PIAS3 enhances the transcriptional activity of HIF-1α by increasing its protein stability

CpSmt3, an ortholog of small ubiquitin-like modifier, is essential for growth, organelle function, virulence, and antiviral defense in Cryphonectria parasitica

Introduction

SUMOylation is an important post-translational modification that regulates the expression, localization, and activity of substrate proteins, thereby participating in various important cellular processes such as the cell cycle, cell metabolism, gene transcription, and antiviral activity. However, the function of SUMOylation in phytopathogenic fungi has not yet been adequately explored.

Methods

A comprehensive analysis composed of proteomics, affinity pull-down, molecular and cellular approaches was performed to explore the roles of SUMOylation in Cryphonectria parasitica, the fungal pathogen responsible for chestnut blight.

Results and discussion

CpSmt3, the gene encoding the SUMO protein CpSmt3 in C. parasitica was identified and characterized. Deletion of the CpSmt3 gene resulted in defects in mycelial growth and hyphal morphology, suppression of sporulation, attenuation of virulence, weakening of stress tolerance, and elevated accumulation of hypovirus dsRNA. The ΔCpSmt3 deletion mutant exhibited an increase in mitochondrial ROS, swollen mitochondria, excess autophagy, and thickened cell walls. About 500 putative SUMO substrate proteins were identified by affinity pull-down, among which many were implicated in the cell cycle, ribosome, translation, and virulence. Proteomics and SUMO substrate analyses further revealed that deletion of CpSmt3 reduced the accumulation of CpRho1, an important protein that is involved in TOR signal transduction. Silencing of CpRho1 resulted in a phenotype similar to that of ΔCpSmt3, while overexpression of CpRho1 could partly rescue some of the prominent defects in ΔCpSmt3. Together, these findings demonstrate that SUMOylation by CpSmt3 is vitally important and provide new insights into the SUMOylation-related regulatory mechanisms in C. parasitica.

PIAS family in cancer: from basic mechanisms to clinical applications

Protein inhibitors of activated STATs (PIAS) are proteins for cytokine signaling that activate activator-mediated gene transcription. These proteins, as versatile cellular regulators, have been described as regulators of approximately 60 proteins. Dysregulation of PIAS is associated with inappropriate gene expression that promotes oncogenic signaling in multiple cancers. Multiple lines of evidence have revealed that PIAS family members show modulated expressions in cancer cells. Most frequently reported PIAS family members in cancer development are PIAS1 and PIAS3. SUMOylation as post-translational modifier regulates several cellular machineries. PIAS proteins as SUMO E3 ligase factor promotes SUMOylation of transcription factors tangled cancer cells for survival, proliferation, and differentiation. Attenuated PIAS-mediated SUMOylation mechanism is involved in tumorigenesis. This review article provides the PIAS/SUMO role in the modulation of transcriptional factor control, provides brief update on their antagonistic function in different cancer types with particular focus on PIAS proteins as a bonafide therapeutic target to inhibit STAT pathway in cancers, and summarizes natural activators that may have the ability to cure cancer.

The emerging roles of SUMOylation in the tumor microenvironment and therapeutic implications

Tumor initiation, progression, and response to therapies depend to a great extent on interactions between malignant cells and the tumor microenvironment (TME), which denotes the cancerous/non-cancerous cells, cytokines, chemokines, and various other factors around tumors. Cancer cells as well as stroma cells can not only obtain adaption to the TME but also sculpt their microenvironment through a series of signaling pathways. The post-translational modification (PTM) of eukaryotic cells by small ubiquitin-related modifier (SUMO) proteins is now recognized as a key flexible pathway. Proteins involved in tumorigenesis guiding several biological processes including chromatin organization, DNA repair, transcription, protein trafficking, and signal conduction rely on SUMOylation. The purpose of this review is to explore the role that SUMOylation plays in the TME formation and reprogramming, emphasize the importance of targeting SUMOylation to intervene in the TME and discuss the potential of SUMOylation inhibitors (SUMOi) in ameliorating tumor prognosis.

