CDK-associated Cullin 1 can promote cell proliferation and inhibit cisplatin-induced apoptosis in the AGS gastric cancer cell line

UPS: Opportunities and challenges for gastric cancer treatment

Gastric cancer remains the fourth most frequently diagnosed malignancy and the fifth leading cause of cancer-related mortality worldwide owning to the lack of efficient drugs and targets for therapy. Accumulating evidence indicates that UPS, which consists of E1, E2, and E3 enzymes and proteasome, plays an important role in the GC tumorigenesis. The imbalance of UPS impairs the protein homeostasis network during development of GC. Therefore, modulating these enzymes and proteasome may be a promising strategy for GC target therapy. Besides, PROTAC, a strategy using UPS to degrade the target protein, is an emerging tool for drug development. Thus far, more and more PROTAC drugs enter clinical trials for cancer therapy. Here, we will analyze the abnormal expression enzymes in UPS and summarize the E3 enzymes which can be developed in PROTAC so that it can contribute to the development of UPS modulator and PROTAC technology for GC therapy.

CDK-associated Cullin 1 promotes Cell Proliferation and inhibits Cell Apoptosis in Human Glioblastoma

BACKGROUND

Glioma is the most common intracranial primary tumour of adult humans, and its pathological mechanism and molecular characteristics are under investigation. CDK-associated cullin 1 (CACUL1) has been shown to regulate colorectal carcinoma, lung cancer and gastric cancer development.

OBJECTIVE

This study aims to explore the role of CACUL1 in the pathogenesis of human glioma.

METHODS

CACUL1 levels in human glioma tissue microarrays were detected by immunohistochemistry analysis. Two glioblastoma cell lines, namely, U87 and U251, were transfected with CACUL1 siRNA, and cell proliferation, cell cycle, cell apoptosis and regulating molecules including cyclin E1, cyclin A2, CDK2, p21, Bcl2 and Bax were assessed by CCK8, flow cytometry and Western blot.

RESULTS

CACUL1 expression in glioma tissue was significantly higher than that in normal brain tissue. CACUL1 knockdown impeded cell proliferation, induced cell apoptosis and caused G1/S transition arrest in glioblastoma cells. The cell cycle-related proteins CDK2, cyclin E1 and cyclin A2 were dramatically decreased in the CACUL1 siRNA group compared to the non-targeting siRNA group in both U87 and U251 cells, while the CDK inhibitory protein p21 was increased in U87 cells. Additionally, the Bcl-2/Bax ratio was significantly decreased.

CONCLUSION

CACUL1 can promote cell proliferation and suppress apoptosis of glioma cells and might serve as a potential oncogene for gliomas.

Cullin-RING Ligases as Promising Targets for Gastric Carcinoma Treatment

Gastric carcinoma has serious morbidity and mortality, which seriously threats human health. The studies on gastrointestinal cell biology have shown that the ubiquitination modification that occurs after protein translation plays an essential role in the pathogenesis of gastric carcinoma. Protein ubiquitination is catalyzed by E3 ubiquitin ligase and can regulate various substrate proteins in different cellular pathways. Cullin-RING E3 ligase (CRLs) is a representative of the E3 ubiquitin ligase family, which requires cullin (CUL) neddylation modification for activation to regulate homeostasis of ~20% of cellular proteins. The substrate molecules regulated by CRLs are often involved in many cell progressions such as cell cycle progression, cell apoptosis, DNA damage and repair. Given that CRLs play an important role in modulation of biological activities, so targeting a certain CULs member neddylation may be an attractive strategy for selectively controlling the cellular proteins levels to achieve the goal of cancer treatment. In this review, we will discuss the roles of CULs and Ring protein in gastric carcinoma and summarize the current neddylation modulators for gastric carcinoma treatment.

Roles of E3 ubiquitin ligases in gastric cancer carcinogenesis and their effects on cisplatin resistance

Although gastric cancer (GC) is one of the most common cancers with high incidence and mortality rates, its pathogenesis is still not elucidated. GC carcinogenesis is complicated and involved in the activation of oncoproteins and inactivation of tumor suppressors. The ubiquitin-proteasome system (UPS) is crucial for protein degradation and regulation of physiological and pathological processes. E3 ubiquitin ligases are pivotal enzymes in UPS, containing various subfamily proteins. Previous studies report that some E3 ligases, including SKP2, CUL1, and MDM2, act as oncoproteins in GC carcinogenesis. On the other hand, FBXW7, FBXL5, FBXO31, RNF43, and RNF180 exert as tumor suppressors in GC carcinogenesis. Moreover, E3 ligases modulate cell growth, cell apoptosis, and cell cycle; thus, it is complicated to confer cisplatin resistance/sensitivity in GC cells. The intrinsic and acquired cisplatin resistance limits its clinical application against GC. In this review, we explore oncogenic and tumor suppressive roles of E3 ligases in GC carcinogenesis and focus on the effects of E3 ligases on cisplatin resistance in GC cells, which will provide novel therapeutic targets for GC therapy, especially for cisplatin-resistant patients.

