechanism that culminates with the lysosomal degradation of superfluous or potentially dangerous cytosolic entities. Over the past 2 decades, the molecular mechanisms underlying several variants of autophagy have been characterized in detail. Accumulating evidence suggests that most, if not all, components of the molecular machinery for autophagy also mediate autophagy-independent functions. Here, we discuss emerging data on the non-autophagic functions of autophagy-relevant proteins.

How autophagy is tied to inflammation and cancer

It is not completely understood how autophagy is tied to inflammation and age-related cancer predisposition. Here, we used a mouse model with inducible expression of a cancer-derived frameshift mutation in UV radiation resistance associated (UVRAG) to demonstrate that intervention with autophagy suppressor could exacerbate inflammation and promote age-related spontaneous cancers.

Autophagy as a Cellular Stress Response Mechanism in the Nervous System

Cells of an organism face with various types of insults during their lifetime. Exposure to toxins, metabolic problems, ischaemia/reperfusion, physical trauma, genetic diseases, neurodegenerative diseases are among the conditions that trigger cellular stress responses. In this context, autophagy is one of the mechanisms that supports cell survival under stressful conditions. Autophagic vesicle engulfs the cargo and transports it to lysosome for degradation and turnover. As such, autophagy eliminates abnormal proteins, clears damaged organelles, limits oxidative stress and helps to improve metabolic balance. Nervous system cells and particularly postmitotic neurons are highly sensitive to a spectrum of insults, and autophagy emerges as one of the key stress response mechanism, ensuring health and survival of these vulnerable cell types. In this review, we will overview mechanisms through which cells cope with stress, and how these stress responses regulate autophagy, with a special focus on the nervous system.

A truncating mutation in the autophagy gene UVRAG drives inflammation and tumorigenesis in mice

Aberrant autophagy is a major risk factor for inflammatory diseases and cancer. However, the genetic basis and underlying mechanisms are less established. UVRAG is a tumor suppressor candidate involved in autophagy, which is truncated in cancers by a frameshift (FS) mutation and expressed as a shortened UVRAGFS. To investigate the role of UVRAGFS in vivo, we generated mutant mice that inducibly express UVRAGFS (iUVRAGFS). These mice are normal in basal autophagy but deficient in starvation- and LPS-induced autophagy by disruption of the UVRAG-autophagy complex. iUVRAGFS mice display increased inflammatory response in sepsis, intestinal colitis, and colitis-associated cancer development through NLRP3-inflammasome hyperactivation. Moreover, iUVRAGFS mice show enhanced spontaneous tumorigenesis related to age-related autophagy suppression, resultant β-catenin stabilization, and centrosome amplification. Thus, UVRAG is a crucial autophagy regulator in vivo, and autophagy promotion may help prevent/treat inflammatory disease and cancer in susceptible individuals.

Pro-survival autophagy and cancer cell resistance to therapy

Resistance to therapy is one of the prime causes for treatment failure in cancer and recurrent disease. In recent years, autophagy has emerged as an important cell survival mechanism in response to different stress conditions that are associated with cancer treatment and aging. Autophagy is an evolutionary conserved catabolic process through which damaged cellular contents are degraded after uptake into autophagosomes that subsequently fuse with lysosomes for cargo degradation, thereby alleviating stress. In addition, autophagy serves to maintain cellular homeostasis by enriching nutrient pools. Although autophagy can act as a double-edged sword at the interface of cell survival and cell death, increasing evidence suggest that in the context of cancer therapy-induced stress responses, it predominantly functions as a cell survival mechanism. Here, we provide an up-to-date overview on our current knowledge of the role of pro-survival autophagy in cancer therapy at the preclinical and clinical stages and delineate the molecular mechanisms of autophagy regulation in response to therapy-related stress conditions. A better understanding of the interplay of cancer therapy and autophagy may allow to unveil new targets and avenues for an improved treatment of therapy-resistant tumors in the foreseeable future.

