Regulation of the final stage of mitosis by components of the pre-replicative complex and a polo kinase

NKX6.3 modulation of mitotic dynamics and genomic stability in gastric carcinogenesis

BACKGROUND

Gastric cancer remains a significant global health challenge, characterized by poor prognosis and high mortality rates. Mitotic integrity and genomic stability are crucial in maintaining cellular homeostasis and preventing tumorigenesis. The transcription factor NKX6.3 has emerged as a potential regulator of these processes in gastric epithelial cells, prompting an investigation into its role in gastric cancer development.

METHODS

We employed a combination of in vitro and in vivo techniques to elucidate the impact of NKX6.3 depletion on mitotic dynamics and genomic stability in gastric epithelial cells. Quantitative real-time PCR and Western blot analyses were conducted to assess the expression of mitosis-related genes and proteins. Flow cytometry was utilized to evaluate cell cycle distribution, while immunofluorescence microscopy enabled the visualization of mitotic abnormalities. Statistical analyses, including Student's t-test and ANOVA, were performed to determine the significance of our findings.

RESULTS

Our results demonstrate that NKX6.3 depletion leads to significant mitotic defects, characterized by increased chromosome misalignment and lagging chromosomes during anaphase. These abnormalities corresponded with elevated levels of genomic instability markers, indicating compromised genomic integrity. Furthermore, the loss of NKX6.3 resulted in altered expression of key regulatory proteins involved in mitosis and DNA repair pathways, suggesting a mechanistic link between NKX6.3 and the maintenance of genomic stability in gastric epithelial cells. Depletion of NKX6.3 resulted in accelerated cell cycle progression and the formation of abnormal mitotic figures, leading to genomic instability characterized by increased DNA content and structural abnormalities. In both in vitro and xenograft models, the depletion of NKX6.3 significantly upregulated AurkA and TPX2, which correlated with gains in DNA copy number. An inverse relationship was observed between NKX6.3 expression and the levels of AurkA and TPX2 in human gastric cancer tissues.

CONCLUSIONS

This study highlights the essential role of NKX6.3 in regulating mitotic integrity and genomic stability in gastric carcinogenesis. The findings suggest that targeting NKX6.3 may offer a novel therapeutic strategy for improving treatment outcomes in gastric cancer by restoring mitotic fidelity and genomic stability.

TRIAL REGISTRATION

This study was not registered.

The Effect of High CDC6 Levels on Predicting Poor Prognosis in Colorectal Cancer

INTRODUCTION

We investigated the function of cell division cycle 6 (CDC6) on the prognosis in colorectal carcinoma (CRC).

METHODS

CDC6 protein expression levels in 121 patients with colorectal cancer and adjacent normal mucosa were detected by immunohistochemistry.

RESULTS

Compared to adjacent normal tissues, CDC6 mRNA level was overexpressed in CRC tissues. Moreover, CDC6 protein levels were expressed up to 93.39% (113/121) in CRC tissues in the cell nucleus or cytoplasm. However, there were only 5.79% (7/121) in normal mucosal tissues with nuclear expression. CDC6 expression was significantly correlated with TNM stage and tumor metastasis. The 5-year survival rate was lower in the high CDC6 expression group than the low group. After silencing of CDC6 expression in SW620 cells, cell proliferation was slowed, the tumor clones were decreased, and the cell cycle was arrested in G1 phase. In multivariate analysis, increased CDC6 protein expression levels in colon cancer tissues were associated with cancer metastasis, TNM stage, and patient survival time.

CONCLUSION

CDC6 is highly expressed in CRC, and downregulation of CDC6 can slow the growth of CRC cells in vitro. It is also an independent predictor for poor prognosis and may be a useful biomarker for targeted therapy and prognostic evaluation.

