Minichromosome maintenance 2 bound with retroviral Gp70 is localized to cytoplasm and enhances DNA-damage-induced apoptosis

DNA replication: Mechanisms and therapeutic interventions for diseases

Accurate and integral cellular DNA replication is modulated by multiple replication-associated proteins, which is fundamental to preserve genome stability. Furthermore, replication proteins cooperate with multiple DNA damage factors to deal with replication stress through mechanisms beyond their role in replication. Cancer cells with chronic replication stress exhibit aberrant DNA replication and DNA damage response, providing an exploitable therapeutic target in tumors. Numerous evidence has indicated that posttranslational modifications (PTMs) of replication proteins present distinct functions in DNA replication and respond to replication stress. In addition, abundant replication proteins are involved in tumorigenesis and development, which act as diagnostic and prognostic biomarkers in some tumors, implying these proteins act as therapeutic targets in clinical. Replication-target cancer therapy emerges as the times require. In this context, we outline the current investigation of the DNA replication mechanism, and simultaneously enumerate the aberrant expression of replication proteins as hallmark for various diseases, revealing their therapeutic potential for target therapy. Meanwhile, we also discuss current observations that the novel PTM of replication proteins in response to replication stress, which seems to be a promising strategy to eliminate diseases.

MCM2 in human cancer: functions, mechanisms, and clinical significance

Background

Aberrant DNA replication is the main source of genomic instability that leads to tumorigenesis and progression. MCM2, a core subunit of eukaryotic helicase, plays a vital role in DNA replication. The dysfunction of MCM2 results in the occurrence and progression of multiple cancers through impairing DNA replication and cell proliferation.

Conclusions

MCM2 is a vital regulator in DNA replication. The overexpression of MCM2 was detected in multiple types of cancers, and the dysfunction of MCM2 was correlated with the progression and poor prognoses of malignant tumors. According to the altered expression of MCM2 and its correlation with clinicopathological features of cancer patients, MCM2 was thought to be a sensitive biomarker for cancer diagnosis, prognosis, and chemotherapy response. The anti-tumor effect induced by MCM2 inhibition implies the potential of MCM2 to be a novel therapeutic target for cancer treatment. Since DNA replication stress, which may stimulate anti-tumor immunity, frequently occurs in MCM2 deficient cells, it also proposes the possibility that MCM2 targeting improves the effect of tumor immunotherapy.

Random-forest algorithm based biomarkers in predicting prognosis in the patients with hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) one of the most common digestive system tumors, threatens the tens of thousands of people with high morbidity and mortality world widely. The purpose of our study was to investigate the related genes of HCC and discover their potential abilities to predict the prognosis of the patients.

Methods

We obtained RNA sequencing data of HCC from The Cancer Genome Atlas (TCGA) database and performed analysis on protein coding genes. Differentially expressed genes (DEGs) were selected. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment were conducted to discover biological functions of DEGs. Protein and protein interaction (PPI) was performed to investigate hub genes. In addition, a method of supervised machine learning, recursive feature elimination (RFE) based on random forest (RF) classifier, was used to screen for significant biomarkers. And the basic experiment was conducted by lab, we constructe a clinical patients’ database, and obtained the data and results of immunohistochemistry.

Results

We identified five biomarkers with significantly high expression to predict survival risk of the HCC patients. These prognostic biomarkers included SPC25, NUF2, MCM2, BLM and AURKA. We also defined a risk score model with these biomarkers to identify the patients who is in high risk. In our single-center experiment, 95 pairs of clinical samples were used to explore the expression levels of NUF2 and BLM in HCC. Immunohistochemical staining results showed that NUF2 and BLM were significantly up-regulated in immunohistochemical staining. High expression levels of NUF2 and BLM indicated poor prognosis.

Conclusion

Our investigation provided novel prognostic biomarkers and model in HCC and aimed to improve the understanding of HCC. In the results obtained, we also conducted a part of experiments to verify the theory described earlier, The experimental results did verify our theory.