Ubiquitination of UVRAG by SMURF1 promotes autophagosome maturation and inhibits hepatocellular carcinoma growth

UVRAG (UV radiation resistance associated) is an important regulator of mammalian macroautophagy/autophagy by interacting with BECN1, PIK3C3, and RUBCN. Phosphorylation of UVRAG by MTORC1 negatively regulates autophagosome maturation under nutrient-enriched conditions. However, how UVRAG ubiquitination is regulated is still unknown. Here we report that UVRAG is ubiquitinated by SMURF1 at lysine residues 517 and 559, which decreases the association of UVRAG with RUBCN and promotes autophagosome maturation. However, the deubiquitinase ZRANB1 specifically cleaves SMURF1-induced K29 and K33-linked polyubiquitin chains from UVRAG, thereby increasing the binding of UVRAG to RUBCN and inhibiting autophagy flux. We also demonstrate that CSNK1A1-mediated UVRAG phosphorylation at Ser522 disrupts the binding of SMURF1 to UVRAG through PPxY motif and blocks UVRAG ubiquitination-mediated autophagosome maturation. Interestingly, ZRANB1 is phosphorylated at Thr35, and Ser209 residues by CSNK1A1, and this phosphorylation activates its deubiquitinating activity. Importantly, we provide in vitro and in vivo evidence that UVRAG ubiquitination at lysine residues 517 and 559 or prevention of Ser522 phosphorylation by D4476, a CSNK1A1 inhibitor, enhances the lysosomal degradation of EGFR, which significantly inhibits hepatocellular carcinoma (HCC) growth. Furthermore, UVRAG S522 phosphorylation levels correlate with ZRANB1 T35/S209 phosphorylation levels and poor prognosis in HCC patients. These findings identify a novel molecular mechanism by which ubiquitination and phosphorylation of UVRAG regulate its function in autophagosome maturation and HCC growth, encouraging further study of their potential therapeutic implications.

Abbreviations: ATG: autophagy related; BafA₁: bafilomycin A₁; BECN1: beclin 1; CHX: cycloheximide; CSNK1A1/CK1α: casein kinase 1 alpha 1; CQ: chloroquine; DUB: deubiquitinase; EBSS: Earle’s balanced salt solution; EGF: epidermal growth factor; GFP: green fluorescent protein; GST: glutathione S-transferase; HBSS: Hanks balanced salts solution; HCC: hepatocellular carcinoma; MAP1LC3B/LC3: microtubule associated protein 1 light chain 3 beta; MEFs: mouse embryo fibroblasts; mRFP: monomeric red fluorescent protein; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PTMs: post-translational modifications; RUBCN: rubicon autophagy regulator; siRNA: small interfering RNA; SMURF1: SMAD specific E3 ubiquitin protein ligase 1; SQSTM1: sequestosome 1; Ub-AMC: ubiquitin-7-amido-4-methylcoumarin: a fluorogenic substrate; UVRAG: UV radiation resistance associated; ZRANB1/TRABID: zinc finger RANBP2-type containing 1

Activation of RIG-I-Mediated Antiviral Signaling Triggers Autophagy Through the MAVS-TRAF6-Beclin-1 Signaling Axis

Autophagy has been implicated in innate immune responses against various intracellular pathogens. Recent studies have reported that autophagy can be triggered by pathogen recognizing sensors, including Toll-like receptors and cyclic guanosine monophosphate-adenosine monophosphate synthase, to participate in innate immunity. In the present study, we examined whether the RIG-I signaling pathway, which detects viral infections by recognizing viral RNA, triggers the autophagic process. The introduction of polyI:C into the cytoplasm, or Sendai virus infection, significantly induced autophagy in normal cells but not in RIG-I-deficient cells. PolyI:C transfection or Sendai virus infection induced autophagy in the cells lacking type-I interferon signaling. This demonstrated that the effect was not due to interferon signaling. RIG-I-mediated autophagy diminished by the deficiency of mitochondrial antiviral signaling protein (MAVS) or tumor necrosis factor receptor-associated factor (TRAF)6, showing that the RIG-I-MAVS-TRAF6 signaling axis was critical for RIG-I-mediated autophagy. We also found that Beclin-1 was translocated to the mitochondria, and it interacted with TRAF6 upon RIG-I activation. Furthermore, Beclin-1 underwent K63-polyubiquitination upon RIG-I activation, and the ubiquitination decreased in TRAF6-deficient cells. This suggests that the RIG-I-MAVS-TRAF6 axis induced K63-linked polyubiquitination of Beclin-1, which has been implicated in triggering autophagy. As deficient autophagy increases the type-I interferon response, the induction of autophagy by the RIG-I pathway might also contribute to preventing an excessive interferon response as a negative-feedback mechanism.

