Sentrin/SUMO-specific Protease 1 Research Articles

Baicalin Attenuates Diabetic Cardiomyopathy In Vivo and In Vitro by Inhibiting Autophagy and Cell Death through SENP1/SIRT3 Signaling Pathway Activation.

Diabetic heart damage can lead to cardiomyocyte death, which endangers human health. Baicalin (BAI) is a bioactive compound that plays an important role in cardiovascular diseases. Sentrin/SUMO-specific protease 1 (SENP1) regulates the de-small ubiquitin-like modifier (deSUMOylation) process of Sirtuin 3 (SIRT3) and plays a crucial role in regulating mitochondrial mass and preventing cell injury. Our hypothesis is that BAI regulates the deSUMOylation level of SIRT3 through SENP1 to enhance mitochondrial quality control and prevent cell death, ultimately improving diabetic cardiomyopathy (DCM). The protein expression of SENP1 decreased in cardiomyocytes induced by high glucose and in db/db mice. The cardioprotective effects of BAI were eliminated by silencing endogenous SENP1, while overexpression of SENP1 showed similar cardioprotective effects to those of BAI. Furthermore, Co-Immunoprecipitation (CO-IP) experiments showed that BAI's cardioprotective effect was due to the inhibition of the SUMOylation modification level of SIRT3 by SENP1. Inhibition of SENP1 expression resulted in an increase in SUMOylation of SIRT3. This led to increased acetylation of mitochondrial protein, accumulation of reactive oxygen species, impaired autophagy, impaired mitochondrial oxidative phosphorylation and increased cell death. None of these changes could be reversed by BAI. BAI improves DCM by promoting SIRT3 deSUMOylation through SENP1, restoring mitochondrial stability, and preventing the cell death of cardiomyocytes. This study proposes for the first time that SIRT3 SUMOylation modification is involved in the development of DCM, provides in vivo and in vitro data support that BAI inhibits cardiomyocyte ferroptosis and apoptosis in DCM through SENP1.

SENP1 attenuates hypoxia‑reoxygenation injury in liver sinusoid endothelial cells by relying on the HIF‑1α signaling pathway.

Liver sinusoidal endothelial cells (LSECs) have an important role in hepatic ischemia‑reperfusion injury (I/R), but the specific molecular mechanism of action is unknown. LSEC proliferation is regulated and fenestration is maintained via the Sentrin/SUMO‑specific protease 1 (SENP1)/hypoxia‑inducible factor‑1α (HIF‑1α) signaling axis under hypoxic conditions. In the present study, a hypoxia‑reoxygenation (H‑R) injury model was established using mouse LSECs to explore the relationship between SENP1 and H‑R injury invitro, and the specific underlying mechanism was identified, revealing new targets for the clinical attenuation of hepatic I/R injury. Following the culture of LSECs under H‑R conditions, it was demonstrated that the expression of SENP1 was upregulated by reverse transcription‑quantitative polymerase chain reaction and western blotting (WB). In addition, scanning electron microscopy indicated that fenestrae damage was increased, a Cell Counting Kit‑8 assay demonstrated that the proliferation of cells was impaired and flow cytometry showed that apoptosis was increased. After silencing SENP1 expression with short interfering RNA, the proliferation activity of LSECs decreased, the fenestrae damage increased, the apoptosis rate increased and the expression levels of SENP1, HIF‑1α, heme oxygenase and Bcl‑2 were downregulated (as demonstrated by WB), while the expression levels of apoptosis‑related proteins, cleaved‑caspase‑3 and Bax, were upregulated. Enzyme‑linked immunosorbent assay detection showed that the level of vascular endothelial growth factor in the supernatant decreased and the level of IL‑6 and TNF‑α increased. Following the administration of an HIF‑1α signaling pathway agonist, the situation was reversed. These results therefore suggested that SENP1 attenuated the reduction in proliferation, apoptosis and fenestration of LSECs observed following H‑R injury through the HIF‑1α signaling pathway. In conclusion, SENP1 may attenuate H‑R injury in LSECs in a HIF‑1α signaling pathway‑dependent manner.

