Characterization of the regulatory roles of the SUMO

The role of protein SUMOylation in rheumatoid arthritis

Small ubiquitin-like modifier (SUMO) proteins, as a subgroup of post-translational modifiers, act to change the function of proteins. Through their interactions with different targets, immune pathways, and the responses they elicit, can be affected by these SUMO conjugations. Thus, both a change to protein function and involvement in immune pathways has the potential to promote an efficient immune response to either a pathogenic challenge, or the development of an imbalance that could lead to an autoimmune-based disease. Also, a variety of changes such as mutations and polymorphisms can interfere with common functions of these modifications and move an effective immune response in the direction of an autoimmune disease. The present review discusses the general characteristics of SUMO proteins and focuses on their involvement in rheumatoid arthritis as an autoimmune disease.

SUMO1/UBC9‑decreased Nox1 activity inhibits reactive oxygen species generation and apoptosis in diabetic retinopathy

Diabetic retinopathy (DR) is an increasing global health concern that causes vision loss and blindness. Reactive oxygen species (ROS) are considered to be a principal cause of DR. An important source of ROS is the oxidization of NADPH. In the present study, NADPH oxidase 1 (Nox1)-expressing human retinal epithelial cell (HREC) lines were generated and infected with small ubiquitin-like modifier 1 (SUMO1) and/or ubiquitin conjugating enzyme E2 I (UBC9) lentiviral pGMLV constructs. The viabilities, apoptotic capacities and ROS production levels of the HREC lines were quantified using Hoechst 33258, annexin V/propidium iodide and dichlorodihydrofluorescein diacetate assays, respectively. Additionally, rat DR models were established. From these models, the apoptotic capacities of retinal tissues were visualized using terminal deoxynucleotidyl transferase dUTP nick end labeling assays, and the pathologies were evaluated. The mRNA and protein expression levels of SUMO1, UBC9 and Nox1 were analyzed using reverse transcription-quantitative polymerase chain reaction and western blot analyses, respectively. Compared with controls, the relative mRNA levels of SUMO1 and UBC9 were significantly upregulated, and the Nox1 levels significantly downregulated, in cells infected with SUMO1 or UBC9 alone or in combination. The ROS production and apoptosis rates of cells and retinal tissues were decreased. In addition, pathological symptoms in DR tissues improved when they were simultaneously transfected with SUMO1 and UBC9 via intraocular injection. In conclusion, the SUMO1/UBC9 axis may regulate Nox1-mediated DR by inhibiting ROS generation and apoptosis in rat and cellular model systems.

Clinical significance and functional validation of PPA1 in various tumors

The aim of the study was to detect PPA1 expression in various tumors and to investigate the relationship between PPA1 expression and clinicopathological parameters to further analyze its clinical significance. Immunohistochemical staining detected PPA1 expression in 305 noncancerous tissues and 675 tumor tissues, which included 12 different tumor types. QPCR and western blot examined PPA1 expression in tumor-derived cell lines including those derived from liver, breast, lung, and ovarian cancers. Cell proliferation and apoptosis assays were used to investigate PPA1-regulated cell growth in tumor cells. Finally, a bioinformatics analysis was used to verify the role of PPA1 in carcinogenesis. Among the 12 types of tumors, PPA1 expression was significantly higher in lung and ovarian cancers (P < 0.001). In lung cancer, PPA1 expression was associated with tumor size, patients' age, and smoking status, whereas in ovarian cancer, PPA1 expression was associated with pathological grade (P < 0.05). Moreover, we found that PPA1 expression was up-regulated in lung and ovarian cancer cell lines compared with nontumor cells. In addition, suppression of PPA1 expression by RNA interference in lung and ovarian cancer cells showed increased cell apoptosis and decreased cell proliferation, which was mediated by TP53 and p21 signaling. Notably, a bioinformatics analysis was used to verify the function of PPA1 in the development and progression of tumors. PPA1 expression is significantly higher in many tumors, especially those of lung and ovarian origin, which suggests that PPA1 plays an important role in carcinogenesis and in the development of some tumors.

Predicting diabetes mellitus genes via protein-protein interaction and protein subcellular localization information

BACKGROUND

Diabetes mellitus characterized by hyperglycemia as a result of insufficient production of or reduced sensitivity to insulin poses a growing threat to the health of people. It is a heterogeneous disorder with multiple etiologies consisting of type 1 diabetes, type 2 diabetes, gestational diabetes and so on. Diabetes-associated protein/gene prediction is a key step to understand the cellular mechanisms related to diabetes mellitus. Compared with experimental methods, computational predictions of candidate proteins/genes are cheaper and more effortless. Protein-protein interaction (PPI) data produced by the high-throughput technology have been used to prioritize candidate disease genes/proteins. However, the false interactions in the PPI data seriously hurt computational methods performance. In order to address that particular question, new methods are developed to identify candidate disease genes/proteins via integrating biological data from other sources.

