SUMOylation modulates the stability and function of PI3K-p110β

SENP1 knockdown-mediated CTCF SUMOylation enhanced its stability and alleviated lipopolysaccharide-evoked inflammatory injury in human lung fibroblasts via regulation of FOXA2 transcription

BACKGROUND

Excessive inflammation is the main cause of treatment failure in neonatal pneumonia (NP). CCCTC-binding factor (CTCF) represents an important node in various inflammatory diseases. In the present study, we tried to clarify the function and underlying molecular mechanism of CTCF on an in vitro cellular model of NP, which was generated by simulating the human lung fibroblast cell line WI-38 with lipopolysaccharide (LPS).

METHODS

The SUMOylation level and protein interaction were verified by Co-immunoprecipitation assay. Cell viability was measured by Cell Counting Kit-8 assay. Inflammatory factors were examined by Enzyme-linked immunosorbent assay. Cell apoptosis was evaluated by TUNEL assay. The binding activity of CTCF to target promoter was tested by chromatin immunoprecipitation and luciferase reporter assay.

RESULTS

LPS treatment restrained cell viability, promoted the production of inflammatory factors, and enhanced cell apoptosis. CTCF overexpression played anti-inflammatory and anti-apoptotic roles. Furthermore, CTCF was modified by SUMOylation with small ubiquitin-like modifier protein 1 (SUMO1). Interfering with sumo-specific protease 1 (SENP1) facilitated CTCF SUMOylation and protein stability, thus suppressing LPS-evoked inflammatory and apoptotic injuries. Moreover, CTCF could bind to the forkhead box protein A2 (FOXA2) promoter region to promote FOXA2 expression. The anti-inflammatory and anti-apoptotic roles of CTCF are associated with FOXA2 activation. In addition, SENP1 knockdown increased FOXA2 expression by enhancing the abundance and binding ability of CTCF.

CONCLUSIONS

SUMOylation of CTCF by SENP1 knockdown enhanced its protein stability and binding ability and it further alleviated LPS-evoked inflammatory injury in human lung fibroblasts by positively regulating FOXA2 transcription.

SUMOylation and coupling of eNOS mediated by PIAS1 contribute to maintenance of vascular homeostasis

Endothelial dysfunction (ED) is commonly considered a crucial initiating step in the pathogenesis of numerous cardiovascular diseases. The coupling of endothelial nitric oxide synthase (eNOS) is important in maintaining normal endothelial functions. However, it still remains elusive whether and how eNOS SUMOylation affects the eNOS coupling. In the study, we investigate the roles and possible action mechanisms of protein inhibitor of activated STAT 1 (PIAS1) in ED. Human umbilical vein endothelial cells (HUVECs) treated with palmitate acid (PA) in vitro and ApoE-/- mice fed with high-fat diet (HFD) in vivo were constructed as the ED models. Our in vivo data show that PIAS1 alleviates the dysfunction of vascular endothelium by increasing nitric oxide (NO) level, reducing malondialdehyde (MDA) level, and activating the phosphatidylinositol 3-kinase-protein kinase B-endothelial nitric oxide synthase (PI3K-AKT-eNOS) signaling in ApoE-/- mice. Our in vitro data also show that PIAS1 can SUMOylate eNOS under endogenous conditions; moreover, it antagonizes the eNOS uncoupling induced by PA. The findings demonstrate that PIAS1 alleviates the dysfunction of vascular endothelium by promoting the SUMOylation and inhibiting the uncoupling of eNOS, suggesting that PIAS1 would become an early predictor of atherosclerosis and a new potential target of the hyperlipidemia-related cardiovascular diseases.

Phosphorylation at tyrosine 317 and 508 are crucial for PIK3CA/p110α to promote CRC tumorigenesis

BACKGROUND

PI3K/AKT signaling pathway plays important role in tumorigenesis of human cancer. Protein phosphorylation is crucial for signaling transduction of this pathway. PIK3CA, encoding the catalytic subunit p110α of PI3K complex, is one of the most frequently mutated oncogenes in human cancers. However, phosphorylation sites of PIK3CA/p110α and their underlying mechanism in tumorigenesis are largely unknown.

METHODS

Tyrosine phosphorylation sites of PIK3CA/p110α are identified with Mass-Spectrum. Crispr/CAS9 strategy is applied to generate Y317F and Y508F mutant knock-in cell clones. The growth and metastasis abilities of cells are evaluated in vitro and in vivo. Phospho-proteomics analysis and Western blots are used to demonstrate downstream signaling pathways of PIK3CA/p110α tyrosine phosphorylation. In vitro kinase assay is applied to identify the kinase of PIK3CA/p110α tyrosine phosphorylation.