Investigating aberrantly expressed microRNAs in peripheral blood mononuclear cells from patients with treatment‑resistant schizophrenia using miRNA sequencing and integrated bioinformatics

Treatment-resistant schizophrenia (TRS) is a common phenotype of schizophrenia that places a considerable burden on patients as well as on society. TRS is known for its tendency to relapse and uncontrollable nature, with a poor response to antipsychotics other than clozapine. Therefore, it is urgent to identify objective biological markers, so as to guide its treatment and associated clinical work. In the present study, the peripheral blood mononuclear cells (PBMCs) of patients with TRS and a healthy control group, which were gender-, age- and ethnicity-matched, were subjected to microRNA (miRNA/miR) sequencing to screen out the top three miRNAs with the highest fold change values. These were then validated in the TRS (n=34) and healthy control (n=31) groups by reverse transcription-quantitative PCR. For two of the top three miRNAs, the PCR results were in accordance with the sequencing result (P<0.01), while the third miRNA exhibited the opposite trend (P<0.01). To elucidate the functions of these two miRNAs, Homo sapiens (hsa)-miR-218-5p and hsa-miR-1262 and their regulatory network, target gene prediction was first performed using online TargetScan and Diana-micro T software. Bioinformatics analysis was then performed using functional enrichment analysis to determine the Gene Ontology terms in the category biological process and the Kyoto Encyclopedia of Genes and Genomes pathways. It was revealed that these target genes were markedly associated with the nervous system and brain function, and it was obvious that the differentially expressed miRNAs most likely participated in the pathogenesis of TRS. A receiver operating characteristic curve was generated to confirm the distinct diagnostic value of these two miRNAs. It was concluded that aberrantly expressed miRNAs in PMBCs may be implicated in the pathogenesis of TRS and may serve as specific peripheral blood-based biomarkers for the early diagnosis of TRS.

Omental Tissue-Mediated Tumorigenesis of Gastric Cancer Peritoneal Metastases

The peritoneal cavity, especially the omentum, is a common site for gastric cancer metastasis, representing advanced disease stage and poor prognosis. Here, we studied the effects of omental tissue on gastric cancer tumor progression in vitro and in vivo. Utilizing in vitro models, we found that omental tissue secreted factors increased gastric cancer cellular growth (by 30–67%, P < 0.05), motility (>8-fold, P < 0.05), invasiveness (>7-fold, P < 0.05) and chemoresistance to platinum-based chemotherapeutic agents (>1.2-fold for oxaliplatin and >1.6-fold for cisplatin, P < 0.05). Using a robust proteomic approach, we identified numerous molecules secreted into the omental tissue conditioned medium (CM) which may promote gastric cancer cellular aggressiveness (i.e., IL-6, IL-8, MMP9, FN1, and CXCL-5). Next, an in vivo xenograft mouse model showed an increased human gastric adenocarcinoma tumor volume of cells co-cultured with human omental tissue secreted factors; 1.6 ± 0.55 vs. 0.3 ± 0.19 cm³ (P < 0.001), as well as increased angiogenesis. Finally, exosomes were isolated from human omental tissue CM of gastric cancer patients. These exosomes were taken up by gastric cancer cells enhancing their growth (>8-fold, P < 0.01) and invasiveness (>8-fold, P < 0.001). Proteomic analysis of the content of these exosomes identified several established cancer- related proteins (i.e., IL-6, IL-8, ICAM-1, CCl2, and OSM). Taken together, our findings imply that the omentum play an active role in gastric cancer metastasis. The data also describe specific cytokines that are involved in this cross talk, and that omental tissue- derived exosomes may contribute to these unique cellular interactions with gastric cancer cells. Further studies aimed at understanding the biology of gastric cancer intra peritoneal spread are warranted. Hopefully, such data will enable to develop future novel therapeutic strategies for the treatment of metastatic gastric cancer.