Bone marrow niches in myeloid neoplasms

Pathological phenotypes of myeloid neoplasms are closely related to genetic/chromosomal abnormalities of neoplastic cells whereas the bone marrow microenvironment, including stromal elements and hematopoietic stem cell niche cells, have a great influence on the differentiation/proliferation of both hematopoietic and neoplastic cells. The pathology of myeloid neoplasms might be generated through the interaction of hematopoietic (stem) cells and stromal cells. The present study aims to provide the morphological/functional aspects of the bone marrow environment in myeloid neoplasms. Among the myeloid neoplasms, myelodysplastic syndromes (MDS) exhibit significant and complex interactions between neoplastic cells and stromal cells. Hematopoietic cells in MDS are greatly influenced by macrophages/niche cells via several signaling pathways. As such, the pathological significance of cell proliferation, cell apoptosis, and anti‐apoptosis signals in the bone marrow of myeloid neoplasms, especially MDS bone marrow, will be discussed.

Subcellular localization of MCM2 correlates with the prognosis of ovarian clear cell carcinoma

Highly malignant tumors overexpress the minichromosome maintenance 2 (MCM2) protein in the nucleus, which is associated with advanced tumor grade, advanced stage, and poor prognosis. In this study, we showed that MCM2 is highly expressed in clinical samples of ovarian clear cell carcinoma. Although MCM2 expression was mainly localized to the nuclei as in other cancers, a few cases exhibited cytoplasmic localization of MCM2. Surprisingly, tumor samples with cytoplasmic MCM2 demonstrated excellent prognosis, showing 100% survival during the observation period of more than 200 months. However, cases with nuclear expression of MCM2 exhibited approximately 78% 5-year-survival rate. In a previous study, we showed that Friend leukemia virus (FLV) envelope protein gp70 bound to MCM2, impaired its nuclear translocation, and enhanced DNA damage-induced apoptosis in FLV-infected hematopoietic cells with high levels of MCM2. As expected, clear cell carcinoma cells with cytoplasmic expression of MCM2 exhibited significantly higher apoptotic cell ratio than that of cells with nuclear MCM2 expression. In vitro experiments using ovarian cancer cells with cytoplasmic expression of MCM2 demonstrated that transfection of MCM2-ΔN enhanced DNA damage-induced apoptosis. Therefore, cytoplasmic localization of MCM2 significantly correlated with increased apoptosis in clear cell carcinoma cells, resulting in improved prognosis.

Distinct Diagnostic and Prognostic Values of Minichromosome Maintenance Gene Expression in Patients with Hepatocellular Carcinoma

Background: The aim of the present study was to identify diagnostic and prognostic values of minichromosome maintenance (MCM) gene expression in patients with hepatocellular carcinoma (HCC).

Methods: The biological function of the MCM genes were investigated by bioinformatics analysis. The diagnostic and prognostic values of the MCM genes were investigated by using the data of HCC patients from the GSE14520 and The Cancer Genome Atlas (TCGA) databases.

Results: Bioinformatics analysis of the MCM genes substantiated that MCM2-7 genes were significantly enriched in DNA replication and cell cycle, and co-expressed with each other. These genes also co-expressed in HCC tumor tissue in both the GSE14520 and TCGA cohort. We also observed that the expression of the MCM2-7 genes was increased in tumor tissue, and diagnostic receiver operating characteristic analysis of MCM2-7 indicated that these genes could serve as sensitive diagnostic markers in HCC. Survival analysis in the GSE14520 cohort suggested that expression of MCM2, MCM4, MCM5, and MCM6 were significantly associated with hepatitis B virus-related HCC overall survival (OS). However, none of the MCM genes were associated with recurrence-free survival in the GSE14520 cohort. The validation cohort of TCGA suggested that the expression of MCM2, MCM6, and MCM7 were significantly correlated with HCC OS.

Conclusion: Our study indicated that MCM2-7 genes may be potential diagnostic biomarkers in patients with HCC. Among them, MCM2 and MCM6 may serve as potential prognostic biomarkers for HCC.

