YAP ISGylation increases its stability and promotes its positive regulation on PPP by stimulating 6PGL transcription

HERC5/ISG15 Enhances Glioblastoma Stemness and Tumor Progression by mediating SERBP1protein stability

Glioblastoma (GBM) is the most common malignant brain tumor, and has a low survival rate and a poor prognosis. Intensive studies of pathogenic mechanisms are essential for exploring therapeutic targets for GBM. In this study, the roles played by interferon-stimulated gene 15 (ISG15), HECT, RCC1-containing protein 5 (HERC5), and SERPINE1 mRNA binding protein 1 (SERBP1) in regulating GBM cell stemness were investigated. The real-time quantitative polymerase chain reaction (qPCR), western blotting (WB), and immunohistochemistry (IHC) were used to determine the expression levels of HERC5, ISG15, and SERBP1. Cell stemness was analyzed using a cell sphere formation assay. Colony formation and cell counting kit-8 (CCK-8) assays were performed to assess cell proliferation, Transwell assays used to evaluate cell migration and invasion, and flow cytometry was used to assess cell apoptosis after treatment with temozolomide. SERBP1 stability was assessed by a CHX chase assay. A co-immunoprecipitation (Co-IP) assay verified the binding of ISG15 and HERC5 onto SERBP1. Our results showed that HERC5 and ISG15 were highly expressed in GBM. HERC5 and ISG15 promoted the cell stemness of GBM, and increased cell proliferation, sphere formation, migration, invasion, and chemoresistance. Moreover, HERC5 and ISG15 played a synergistic role in promoting the cell stemness of GBM. We also found that HERC5/ISG15 promoted the stability of SERBP1, which also promoted the cell stemness of GBM. The tumor-promoting role of HERC5 and ISG15 was also confirmed in a subcutaneous xenograft tumor model. Collectively, HERC5/ISG15 was found to regulate GBM stemness and tumor progression by mediating SERBP1 protein stability. Our present study suggests a promising therapeutic target for GBM.

YAP K236 acetylation facilitates its nucleic export and deprived the protection against cardiac hypertrophy in mice

The subcellular localization of Yes-associated protein (YAP) is dynamically regulated by post-transcriptional modifications, critically influencing cardiac function. Despite its significance, the precise mechanism controlling YAP nuclear sequestration and its role in cardiac hypertrophy remain poorly defined. In this study, utilizing immunoprecipitation-mass spectrometry, we identified potential acetylation sites and interacting proteins of YAP. Co-immunoprecipitation and immunofluorescence assays were used to elucidate the protein interactions and subcellular colocalization. We found that YAP protected against ISO-induced pathological cardiac hypertrophy both in vivo and in vitro. During cardiac hypertrophy YAP acetylation increased while its nuclear accumulation reduced without altering Ser127 phosphorylation. Notably, lysine 236 was identified as a novel acetylation site on YAP. Acetylation at K236 facilitated YAP's nucleic export, suppressed the expression of target genes such as NRF1 and Cox IV, and counteracted YAP's anti-hypertrophic effects. Importantly, deacetylase SIRT6 was identified as a regulator of YAP deacetylation, disrupting the YAP with chaperone protein 14-3-3 interaction and inhibiting YAP's nuclear export, thereby facilitating cardiac protective role of YAP. This study identified YAP K236 acetylation as a key regulator of its nuclear retention in cardiomyocytes, with SIRT6-mediated deacetylation facilitating YAP's protective effects against cardiac hypertrophy. Targeting YAP acetylation may offer a promising therapeutic strategy for cardiac hypertrophy.

YAP phosphorylation within integrin adhesions: Insights from a computational model

Mechanical and biochemical cues intricately activate Yes-associated protein (YAP), which is pivotal for the cellular responses to these stimuli. Recent findings reveal an unexplored role of YAP in influencing the apoptotic process. It has been shown that, on soft matrices, YAP is recruited to small adhesions, phosphorylated at Y357, and translocated into the nucleus triggering apoptosis. Interestingly, YAP Y357 phosphorylation is significantly reduced in larger mature focal adhesions on stiff matrices. Building upon these novel insights, we have developed a stochastic model to delve deeper into the complex dynamics of YAP phosphorylation within integrin adhesions. Our findings emphasize several key points: firstly, increasing the cytosolic diffusion rate of YAP correlates with higher levels of phosphorylated YAP (pYAP); secondly, increasing the number of binding sites and distributing them across the membrane surface, mimicking smaller adhesions, leads to higher pYAP levels, particularly at lower diffusion rates. Moreover, we show that the binding and release rate of YAP to adhesions as well as adhesion lifetimes significantly influence the size effect of adhesion-induced YAP phosphorylation. The results highlight the complex and dynamic interplay between adhesion lifetime, the rate of pYAP unbinding from adhesions, and dephosphorylation rates, collectively shaping overall pYAP levels. In summary, our work advances the understanding of YAP mechanotransduction and opens avenues for experimental validation.