SUMOtherapeutics for Ischemic Stroke

The small, ubiquitin-like modifier (SUMO) is a post-translational modifier with a profound influence on several key biological processes, including the mammalian stress response. Of particular interest are its neuroprotective effects, first recognized in the 13-lined ground squirrel (Ictidomys tridecemlineatus), in the context of hibernation torpor. Although the full scope of the SUMO pathway is yet to be elucidated, observations of its importance in managing neuronal responses to ischemia, maintaining ion gradients, and the preconditioning of neural stem cells make it a promising therapeutic target for acute cerebral ischemia. Recent advances in high-throughput screening have enabled the identification of small molecules that can upregulate SUMOylation, some of which have been validated in pertinent preclinical models of cerebral ischemia. Accordingly, the present review aims to summarize current knowledge and highlight the translational potential of the SUMOylation pathway in brain ischemia.

Genetic deficiency of protein inhibitor of activated STAT3 suppresses experimental abdominal aortic aneurysms

Aim

Signal transducer and activator of transcription (STAT) signaling is critical for the pathogenesis of abdominal aortic aneurysms (AAAs). Though protein inhibitor of activated STAT3 (PIAS3) negatively modulates STAT3 activity, but its role in AAA disease remains undefined.

Method

AAAs were induced in PIAS3 deficient (PIAS3−/−) and wild type (PIAS3+/+) male mice via transient intra-aortic elastase infusion. AAAs were assessed by in situ measurements of infrarenal aortic external diameters prior to (day 0) and 14 days after elastase infusion. Characteristic aneurysmal pathologies were evaluated by histopathology.

Results

Fourteen days following elastase infusion, aneurysmal aortic diameter was reduced by an approximately 50% in PIAS3−/− as compared to PIAS3+/+ mice. On histological analyses, PIAS3−/− mice showed less medial elastin degradation (media score: 2.5) and smooth muscle cell loss (media score: 3.0) than those in PIAS3+/+ mice (media score: 4 for both elastin and SMC destruction). Aortic wall leukocyte accumulation including macrophages, CD4+ T cells, CD8+ T cells and B cells as well as mural neovessel formation were significantly reduced in PIAS3−/− as compared to PIAS3+/+ mice. Additionally, PIAS3 deficiency also downregulated the expression levels of matrix metalloproteinases 2 and 9 by 61% and 70%, respectively, in aneurysmal lesion.

Conclusion

PIAS3 deficiency ameliorated experimental AAAs in conjunction with reduced medial elastin degradation and smooth muscle cell depletion, mural leukocyte accumulation and angiogenesis.

Dual roles of AMAP1 in the transcriptional regulation and intracellular trafficking of carbonic anhydrase IX

BACKGROUND

The cell-surface enzyme carbonic anhydrase IX (CAIX/CA9) promotes tumor growth, survival, invasion, and metastasis, mainly via its pH-regulating functions. Owing to its tumor-specific expression, CAIX-targeting antibodies/chemicals are utilized for therapeutic and diagnostic purposes. However, mechanisms of CAIX trafficking, which affects such CAIX-targeting modalities remain unclear. In this study, roles of the AMAP1-PRKD2 pathway, which mediates integrin recycling of invasive cancer cells, in CAIX trafficking were investigated.

METHODS

Using highly invasive MDA-MB-231 breast cancer cells, the physical association and colocalization of endogenous proteins were analyzed by immunoprecipitation and immunofluorescence, protein/mRNA levels were quantified by western blotting/qPCR, and cell-surface transport and intracellular/extracellular pH regulation were measured by biotin-labeling and fluorescent dye-based assays, respectively. The correlation between mRNA levels and patients' prognoses was analyzed using a TCGA breast cancer dataset.