SUMOylation of Smad2 mediates TGF-β-regulated endothelial–mesenchymal transition

Endothelial-mesenchymal transition (EndoMT) is a complex biological process in which endothelial cells are transformed into mesenchymal cells, and dysregulated EndoMT causes a variety of pathological processes. Transforming growth factor beta (TGF-β) signaling effectively induces the EndoMT process in endothelial cells, and Smad2 is the critical protein of the TGF-β signaling pathway. However, whether small ubiquitin-like modifier modification (SUMOylation) is involved in EndoMT remains unclear. Here, we show that Smad2 is predominantly modified by SUMO1 at two major SUMOylation sites with PIAS2α as the primary E3 ligase, whereas SENP1 (sentrin/SUMO-specific protease 1) mediates the deSUMOylation of Smad2. In addition, we identified that SUMOylation significantly enhances the transcriptional activity and protein stability of Smad2, regulating the expression of downstream target genes. SUMOylation increases the phosphorylation of Smad2 and the formation of the Smad2-Smad4 complex, thus promoting the nuclear translocation of Smad2. Ultimately, the wildtype, but not SUMOylation site mutant Smad2 facilitated the EndoMT process. More importantly, TGF-β enhances the nuclear translocation of Smad2 by enhancing its SUMOylation and promoting the EndoMT process. These results demonstrate that SUMOylation of Smad2 plays a critical role in the TGF-β-mediated EndoMT process, providing a new theoretical basis for the treatment and potential drug targets of EndoMT-related clinical diseases.

Lactate: an intracellular metabolite regulates cell cycle progression

Abstract The Chouchani lab recently reported in Nature that a dynamic intracellular lactate is a physiological regulator for cell cycle progress. They also showed that accumulated lactate in cell mitosis directly binds and inhibits Sentrin/SUMO-specific protease 1 (SENP1) to enrich SUMO2/3-modification of anaphase-promoting complex 4 (APC4), which promotes the degradation of APC/C complexes, leading to mitosis exit.

Plasma Exosome-Derived Sentrin SUMO-Specific Protease 1: A Prognostic Biomarker in Patients With Osteosarcoma.

BackgroundThe exosomes contain many important proteins that can be used for early tumor diagnosis or patient prognosis analysis. In this study, we investigated plasma exosome-derived sentrin SUMO-specific protease 1 (SENP1) levels as a prognostic biomarker in patients with osteosarcoma.MethodsThe expression of SENP1 protein in osteosarcoma tissues and adjacent tissues was detected by immunohistochemistry (IHC). The exosomes were identified by transmission electron microscopy, nanoparticle tracking analysis, and western blotting. ELISA was used to detect plasma exosome-derived SENP1 levels to assess prognosis in patients with osteosarcoma.ResultsIHC showed that the positive expression rate of SENP1 in osteosarcoma tissues was 88.33%, whereas that in adjacent tissues was 46.67% (P < 0.05). Plasma exosome-derived SENP1 levels were related to tumor size, tumor location, necrosis rate, pulmonary metastasis, and surgical stage. Both disease-free survival (DFS) and overall survival (OS) were worse in patients who had higher plasma exosome-derived SENP1 levels compared with those in patients with lower plasma exosome-derived SENP1 levels (P < 0.001). The area under the receiver operating characteristic curve (AUROC) of plasma exosome-derived SENP1, as 1-year DFS and 3-year DFS prognostic biomarkers, was 0.90 (95% CI: 0.83–0.98) and 0.96 (95% CI: 0.94–0.99), respectively. As to OS, the AUROC of plasma exosome-derived SENP1 for 1-year and 3-year prediction was 0.90 (95% CI: 0.82–0.99) and 0.96 (0.93–0.98), respectively. The plasma exosome-derived SENP1 was better than plasma SENP1 as a prognostic biomarker both in DFS and OS.ConclusionsOur findings show that the plasma exosome-derived SENP1 may serve as a novel and independent prognostic predictor in clinical applications.