Targeting MCM2 function as a novel strategy for the treatment of highly malignant breast tumors

Highly malignant tumors express high levels of the minichromosome maintenance 2 (MCM2) protein, which is associated with advanced tumor grade, advanced stage, and poor prognosis. In a previous study, we showed that Friend leukemia virus (FLV) envelope protein gp70 bound MCM2, impaired its nuclear translocation, and enhanced DNA-damage-induced apoptosis in FLV-infected hematopoietic cells when the cells expressed high levels of MCM2. Here, we show that MCM2 is highly expressed in clinical samples of invasive carcinoma of the breast, especially triple-negative breast cancer (TNBC), and in cancer stem cell (CSC) marker-positive breast cancer cells. To generate a cancer therapy model using gp70, we introduced the gp70 protein into the cytoplasm of murine breast cancer cells that express high levels of MCM2 by conjugating the protein transduction domain (PTD) of Hph-1 to gp70 (Hph- 1-gp70). Hph-1-gp70 was successfully transduced into the cytoplasm of breast cancer cells. The transduced protein enhanced the DNA damage-induced apoptosis of cancer cells in vitro and in vivo. Therefore, an MCM2-targeted strategy using Hph-1-gp70 treatment to induce DNA damage might be a successful therapy for highly malignant breast cancers such as TNBC and for the eradication of CSC-like cells from breast cancer tissue.

MCM5 as a target of BET inhibitors in thyroid cancer cells

Anaplastic thyroid carcinoma (ATC) is an extremely aggressive thyroid cancer subtype, refractory to the current medical treatment. Among various epigenetic anticancer drugs, bromodomain and extra-terminal inhibitors (BETis) are considered to be an appealing novel class of compounds. BETi target the bromodomain and extra-terminal of BET proteins that act as regulators of gene transcription, interacting with histone acetyl groups. The goal of this study is to delineate which pathway underlies the biological effects derived from BET inhibition, in order to find new potential therapeutic targets in ATC. We investigated the effects of BET inhibition on two human anaplastic thyroid cancer-derived cell lines (FRO and SW1736). The treatment with two BETis, JQ1 and I-BET762, decreased cell viability, reduced cell cycle S-phase, and determined cell death. In order to find BETi effectors, FRO and SW1736 were subjected to a global transcriptome analysis after JQ1 treatment. A significant portion of deregulated genes belongs to cell cycle regulators. Among them, MCM5 was decreased at both mRNA and protein levels in both tested cell lines. Chromatin immunoprecipitation (ChIP) experiments indicate that MCM5 is directly bound by the BET protein BRD4. MCM5 silencing reduced cell proliferation, thus underlining its involvement in the block of proliferation induced by BETis. Furthermore, MCM5 immunohistochemical evaluation in human thyroid tumor tissues demonstrated its overexpression in several papillary thyroid carcinomas and in all ATCs. MCM5 was also overexpressed in a murine model of ATC, and JQ1 treatment reduced Mcm5 mRNA expression in two murine ATC cell lines. Thus, MCM5 could represent a new target in the therapeutic approach against ATC.

Whole Exome Sequencing Identified MCM2 as a Novel Causative Gene for Autosomal Dominant Nonsyndromic Deafness in a Chinese Family

We report the genetic analysis of autosomal dominant, nonsyndromic, progressive sensorineural hearing loss in a Chinese family. Using whole exome sequencing, we identified a missense variant (c.130C>T, p.R44C) in the MCM2 gene, which has a pro-apoptosis effect and is involved in the initiation of eukaryotic genome replication. This missense variant is very likely to be the disease causing variant. It segregated with hearing loss in this pedigree, and was not found in the dbSNP database or databases of genomes and SNP in the Chinese population, in 76 patients with sporadic hearing loss, or in 145 normal individuals. We performed western blot and immunofluorescence to test the MCM2 protein expression in the cochlea of rats and guinea pigs, demonstrating that MCM2 was widely expressed in the cochlea and was also surprisingly expressed in the cytoplasm of terminally differentiated hair cells. We then transiently expressed the variant MCM2 cDNA in HEK293 cells, and found that these cells displayed a slight increase in apoptosis without any changes in proliferation or cell cycle, supporting the view that this variant is pathogenic. In summary, we have identified MCM2 as a novel gene responsible for nonsyndromic hearing loss of autosomal dominant inheritance in a Chinese family.

