Conditional expression of MCM7 increases tumor growth without altering DNA replication activity

YAP and TAZ in Lung Cancer: Oncogenic Role and Clinical Targeting

Lung cancer is the leading cause of cancer death in the world and there is no current treatment able to efficiently treat the disease as the tumor is often diagnosed at an advanced stage. Moreover, cancer cells are often resistant or acquire resistance to the treatment. Further knowledge of the mechanisms driving lung tumorigenesis, aggressiveness, metastasization, and resistance to treatments could provide new tools for detecting the disease at an earlier stage and for a better response to therapy. In this scenario, Yes Associated Protein (YAP) and Trascriptional Coactivator with PDZ-binding motif (TAZ), the final effectors of the Hippo signaling transduction pathway, are emerging as promising therapeutic targets. Here, we will discuss the most recent advances made in YAP and TAZ biology in lung cancer and, more importantly, on the newly discovered mechanisms of YAP and TAZ inhibition in lung cancer as well as their clinical implications.

The Human Replicative Helicase, the CMG Complex, as a Target for Anti-cancer Therapy

DNA helicases unwind or rearrange duplex DNA during replication, recombination and repair. Helicases of many pathogenic organisms such as viruses, bacteria, and protozoa have been studied as potential therapeutic targets to treat infectious diseases, and human DNA helicases as potential targets for anti-cancer therapy. DNA replication machineries perform essential tasks duplicating genome in every cell cycle, and one of the important functions of these machineries are played by DNA helicases. Replicative helicases are usually multi-subunit protein complexes, and the minimal complex active as eukaryotic replicative helicase is composed of 11 subunits, requiring a functional assembly of two subcomplexes and one protein. The hetero-hexameric MCM2-7 helicase is activated by forming a complex with Cdc45 and the hetero-tetrameric GINS complex; the Cdc45-Mcm2-7-GINS (CMG) complex. The CMG complex can be a potential target for a treatment of cancer and the feasibility of this replicative helicase as a therapeutic target has been tested recently. Several different strategies have been implemented and are under active investigations to interfere with helicase activity of the CMG complex. This review focuses on the molecular function of the CMG helicase during DNA replication and its relevance to cancers based on data published in the literature. In addition, current efforts made to identify small molecules inhibiting the CMG helicase to develop anti-cancer therapeutic strategies were summarized, with new perspectives to advance the discovery of the CMG-targeting drugs.

MCM7 and its hosted miR-25, 93 and 106b cluster elicit YAP/TAZ oncogenic activity in lung cancer

Lung cancer is the first cause of cancer death worldwide and the Hippo pathway transcriptional coactivators YAP/TAZ have a pro-oncogenic role in this context. In order to understand the mechanisms through which YAP/TAZ elicit their oncogenic role in different systems, many studies are focused on YAP/TAZ target genes involved in the regulation of cell proliferation/survival and migration. However, there is scarce evidence on the role of YAP/TAZ in microRNA regulation while there is increasing evidence supporting the role of microRNAs in the main oncogenic processes. Here, we showed that YAP/TAZ were able to regulate several microRNAs in non-small cell lung cancer (NSCLC) cell lines. In detail, we focused on a cluster of three oncogenic microRNAs (miR-25, 93 and 106b) hosted in the MCM7 gene that were overexpressed in lung tumors compared to normal tissues. In addition, similar behavior was observed in breast cancer and head and neck tumor casuistries, where they showed a prognostic role. In NSCLC cells, YAP/TAZ induced the transcription of the MCM7 gene and its hosted miRs, thereby promoting cell proliferation through the post-transcriptional inhibition of the p21 cell cycle regulator. Accordingly, p21 was maintained at low levels in lung tumors compared to normal tissues. Conversely, its expression was restored in NSCLC cells upon YAP/TAZ interference or upon treatment with the statin cerivastatin. In summary, we provide evidence for a novel mechanism of modulation supporting the protumorigenic functions of the YAP/TAZ factors through the modulation of a bioncogenic locus consisting of one gene and three hosted microRNAs.