Hypoxia maintains the fenestration of liver sinusoidal endothelial cells and promotes their proliferation through the SENP1/HIF-1α/VEGF signaling axis

Liver sinusoidal endothelial cells (LSECs), which play a very critical role in liver regeneration, function in hypoxic environments, but few studies have elucidated the specific mechanism. As a hypoxia-sensitive gene, Sentrin/SUMO-specific protease 1(SENP1) is upregulated in solid tumors due to hypoxia and promotes tumor proliferation. We speculate that LSECs may upregulate SENP1 in hypoxic environments and that SENP1 may act on downstream genes to allow the cells to adapt to the hypoxic environment. To elucidate the reasons for the survival of LSECs under hypoxia, we designed experiments to explore the possible mechanism. First, we cultured murine LSECs in hypoxic conditions for a certain time (24 h and 72 h), and then, we observed that the proliferation ability of the hypoxia group was higher than that of the normoxia group, and the number of unique fenestrae of the LSECs in the hypoxia group was more than that of the LSECs in the normoxia group. Then, we divided the LSECs into several groups for hypoxic culture for time points (6 h, 12 h, 24 h, 36 h, and 72 h), and we found that the expression of SENP1, HIF-1α and VEGF was significantly upregulated. Then, we silenced SENP1 and HIF-1α with si-SENP1 and si–HIF–1α, respectively. SENP1, HIF-1α and VEGF were significantly downregulated, as determined by RT-PCR, WB and ELISA. Unexpectedly, the proliferation activity of the LSECs decreased and the fenestrae disappeared more in the si-SENP1 and si–HIF–1α groups than in the control group. It is concluded that LSECs cultured under hypoxic conditions may maintain fenestrae and promote proliferation through the SENP1/HIF-1α/VEGF signaling axis, thereby adapting to the hypoxic environment.

Complex regulation of orphan nuclear receptor Nur77 (Nr4a1) transcriptional activity by SUMO2 and PIASγ

Nur77 (NGFI-B) is a nuclear receptor that belongs to the Nr4a family of orphan nuclear receptors (Nr4a1). This transcription factor has been implicated in the regulation of multiple functions, such as cell cycle regulation, apoptosis, inflammation, glucose and lipid metabolism, and brain function. However, the mechanisms involved in its different regulatory properties remain unclear. In search for regulatory mechanisms of Nur77 function, we identified that Protein Inhibitor of Activated STAT gamma (PIASγ), an E3 SUMO-protein ligase, potently repressed Nur77 transcriptional activity in HEK-293T cells. This PIASγ activity was sensitive to Sentrin SUMO-specific protease 1 (SENP1). Substitution of two putative phylogenetically well-conserved small ubiquitin-like modifier (SUMO) acceptor sites, lysine 102 (K102) and 577 (K577) by arginine residues (R) modulated Nur77 transcriptional activity. In particular, Nur77-K102R and Nur77-K102R/K577R mutants strongly decreased the transcriptional activity of Nur77, whereas single K577R substitution increased transcriptional activity of Nur77. Repression of Nur77 transcriptional activity by SUMO2 and PIASγ was reduced by the K577R mutation, whereas the K102R mutant remained insensitive to SUMO2. Interestingly, the roles of these SUMO acceptor sites in Nur77 are distinct from previously observed activities on its close homolog Nurr1. Thus, the present study identified SUMO2 and PIASγ as important transcriptional co-regulators of Nur77.