CAC1 knockdown reverses drug resistance through the downregulation of P-gp and MRP-1 expression in colorectal cancer

CDK2-associated cullin domain 1 (CAC1) is as a novel cell cycle regulator widely expressed in colorectal cancer (CRC). However, its expression and function in drug resistant CRC cells remains elusive. Therefore, the present study aimed to assess the biochemical function and relevance of CAC1 in drug resistant CRC cells, and detect the potential mechanism. For this purpose, a total of 83 CRC cases were collected for the immunohistochemical analysis of CAC1 expression. Functional studies (stable transfection, flow cytometry, colony formation, and invasion and migration assays) were performed in SW480, LoVo and their corresponding 5-FU resistant cells. In addition, a nude mice xenograft model was established for further observation in vivo. In the present study, CAC1 protein expression was higher in CRC tissues than that in normal tissues (P<0.05). Furthermore, CAC1 protein expression was higher in SW480/5-FU cells than in SW480 cells. CAC1 knockdown arrested 5-FU resistant cells at the G1/S phase and increased the sensitivity of 5-FU resistant cells to 5-FU by inducing apoptosis. In addition, CAC1 reduced the invasive and migration ability of SW480/5-FU and LoVo/5-FU cells in vitro, and reduced their tumorigenicity and metastatic ability in vivo. Finally, CAC1 knockdown resulted in decreased P-glycoprotein and MRP-1 protein expression. Based on these results, it can be concluded that CAC1 plays an important role in the occurrence and promotion of drug resistance in CRC. Therefore, the knockdown of CAC1 may be considered as a new strategy for the development of CRC drug resistance treatments in the future.

Delineating Crosstalk Mechanisms of the Ubiquitin Proteasome System That Regulate Apoptosis

Regulatory functions of the ubiquitin-proteasome system (UPS) are exercised mainly by the ubiquitin ligases and deubiquitinating enzymes. Degradation of apoptotic proteins by UPS is central to the maintenance of cell health, and deregulation of this process is associated with several diseases including tumors, neurodegenerative disorders, diabetes, and inflammation. Therefore, it is the view that interrogating protein turnover in cells can offer a strategy for delineating disease-causing mechanistic perturbations and facilitate identification of drug targets. In this review, we are summarizing an overview to elucidate the updated knowledge on the molecular interplay between the apoptosis and UPS pathways. We have condensed around 100 enzymes of UPS machinery from the literature that ubiquitinates or deubiquitinates the apoptotic proteins and regulates the cell fate. We have also provided a detailed insight into how the UPS proteins are able to fine-tune the intrinsic, extrinsic, and p53-mediated apoptotic pathways to regulate cell survival or cell death. This review provides a comprehensive overview of the potential of UPS players as a drug target for cancer and other human disorders.

The role of cullin proteins in gastric cancer

The cullin proteins are a family of scaffolding proteins that associate with RING proteins and ubiquitin E3 ligases and mediate substrate-receptor bindings. Thus, cullin proteins regulate the specificity of ubiquitin targeting in the regulation of proteins involved in various cellular processes, including proliferation, differentiation, and apoptosis. There are seven cullin proteins that have been identified in eukaryotes: CUL1, CUL2, CUL3, CUL4A, CUL4B, CUL5, and CUL7/p53-associated parkin-like cytoplasmic protein. All of these proteins contain a conserved cullin homology domain that binds to RING box proteins. Cullin-RING ubiquitin ligase complexes are activated upon post-translational modification by neural precursor cell-expressed, developmentally downregulated protein 8. The aberrant expression of several cullin proteins has been implicated in many cancers though the significance in gastric cancer has been less well investigated. This review provides the first systematic discussion of the associations between all members of the cullin protein family and gastric cancer. Functional and regulatory mechanisms of cullin proteins in gastric carcinoma progression are also summarized along with a discussion concerning future research areas. Accumulating evidence suggests a critical role of cullin proteins in tumorigenesis, and a better understanding of the function of these individual cullin proteins and their targets will help identify potential biomarkers and therapeutic targets.

CACUL1/CAC1 Regulates the Antioxidant Response by Stabilizing Nrf2

Nrf2 is the pre-dominant transcription activator responsible for coordinated up-regulation of ARE-driven antioxidant and detoxification genes. The activity of Nrf2 is tightly regulated at basal levels through its ubiquitination by Cul3-Keap1 and consequential degradation. Upon exposure to stress, the Cul3-Keap1 ligase is inhibited, leading to Nrf2 stabilization and activation. Here we describe CACUL1/CAC1 as a positive regulator of the Nrf2 pathway. We found that CACUL1 is up-regulated by Nrf2-activating oxidative stresses in cells and in mice. The association of CACUL1 with the Cul3-Keap1 complex led to a decrease in Nrf2 ubiquitination levels at non-stressed as well as stressed conditions, and sensitized cells for higher Nrf2 activation. Furthermore, CACUL1 knock-down led to a decrease in Nrf2 activity and cell viability under stress. Our results show that CACUL1 is a regulator of Nrf2 ubiquitination, adding another regulatory layer to the Nrf2 antioxidant stress response.