ABCG2 shields against epilepsy, relieves oxidative stress and apoptosis via inhibiting the ISGylation of STAT1 and mTOR

The transporter protein ABC subfamily G member 2 (ABCG2) is implicated in epilepsy; however, its specific role remains unclear. In this study, we assessed changes in ABCG2 expression and its role in epilepsy both in vitro and in vivo. We observed an instantaneous increase in ABCG2 expression in epileptic animals and cells. Further, ABCG2 overexpression significantly suppressed the oxidative stress and apoptosis induced by glutamate, kainic acid (KA), and lipopolysaccharide (LPS) in neuronal and microglia cells. Furthermore, inhibiting ABCG2 activity offset this protective effect. ABCG2-deficient mice (ABCG2-/-) showed shorter survival times and decreased survival rates when administered with pentylenetetrazole (PTZ). We also noticed the accumulation of signal transducer and activator of transcription 1 (STAT1) and decreased phosphorylation of mammalian target of rapamycin kinase (mTOR) along with increased ISGylation in ABCG2-/- mice. ABCG2 overexpression directly interacted with STAT1 and mTOR, leading to a decrease in their ISGylation. Our findings indicate the rapid increase in ABCG2 expression acts as a shield in epileptogenesis, indicating ABCG2 may serve as a potential therapeutic target for epilepsy treatment.

Advances of E3 ligases in lung cancer

Lung cancer is a leading cause of cancer-related death, and the most common type of lung cancer is non-small cell lung cancer, which accounts for approximately 85 % of lung cancer diagnoses. Recent studies have revealed that ubiquitination acts as a crucial part of the development and progression of lung cancer. The E1-E2-E3 three-enzyme cascade has a core function in ubiquitination, so targeted adjustments of E3 ligases could be used in lung cancer treatment. Hence, we elucidate research advances in lung cancer-related E3 ligases by briefly describing the structure and categorization of E3 ligases. Here, we provide a detailed review of the mechanisms by which lung cancer-related E3 ligases modify substrate proteins and regulate signaling pathways to facilitate or suppress cancer progression. We hope to show a new perspective on targeted precision therapy for lung cancer.

Regulation of myocardial glucose metabolism by YAP/TAZ signaling

The heart utilizes glucose and its metabolites as both energy sources and building blocks for cardiac growth and survival under both physiological and pathophysiological conditions. YAP/TAZ, transcriptional co-activators of the Hippo pathway, are key regulators of cell proliferation, survival, and metabolism in many cell types. Increasing lines of evidence suggest that the Hippo-YAP/TAZ signaling pathway is involved in the regulation of both physiological and pathophysiological processes in the heart. In particular, YAP/TAZ play a critical role in mediating aerobic glycolysis, the Warburg effect, in cardiomyocytes. Here, we summarize what is currently known about YAP/TAZ signaling in the heart by focusing on the regulation of glucose metabolism and its functional significance.

Porcine HERC6 acts as major E3 ligase for ISGylation and is auto-ISGylated for effective ISGylation in porcine

Interferon-stimulated gene product 15 (ISG15) can be conjugated to substrates through ISGylation. Currently, the E3 ligase for porcine ISGylation remains unclear. Here, we identified porcine HERC5 and HERC6 (pHERC5/6) as ISGylation E3 ligases with pHERC6 acting as a major one by reconstitution of porcine ISGylation system in HEK-293 T cell via co-transfecting E1, E2 and porcine ISG15(pISG15) genes. Meanwhile, our data demonstrated that co-transfection of pISG15 and pHERC5/6 was sufficient to confer ISGylation, suggesting E1 and E2 of ISGylation are interchangeable between human and porcine. Using an immunoprecipitation based ISGylation analysis, our data revealed pHERC6 was a substrate for ISGylation and confirmed that K707 and K993 of pHERC6 were auto-ISGylation sites. Mutation of these sites reduced pHERC6 half-life and inhibited ISGylation, suggesting that auto-ISGylation of pHERC6 was required for effective ISGylation. Conversely, sustained ISGylation induced by overexpression of pISG15 and pHERC6 could be inhibited by a well-defined porcine ISGylation antagonist, the ovarian tumor (OTU) protease domain of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)-nsp2 and PRRSV-nsp1β, further indicating such method could be used for identification of virus-encoded ISG15 antagonist. In conclusion, our study contributes new insights towards porcine ISGylation system and provides a novel tool for screening viral-encoded ISG15 antagonist.