Sumoylation enhances the activity of the TGF-β/SMAD and HIF-1 signaling pathways in keloids

Excessive fibrosis and extracellular matrix deposition resulting from upregulation of target genes expression mediated by transforming growth factor-beta (TGF-β)/SMAD and hypoxia inducible factor-1 (HIF-1) signaling pathways are the main mechanisms that drive keloid formation. Sumoylation is a protein posttranslational modification that regulates the function of proteins in many biological processes. In the present study, we aimed to investigate the mechanism underlying the effects of sumoylation on the TGF-β/SMAD and HIF-1 signaling pathways in keloids. We used 2-D08 to block sumoylation and silenced the expression of sentrin sumo-specific protease 1 (SENP1) to enhance sumoylation in human foreskin fibroblasts (HFFs) and human keloid fibroblasts (HKFs). We also reduced and increased intracellular SUMO1 levels by silencing SUMO1 and transfecting cells with a SUMO1 overexpression lentivirus, respectively. Sumoylation has the ability to amplify TGF-β/SMAD and HIF-1 signals in keloids, while SUMO1, especially the SUMO1-RanGAP1 complex, is the key molecule affecting the TGF-β/SMAD and HIF-1 signaling pathways. In addition, we also found that hypoxia promotes sumoylation in keloids and that HIF-1α is covalently modified by SUMO1 at Lys 391 and Lys 477 in HKFs. In summary, we elucidated the role and molecular mechanism of sumoylation in the formation of keloids, providing a new perspective for a potential therapeutic target of keloids.

Chloramphenicol Induces Autophagy and Inhibits the Hypoxia Inducible Factor-1 Alpha Pathway in Non-Small Cell Lung Cancer Cells.

Chloramphenicol is an inexpensive and excellent bactericidal antibiotic. It is used to combat anaerobic infections in the Third World countries, whereas its systemic application has been abandoned in developed countries. However, in recent years, clinicians have reintroduced chloramphenicol in clinical practice. In this study, chloramphenicol was found to repress the oxygen-labile transcription factor, hypoxia inducible factor-1 alpha (HIF-1α), in hypoxic A549 and H1299 cells. Furthermore, it suppressed the mRNA levels of vascular endothelial growth factor (VEGF) and glucose transporter 1, eventually decreasing VEGF release. Chloramphenicol initiated the autophagy pathway in treated cells, as observed by the increase in formation of Atg12-Atg5 conjugates, and in beclin-1 and LC3-II levels. The chloramphenicol-mediated HIF-1α degradation was completely reverted by autophagic flux blockage. In HIF-1α-overexpressing cells, the formation of HIF-1α/SENP-1 (Sentrin/SUMO-specific protease 1) protein complex seemed to facilitate the escape of HIF-1α from degradation. Chloramphenicol inhibited HIF-1α/SENP-1 protein interaction, thereby destabilizing HIF-1α protein. The enhancement in HIF-1α degradation due to chloramphenicol was evident during the incubation of the antibiotic before hypoxia and after HIF-1α accumulation. Since HIF-1α plays multiple roles in infections, inflammation, and cancer cell stemness, our findings suggest a potential clinical value of chloramphenicol in the treatment of these conditions.

SENP1 promotes proliferation of clear cell renal cell carcinoma through activation of glycolysis.

Metabolic shift toward aerobic glycolysis is a fundamental element contributing to the development and progression of clear cell renal cell carcinoma (ccRCC). We and others previously observed enhanced glycolysis and diminished tricarboxylic acid (TCA) cycle activity in ccRCC tissue. Here, by integrated gene expression and metabolomic analyses of 36 matched pairs of tumor and adjacent normal tissues, we showed that expression of Sentrin/SUMO-specific protease 1 (SENP1) is positively associated with glycolysis levels in ccRCC. Moreover, SENP1 knockdown in RCC4/VHL cells downregulated expression of key glycolytic enzymes under normoxic and hypoxic conditions and inhibited cell proliferation under hypoxic conditions, possibly due to ineffective deSUMOylation and stablization of Hif-1α related to the SENP-1 deficiency. Finally, SENP1 expression correlated positively with tumor pathological grade and was an indicator of poor overall survival and advanced tumor progression in ccRCC. Altered VHL gene function is found in 60–90% ccRCC cases of ccRCC, but therapies targeting VHL-related signaling pathways have been ineffective, spurring exploration of alternative pathological signaling events. Our results provide a possible mechanistic explanation for the role of SENP1 in the initiation and development of ccRCC with normal VHL activity, and identifies SENP1 as a potential treatment target for the disease.