CXCL12+ stromal cells as bone marrow niche for CD34+ hematopoietic cells and their association with disease progression in myelodysplastic syndromes

The bone marrow microenvironment, known as 'hematopoietic stem cell niche,' is essential for the survival and maintenance of hematopoietic stem cells. Myelodysplastic syndromes (MDS) are a group of clonal hematopoietic stem cell diseases, which eventually result in leukemic transformation (acute myelogenous leukemia with myelodysplasia-related changes, AML-MRC). However, the precise components and functions of the MDS niche remain unclear. Recently, CXCL12-abundant reticular cells were shown to act as a hematopoietic stem cell niche in the murine bone marrow. Using immunohistochemistry, we show here that CXCL12(+) cells were located in the cellular marrow or perivascular area, and were in contact with CD34(+) hematopoietic cells in control and MDS/AML-MRC bone marrow. MDS bone marrow exhibited higher CXCL12(+) cell density than control or AML, not otherwise specified (AML-NOS) bone marrow. Moreover, AML-MRC bone marrow also exhibited higher CXCL12(+) cell density than control bone marrow. CXCL12(+) cell density correlated positively with bone marrow blast ratio in MDS cases. CXCL12 mRNA level was also higher in MDS bone marrow than in control or AML-NOS bone marrow. In vitro coculture analysis revealed that overexpression of CXCL12 in stromal cells upregulated BCL-2 expression of leukemia cell lines. Triple immunostaining revealed that the CD34(+) hematopoietic cells of MDS bone marrow in contact with CXCL12(+) cells were BCL-2-positive and TUNEL-negative. In the bone marrow of MDS cases, CXCL12-high group showed significantly higher Bcl-2(+)/CD34(+) cell ratio and lower apoptotic cell ratio than CXCL12-low group. Moreover, CXCL12-high refractory cytopenia with multilineage dysplasia (RCMD) cases had a greater tendency to progress to refractory anemia with excess blasts (RAEBs) or AML-MRC than CXCL12-low RCMD cases. These results suggest that CXCL12(+) cells constitute the niche for CD34(+) hematopoietic cells, and may be associated with the survival/antiapoptosis of CD34(+) hematopoietic cells and disease progression in MDS. Thus, CXCL12(+) cells may represent a novel MDS therapeutic target.

Peptide-LNA oligonucleotide conjugates

Although peptide-oligonucleotide conjugates (POCs) are well-known for nucleic acids delivery and therapy, reports on internal attachment of peptides to oligonucleotides are limited in number. To develop a convenient route for preparation of internally labeled POCs with improved biomedical properties, peptides were introduced into oligonucleotides via a 2'-alkyne-2'-amino-LNA scaffold. Derivatives of methionine- and leucine-enkephalins were chosen as model peptides of mixed amino acid content, which were singly and doubly incorporated into LNA/DNA strands using highly efficient copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry. DNA/RNA target binding affinity and selectivity of the resulting POCs were improved in comparison to LNA/DNA mixmers and unmodified DNA controls. This clearly demonstrates that internal attachment of peptides to oligonucleotides can significantly improve biomolecular recognition by synthetic nucleic acid analogues. Circular dichroism (CD) measurements showed no distortion of the duplex structure by the incorporated peptide chains while studies in human serum indicated superior stability of the POCs compared to LNA/DNA mixmers and unmodified DNA references. Molecular modeling suggests strong interactions between positively charged regions of the peptides and the negative oligonucleotide backbones which leads to clamping of the peptides in a fixed orientation along the duplexes.