Cell-cycle phospho-regulation of the kinetochore

The kinetochore is a mega-dalton protein assembly that forms within centromeric regions of chromosomes and directs their segregation during cell division. Here we review cell cycle-mediated phosphorylation events at the kinetochore, with a focus on the budding yeast Saccharomyces cerevisiae and the insight gained from forced associations of kinases and phosphatases. The point centromeres found in the budding yeast S. cerevisiae are one of the simplest such structures found in eukaryotes. The S. cerevisiae kinetochore comprises a single nucleosome, containing a centromere-specific H3 variant Cse4^CENP-A, bound to a set of kinetochore proteins that connect to a single microtubule. Despite the simplicity of the budding yeast kinetochore, the proteins are mostly homologous with their mammalian counterparts. In some cases, human proteins can complement their yeast orthologs. Like its mammalian equivalent, the regulation of the budding yeast kinetochore is complex: integrating signals from the cell cycle, checkpoints, error correction, and stress pathways. The regulatory signals from these diverse pathways are integrated at the kinetochore by post-translational modifications, notably phosphorylation and dephosphorylation, to control chromosome segregation. Here we highlight the complex interplay between the activity of the different cell-cycle kinases and phosphatases at the kinetochore, emphasizing how much more we have to understand this essential structure.

c-MYB is a transcriptional regulator of ESPL1/Separase in BCR-ABL-positive chronic myeloid leukemia

Background

Genomic instability and clonal evolution are hallmarks of progressing chronic myeloid leukemia (CML). Recently, we have shown that clonal evolution and blast crisis correlate with altered expression and activity of Separase, a cysteine endopeptidase that is a mitotic key player in chromosomal segregation and centriole duplication. Hyperactivation of Separase in human hematopoietic cells has been linked to a feedback mechanism that posttranslationally stimulates Separase proteolytic activity after imatinib therapy-induced reduction of Separase protein levels.

Methods and Results

In search for potential therapy-responsive transcriptional mechanisms we have investigated the role of the transcription factor c-MYB for Separase expression in CML cell lines (LAMA-84, K562, BV-173) and in clinical samples. Quantitative RT-PCR and Western blot immunostaining experiments revealed that c-MYB expression levels are decreased in an imatinib-dependent manner and positively correlate with Separase expression levels in cell lines and in clinical CML samples. RNA silencing of c-MYB expression in CML cell lines resulted in reduced Separase protein levels. Gelshift and ChIP assays confirmed that c-MYB binds to a putative c-MYB binding sequence located within the ESPL1 promoter.

Conclusions

Our data suggest that ESPL1/Separase is a regulatory target of c-MYB. Therefore, c-MYB, known to be required for BCR-ABL-dependent transformation of hematopoietic progenitors and leukemogenesis, may also control the Separase-dependent fidelity of mitotic chromosomal segregation and centriole duplication essential for maintenance of genomic stability.

miR-26a inhibits the proliferation of ovarian cancer cells via regulating CDC6 expression

MicroRNAs (miRNA) play important regulatory roles in the occurrence and development of cancers. This study aimed to investigate the effects of miR-26a on the proliferation and apoptosis of ovarian cancer cells and explore the potential mechanism. qRT-PCR was performed to measure the miR-26a expression in 46 ovarian cancer tissues, and results showed miR-26a expression reduced significantly when compared with normal ovarian tissues (P<0.05). Moreover, miR-26a expression was related to the extent of cell differentiation and clinical stage of ovarian cancer (P<0.05). miR-26a mimic was transfected into SKOV3 cells and ES2 cells, and CCK8 assay, colony formation assay and flow cytometry showed miR-26a over-expression could significantly inhibit the proliferation of ovarian cancer cells and induce their apoptosis. Bioinformatics analysis revealed Cdc6 was a target gene of miR-26a. dual-luciferase assay and validation assay showed miR-26a could act on the 3'UTR of Cdc6 to regulate Cdc6 expression. These findings suggest that miR-26a may act on the 3'UTR of Cdc6 to regulate Cdc6 expression, which then inhibit the proliferation of ovarian cancer cells and induce their apoptosis. Our findings provide a new target for the diagnosis and therapy of ovarian cancer.

Measurement of separase proteolytic activity in single living cells by a fluorogenic flow cytometry assay

