The DNA replication protein Cdc6 inhibits the microtubule-organizing activity of the centrosome

Exploring Bioinformatics Tools to Analyze the Role of CDC6 in the Progression of Polycystic Ovary Syndrome to Endometrial Cancer by Promoting Immune Infiltration

Cell division cycle 6 (CDC6) is essential for the initiation of DNA replication in eukaryotic cells and contributes to the development of various human tumors. Polycystic ovarian syndrome (PCOS) is a reproductive endocrine disease in women of childbearing age, with a significant risk of endometrial cancer (EC). However, the role of CDC6 in the progression of PCOS to EC is unclear. Therefore, we examined CDC6 expression in patients with PCOS and EC. We evaluated the relationship between CDC6 expression and its prognostic value, potential biological functions, and immune infiltrates in patients with EC. In vitro analyses were performed to investigate the effects of CDC6 knockdown on EC proliferation, migration, invasion, and apoptosis. CDC6 expression was significantly upregulated in patients with PCOS and EC. Moreover, this protein caused EC by promoting the aberrant infiltration of macrophages into the immune microenvironment in patients with PCOS. A functional enrichment analysis revealed that CDC6 exerted its pro-cancer and pro-immune cell infiltration functions via the PI3K-AKT pathway. Moreover, it promoted EC proliferation, migration, and invasion but inhibited apoptosis. This protein significantly reduced EC survival when mutated. These findings demonstrate that CDC6 regulates the progression of PCOS to EC and promotes immune infiltration.

Deubiquitination of CDC6 by OTUD6A promotes tumour progression and chemoresistance

BACKGROUND

CDC6 is an oncogenic protein whose expression level fluctuates during the cell cycle. Although several E3 ubiquitin ligases responsible for the ubiquitin-mediated proteolysis of CDC6 have been identified, the deubiquitination pathway for CDC6 has not been investigated.

METHODS

The proteome-wide deubiquitinase (DUB) screening was used to identify the potential regulator of CDC6. Immunofluorescence, protein half-life and deubiquitination assays were performed to determine the protein stability of CDC6. Gain- and loss-of-function experiments were implemented to analyse the impacts of OUTD6A-CDC6 axis on tumour growth and chemosensitivity in vitro. N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN)-induced conditional Otud6a knockout (CKO) mouse model and tumour xenograft model were performed to analyse the role of OTUD6A-CDC6 axis in vivo. Tissue specimens were used to determine the association between OTUD6A and CDC6.

RESULTS

OTUD6A interacts with, depolyubiquitinates and stabilizes CDC6 by removing K6-, K33-, and K48-linked polyubiquitination. Moreover, OTUD6A promotes cell proliferation and decreases sensitivity to chemotherapy by upregulating CDC6. CKO mice are less prone to BCa tumorigenesis induced by BBN, and knockdown of OTUD6A inhibits tumour progression in vivo. Furthermore, OTUD6A protein level has a positive correlation with CDC6 protein level, and high protein levels of OTUD6A and CDC6 are associated with poor prognosis in patients with bladder cancer.

CONCLUSIONS

We reveal an important yet missing piece of novel DUB governing CDC6 stability. In addition, our findings propose a model for the OTUD6A-CDC6 axis that provides novel insights into cell cycle and chemosensitivity regulation, which may become a potential biomarker and promising drug target for cancer treatment.

DNA Replication proteins in primary microcephaly syndromes

SCOPE

Improper expansion of neural stem and progenitor cells during brain development manifests in primary microcephaly. It is characterized by a reduced head circumference, which correlates with a reduction in brain size. This often corresponds to a general underdevelopment of the brain and entails cognitive, behavioral and motoric retardation. In the past decade significant research efforts have been undertaken to identify genes and the molecular mechanisms underlying microcephaly. One such gene set encompasses factors required for DNA replication. Intriguingly, a growing body of evidence indicates that a substantial number of these genes mediate faithful centrosome and cilium function in addition to their canonical function in genome duplication. Here, we summarize, which DNA replication factors are associated with microcephaly syndromes and to which extent they impact on centrosomes and cilia. This article is protected by copyright. All rights reserved.