RESULTS

In this study, a new framework called PDMG is proposed to predict candidate disease genes/proteins. First, the weighted networks are building in terms of the combination of the subcellular localization information and PPI data. To form the weighted networks, the importance of each compartment is evaluated based on the number of interacted proteins in this compartment. This is because the very different roles played by different compartments in cell activities. Besides, some compartments are more important than others. Based on the evaluated compartments, the interactions between proteins are scored and the weighted PPI networks are constructed. Second, the known disease genes are extracted from OMIM database as the seed genes to expand disease-specific networks based on the weighted networks. Third, the weighted values between a protein and its neighbors in the disease-related networks are added together and the sum is as the score of the protein. Last but not least, the proteins are ranked based on descending order of their scores. The candidate proteins in the top are considered to be associated with the diseases and are potential disease-related proteins. Various types of data, such as type 2 diabetes-associated genes, subcellular localizations and protein interactions, are used to test PDMG method.

CONCLUSIONS

The results show that the proteins/genes functionally exerting a direct influence over diabetes are consistently placed at the head of the queue. PDMG expands and ranks 445 candidate proteins from the seed set including original 27 type 2 diabetes proteins. Out of the top 27 proteins, 14 proteins are the real type 2 diabetes proteins. The literature extracted from the PubMed database has proved that, out of 13 novel proteins, 8 proteins are associated with diabetes.

SENP2 regulated the stability of β-catenin through WWOX in hepatocellular carcinoma cell

SUMOylation and deSUMOylation are dynamic mechanisms regulating a spectrum of protein activities. The SUMO proteases (SENP) remove SUMO conjugate from proteins, and their expression is deregulated in cancers. SENP2 has been reported to play a critical role in the control of hepatocellular carcinoma (HCC) cell growth by modulating the stability of β-catenin. However, the underlying mechanism remains largely unknown. Here, we show that the WW domain-containing oxidoreductase (WWOX), a novel inhibitor of the Wnt/β-catenin pathway, is required for stabilization of β-catenin regulated by SENP2 in HCC cells. The transcriptional level of WWOX is tightly regulated by SENP2. Moreover, knockdown of WWOX by siRNA attuned SENP2-induced β-catenin degradation and decreased SENP2-mediated HCC cell proliferation arrest. Taken together, our data suggested that WWOX is a key downstream modulator of the SENP2 tumor suppressor function in HCC cell.

Inhibition of SENP5 suppresses cell growth and promotes apoptosis in osteosarcoma cells

SUMOylation is a dynamic and reversible process. Several SUMO-specific proteases (SENPs) that remove SUMO from substrates have been shown to be amplified in a subset of cancers. SENP5 is required for cell division, as well as maintaining mitochondrial morphology and function. SENP5 has been reported to be predominantly localized to the cytoplasm of oral squamous cell carcinoma (OSCC) and is associated with the differentiation of OSCC. Western blot was used to detect the protein expression of SENP5 in osteosarcoma cells and tissue. Lentivirus-mediated siRNA was used to silence the expression of SENP5. Cell cycle distribution was determined by FACS analysis. The present study showed that SENP5 is overexpressed in osteosarcoma cells. In addition, lentivirus-mediated small interfering RNA (siRNA) of SENP5 significantly inhibited cell growth and induced apoptosis in osteosarcoma cells. SENP5 inhibition suppressed the growth and colony formation capacity of two osteosarcoma cell lines, U2OS and Saos-2. Silencing the expression of SENP5 in serum-starved U2OS and Saos-2 cells induced an increase in caspase-3/-7 activity and a decrease in cyclin B1 expression. These observations indicate that SENP5 is required for cell growth and apoptosis and may therefore be a promising drug target for antiosteosarcoma treatment.

Inhibition of SENP6-induced radiosensitization of human hepatocellular carcinoma cells by blocking radiation-induced NF-κB activation

Hepatocellular carcinoma is the most common type of liver cancer. Radiotherapy combined with chemotherapy is the treatment of choice for hepatocellular carcinoma, but radioresistance of the cancer remains a significant therapeutic hindrance. Here, we provided several lines of evidence that small ubiquitin-like modifier (SUMO)-specific protease 6 (SENP6) could be an attractive molecular target for the treatment of hepatocellular carcinoma. By using immunohistochemical and real-time PCR, we showed that SENP6 was overexpressed in more than half of the hepatocellular carcinoma tissues. The growth retardation and radiosensitization were caused by silencing of SENP6 in the hepatocellular carcinoma cell lines using lentiviral shRNA. Moreover, SENP6 was required for radiation-induced NF-κB activation and the half-life of IκBα, a well-known inhibitor of NF-κB, and was extended by SENP6 silencing. Thus, our data demonstrated that SENP6 is an attractive drug target for anticancer therapy and radiosensitization.