Localization Analysis of Seven De-sumoylation Enzymes (SENPs) in Ocular Cell Lines

Endothelial FIS1 DeSUMOylation Protects Against Hypoxic Pulmonary Hypertension

BACKGROUND

Hypoxia is a major cause and promoter of pulmonary hypertension (PH), a representative vascular remodeling disease with poor prognosis and high mortality. However, the mechanism underlying how pulmonary arterial system responds to hypoxic stress during PH remains unclear. Endothelial mitochondria are considered signaling organelles on oxygen tension. Results from previous clinical research and our studies suggested a potential role of posttranslational SUMOylation (small ubiquitin-like modifier modification) in endothelial mitochondria in hypoxia-related vasculopathy.

METHODS

Chronic hypoxia mouse model and Sugen/hypoxia rat model were employed as PH animal models. Mitochondrial morphology and subcellular structure were determined by transmission electron and immunofluorescent microscopies. Mitochondrial metabolism was determined by mitochondrial oxygen consumption rate and extracellular acidification rate. SUMOylation and protein interaction were determined by immunoprecipitation.

RESULTS

The involvement of SENP1 (sentrin-specific protease 1)-mediated SUMOylation in mitochondrial remodeling in the pulmonary endothelium was identified in clinical specimens of hypoxia-related PH and was verified in human pulmonary artery endothelial cells under hypoxia. Further analyses in clinical specimens, hypoxic rat and mouse PH models, and human pulmonary artery endothelial cells and human embryonic stem cell-derived endothelial cells revealed that short-term hypoxia-induced SENP1 translocation to endothelial mitochondria to regulate deSUMOylation (the reversible process of SUMOylation) of mitochondrial fission protein FIS1 (mitochondrial fission 1), which facilitated FIS1 assembling with fusion protein MFN2 (mitofusin 2) and mitochondrial gatekeeper VDAC1 (voltage-dependent anion channel 1), and the membrane tethering activity of MFN2 by enhancing its oligomerization. Consequently, FIS1 deSUMOylation maintained the mitochondrial integrity and endoplasmic reticulum-mitochondria calcium communication across mitochondrial-associated membranes, subsequently preserving pulmonary endothelial function and vascular homeostasis. In contrast, prolonged hypoxia disabled the FIS1 deSUMOylation by diminishing the availability of SENP1 in mitochondria via inducing miR (micro RNA)-138 and consequently resulted in mitochondrial dysfunction and metabolic reprogramming in pulmonary endothelium. Functionally, introduction of viral-packaged deSUMOylated FIS1 within pulmonary endothelium in mice improved pulmonary endothelial dysfunction and hypoxic PH development, while knock-in of SUMO (small ubiquitin-like modifier)-conjugated FIS1 in mice exaggerated the diseased cellular and tissue phenotypes.

CONCLUSIONS

By maintaining endothelial mitochondrial homeostasis, deSUMOylation of FIS1 adaptively preserves pulmonary endothelial function against hypoxic stress and consequently protects against PH. The FIS1 deSUMOylation-SUMOylation transition in pulmonary endothelium is an intrinsic pathogenesis of hypoxic PH.

Protein posttranslational modifications in health and diseases: Functions, regulatory mechanisms, and therapeutic implications

Protein posttranslational modifications (PTMs) refer to the breaking or generation of covalent bonds on the backbones or amino acid side chains of proteins and expand the diversity of proteins, which provides the basis for the emergence of organismal complexity. To date, more than 650 types of protein modifications, such as the most well-known phosphorylation, ubiquitination, glycosylation, methylation, SUMOylation, short-chain and long-chain acylation modifications, redox modifications, and irreversible modifications, have been described, and the inventory is still increasing. By changing the protein conformation, localization, activity, stability, charges, and interactions with other biomolecules, PTMs ultimately alter the phenotypes and biological processes of cells. The homeostasis of protein modifications is important to human health. Abnormal PTMs may cause changes in protein properties and loss of protein functions, which are closely related to the occurrence and development of various diseases. In this review, we systematically introduce the characteristics, regulatory mechanisms, and functions of various PTMs in health and diseases. In addition, the therapeutic prospects in various diseases by targeting PTMs and associated regulatory enzymes are also summarized. This work will deepen the understanding of protein modifications in health and diseases and promote the discovery of diagnostic and prognostic markers and drug targets for diseases.