Over-expression of cancerous inhibitor of PP2A (CIP2A) in bone marrow cells from patients with a group of high-risk myelodysplastic syndromes

Cancerous inhibitor of PP2A (protein phosphatase 2A) (CIP2A) is an inhibitor of PP2A, a phosphatase and tumor suppressor that regulates cell proliferation, differentiation, and survival. The aim of this study was to investigate whether CIP2A plays a role in the progression of myelodysplastic syndromes (MDS). Immunohistochemical analysis revealed that a fraction patients having refractory anemia with excess blasts (RAEB)-1 (4 out of 12) and RAEB-2 (10 out of 14) exhibited significant expression of CIP2A in bone marrow hematopoietic cells, while all patients with refractory cytopenia with unilineage or multilineage dysplasia (RCUD/RCMD) (0 out of 18) and the control group (0 out of 17) were negative. CIP2A was mainly expressed by the MPO-positive myeloid series of cells and partly by the CD34-positive cells in association with the expression of phosphorylated c-MYC (p-c-MYC) protein and the cell cycle-related proteins Ki-67, MCM2, and geminin. The percentage of p-c-MYC-positive cells in the bone marrow of CIP2A-positive MDS cases was significantly higher than that in CIP2A-negative MDS cases (P < 0.01). The expression levels of mRNA for CIP2A and PP2A exhibited positive correlation in MDS/control bone marrow. These results suggest that up-regulated expression of CIP2A might play a role in the proliferation of blasts in the MDS bone marrow and in disease progression in at least some cases.

Photodynamic therapy plus regulatory T-cell depletion produces immunity against a mouse tumour that expresses a self-antigen

Background:

Photodynamic therapy (PDT) can lead to development of antigen-specific immune response and PDT-mediated immunity can be potentiated by T regulatory cell (Treg) depletion. We investigated whether the combination of PDT with cyclophosphamide (CY) could foster immunity against wild-type tumours expressing self-antigen (gp70).

Methods:

Mice with CT26 tumours were treated with PDT alone or in combination with low-dose CY. T regulatory cell numbers and transforming growth factor-β (TGF-β) levels were measured at several time points after treatment. Mice cured by PDT+CY were rechallenged with CT26 and monitored for long-term survival.

Results:

Photodynamic therapy+CY led to complete tumour regression and long-term survival in 90% of treated mice while the absolute numbers of Treg decreased after PDT+CY and the TGF-β levels were reduced to a level comparable to naïve mice. Sixty-five percent of the mice treated with PDT+CY that survived over 90 days tumour free rejected the rechallenge with the same tumour when a second dose of CY was administered before rechallenge but not without.

Conclusion:

Administration of CY before PDT led to depletion of Treg and potentiated PDT-mediated immunity, leading to long-term survival and development of memory immunity that was only uncovered by second Treg depletion.

Phosphorylation of minichromosome maintenance protein 7 (MCM7) by cyclin/cyclin-dependent kinase affects its function in cell cycle regulation

MCM7 is one of the subunits of the MCM2-7 complex that plays a critical role in DNA replication initiation and cell proliferation of eukaryotic cells. After forming the pre-replication complex (pre-RC) with other components, the MCM2-7 complex is activated by DDK/cyclin-dependent kinase to initiate DNA replication. Each subunit of the MCM2-7 complex functions differently under regulation of various kinases on the specific site, which needs to be investigated in detail. In this study, we demonstrated that MCM7 is a substrate of cyclin E/Cdk2 and can be phosphorylated on Ser-121. We found that the distribution of MCM7-S121A is different from wild-type MCM7 and that the MCM7-S121A mutant is much less efficient to form a pre-RC complex with MCM3/MCM5/cdc45 compared with wild-type MCM7. By using the Tet-On inducible HeLa cell line, we revealed that overexpression of wild-type MCM7 but not MCM7-S121A can block S phase entry, suggesting that an excess of the pre-RC complex may activate the cell cycle checkpoint. Further analysis indicates that the Chk1 pathway is activated in MCM7-overexpressed cells in a p53-dependent manner. We performed experiments with the human normal cell line HL-7702 and also observed that overexpression of MCM7 can cause S phase block through checkpoint activation. In addition, we found that MCM7 could also be phosphorylated by cyclin B/Cdk1 on Ser-121 both in vitro and in vivo. Furthermore, overexpression of MCM7-S121A causes an obvious M phase exit delay, which suggests that phosphorylation of MCM7 on Ser-121 in M phase is very important for a proper mitotic exit. These data suggest that the phosphorylation of MCM7 on Ser-121 by cyclin/Cdks is involved in preventing DNA rereplication as well as in regulation of the mitotic exit.