Ultraviolet radiation-mediated development of cutaneous melanoma: An update

Ultraviolet (UV) light is absorbed by nucleic acids, proteins or other endogenous chromophores, such as porphyrins, flavins and melanin, triggering biological processes in skin cells. Both UV-induced mutations in melanocytes and changes in the immune microenvironment are understood to play a role in the development of cutaneous melanoma. The degree of UV-induced stress and the protection against this stress are influenced by both intracellular and intercellular molecular interactions. The present review summarizes the known major molecular biological changes induced by UV light in the skin that play a role in melanoma initiation and promotion. Nevertheless, cutaneous melanoma is not a homogenous disease, and the interaction of variable environmental exposure and different genetic susceptibility and other host factors lead to the formation of melanomas with different biological behavior and clinical characteristics. This review highlights the challenges in the understanding of how UV radiation contributes to the formation of cutaneous melanoma, and reviews the new results of photobiology and their link to tumor genetics and tumor immunology with potential implications on melanoma prevention and therapeutic strategies. The information presented here is expected to add clarity to ongoing research efforts in this field to aid the development of novel strategies to prevent and treat melanoma.

Central role of autophagic UVRAG in melanogenesis and the suntan response

UV-induced cell pigmentation represents an important mechanism against skin cancers. Sun-exposed skin secretes α-MSH, which induces the lineage-specific transcriptional factor MITF and activates melanogenesis in melanocytes. Here, we show that the autophagic tumor suppressor UVRAG plays an integral role in melanogenesis by interaction with the biogenesis of lysosome-related organelles complex 1 (BLOC-1). This interaction is required for BLOC-1 stability and for BLOC-1-mediated cargo sorting and delivery to melanosomes. Absence of UVRAG dispersed BLOC-1 distribution and activity, resulting in impaired melanogenesis in vitro and defective melanocyte development in zebrafish in vivo. Furthermore, our results establish UVRAG as an important effector for melanocytes' response to α-MSH signaling as a direct target of MITF and reveal the molecular basis underlying the association between oncogenic BRAF and compromised UV protection in melanoma.

The replication initiation determinant protein (RepID) modulates replication by recruiting CUL4 to chromatin

Cell cycle progression in mammals is modulated by two ubiquitin ligase complexes, CRL4 and SCF, which facilitate degradation of chromatin substrates involved in the regulation of DNA replication. One member of the CRL4 complex, the WD-40 containing protein RepID (DCAF14/PHIP), selectively binds and activates a group of replication origins. Here we show that RepID recruits the CRL4 complex to chromatin prior to DNA synthesis, thus playing a crucial architectural role in the proper licensing of chromosomes for replication. In the absence of RepID, cells rely on the alternative ubiquitin ligase, SKP2-containing SCF, to progress through the cell cycle. RepID depletion markedly increases cellular sensitivity to SKP2 inhibitors, which triggered massive genome re-replication. Both RepID and SKP2 interact with distinct, non-overlapping groups of replication origins, suggesting that selective interactions of replication origins with specific CRL components execute the DNA replication program and maintain genomic stability by preventing re-initiation of DNA replication.

RepID has previously been shown to promote origin firing. Here the authors reveal that RepID regulates replication origins via the recruitment of the CRL4 complex, and prevents re-initiation and unscheduled DNA replication.