RESULTS

Tyrosine phosphorylation of PIK3CA/p110α is stimulated by growth factors such as EGF, HGF and PDGF. Two tyrosine residues, Y317 and Y508, are identified on PIK3CA/p110α. Either Y317 or Y508 phosphorylation is essential for tumorigenesis of CRC. Mutation at Y317 of p110α reduces the proliferation, migration, and invasion of cancer cells through Src-MLC2 pathway, while mutation at Y508 of p110α impairs AKT signaling. Moreover, Src interacts with and phosphorylates p110α.

CONCLUSIONS

PIK3CA/p110α phosphorylation at Y317 and Y508 play important role in tumorigenesis of colorectal cancer through two independent pathways.

Paradoxes of Cellular SUMOylation Regulation: A Role of Biomolecular Condensates?

Protein SUMOylation is a major post-translational modification essential for maintaining cellular homeostasis. SUMOylation has long been associated with stress responses as a diverse array of cellular stress signals are known to trigger rapid alternations in global protein SUMOylation. In addition, while there are large families of ubiquitination enzymes, all small ubiquitin-like modifiers (SUMOs) are conjugated by a set of enzymatic machinery comprising one heterodimeric SUMO-activating enzyme, a single SUMO-conjugating enzyme, and a small number of SUMO protein ligases and SUMO-specific proteases. How a few SUMOylation enzymes specifically modify thousands of functional targets in response to diverse cellular stresses remains an enigma. Here we review recent progress toward understanding the mechanisms of SUMO regulation, particularly the potential roles of liquid-liquid phase separation/biomolecular condensates in regulating cellular SUMOylation during cellular stresses. In addition, we discuss the role of protein SUMOylation in pathogenesis and the development of novel therapeutics targeting SUMOylation. SIGNIFICANCE STATEMENT: Protein SUMOylation is one of the most prevalent post-translational modifications and plays a vital role in maintaining cellular homeostasis in response to stresses. Protein SUMOylation has been implicated in human pathogenesis, such as cancer, cardiovascular diseases, neurodegeneration, and infection. After more than a quarter century of extensive research, intriguing enigmas remain regarding the mechanism of cellular SUMOylation regulation and the therapeutic potential of targeting SUMOylation.

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.

Overview of the regulation of the class IA PI3K/AKT pathway by SUMO

The phosphatidylinositol-3-kinase (PI3K)/AKT pathway is a major regulator of metabolism, migration, survival, proliferation, and antiviral immunity. Both an overactivation and an inhibition of the PI3K/AKT pathway are related to different pathologies. Activation of this signaling pathway is tightly controlled through a multistep process and its deregulation can be associated with aberrant post-translational modifications including SUMOylation. Here, we review the complex modulation of the PI3K/AKT pathway by SUMOylation and we discuss its putative incvolvement in human disease.

SUMOylation of Nuclear γ-Actin by SUMO2 supports DNA Damage Repair against Myocardial Ischemia-Reperfusion Injury

Myocardial infarction triggers oxidative DNA damage, apoptosis and adverse cardiac remodeling in the heart. Small ubiquitin-like modifier (SUMO) proteins mediate post-translational SUMOylation of the cardiac proteins in response to oxidative stress signals. Upregulation of isoform SUMO2 could attenuate myocardial injury via increasing protein SUMOylation. The present study aimed to discover the identity and cardioprotective activities of SUMOylated proteins. A plasmid vector for expressing N-Strep-SUMO2 protein was generated and introduced into H9c2 rat cardiomyocytes. The SUMOylated proteins were isolated with Strep-Tactin^® agarose beads and identified by MALDI-TOF-MS technology. As a result, γ-actin was identified from a predominant protein band of ~42 kDa and verified by Western blotting. The roles of SUMO2 and γ-actin SUMOylation were subsequently determined in a mouse model of myocardial infarction induced by ligating left anterior descending coronary artery and H9c2 cells challenged by hypoxia-reoxygenation. In vitro lentiviral-mediated SUMO2 expression in H9c2 cells were used to explore the role of SUMOylation of γ-actin. SUMOylation of γ-actin by SUMO2 was proven to be a new cardioprotective mechanism from the following aspects: 1) SUMO2 overexpression reduced the number of TUNEL positive cells, the levels of 8-OHdG and p-γ-H2ax while promoted the nuclear deposition of γ-actin in mouse model and H9c2 cell model of myocardial infarction; 2) SUMO-2 silencing decreased the levels of nuclear γ-actin and SUMOylation while exacerbated DNA damage; 3) Mutated γ-actin (K⁶⁸R/K²⁸⁴R) void of SUMOylation sites failed to protect cardiomyocytes against hypoxia-reoxygenation challenge. The present study suggested that SUMO2 upregulation promoted DNA damage repair and attenuated myocardial injury via increasing SUMOylation of γ-actin in the cell nucleus.