ESPL1/Separase, an endopeptidase, is required for centrosome duplication and separation of sister-chromatides in anaphase of mitosis. Overexpression and deregulated proteolytic activity of Separase as frequently observed in human cancers is associated with the occurrence of supernumerary centrosomes, chromosomal missegregation and aneuploidy. Recently, we have hypothesized that increased Separase proteolytic activity in a small subpopulation of tumor cells may serve as driver of tumor heterogeneity and clonal evolution in chronic myeloid leukemia (CML). Currently, there is no quantitative assay to measure Separase activity levels in single cells. Therefore, we have designed a flow cytometry-based assay that utilizes a Cy5- and rhodamine 110 (Rh110)-biconjugated Rad21 cleavage site peptide ([Cy5-D-R-E-I-M-R]₂-Rh110) as smart probe and intracellular substrate for detection of Separase enzyme activity in living cells. As measured by Cy5 fluorescence the cellular uptake of the fluorogenic peptide was fast and reached saturation after 210 min of incubation in human histiocytic lymphoma U937 cells. Separase activity was recorded as the intensity of Rh110 fluorescence released after intracellular peptide cleavage providing a linear signal gain within a 90–180 min time slot. Compared to conventional cell extract-based methods the flow cytometric assay delivers equivalent results but is more reliable, bypasses the problem of vague loading controls and unspecific proteolysis associated with whole cell extracts. Especially suited for the investigaton of blood- and bone marrow-derived hematopoietic cells the flow cytometric Separase assay allows generation of Separase activity profiles that tell about the number of Separase positive cells within a sample i.e. cells that currently progress through mitosis and about the range of intercellular variation in Separase activity levels within a cell population. The assay was used to quantify Separase proteolytic activity in leukemic cell lines and peripheral blood samples from leukemia patients.

Fine-tuning of Cdc6 accumulation by Cdk1 and MAP kinase is essential for completion of oocyte meiotic divisions

Vertebrate oocytes proceed through the 1st and the 2nd meiotic division without intervening S-phase to become haploid. Although DNA replication does not take place, unfertilized oocytes acquire the competence to replicate DNA one hour after the 1st meiotic division, by accumulating an essential factor of the replicative machinery, Cdc6. Here, we discovered that the turnover of Cdc6 is precisely regulated in oocytes to avoid inhibition of Cdk1. At meiosis resumption, Cdc6 starts to be expressed but cannot accumulate due to a degradation mechanism activated through Cdk1. During transition from 1st to 2nd meiotic division, Cdc6 is under antagonistic regulation of Cyclin B, whose interaction with Cdc6 stabilizes the protein, and Mos/MAPK that negatively controls its accumulation. Since overexpressing Cdc6 inhibits Cdk1 reactivation and drives oocytes into a replicative interphasic state, the fine-tuning of Cdc6 accumulation is essential to ensure two meiotic waves of Cdk1 activation and to avoid unscheduled DNA replication during meiotic maturation.

High expression of polo-like kinase 1 is associated with the metastasis and recurrence in urothelial carcinoma of bladder

OBJECTIVES

Polo-like kinase 1 (Plk1) has been widely pursued as an oncology target because it is overexpressed in several human tumor types. To investigate whether Plk1 plays a general role in bladder urothelial carcinoma, we examined the expression of Plk1 protein in bladder urothelial carcinoma and cell lines, and analyzed the relationship among Plk1 protein expression, metastasis, and recurrence of urinary bladder urothelial carcinoma.

METHODS

Immunohistochemistry was used to detect the expression of Plk1 in 120 bladder urothelial carcinoma. Moreover, the expression of Plk1 was analyzed by Western blot in 60 bladder urothelial carcinoma and 21 normal epithelial tissues. MTT assay and flow cytometry and transwell assay were used to examine the proliferative and invasive ability of bladder cancer cells with the treatment of scytonemin (the inhibitor of Plk1). Statistical analysis was used to discuss the association between Plk1 expression and clinicopathologic parameters, tumor metastasis and recurrence, and the proliferative and invasive ability and cell cycle process of the bladder cancer cells.

RESULTS

There was a significantly higher Plk1expressions in bladder urothelial carcinoma and highly invasive bladder T24 cells than those in bladder normal tissues and the superficial bladder BIU-87 cells. Plk1 expression was positively correlated with histologic grade, pT stage, recurrence, and metastasis. With the increasing concentration of scytonemin, we found that not only the cell proliferation and invasion activity decreased significantly, but also the cell cycle was blocked at G2/M stage.

CONCLUSION

Plk1 expression status was closely correlated with important histopathologic characteristics (grades and stages) and the recurrence and metastasis of bladder urothelial carcinomas. Furthermore, Plk1 played an important function on the bladder cancer cells' proliferation by regulating the cancer cell cycle from G1/S to G2/M and probably promoted the invasion and metastasis of bladder cancer.