Vialinin A and thelephantin G, potent inhibitors of tumor necrosis factor-α production, inhibit sentrin/SUMO-specific protease 1 enzymatic activity

Several p-terphenyl compounds have been isolated from the edible Chinese mushroom Thelephora vialis. Vialinin A, a p-terphenyl compound, strongly inhibits tumor necrosis factor-α production and release. Vialinin A inhibits the enzymatic activity of ubiquitin-specific peptidase 5, one of the target molecules in RBL-2H3 cells. Here we examined the inhibitory effect of p-terphenyl compounds, including vialinin A, against sentrin/SUMO-specific protease 1 (SENP1) enzymatic activity. The half maximal inhibitory concentration values of vialinin A and thelephantin G against full-length SENP1 were 1.64±0.23μM and 2.48±0.02μM, respectively. These findings suggest that p-terphenyl compounds are potent SENP1 inhibitors.

SENP1-Mediated Desumoylation of DBC1 Inhibits Apoptosis Induced by High Glucose in Bovine Retinal Pericytes.

Pericyte loss is an early characteristic change in diabetic retinopathy, but its precise molecular mechanisms have not been elucidated. This study investigated the role of SENP1 in pericyte loss in diabetic retinopathy. We demonstrated that a high concentration of glucose inhibited the expression of the Sentrin/SUMO-specific protease 1 (SENP1), which resulted in an increase in DBC1 sumoylation in bovine retinal pericytes (BRPCs). Furthermore, SENP1 overexpression attenuated hyperemia-induced apoptosis of BPRCs, and SENP1 knockdown aggravated this effect. We also provide evidence that DBC1 sumoylation/desumoylation is involved in the SENP1-regulated apoptosis of BRPCs under high glucose conditions. Understanding the role of SENP1 in the pathogenesis of high glucose induced pericyte loss could help elucidate important targets for future pharmacological interventions.

SENP1 desensitizes hypoxic ovarian cancer cells to cisplatin by up-regulating HIF-1α.

Hypoxia-inducible factor 1 alpha (HIF-1α) is closely related to chemoresistance of ovarian cancers. Although it is reported that HIF-1α can be regulated by Sentrin/SUMO-specific protease 1 (SENP1), the effects of SENP1 on HIF-1α is still controversial. In this study, we identified that SENP1 positively regulated the expression of HIF-1α by deSUMOylation and weakened the sensitivity of hypoxic ovarian cancer cells to cisplatin. These results indicate that SENP1 is a positive regulator of HIF-1α and plays a negative role in ovarian cancer chemotherapy.

Adenylosuccinate Is an Insulin Secretagogue Derived from Glucose-Induced Purine Metabolism.

Pancreatic islet failure, involving loss of glucose-stimulated insulin secretion (GSIS) from islet β cells, heralds the onset of type 2 diabetes (T2D). To search for mediators of GSIS, we performed metabolomics profiling of the insulinoma cell line 832/13 and uncovered significant glucose-induced changes in purine pathway intermediates, including a decrease in inosine monophosphate (IMP) and an increase in adenylosuccinate (S-AMP), suggesting a regulatory role for the enzyme that links the two metabolites, adenylosuccinate synthase (ADSS). Inhibition of ADSS or a more proximal enzyme in the S-AMP biosynthesis pathway, adenylosuccinate lyase, lowers S-AMP levels and impairs GSIS. Addition of S-AMP to the interior of patch-clamped human β cells amplifies exocytosis, an effect dependent upon expression of sentrin/SUMO-specific protease 1 (SENP1). S-AMP also overcomes the defect in glucose-induced exocytosis in β cells from a human donor with T2D. S-AMP is, thus, an insulin secretagogue capable of reversing β cell dysfunction in T2D.