Rbfox2 function in RNA metabolism is impaired in hypoplastic left heart syndrome patient hearts

Hypoplastic left heart syndrome (HLHS) is a fatal congenital heart disease in which the left side of the heart is underdeveloped, impairing the systemic circulation. Underdeveloped left ventricle exerts biomechanical stress on the right ventricle that can progress into heart failure. Genome-wide transcriptome changes have been identified at early stages in the right ventricle (RV) of infants with HLHS, although the molecular mechanisms remain unknown. Here, we demonstrate that the RNA binding protein Rbfox2, which is mutated in HLHS patients, is a contributor to transcriptome changes in HLHS patient RVs. Our results indicate that majority of transcripts differentially expressed in HLHS patient hearts have validated Rbfox2 binding sites. We show that Rbfox2 regulates mRNA levels of targets with 3’UTR binding sites contributing to aberrant gene expression in HLHS patients. Strikingly, the Rbfox2 nonsense mutation identified in HLHS patients truncates the protein, impairs its subcellular distribution and adversely affects its function in RNA metabolism. Overall, our findings uncover a novel role for Rbfox2 in controlling transcriptome in HLHS.

Mcm4 C-terminal domain of MCM helicase prevents excessive formation of single-stranded DNA at stalled replication forks

The minichromosome maintenance (MCM) helicase, composed of subunits Mcm2-7, is essential for the initiation and elongation phases of DNA replication. Even when DNA synthesis is blocked, MCM continues DNA unwinding to some extent for activation of the replication checkpoint and then stops. However, the mechanism of regulation of MCM-helicase activity remains unknown. Here, we show that truncation of the Mcm4 C-terminal domain (CTD) in fission yeast results in hypersensitivity to replication block caused by dNTP depletion. The truncation mcm4-c84 does not affect the activation of the replication checkpoint pathway but delays its attenuation during recovery from replication block. Two dimensional gel electrophoresis showed that mcm4-c84 delays the disappearance of replication intermediates, indicating that the Mcm4 CTD is required for efficient recovery of stalled replication forks. Remarkably, chromatin immunoprecipitation revealed that mcm4-c84 brings about an increase rather than a decrease in the association of the single-stranded DNA-binding protein RPA to stalled forks, and MCM and the accessory complex GINS are unaffected. These results suggest that the Mcm4 CTD is required to suspend MCM-helicase activity after the formation of single-stranded DNA sufficient for checkpoint activation.

The medulloblastoma cell line DAOY but not eleven other tumor cell lines expresses minichromosome maintenance protein 4

Minichromosome maintenance proteins (MCM) are required for initiation and elongation of chromosomal DNA, ensuring that DNA replication takes place only once. Although MCMs are considered of utmost importance in tumor biology and as potential marker proteins, they were not unambiguously identified at the protein level and we therefore aimed to characterize MCM 4 in a medulloblastoma cell line and provide a protein chemical analytical tool. In addition, we searched for this protein in twelve tumor cell lines and a series of non-tumor cells. The DAOY medulloblastoma cell line was cultivated, lysed, proteins extracted and run on two-dimensional gel electrophoresis with subsequent in-gel digestion and mass spectrometrical (MS/MS) analysis of protein spots. One spot at pI 6.2 with an observed molecular weight of 98 kDa was identified as minichromosome maintenance protein 4 by peptide fingerprinting. Sequence coverage of 35% along with 25 matched peptides and MS/MS analyses of three matching peptides warranted unambiguous identification. The use of mass spectrometrical identification unequivocally allowed determination of MCM 4 expression in a medulloblastoma cell line exclusively. Given the biological and probable clinical importance of this molecule as a tentative marker protein, a fair analytical tool, independent of antibody availability and specificity is mandatory and determinations at the transcriptional level cannot be extrapolated to protein levels per se, as there is a long and unpredictable way from mRNA to protein.

MCM7 amplification and overexpression are associated with prostate cancer progression

The genomic DNA profiles of prostate cancers with aggressive features were compared to the profiles of matched normal DNA to identify genes that are selectively amplified in the cancer cells. One of the identified genes, MCM7, which is a component of the DNA replication licensing complex, has been studied extensively both at the DNA and protein levels in human prostate tissues. Approximately half of the prostate cancer specimens studied showed MCM7 gene amplification, and 60% of the aggressive prostate cancer specimens had increased MCM7 protein expression. Amplification or overexpression of MCM7 was significantly associated with relapse, local invasion and a worse tumor grade. Constitutive expression of MCM7 in a human prostate cancer cell line, DU145, resulted in markedly increased DNA synthesis and cell proliferation compared to vector-only controls, and an increased cell invasion in vitro. Indeed, MCM7 overexpression produced primary tumors 12 times larger than vector-only controls and resulted in a rapid demise of mice bearing those tumors. These studies implicate MCM7, and the DNA replication licensing gene family, in prostate cancer progression, growth and invasion.