Toll-like receptor 4 regulates hepatitis B virus related hepatic carcinoma cell proliferation by controlling cyclin-dependent kinase 4/6 expression

AIM: To explore the effect of Toll-like receptor 4 (TLR4) on the proliferation of hepatitis B virus (HBV) related hepatic carcinoma cells and the underlying mechanism.

METHODS: The expression of TLR4, cyclin-dependent kinase (CDK) 4 and CDK6 protein in 36 HBV-related hepatic carcinoma tissues and matched adjacent tissues were detected by Western blot, and their correlations in carcinoma tissues were analyzed. Three TLR4 specific siRNAs and a negative control were synthesized and transfected into hepatoma cells Hep-3B using liposomes. The siRNA sequence with the best performance was selected for Western blot analysis. The expression of TLR4, CDK4 and CDK6 proteins was measured by Western blot assay before and after transfection. The proliferation of hepatoma cells was observed by MTT assay and colony formation assay.

RESULTS: The overall expression levels of TLR4, CDK4 and CDK6 proteins in HBV-related hepatic carcinoma were significantly higher than those in the matched adjacent tissues (P < 0.05). There was a positive correlation between TLR4 and CDK4 expression (r = 0.66, P < 0.05), and between TLR4 and CDK6 expression (r = 0.57, P < 0.05). Using the best interference sequence (TLR4-siRNA-03), it was found that the protein levels of CDK4 and CDK6 were significantly decreased in the TLR4-siRNA group (P < 0.05), compared to the control group. In addition, the proliferation of Hep-3B cells and the colony formation rate were both decreased (P < 0.05) in the TLR4-siRNA group.

CONCLUSION: TLR4 may regulate the proliferation of HBV-related hepatic carcinoma cells by controlling the expression of CDK4 and CDK6.

Cullin family proteins and tumorigenesis: genetic association and molecular mechanisms

Cullin family proteins function as scaffolds to form numerous E3 ubiquitin ligases with RING proteins, adaptor proteins and substrate recognition receptors. These E3 ligases further recognize numerous substrates to participate in a variety of cellular processes, such as DNA damage and repair, cell death and cell cycle progression. Clinically, cullin-associated E3 ligases have been identified to involve numerous human diseases, especially with regard to multiple cancer types. Over the past few years, our understanding of cullin proteins and their functions in genome stability and tumorigenesis has expanded enormously. Herein, this review briefly provides current perspectives on cullin protein functions, and mainly summarizes and discusses molecular mechanisms of cullin proteins in tumorigenesis.

Cullin1 regulates proliferation, migration and invasion of glioma cells

This study was designed to explore the role of Cullin1 (Cul1) in the pathogenesis of human glioma and to investigate the role of Cul1 in the growth, migration and invasion of glioma cells. Expression of Cul1 in 191 glioma tissues, 8 normal brain tissues and 8 tumor adjacent normal brain tissues was analyzed by tissue microarray and immunohistochemistry. Cul1 expression in human glioblastoma cells was knocked down by specific siRNA to study the effect of down-regulation of Cul1 on proliferation, invasion and migration of glioma cells. Our results showed that Cul1 expression increased significantly in tissues from the benign tumor and malignant tumor in comparison with those from the tumor-adjacent normal brain (P<0.05 for both). We did not find any correlation between Cul1 expression and clinicopathological parameters. In addition, we found that knockdown of Cul1 by RNA interference markedly inhibited cell proliferation and caused cessation of cell cycle. This reduced cell proliferation was due to G1 phase arrest as cyclinA, cyclinD1 and cyclinE were diminished, whereas p21 and p27 were up-regulated. We further demonstrated that silencing of Cul1 in glioma cells inhibited the cell migration and invasion abilities, and down-regulation of MMP-2 and MMP-9 expression greatly contributed to the reduced cell invasion and migration abilities. Our data indicated that Cul1 expression significantly increased in human glioma, and it may be involved in proliferation, migration and invasion of glioma cells.