How do reducing equivalents increase insulin secretion?

Glucose stimulation of insulin secretion in pancreatic β cells involves cell depolarization and subsequent opening of voltage-dependent Ca2+ channels to elicit insulin granule exocytosis. This pathway alone does not account for the entire magnitude of the secretory response in β cells. In this issue, Ferdaoussi, Dai, and colleagues reveal that insulin secretion is amplified by cytosolic isocitrate dehydrogenase-dependent transfer of reducing equivalents, which generates NADPH and reduced glutathione, which in turn activates sentrin/SUMO-specific protease-1 (SENP1). β Cell-specific deletion of Senp1 in murine models reduced the amplification of insulin exocytosis, resulting in impaired glucose tolerance. Further, their studies demonstrate that restoring intracellular NADPH or activating SENP1 improves insulin exocytosis in human β cells from donors with type 2 diabetes, suggesting a potential therapeutic target to augment insulin production.

Isocitrate-to-SENP1 signaling amplifies insulin secretion and rescues dysfunctional β cells.

Insulin secretion from β cells of the pancreatic islets of Langerhans controls metabolic homeostasis and is impaired in individuals with type 2 diabetes (T2D). Increases in blood glucose trigger insulin release by closing ATP-sensitive K+ channels, depolarizing β cells, and opening voltage-dependent Ca2+ channels to elicit insulin exocytosis. However, one or more additional pathway(s) amplify the secretory response, likely at the distal exocytotic site. The mitochondrial export of isocitrate and engagement with cytosolic isocitrate dehydrogenase (ICDc) may be one key pathway, but the mechanism linking this to insulin secretion and its role in T2D have not been defined. Here, we show that the ICDc-dependent generation of NADPH and subsequent glutathione (GSH) reduction contribute to the amplification of insulin exocytosis via sentrin/SUMO-specific protease-1 (SENP1). In human T2D and an in vitro model of human islet dysfunction, the glucose-dependent amplification of exocytosis was impaired and could be rescued by introduction of signaling intermediates from this pathway. Moreover, islet-specific Senp1 deletion in mice caused impaired glucose tolerance by reducing the amplification of insulin exocytosis. Together, our results identify a pathway that links glucose metabolism to the amplification of insulin secretion and demonstrate that restoration of this axis rescues β cell function in T2D.

Induction of SENP1 in myocardium contributes to abnormities of mitochondria and cardiomyopathy

Defect in mitochondrial biogenesis and cardiac energy metabolism is a critical contributing factor to cardiac hypertrophy and heart failure. Sentrin/SUMO specific protease 1 (SENP1) mediated regulation of PGC-1α transcriptional activity plays an essential role in mitochondrial biogenesis and mitochondrial function. However, whether SENP1 plays a role in cardiac hypertrophy and failure is unknown. We investigated whether alteration in SENP1 expression affects cardiomyopathy and the underlying mechanism. In our present study, we found that the expression of SENP1 was induced in mouse and human failing hearts associated with induced expression of mitochondrial genes. SENP1 expression in cardiomyocytes was induced by hypertrophic stimuli through calcium/calcineurin-NFAT3. SENP1 regulated mitochondrial gene expression by de-SUMOylation of MEF-2C, which enhanced MEF-2C-mediated PGC-1α transcription. Genetic induction of SENP1 led to mitochondrial dysregulation and cardiac dysfunction in vivo. Our data showed that pathogenesis of cardiomyopathy is attributed by SENP1 mediated regulation of mitochondrial abnormities. SENP1 up-regulation in diseased heart is mediated via calcineurin-NFAT/MEF2C-PGC-1α pathway.

Inhibition of p53 deSUMOylation exacerbates puromycin aminonucleoside-induced apoptosis in podocytes.