Transcriptional corepressor activity of CtBP1 is regulated by ISG15 modification

C-terminal binding protein 1 (CtBP1) is a critical transcriptional corepressor of many tumor suppressor genes and plays diverse roles in the progression of cancers. The transcriptional repression function of CtBP1 is mediated by recruiting histone-modifying enzymes, such as histone deacetylases and histone methyltransferases, to target genes by binding with DNA-interacting factors. Several post-translational modifications of CtBP1 have been identified, including ubiquitination, phosphorylation, and SUMOylation. This paper reports that CtBP1 is conjugated by ISG15. Endogenous CtBP1 was modified by ISG15 after interferon-α treatment in HeLa cells. The ISGylation process of CtBP1 was regulated by deISGylation enzyme USP18 and ISG15 E3 ligase EFP. Interestingly, CtBP1 ISGylation affected the binding affinity between CtBP1 and some components of CtBP1-associated transcriptional complexes. HDAC1 and LSD1 bound more efficiently to ISG15-conjugated CtBP1 than non-conjugated CtBP1. On the other hand, binding between CtBP1 and HDAC4 was unaffected by ISG15 modification. Furthermore, ISG15 modification enhanced the transcriptional repression activity of CtBP1 on several target genes related to EMT and apoptosis. These findings suggest that the ISG15 modification of CtBP1 modulates the function and activity of CtBP1 and that CtBP1 ISGylation may provide a new insight for CtBP1-mediated cancers.

Unveiling the Multifaceted Roles of ISG15: From Immunomodulation to Therapeutic Frontiers

The Interferon Stimulated Gene 15 (ISG15), a unique Ubiquitin-like (Ubl) modifier exclusive to vertebrates, plays a crucial role in the immune system. Primarily induced by interferon (IFN) type I, ISG15 functions through diverse mechanisms: (i) covalent protein modification (ISGylation); (ii) non-covalent intracellular action; and (iii) exerting extracellular cytokine activity. These various roles highlight its versatility in influencing numerous cellular pathways, encompassing DNA damage response, autophagy, antiviral response, and cancer-related processes, among others. The well-established antiviral effects of ISGylation contrast with its intriguing dual role in cancer, exhibiting both suppressive and promoting effects depending on the tumour type. The multifaceted functions of ISG15 extend beyond intracellular processes to extracellular cytokine signalling, influencing immune response, chemotaxis, and anti-tumour effects. Moreover, ISG15 emerges as a promising adjuvant in vaccine development, enhancing immune responses against viral antigens and demonstrating efficacy in cancer models. As a therapeutic target in cancer treatment, ISG15 exhibits a double-edged nature, promoting or suppressing oncogenesis depending on the tumour context. This review aims to contribute to future studies exploring the role of ISG15 in immune modulation and cancer therapy, potentially paving the way for the development of novel therapeutic interventions, vaccine development, and precision medicine.

Protein ISGylation: a posttranslational modification with implications for malignant neoplasms

Interferon (IFN)-stimulated gene 15 (ISG15) is a member of the ubiquitin-like (UBL) protein family that can modify specific proteins via a catalytic process called ISGylation. This posttranslational modification can modulate the stability of the ISGylated proteins and protein-protein interactions. Some proteins modified by ISG15 have been identified in malignant neoplasms, suggesting the functional relevance of ISGylation in cancer. This review discusses the ISGylated proteins reported in malignant neoplasms that suggest the potential of ISG15 as a biomarker and therapeutic target in cancer.