SUMOylation as a Therapeutic Target for Myocardial Infarction

Myocardial infarction is a prevalent and life-threatening cardiovascular disease. The main goal of existing interventional therapies is to restore coronary reperfusion while few are designed to ameliorate the pathology of heart diseases via targeting the post-translational modifications of those critical proteins. Small ubiquitin-like modifier (SUMO) proteins are recently discovered to form a new type of protein post-translational modifications (PTM), known as SUMOylation. SUMOylation and deSUMOylation are dynamically balanced in the maintenance of various biological processes including cell division, DNA repair, epigenetic transcriptional regulation, and cellular metabolism. Importantly, SUMOylation plays a critical role in the regulation of cardiac functions and the pathology of cardiovascular diseases, especially in heart failure and myocardial infarction. This review summarizes the current understanding on the effects of SUMOylation and SUMOylated proteins in the pathophysiology of myocardial infarction and identifies the potential treatments against myocardial injury via targeting SUMO. Ultimately, this review recommends SUMOylation as a key therapeutic target for treating cardiovascular diseases.

Glucose Oxidase- and UVA-Induced Changes in the Expression Patterns of Seven De-sumoylation Enzymes (SENPs) Are Associated with Cataract Development

OBJECTIVE

It has been well established that sumoylation acts as an important regulatory mechanism that controls many different cellular processes. We and others have shown that sumoylation plays an indispensable role during mouse eye development. Whether sumoylation is implicated in ocular pathogenesis remains to be further studied. In the present study, we have examined the expression patterns of the de-sumoylation enzymes (SENPs) in the in vitro cataract models induced by glucose oxidase and UVA irradiation.

METHODS

Four-week-old C57BL/6J mice were used in our experiments. Lenses were carefully dissected out from mouse eyes and cultured in M199 medium for 12 hours. Transparent lenses (without surgical damage) were selected for experimentation. The lenses were exposed to UVA for 60 min or treated with 20 mU/mL glucose oxidase (GO) to induce cataract formation. The mRNA levels were analyzed with qRT-PCR. The protein levels were determined with western blot analysis and quantitated with Image J.

RESULTS

GO treatment and UVA irradiation can induce cataract formation in lens cultured in vitro. GO treatment significantly down-regulated the mRNA levels for SENPs from 50% to 85%; on the other hand, expression of seven SENP proteins under GO treatment appeared in 3 situations: upregulation for SENP1, 2 and 6; downregulation for SENP 5 and 8; and unchanged for SENP3 and 7. UVA irradiation upregulates the mRNAs for all seven SENPs; In contrast to the mRNA levels for 7 SENPs, the expression levels for 6 SENPs (SENP1-3, 5-6 and 8) appeared down-regulated from 10% to 50%, and only SENP7 was slightly upregulated.

CONCLUSION

Our results for the first time established the differentiation expression patterns of 7 de-sumoylation enzymes (SENPs) under treatment by GO or UVA, which provide preliminary data to link sumoylation to stress-induced cataractogenesis.

SUMO1 SUMOylates and SENP3 deSUMOylates NLRP3 to orchestrate the inflammasome activation

The NLRP3 inflammasome regulates innate immune and inflammatory responses by promoting caspase1-dependent induction of pro-inflammatory cytokines. However, aberrant inflammasome activation causes diverse diseases, and thus inflammasome activity must be tightly controlled. Here, we reveal a molecular mechanism underlying the regulation of NLRP3 inflammasome. NLRP3 interacts with SUMO-conjugating enzyme (UBC9), which subsequently promotes small ubiquitin-like modifier 1 (SUMO1) to catalyze NLRP3 SUMOylation at residue Lys²⁰⁴. SUMO1-catalyzed SUMOylation of NLRP3 facilitates ASC oligomerization, inflammasome activation, and interleukin-1β secretion. Moreover, this study also reveals that SUMO-specific protease 3 (SENP3) is required for the deSUMOylation of NLRP3. Interestingly, SENP3 deSUMOylates NLRP3 to attenuate ASC recruitment and speck formation, the NLRP3 inflammasome activation, as well as IL-1β cleavage and secretion. In conclusion, we reveal that SUMO1-catalyzed SUMOylation and SENP3-mediated deSUMOylation of NLRP3 orchestrate the inflammasome activation.