Network-based identification of key proteins involved in apoptosis and cell cycle regulation

OBJECTIVES

Cancer cells differ from normal body cells in their ability to divide indefinitely and to evade programmed cell death. Crosstalk between apoptosis and cell cycle processes promotes balance between proliferation and death, and limits population growth and survival of cells. However, intricate relationships between them and how they are able to manipulate the fate of cancer cells still remain to be clarified. Identification of key factors involved in both apoptosis and cell cycle regulation may help to address this problem.

MATERIALS AND METHODS

Identification of such key proteins was carried out, using a series of bioinformatics methods, such as network construction and key protein identification.

RESULTS

In this study, we computationally constructed human apoptotic/cell cycle-related protein-protein interactions (PPIs) networks from five experimentally supported protein interaction databases, and further integrated these high-throughput data sets into a Naïve Bayesian model to predict protein functional connections. On the basis of modified apoptotic/cell cycle related PPI networks, we calculated and ranked all protein members involved in apoptosis and cell cycle regulation. Our results not only identified some already known key proteins such as p53, Rb, Myc and Src but also found that the proteasome, Cullin family members, kinases and transcriptional repressors play important roles in regulating apoptosis and the cell cycle. Furthermore, we found that the top 100 proteins ranked by PeC were enriched in some pathways such as those of cancer, the proteasome, the cell cycle and Wnt signalling.

CONCLUSIONS

We constructed the global human apoptotic/cell cycle related PPI network based on five online databases, and a Naïve Bayesian model. In addition, we systematically identified apoptotic/cell cycle related key proteins in cancer cells. These findings may uncover intricate relationships between apoptosis and cell cycle processes and thus provide further new clues towards future anticancer drug discovery.

High expression of Cullin1 indicates poor prognosis for NSCLC patients

BACKGROUND

Cullin1 is a scaffold protein of the ubiquitin E3 ligase Skp1/Cullin1/Rbx1/F-box protein complex which ubiquitinates a broad range of proteins participating in biochemical events like cell-cycle progression, signal transduction, and transcription. Cullin1 is involved in the progression of several cancers, such as melanoma, breast cancer, and gastric cancer.

METHODS

To investigate the role of Cullin1 in the development of non-small-cell lung cancer (NSCLC), we examined the expression of Cullin1 in 8-paired fresh NSCLC tissues. We then constructed immunohistochemistry (IHC) on 114 paraffin-embedded slices and evaluated the correlation between Cullin1 expression and clinicopathologic variables, as well as patients' overall survival.

RESULTS

We found that Cullin1 was highly expressed in NSCLC tissues and significantly associated with NSCLC's histological differentiation (P=0.002), clinical stage (P=0.010) and Ki-67 (P=0.021). Furthermore, we showed a strong correlation between high Cullin1 expression and worse overall survival rates in NSCLC patients (P<0.001). Cox regression analysis revealed that Cullin1 expression was an independent prognostic factor to predict 5-year patient outcome in NSCLC cancer (P=0.033).

CONCLUSION

These data suggested that Cullin1 might promote the progression of NSCLC and be a biotarget for NSCLC's therapy.

CDK-associated Cullin 1 promotes cell proliferation with activation of ERK1/2 in human lung cancer A549 cells

Lung cancer is one of the most common causes of cancer-related death in the world, but the mechanisms remain unknown. In this study, we investigated the expression of CDK-associated Cullin 1 (CAC1) in lung cancer, the effect of CAC1 on the proliferation of human lung cancer A549 cells, and the activation of signaling pathways of mitogen-activated protein kinases (MAPKs). Results showed that CAC1 expression was higher levels in human lung carcinoma than normal lung tissue, and CAC1 siRNA reduced the proliferation of lung cancer A549 cells by decreasing cell activity and cell division in vitro. The proportion of cells treated with CAC1 siRNA increased in the G1 phase and decreased in the S and G2/M phase, indicative of G1 cell cycle arrest. Furthermore, the proportions of early/late apoptosis in lung cancer A549 cells were enhanced with CAC1 siRNA treatment. It was also found that activation of extracellular signal-regulated protein kinase (ERK) and p38 signaling pathways were involved in the proliferation of A549 cells. After CAC1 siRNA treatment, p-ERK1/2 levels decreased, and meanwhile p-p38 level increased, A549 cell proliferation increased when ERK1/2 signaling is activated by PMA. Our findings demonstrated that CAC1 promoted the proliferation of human lung cancer A549 cells with activation of ERK1/2 signaling pathways, suggesting a potential cure target for treatment of human lung cancer.