Chromosome transfer experiments link regions on chromosome 7 to radiation resistance in human glioblastoma multiforme

Glioblastoma multiforme (GM) is the most lethal form of brain tumor, with a median survival of approximately 1 year. Treatment options are limited. Radiation therapy is a common form of treatment, but many tumors are resistant. In earlier studies, we found that gain of chromosome 7 is associated with radiation resistance in human primary GM. In this study, we extend that result to a model system in which we transferred chromosome 7 to recipient cells and confirmed radiation resistance as a function of chromosome 7 gain. We identified three candidate regions on chromosome 7 that conferred radiation resistance in our model system.

Deregulated minichromosomal maintenance protein MCM7 contributes to oncogene driven tumorigenesis

Minichromosomal maintenance protein 7 (MCM7) is an essential component of the replication helicase complex (MCM2-7) required for DNA replication. Although this function is highly conserved among eukaryotes, additional functions for the MCM molecules continue to be described. Minichromosomal maintenance protein 7 is a marker for proliferation and is upregulated in a variety of tumors including neuroblastoma, prostate, cervical and hypopharyngeal carcinomas. To further investigate the general role of MCM7 in tumorigenesis, we generated a mouse model with deregulated MCM7 expression targeted to the basal layer of the epidermis using the keratin 14 (K14) promoter (K14.MCM7). When subjected to a two-stage chemical carcinogenesis protocol (dimethylbenz[alpha]anthracene (DMBA) initiation with 12-ortho-tetradecanoylphorbol-13-acetate promotion), K14.MCM7 mice showed significantly increased incidence and prevalence of tumor development relative to controls. Furthermore, within 40 weeks of treatment over 45% K14.MCM7 mice exhibited tumors that had converted to squamous cell carcinomas versus none in the control group. As predicted from previous skin carcinogenesis studies using DMBA as the initiating agent, Ras mutations where found in more than 90% of tumors isolated from K14.MCM7 mice. Whereas previous studies have shown that MCM7 is useful as a proliferation marker, our data suggest that deregulated MCM7 expression actively contributes to tumor formation, progression and malignant conversion.

Identification of a novel cell-cycle-induced MCM family protein MCM9

The minichromosome maintenance (MCM) proteins are essential for DNA replication initiation and elongation in eukaryotes. In mammalian cells, MCM2-MCM7 complexes are believed to unwind DNA during chromosomal DNA replication. Here we identified a novel MCM family gene, MCM9, by using bioinformatics. Human, mouse, and rat MCM9 showed approximately 90-91% total-amino acid identity. MCM9 showed 24-31% total-amino acid identity with MCM2-MCM8 protein. Phylogenetic analysis on MCM family members revealed that MCM9 was most closely related to MCM8. Human, mouse, and rat MCM9 gene, consisting of 7, 8, and 7 exons, was mapped to 6q22.1-22.33, 10B3, and 20q11, respectively. We identified transcription factor E2F-binding motifs in the vicinity of the transcription start site among human, mouse, and rat MCM9 gene. MCM9 mRNA was upregulated by transcription factor E2E1 and serum stimulation in NIH3T3 cells.

Gene expression profiling of microdissected pancreatic ductal carcinomas using high-density DNA microarrays

Pancreatic ductal adenocarcinoma (PDAC) remains an important cause of malignancy-related death and is the eighth most common cancer with the lowest overall 5-year relative survival rate. To identify new molecular markers and candidates for new therapeutic regimens, we investigated the gene expression profile of microdissected cells from 11 normal pancreatic ducts, 14 samples of PDAC, and 4 well-characterized pancreatic cancer cell lines using the Affymetrix U133 GeneChip set. RNA was extracted from microdissected samples and cell lines, amplified, and labeled using a repetitive in vitro transcription protocol. Differentially expressed genes were identified using the significance analysis of microarrays program. We found 616 differentially expressed genes. Within these, 140 were also identified in PDAC by others, such as Galectin-1, Galectin-3, and MT-SP2. We validated the differential expression of several genes (e.g., CENPF, MCM2, MCM7, RAMP, IRAK1, and PTTG1) in PDAC by immunohistochemistry and reverse transcription polymerase chain reaction. We present a whole genome expression study of microdissected tissues from PDAC, from microdissected normal ductal pancreatic cells and pancreatic cancer cell lines using high-density microarrays. Within the panel of genes, we identified novel differentially expressed genes, which have not been associated with the pathogenesis of PDAC before.