RESULTS

AMAP1 associated with the CAIX protein complex, and they colocalized at the plasma membrane and tubulovesicular structures. AMAP1 knockdown reduced total/surface CAIX, induced its lysosomal accumulation and degradation, and affected intracellular/extracellular pH. PRKD2 knockdown excluded AMAP1 from the CAIX complex and reduced total CAIX in a lysosome-dependent manner. Unexpectedly, AMAP1 knockdown also reduced CAIX mRNA. AMAP1 interacted with PIAS3, which stabilizes HIF-1α, a transcriptional regulator of CA9. AMAP1 knockdown inhibited the PIAS3-HIF-1α interaction and destabilized the HIF-1α protein. High-ASAP1 (AMAP1-encoding gene) together with high-PIAS3 correlated with high-CA9 and an unfavorable prognosis in breast cancer.

CONCLUSION

The AMAP1-PRKD2 pathway regulates CAIX trafficking, and modulates its total/surface expression. The AMAP1-PIAS3 interaction augments CA9 transcription by stabilizing HIF-1α, presumably contributing to an unfavorable prognosis.

Lessons from Comparison of Hypoxia Signaling in Plants and Mammals

Hypoxia is an important stress for organisms, including plants and mammals. In plants, hypoxia can be the consequence of flooding and causes important crop losses worldwide. In mammals, hypoxia stress may be the result of pathological conditions. Understanding the regulation of responses to hypoxia offers insights into novel approaches for crop improvement, particularly for the development of flooding-tolerant crops and for producing better therapeutics for hypoxia-related diseases such as inflammation and cancer. Despite their evolutionary distance, plants and mammals deploy strikingly similar mechanisms to sense and respond to the different aspects of hypoxia-related stress, including low oxygen levels and the resulting energy crisis, nutrient depletion, and oxidative stress. Over the last two decades, the ubiquitin/proteasome system and the ubiquitin-like protein SUMO have been identified as key regulators that act in concert to regulate core aspects of responses to hypoxia in plants and mammals. Here, we review ubiquitin and SUMO-dependent mechanisms underlying the regulation of hypoxia response in plants and mammals. By comparing and contrasting these mechanisms in plants and mammals, this review seeks to pinpoint conceptually similar mechanisms but also highlight future avenues of research at the junction between different fields of research.

The Role of Sumoylation in the Response to Hypoxia: An Overview

Sumoylation is the covalent attachment of the small ubiquitin-related modifier (SUMO) to a vast variety of proteins in order to modulate their function. Sumoylation has emerged as an important modification with a regulatory role in the cellular response to different types of stress including osmotic, hypoxic and oxidative stress. Hypoxia can occur under physiological or pathological conditions, such as ischemia and cancer, as a result of an oxygen imbalance caused by low supply and/or increased consumption. The hypoxia inducible factors (HIFs), and the proteins that regulate their fate, are critical molecular mediators of the response to hypoxia and modulate procedures such as glucose and lipid metabolism, angiogenesis, erythropoiesis and, in the case of cancer, tumor progression and metastasis. Here, we provide an overview of the sumoylation-dependent mechanisms that are activated under hypoxia and the way they influence key players of the hypoxic response pathway. As hypoxia is a hallmark of many diseases, understanding the interrelated connections between the SUMO and the hypoxic signaling pathways can open the way for future molecular therapeutic interventions.

The Roles of SUMO in Metabolic Regulation

Protein modification with the small ubiquitin-related modifier (SUMO) can affect protein function, enzyme activity, protein-protein interactions, protein stability, protein targeting and cellular localization. SUMO influences the function and regulation of metabolic enzymes within pathways, and in some cases targets entire metabolic pathways by affecting the activity of transcription factors or by facilitating the translocation of entire metabolic pathways to subcellular compartments. SUMO modification is also a key component of nutrient- and metabolic-sensing mechanisms that regulate cellular metabolism. In addition to its established roles in maintaining metabolic homeostasis, there is increasing evidence that SUMO is a key factor in facilitating cellular stress responses through the regulation and/or adaptation of the most fundamental metabolic processes, including energy and nucleotide metabolism. This review focuses on the role of SUMO in cellular metabolism and metabolic disease.