[SENP1 induced protein deSUMO modification increased the chemotherapy sensitivity of endometrial cancer side population cells]

Objective: To inhibit the stemness maintenance potential of endometrial cancer and increase the sensitivity of endometrial cancer side population cells to chemotherapy drugs by inducing extensive deSUMOylation modification of proteins. Methods: Flow cytometry was used to sort and culture CD133(+) CD44(+) KLE endometrial cancer cell clone spheres. Protein expression level of small ubiquitin-related modifier 1 (SUMO1) and two stemness maintenance genes of tumor side population cells, octamer binding transcription factor-4 (Oct4) and sex determining region Y-box2 (Sox2), were detected by western blotting method. Lentivirus-mediated Sentrin/SUMO-specific proteases 1 (SENP1) gene was stably transfected into KLE side population cells. Western blotting was used to detect the protein expressions of SENP1, SUMO1, Oct4 and Sox2. The clone formation rate was compared between KLE side population cells with or without SENP1 overexpression. Flow cytometry was applied to detect cell cycle changes. 3-(4, 5-Dimethylthiazole-2)-2, 5-diphenyl-tetrazolium bromide (MTT) experiment and flow cytometry apoptosis method were used to detect the chemosensitivity of the side population of endometrial cancer cells to cisplatin. Tumor-bearing mouse models of endometrial cancer were established to detect the effect of SENP1 overexpression on the chemotherapy sensitivity of cisplatin. Results: Compared with CD133(-)CD44(-) KLE cells, CD133(+) CD44(+) KLE side population cells could form clonal spheres and express higher levels of SUMO1, Oct4 and Sox2 proteins (P<0.05). Compared with KLE side population cells that were not transfected with SENP1 gene, the expression level of SENP1 protein in KLE side population cells overexpressing SUMO1、Oct4 and Sox2 were lower. The clonal sphere formation rate was reduced from (25.67±5.44)% to (7.46±1.42)%, and cell cycle shifted from G(0)/G(1) phase to G(2) phase. IC(50) of cisplatin decreased from (55.46±6.14) μg/ml to (11.55±3.12) μg/ml, and cell apoptosis rate increased from (9.76±2.09)% to (16.79±3.44)%. Overexpression of SENP1 could reduce the tumorigenesis rate of KLE side population cells in vivo and increase their chemotherapy sensitivity to cisplatin (P<0.05). Conclusion: Overexpression of SENP1 can induce protein deSUMOylation modification, inhibit the stemness maintenance potential of endometrial cancer side population cells, and enhance their chemotherapy sensitivity, which provides a new reference for gene therapy of endometrial cancer.

Small ubiquitin-related modifier-fused bacteriophage tail fiber protein with favorable aqueous solubility for lateral flow assay of Pseudomonas aeruginosa

Rapid and sensitive assay of pathogenic bacteria is critical for minimizing the risk of infectious diseases. Inspired by the interaction between bacteriophages and host bacteria, we obtained a gene sequence of tail fiber protein (TFP) from Pseudomonas aeruginosa (P. aeruginosa) bacteriophage. Then the gene sequence was used to express a recombinant TFP, which can act as a potential capture molecule for P. aeruginosa. Small ubiquitin-related modifier (SUMO) tag was fused onto the TFP fragment to overcome its unfavorable aqueous solubility. The obtained SUMO tag-fused TFP (STFP) can be uniformly distributed onto a nitrocellulose membrane to form a test line due to the improved aqueous solubility, which facilities fabrication of a lateral flow assay strip. Thus we developed a lateral flow assay method by using STFP as a capture molecule and AuCo nanoparticles-labeled aptamer as a signal tracer for point-of-care testing of P. aeruginosa. By using the test strip, P. aeruginosa can be semi quantified with color band and quantified with chemiluminescent (CL) signal catalyzed by AuCo nanoparticles. The concentration range for quantification is 3.3 × 10² CFU/mL to 3.3 × 10⁷ CFU/mL. The test strip was applied to assay P. aeruginosa in different sample matrixes including cerebrospinal fluid, physiological salt solution, drinking water and pear juice. The results demonstrate the application potential of the STFP-based lateral flow assay for medical diagnosis, food and drug safety monitoring.

Roles and mechanisms of SUMOylation on key proteins in myocardial ischemia/reperfusion injury

Myocardial ischemia/reperfusion (MI/R) injury has a great influence on the prognosis of patients with acute coronary occlusion. The underlying mechanisms of MI/R injury are complex. While the incidence of MI/R injury is increasing every year, the existing therapies are not satisfactory. Recently, small ubiquitin-related modifier (SUMO), which is a post-translational modification and involved in many cell processes, was found to play remarkable roles in MI/R injury. Several proteins that can be SUMOylated were found to interfere with different mechanisms of MI/R injury. Sarcoplasmic reticulum Ca²⁺ ATPase pump SUMOylation alleviated calcium overload. Among the histone deacetylase (HDAC) members, SUMOylation of HDAC4 reduced reactive oxygen species generation, whereas Sirt1 played protective roles in the SUMOylated form. Dynamic-related protein 1 modified by different SUMO proteins exerted opposite effects on the function of mitochondria. SUMOylation of hypoxia-inducible factors was fundamental in oxygen homeostasis, while eukaryotic elongation factor 2 SUMOylation induced cardiomyocyte apoptosis. The impact of other SUMOylation substrates in MI/R injury remains unclear. Here we reviewed how these SUMOylated proteins alleviated or exacerbated myocardial impairments by effecting the MI/R injury mechanisms. This may suggest methods for relieving MI/R injury in clinical practice and provide a reference for further study of SUMOylation in MI/R injury.