On the Value of In Vitro Cell Systems for Mechanobiology from the Perspective of Yes-Associated Protein/Transcriptional Co-Activator with a PDZ-Binding Motif and Focal Adhesion Kinase and Their Involvement in Wound Healing, Cancer, Aging, and Senescence

Mechanobiology comprises how cells perceive different mechanical stimuli and integrate them into a process called mechanotransduction; therefore, the related mechanosignaling cascades are generally important for biomedical research. The ongoing discovery of key molecules and the subsequent elucidation of their roles in mechanobiology are fundamental to understanding cell responses and tissue conditions, such as homeostasis, aging, senescence, wound healing, and cancer. Regarding the available literature on these topics, it becomes abundantly clear that in vitro cell systems from different species and tissues have been and are extremely valuable tools for enabling the discovery and functional elucidation of key mechanobiological players. Therefore, this review aims to discuss the significant contributions of in vitro cell systems to the identification and characterization of three such key players using the selected examples of yes-associated protein (YAP), its paralog transcriptional co-activator with a PDZ-binding motif (TAZ), and focal adhesion kinase (FAK) and their involvement in wound healing, cancer, aging, and senescence. In addition, the reader is given suggestions as to which future prospects emerge from the in vitro studies discussed herein and which research questions still remain open.

The Functional Roles of ISG15/ISGylation in Cancer

The protein ISG15 encoded by interferon-stimulated gene (ISG) 15 is the first identified member of the ubiquitin-like protein family and exists in the form of monomers and conjugated complexes. Like ubiquitin, ISG15 can mediate an ubiquitin-like modification by covalently modifying other proteins, known as ISGylation. There is growing evidence showing that both the free and conjugated ISG15 are involved in multiple key cellular processes, including autophagy, exosome secretion, DNA repair, immune regulation, and cancer occurrence and progression. In this review, we aim to further clarify the function of ISG15 and ISGylation in cancer, demonstrate the important relationship between ISG15/ISGylation and cancer, and emphasize new insights into the different roles of ISG15/ISGylation in cancer progression. This review may contribute to therapeutic intervention in cancer. However, due to the limitations of current research, the regulation of ISG15/ISGylation on cancer progression is not completely clear, thus further comprehensive and sufficient correlation studies are still needed.

Underlying mechanisms of epithelial splicing regulatory proteins in cancer progression

Cancer is the second-leading disease-related cause of global mortality after cardiovascular disease. Despite significant advances in cancer therapeutic strategies, cancer remains one of the major obstacles to human life extension. Cancer pathogenesis is extremely complicated and not fully understood. Epithelial splicing regulatory proteins (ESRPs), including ESRP1 and ESRP2, belong to the heterogeneous nuclear ribonucleoprotein family of RNA-binding proteins and are crucial regulators of the alternative splicing of messenger RNAs (mRNAs). The expression and activity of ESRPs are modulated by various mechanisms, including post-translational modifications and non-coding RNAs. Although a growing body of evidence suggests that ESRP dysregulation is closely associated with cancer progression, the detailed mechanisms remain inconclusive. In this review, we summarize recent findings on the structures, functions, and regulatory mechanisms of ESRPs and focus on their underlying mechanisms in cancer progression. We also highlight the clinical implications of ESRPs as prognostic biomarkers and therapeutic targets in cancer treatment. The information reviewed herein could be extremely beneficial to the development of individualized therapeutic strategies for cancer patients.

ISGylation of EMD promotes its interaction with PDHA to inhibit aerobic oxidation in lung adenocarcinoma

Abnormal nuclear structure caused by dysregulation of skeletal proteins is a common phenomenon in tumour cells. However, how skeletal proteins promote tumorigenesis remains uncovered. Here, we revealed the mechanism by which skeletal protein Emerin (EMD) promoted glucose metabolism to induce lung adenocarcinoma (LUAD). Firstly, we identified that EMD was highly expressed and promoted the malignant phenotypes in LUAD. The high expression of EMD might be due to its low level of ubiquitination. Additionally, the ISGylation at lysine 37 of EMD inhibited lysine 36 ubiquitination and upregulated EMD stability. We further explored that EMD could inhibit aerobic oxidation and stimulate glycolysis. Mechanistically, via its β‐catenin interaction domain, EMD bound with PDHA, stimulated serine 293 and 300 phosphorylation and inhibited PDHA expression, facilitated glycolysis of glucose that should enter the aerobic oxidation pathway, and EMD ISGylation was essential for EMD‐PDHA interaction. In clinical LUAD specimens, EMD was negatively associated with PDHA, while positively associated with EMD ISGylation, tumour stage and diameter. In LUAD with higher glucose level, EMD expression and ISGylation were higher. Collectively, EMD was a stimulator for LUAD by inhibiting aerobic oxidation via interacting with PDHA. Restricting cancer‐promoting role of EMD might be helpful for LUAD treatment.