SENP1 regulates the transformation of lung resident mesenchymal stem cells and is associated with idiopathic pulmonary fibrosis progression

BACKGROUND

Lung resident mesenchymal stem cells (LR-MSCs) play an important role in idiopathic pulmonary fibrosis (IPF) by transforming into myofibroblasts, thereby losing their repair ability. Evidence suggests that key proteins of multiple signaling pathways are involved in myofibroblast differentiation of LR-MSCs, such as β-Catenin and GLI family zinc finger 1 (GLI1). These proteins are regulated by SUMO (small ubiquitin-like modifier) modification, which is a post-translational modification that promotes protein degradation, while Sumo specific protein 1 (SENP1)-mediated deSUMOylation produces the opposite biological effects. Therefore, we speculated that SENP1 might be a potential target for treating pulmonary fibrosis by preventing the myofibroblast differentiation of LR-MSCs.

METHODS

LR-MSCs were isolated from mice by using immunomagnetic beads. The extracted LR-MSCs were identified by flow cytometric analysis and multilineage differentiation assays. Lentivirus packaged shRNA silenced the expression of SENP1 in vitro and vivo. The silencing efficacy of SENP1 was verified by real-time quantitative PCR. The effect of down-regulated SENP1 on the myofibroblast differentiation of LR-MSCs was assessed by Immunofluorescence and Western blot. Immunoprecipitation was used to clarify that SENP1 was a key target for regulating the activity of multiple signaling pathways in the direction of LR-MSCs differentiation. LR-MSCs resident in the lung was analyzed with in vivo imaging system. HE and Masson staining was used to evaluate the therapeutic effect of LR-MSCs with SENP1 down-regulation on the lung of BLM mice.

RESULTS

In this study, we found that the myofibroblast differentiation of LR-MSCs in IPF lung tissue was accompanied by enhanced SENP1-mediated deSUMOylation. The expression of SENP1 increased in LR-MSCs transition of bleomycin (BLM)-induced lung fibrosis. Interfering with expression of SENP1 inhibited the transformation of LR-MSCs into myofibroblasts in vitro and in vivo and restored their therapeutic effect in BLM lung fibrosis. In addition, activation of the WNT/β-Catenin and Hedgehog/GLI signaling pathways depends on SENP1-mediated deSUMOylation.

CONCLUSIONS

SENP1 might be a potential target to restore the repair function of LR-MSCs and treat pulmonary fibrosis. Video Abstract.

Crosstalk between circRNAs and the PI3K/AKT signaling pathway in cancer progression

Circular RNAs (circRNAs), covalently closed noncoding RNAs, are widely expressed in eukaryotes and viruses. They can function by regulating target gene expression, linear RNA transcription and protein generation. The phosphoinositide 3-kinase (PI3K)/AKT signaling pathway plays key roles in many biological and cellular processes, such as cell proliferation, growth, invasion, migration, and angiogenesis. It also plays a pivotal role in cancer progression. Emerging data suggest that the circRNA/PI3K/AKT axis modulates the expression of cancer-associated genes and thus regulates tumor progression. Aberrant regulation of the expression of circRNAs in the circRNA/PI3K/AKT axis is significantly associated with clinicopathological characteristics and plays an important role in the regulation of biological functions. In this review, we summarized the expression and biological functions of PI3K-AKT-related circRNAs in vitro and in vivo and assessed their associations with clinicopathological characteristics. We also further discussed the important role of circRNAs in the diagnosis, prognostication, and treatment of cancers.

Regulation of transforming growth factor-β signalling by SUMOylation and its role in fibrosis

Fibrosis is an abnormal healing process that only repairs the structure of an organ after injury and does not address damaged functions. The pathogenesis of fibrosis is multifactorial and highly complex; numerous signalling pathways are involved in this process, with the transforming growth factor-β (TGF-β) signalling pathway playing a central role. TGF-β regulates the generation of myofibroblasts and the epithelial-mesenchymal transition by regulating transcription and translation of downstream genes and precisely regulating fibrogenesis. The TGF-β signalling pathway can be modulated by various post-translational modifications, of which SUMOylation has been shown to play a key role. In this review, we focus on the function of SUMOylation in canonical and non-canonical TGF-β signalling and its role in fibrosis, providing promising therapeutic strategies for fibrosis.