Sumoylation of IkB attenuates NF-kB-induced nitrosative stress at rostral ventrolateral medulla and cardiovascular depression in experimental brain death

BACKGROUND

Small ubiquitin-related modifier (SUMO) is a group of proteins that participates in post-translational modifications. One known SUMO target is the transcription factor nuclear factor-kB (NF-kB) that plays a pivotal role in many disease processes; sumoylation inactivates NF-kB by conjugation with inhibitors of NF-kB (IkB). Our laboratory demonstrated previously that transcriptional upregulation of nitric oxide synthase II (NOS II) by NF-kB, leading to nitrosative stress by the formation of peroxynitrite in the rostral ventrolateral medulla (RVLM), underpins the defunct brain stem cardiovascular regulation that precedes brain death. Based on an experimental endotoxemia model, this study evaluated the hypothesis that sumoylation plays a pro-life role in brain death by interacting with the NF-kB/NOS II/peroxynitrite signaling pathway in the RVLM.

RESULTS

In Sprague-Dawley rats, intravenous administration of Escherichia coli lipopolysaccharide (LPS; 10 mg kg-1) elicited an augmentation of SUMO-1 and ubiquitin-conjugase 9 (Ubc9) mRNA or protein levels, alongside SUMO-1-conjugated proteins in the RVLM. Immunoneutralization of SUMO-1 or Ubc9 in the RVLM significantly potentiated the already diminished sumoylation of IkBα and intensified NF-kB activation and NOS II/peroxynitrite expression in this brain stem substrate, together with exacerbated fatality, cardiovascular depression and reduction of an experimental index of a life-and-death signal detected from arterial pressure that disappears in comatose patients signifying failure of brain stem cardiovascular regulation before brain death.

CONCLUSION

We conclude that sumoylation of IkB in the RVLM ameliorates the defunct brain stem cardiovascular regulation that underpins brain death in our experimental endotoxemia modal by reducing nitrosative stress via inhibition of IkB degradation that diminishes the induction of the NF-kB/NOS II/peroxynitrite signaling cascade.

Chronic hyperglycemia downregulates GLP-1 receptor signaling in pancreatic β-cells via protein kinase A

Objective

Glucagon-like peptide 1 (GLP-1) enhances insulin secretion and protects β-cell mass. Diabetes therapies targeting the GLP-1 receptor (GLP-1R), expressed in numerous tissues, have diminished dose-response in patients with type 2 diabetes compared with healthy human controls. The aim of this study was to determine the mechanistic causes underlying the reduced efficacy of GLP-1R ligands.

Methods

Using primary mouse islets and the β-cell line MIN6, outcomes downstream of the GLP-1R were analyzed: Insulin secretion; phosphorylation of the cAMP-response element binding protein (CREB); cAMP responses. Signaling systems were studied by immunoblotting and qRT-PCR, and PKA activity was assayed. Cell surface localization of the GLP-1R was studied by confocal microscopy using a fluorescein-tagged exendin-4 and GFP-tagged GLP-1R.

Results

Rodent β-cells chronically exposed to high glucose had diminished responses to GLP-1R agonists including: diminished insulin secretory response; reduced phosphorylation of (CREB); impaired cAMP response, attributable to chronically increased cAMP levels. GLP-1R signaling systems were affected by hyperglycemia with increased expression of mRNAs encoding the inducible cAMP early repressor (ICER) and adenylyl cyclase 8, reduced PKA activity due to increased expression of the PKA-RIα subunit, reduced GLP-1R mRNA expression and loss of GLP-1R from the cell surface. To specifically examine the loss of GLP-1R from the plasma membrane a GLP-1R-GFP fusion protein was employed to visualize subcellular localization. Under low glucose conditions or when PKA activity was inhibited, GLP-1R-GFP was found at the plasma membrane. Conversely high glucose, expression of a constitutively active PKA subunit, or exposure to exendin-4 or forskolin led to GLP-1R-GFP internalization. Mutation of serine residue 301 of the GLP-1R abolished the glucose-dependent loss of the receptor from the plasma membrane. This was associated with a loss of an interaction between the receptor and the small ubiquitin-related modifier (SUMO), an interaction that was found to be necessary for internalization of the receptor.

Conclusions

These data show that glucose acting, at least in part, via PKA leads to the loss of the GLP-1R from the cell surface and an impairment of GLP-1R signaling, which may underlie the reduced clinical efficacy of GLP-1R based therapies in individuals with poorly controlled hyperglycemia.