Knockdown of Cdc6 inhibits proliferation of tongue squamous cell carcinoma Tca8113 cells

The present study aimed at evaluating the effects of Cdc6 downregulation on the proliferation of Tca8113 cells. Two lentiviral vectors (KD1 and KD2) expression cdc6 siRNA were constructed and then infected into Tca8113 cells. Real-time PCR and Western blot analysis were performed to detect the mRNA and protein expression of Cdc6. MTT assays were employed to delineate the growth curves, and flow cytometry was performed to assess cell-cycle progression and apoptosis in Tca8113 cells. Following infection with the lentiviral vectors, real-time PCR and Western blot analysis revealed that Cdc6 expression was markedly suppressed in Tca8113 cells. When compared with the negative control group, the mRNA expression of Cdc6 was reduced by 50% and 65% and the protein expression by 65.87% and 79.38% in cells harboring KD1 or KD2, respectively. Cell growth was slowed, and the growth inhibition rate was 25.84% and 30.34% in Tca8113 cells following infection with KD1 or KD2, respectively. In addition, cell-cycle progression was altered. In KD- infected Tca8113 cells, the proportion of cells in the S phase was markedly reduced, but the proportion in the G1 phase was significantly increased; this was accompanied by an increase in cell apoptosis. Downregulation of Cdc6 effectively inhibited the proliferation of Tca8113 cells.

The proteolytic activity of separase in BCR-ABL-positive cells is increased by imatinib

Separase, an endopeptidase required for the separation of sister-chromatides in mitotic anaphase, triggers centriole disengagement during centrosome duplication. In cancer, separase is frequently overexpressed, pointing to a functional role as an aneuploidy promoter associated with centrosomal amplification and genomic instability. Recently, we have shown that centrosomal amplification and subsequent chromosomal aberrations are a hallmark of chronic myeloid leukemia (CML), increasing from chronic phase (CP) toward blast crisis (BC). Moreover, a functional linkage of p210BCR-ABL tyrosine kinase activity with centrosomal amplification and clonal evolution has been established in long-term cell culture experiments. Unexpectedly, therapeutic doses of imatinib (IM) did not counteract; instead induced similar centrosomal alterations in vitro. We investigated the influence of IM and p210BCR-ABL on Separase as a potential driver of centrosomal amplification in CML. Short-term cell cultures of p210BCR-ABL-negative (NHDF, UROtsa, HL-60, U937), positive (K562, LAMA-84) and inducible (U937p210BCR-ABL/c6 (Tet-ON)) human cell lines were treated with therapeutic doses of IM and analyzed by qRT-PCR, Western blot analysis and quantitative Separase activity assays. Decreased Separase protein levels were observed in all cells treated with IM in a dose dependent manner. Accordingly, in all p210BCR-ABL-negative cell lines, decreased proteolytic activity of Separase was found. In contrast, p210BCR-ABL-positive cells showed increased Separase proteolytic activity. This activation of Separase was consistent with changes in the expression levels of Separase regulators (Separase phosphorylation at serine residue 1126, Securin, CyclinB1 and PP2A). Our data suggest that regulation of Separase in IM-treated BCR-ABL-positive cells occurs on both the protein expression and the proteolytic activity levels. Activation of Separase proteolytic activity exclusively in p210BCR-ABL-positive cells during IM treatment may act as a driving force for centrosomal amplification, contributing to genomic instability, clonal evolution and resistance in CML.

Cdc6 is required for meiotic spindle assembly in Xenopus oocytes

During the maturation of Xenopus oocytes, Cdc6 expression is necessary to establish replication competence to support early embryonic DNA replication. However, Cdc6 is expressed before the completion of MI, at a time when its function as a replication factor is not required, suggesting additional roles for Cdc6 in meiosis. Confocal immunofluorescence microscopy revealed that Cdc6 protein was distributed around the spindle precursor at the time of germinal vesicle breakdown (GVBD), and localized to the margin of the nascent spindle early in prometaphase. Cdc6 subsequently localized to spindle poles in late prometaphase, where it remained until metaphase arrest. Microinjection of antisense oligonucleotides specific for Cdc6 mRNA disrupted spindle assembly, resulting in defects including delayed spindle assembly, misoriented and unattached anaphase spindles, monasters, multiple spindles, microtubule aggregates associated with condensed chromosomes, or the absence of recognizable spindle-like structures, depending on the level of residual Cdc6 expression. Furthermore, Cdc6 co-localized with γ-tubulin in centrosomes during interphase in all somatic cells analyzed, and associated with spindle poles in mitotic COS cells. Our data suggest a role for Cdc6 in spindle formation in addition to its role as a DNA replication factor.