Increased CDC6 Expression Associates With Poor Prognosis in Patients With Clear Cell Renal Cell Carcinoma

Background

CDC6 (Cell division control protein 6), located at chromosome 17q21.3, plays an important role in the early stage of DNA replication and has unique functions in various malignant tumors. Here, we evaluate the relationship between CDC6 expression and oncology outcomes in patients with clear cell renal cell carcinoma (ccRCC).

Methods

A retrospective analysis of 118 ccRCC patients in Affiliated Hospital of Nantong University from 2015 to 2017 was performed. Triplicate tissue microarrays (TMA) were prepared from formalin-fixed and paraffin-embedded specimens. Immunohistochemistry (IHC) was conducted to evaluate the relationship between CDC6 expression and standard pathological features and prognosis. The RNA sequencing data and corresponding clinical information were acquired from the TCGA database. GSEA was used to identify signal pathways related to CDC6. Cox regression analysis was used to assess independent prognostic factors. In addition, the relationship between CDC6 and immunity was also investigated.

Results

The results of Kaplan–Meier curve indicated that the OS of the patients with high expression of CDC6 was shorter than that of the patients with low CDC6 expression. Integrating the TCGA database and IHC staining, the results showed that CDC6 in ccRCC tissue was obviously up-regulated compared with adjacent normal kidney tissue. The results of Logistic regression analysis demonstrated that ccRCC patients with high expression of CDC6 are more likely to develop advanced disease than ccRCC patients with low CDC6 expression. The results of GSEA showed that the high expression of CDC6 was related to multiple signaling pathways. As for immunity, it was also related to TMB, immune checkpoint molecules, tumor microenvironment and immune infiltration. There were significantly correlations with CDC6 and immune cell infiltration levels and tumor microenvironment. The results of further results of the TCGA database showed that CDC6 was obviously related to immune checkpoint molecules and immune cells.

Conclusions

Increased expression of CDC6 is a potentially prognostic factor of poor prognosis in ccRCC patients.

Cdc6 disruption leads to centrosome abnormalities and chromosome instability in pancreatic cancer cells

Cell division cycle 6 (Cdc6) plays key roles in regulating DNA replication, and activation and maintenance of cell cycle check points. In addition, Cdc6 exerts oncogenic properties via genomic instability associated with incomplete DNA replication. This study aimed to examine the effects of Cdc6 on pancreatic cancer (PC) cells. Our results showed that Cdc6 expression was higher in clinical PC specimens (based on analysis of the GEPIA database) and cell lines, and the high Cdc6 expression was associated with poorer survival in The Cancer Genome Atlas-PC cohort. In addition, Cdc6-depleted PC cells significantly inhibited cell proliferation and colony formation, delayed G₂/M cell cycle progression, and increased expression of p-histone H3 and cyclin A2 levels. These observations could be explained by Cdc6 depletion leading to multipolar and split spindles via centrosome amplification and microtubule disorganization which eventually increases chromosome missegregation. Furthermore, Cdc6-depleted PC cells showed significantly increased apoptosis, which was consistent with increased caspase-9 and caspase-3 activation. Collectively, our results demonstrated that Cdc6-depleted PC cells are arrested in mitosis and eventually undergo cell death by induced multipolar spindles, centrosome aberrations, microtubule disorganization, and chromosome instability. In conclusion, Cdc6 may be a potential biomarker and therapeutic target for PC.