Apoptosis is a major cause of reduced podocyte numbers, which leads to proteinuria and/or glomerulosclerosis. Emerging evidence has indicated that deSUMOylation, a dynamic post-translational modification that reverses SUMOylation, is involved in the apoptosis of Burkitt’s lymphoma cells and cardiomyocytes; however, the impact of deSUMOylation on podocyte apoptosis remains unexplored. The p53 protein plays a major role in the pathogenesis of podocyte apoptosis, and p53 can be SUMOylated. Therefore, in the present study, we evaluated the effect of p53 deSUMOylation, which is regulated by sentrin/SUMO-specific protease 1 (SENP1), on podocyte apoptosis. Our results showed that SENP1 deficiency significantly increases puromycin aminonucleoside (PAN)-induced podocyte apoptosis. Moreover, SENP1 knockdown results in the accumulation of SUMOylated p53 protein and the increased expression of the p53 target pro-apoptotic genes, BAX, Noxa and PUMA, in podocytes during PAN stimulation. Thus, SENP1 may be essential for preventing podocyte apoptosis, at least partly through regulating the functions of p53 protein via deSUMOylation. The regulation of deSUMOylation may provide a novel strategy for the treatment of glomerular disorders that involve podocyte apoptosis.

SUMO1 enhances cAMP-dependent exocytosis and glucagon secretion from pancreatic α-cells.

Post-translational modification by the small ubiquitin-like modifier-1 (SUMO1) limits insulin secretion from β-cells by inhibiting insulin exocytosis and glucagon-like peptide-1 (GLP-1) receptor signalling. The secretion of glucagon from α-cells is regulated in a manner opposite to that of insulin; it is inhibited by elevated glucose and GLP-1, and increased by adrenergic signalling. We therefore sought to determine whether SUMO1 modulates mouse and human α-cell function. Action potentials (APs), ion channel function and exocytosis in single α-cells from mice and humans, identified by glucagon immunostaining, and glucagon secretion from intact islets were measured. The effects of SUMO1 on α-cell function and the respective inhibitory and stimulatory effects of exendin 4 and adrenaline were examined. Upregulation of SUMO1 increased α-cell AP duration, frequency and amplitude, in part as a result of increased Ca(2+) channel activity that led to elevated exocytosis. The ability of SUMO1 to enhance α-cell exocytosis was cAMP-dependent and resulted from an increased L-type Ca(2+) current and a shift away from exocytosis dependent on non-L-type channels, an effect that was mimicked by knockdown of the deSUMOylating enzyme sentrin/SUMO-specific protease-1 (SENP1). Finally, although SUMO1 prevented GLP-1 receptor-mediated inhibition of α-cell Na(+) channels and single-cell exocytosis, it failed to prevent the exendin 4-mediated inhibition of glucagon secretion. Consistent with its cAMP dependence, however, SUMO1 enhanced α-cell exocytosis and glucagon secretion stimulated by adrenaline. Thus, by contrast with its inhibitory role in β-cell exocytosis, SUMO1 is a positive regulator of α-cell exocytosis and glucagon secretion under conditions of elevated cAMP.

Up-regulation of microRNA-138 induce radiosensitization in lung cancer cells

Deregulation of microRNAs (miRNAs) is implicated in tumor progression. We attempt to identify the association between miR-138 and Sentrin/SUMO-specific protease 1 (SENP1) as a radiosensitization-related gene and characterize the biological function by which SENP1 was regulated by miR-138 to influence radiosensitization in lung cancer cells. In this study, we showed that miRNA-138 is reduced in both lung cancer clinical specimens and cell lines and is effective to inhibit SENP1 expression. Moreover, high levels of miR-138 are associated with lower levels of lung cancer cell proliferation and colony formation. Then, we investigated the underlying mechanisms responsible for the increase in the radiosensitivity of lung cancer cells when SENP1 is inhibited by miR-138. We further show that the increased radiosensitivity may be the result of an increased γ-H2AX expression, an increased rate of apoptosis, and changes in the cell cycle. In conclusion, our data demonstrate that the miR-138/SENP1 cascade is relative to radiosensitization in lung cancer cells and is a potential radiotherapy target.