Autophagy Roles in the Modulation of DNA Repair Pathways

Autophagy and DNA repair are biological processes vital for cellular homeostasis maintenance and when dysfunctional, they lead to several human disorders including premature aging, neurodegenerative diseases, and cancer. The interchange between these pathways is complex and it may occur in both directions. Autophagy is activated in response to several DNA lesions types and it can regulate different mechanisms and molecules involved in DNA damage response (DDR), such as cell cycle checkpoints, cell death, and DNA repair. Thus, autophagy may modulate DNA repair pathways, the main focus of this review. In addition to the already well-documented autophagy positive effects on homologous recombination (HR), autophagy has also been implicated with other DNA repair mechanisms, such as base excision repair (BER), nucleotide excision repair (NER), and mismatch repair (MMR). Given the relevance of these cellular processes, the clinical applications of drugs targeting this autophagy-DNA repair interface emerge as potential therapeutic strategies for many diseases, especially cancer.

Autophagy in UV Damage Response

UV radiation exposure from sunlight and artificial tanning beds is the major risk factor for the development of skin cancer and skin photoaging. UV-induced skin damage can trigger a cascade of DNA damage response signaling pathways, including cell cycle arrest, DNA repair and, if damage is irreparable, apoptosis. Compensatory proliferation replaces the apoptotic cells to maintain skin barrier integrity. Disruption of these processes can be exploited to promote carcinogenesis by allowing the survival and proliferation of damaged cells. UV radiation also induces autophagy, a catabolic process that clears unwanted or damaged proteins, lipids and organelles. The mechanisms by which autophagy is activated following UV exposure, and the functions of autophagy in UV response, are only now being clarified. Here, we summarize the current understanding of the mechanisms governing autophagy regulation by UV, the roles of autophagy in regulating cellular response to UV-induced photodamage and the implications of autophagy modulation in the treatment and prevention of photoaging and skin cancer.

Nucleotide Excision Repair: From Neurodegeneration to Cancer

DNA damage poses a constant threat to genome integrity taking a variety of shapes and arising by normal cellular metabolism or environmental insults. Human syndromes, characterized by increased cancer pre-disposition or early onset of age-related pathology and developmental abnormalities, often result from defective DNA damage responses and compromised genome integrity. Over the last decades intensive research worldwide has made important contributions to our understanding of the molecular mechanisms underlying genomic instability and has substantiated the importance of DNA repair in cancer prevention in the general population. In this chapter, we discuss Nucleotide Excision Repair pathway, the causative role of its components in disease-related pathology and recent technological achievements that decipher mutational landscapes and may facilitate pathological classification and personalized therapy.

DNA Damage Response and Autophagy: A Meaningful Partnership

Autophagy and the DNA damage response (DDR) are biological processes essential for cellular and organismal homeostasis. Herein, we summarize and discuss emerging evidence linking DDR to autophagy. We highlight published data suggesting that autophagy is activated by DNA damage and is required for several functional outcomes of DDR signaling, including repair of DNA lesions, senescence, cell death, and cytokine secretion. Uncovering the mechanisms by which autophagy and DDR are intertwined provides novel insight into the pathobiology of conditions associated with accumulation of DNA damage, including cancer and aging, and novel concepts for the development of improved therapeutic strategies against these pathologies.

Transcriptional and Posttranslational Regulation of Nucleotide Excision Repair: The Guardian of the Genome against Ultraviolet Radiation

Ultraviolet (UV) radiation from sunlight represents a constant threat to genome stability by generating modified DNA bases such as cyclobutane pyrimidine dimers (CPD) and pyrimidine-pyrimidone (6-4) photoproducts (6-4PP). If unrepaired, these lesions can have deleterious effects, including skin cancer. Mammalian cells are able to neutralize UV-induced photolesions through nucleotide excision repair (NER). The NER pathway has multiple components including seven xeroderma pigmentosum (XP) proteins (XPA to XPG) and numerous auxiliary factors, including ataxia telangiectasia and Rad3-related (ATR) protein kinase and RCC1 like domain (RLD) and homologous to the E6-AP carboxyl terminus (HECT) domain containing E3 ubiquitin protein ligase 2 (HERC2). In this review we highlight recent data on the transcriptional and posttranslational regulation of NER activity.