MicroRNA-1297 inhibits proliferation and promotes apoptosis in gastric cancer cells by downregulating CDC6 expression

Gastric cancer (GC), one of the most common malignant tumors and the second most common leading cause of cancer-related death worldwide, is a biologically heterogeneous disease accompanied by various genetic and epigenetic alterations. However, the molecular mechanisms underlying this disease are complex and not completely understood. Increasing studies have shown that aberrant microRNA (miRNA) expression is associated with GC tumorigenesis and growth. MiR-1297 has been confirmed to be a cancer suppressor in diverse tumors in humans. However, to date, the function and mechanism of miR-1297 in GC have not been determined. Here, we found that the expression of miR-1297 was significantly reduced in GC tissues or GC cell lines compared with paracarcinoma normal tissue or normal cell lines. Exogenic overexpression of miR-1297 in GC cell lines can inhibit cell proliferation and colony formation and induce apoptosis, and inhibition of miR-1297 in GC cell lines can promote cell proliferation and colony formation, and reduce apoptosis in vitro. We further confirmed that miR-1297 acted as a tumor suppressor through targeting cell division control protein 6 (CDC6) in GC. Moreover, the inverse relationship between miR-1297 and CDC6 was verified in GC cell lines. Our results indicated that miR-1297 is a potent tumor suppressor in GC, and its antiproliferative and gene-regulatory effects are, in part, mediated through its downstream target gene, CDC6. These findings implied that miR-1297 might be used as a novel therapeutic target of GC.

Wogonin Induces Apoptosis and Reverses Sunitinib Resistance of Renal Cell Carcinoma Cells via Inhibiting CDK4-RB Pathway

Wogonin, an active component derived from Scutellaria baicalensis, has shown anti-tumor activities in several malignancies. However, the roles of wogonin in RCC cells remain elusive. Here, we explored the effects of wogonin on RCC cells and the underlying mechanisms. We found that wogonin showed significant cytotoxic effects against RCC cell lines 786-O and OS-RC-2, with much lower cytotoxic effects on human normal embryonic kidney cell line HEK-293 cells. Wogonin treatment dramatically inhibited the proliferation, migration, and invasion of RCC cells. We further showed that by inhibiting CDK4-RB pathway, wogonin transcriptionally down-regulated CDC6, disturbed DNA replication, induced DNA damage and apoptosis in RCC cells. Moreover, we found that the levels of p-RB, CDK4, and Cyclin D1 were up-regulated in sunitinib resistant 786-O, OS-RC-2, and TK-10 cells, and inhibition of CDK4 by palbociclib or wogonin effectively reversed the sunitinib resistance, indicating that the hyperactivation of CDK4-RB pathway may at least partially contribute to the resistance of RCC to sunitinib. Together, our findings demonstrate that wogonin could induce apoptosis and reverse sunitinib resistance of RCC cells via inhibiting CDK4-RB pathway, thus suggesting a potential therapeutic implication in the future management of RCC patients.

CDC6 regulates both G2/M transition and metaphase-to-anaphase transition during the first meiosis of mouse oocytes

Cell division cycle protein, CDC6, is essential for the initiation of DNA replication. CDC6 was recently shown to inhibit the microtubule-organizing activity of the centrosome. Here, we show that CDC6 is localized to the spindle from pro-metaphase I (MI) to MII stages of oocytes, and it plays important roles at two critical steps of oocyte meiotic maturation. CDC6 depletion facilitated the G2/M transition (germinal vesicle breakdown [GVBD]) through regulation of Cdh1 and cyclin B1 expression and CDK1 (CDC2) phosphorylation in a GVBD-inhibiting culture system containing milrinone. Furthermore, GVBD was significantly decreased after knockdown of cyclin B1 in CDC6-depleted oocytes, indicating that the effect of CDC6 loss on GVBD stimulation was mediated, at least in part, by raising cyclin B1. Knockdown of CDC6 also caused abnormal localization of γ-tubulin, resulting in defective spindles, misaligned chromosomes, cyclin B1 accumulation, and spindle assembly checkpoint (SAC) activation, leading to significant pro-MI/MI arrest and PB1 extrusion failure. These phenotypes were also confirmed by time-lapse live cell imaging analysis. The results indicate that CDC6 is indispensable for maintaining G2 arrest of meiosis and functions in G2/M checkpoint regulation in mouse oocytes. Moreover, CDC6 is also a key player regulating meiotic spindle assembly and metaphase-to-anaphase transition in meiotic oocytes.

miR-215-5p decreases migration and invasion of trophoblast cells through regulating CDC6 in preeclampsia

Preeclampsia (PE) is a serious disease that occurs after 20 weeks during pregnancy. There are some aberrant microRNAs (miRNAs) that are associated with the etiology of PE. As discovered by scholars, there was an increased level of miR-215-5p in plasma of PE patients compared with the control group; nonetheless, there is still no knowledge of the mechanism of miR-215-5p in PE. We carried out the comparison of the expression levels of miR-215-5p, and the supposed target gene cell division cycle 6 (CDC6) in 30 placentas from PE patients as well as 30 placentas from normal pregnant women. The verification of the impacts of miR-215-5p and CDC6 was carried out by functional assays in HTR-8/SVneo cells transfected with the miR-215-5p mimic or siR-CDC6. As indicated by findings, miR-215-5p showed an apparent increase; conversely, CDC6 was inhibited in the experiment group. The upregulation of miR-215-5p inhibited both the migration and invasive potential of trophoblasts, besides decreasing the G1-S transition and downregulating CDC6 in HTR-8/SVneo cells; nonetheless, it did not significantly impact the cell proliferation. Furthermore, siR-CDC6 replicated the functions of the miR-215-5p mimic. Also, the miR-215-5p mimic and siR-CDC6 both decreased the epithelial-mesenchymal transition (EMT) with additional E-cadherin level and decreased the expressions of N-cadherin as well as vimentin in trophoblast cells. To conclude, miR-215-5p decreased not only the migration but also the invasion of trophoblasts through regulating CDC6, which indicated that miR-215-5p might be associated with the etiology of PE. SIGNIFICANCE OF THE STUDY: More and more attention has been paid on the roles of miRNAs in the pathogenesis of PE. However, there is no study of miR-215-5p in the etiology of PE. We first investigated the mechanism of miR-215-5p in placental tissues and HTR-8/SVneo cells. It was suggested that miR-215-5p decreased the abilities of migration and invasion of trophoblasts through regulating CDC6 in PE. miR-215-5p might be used as an target for the early diagnosis and treatment of PE in the future.

The Replication Protein Cdc6 Suppresses Centrosome Over-Duplication in a Manner Independent of Its ATPase Activity

The Cdc6 protein is essential for the initiation of chromosomal replication and functions as a licensing factor to maintain chromosome integrity. During the S and G2 phases of the cell cycle, Cdc6 has been found to inhibit the recruitment of pericentriolar material (PCM) proteins to the centrosome and to suppress centrosome over-duplication. In this report, we analyzed the correlation between these two functions of Cdc6 at the centrosome. Cdc6 depletion increased the population of cells showing centrosome over-duplication and premature centrosome separation; Cdc6 expression reversed these changes. Deletion and fusion experiments revealed that the 18 amino acid residues (197-214) of Cdc6, which were fused to the Cdc6-centrosomal localization signal, suppressed centrosome over-duplication and premature centrosome separation. Cdc6 mutant proteins that showed defective ATP binding or hydrolysis did not exhibit a significant difference in suppressing centrosome over-duplication, compared to the wild type protein. In contrast to the Cdc6-mediated inhibition of PCM protein recruitment to the centrosome, the independence of Cdc6 on its ATPase activity for suppressing centrosome over-duplication, along with the difference between the Cdc6 protein regions participating in the two functions, suggested that Cdc6 controls centrosome duplication in a manner independent of its recruitment of PCM proteins to the centrosome.