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Results for “Minichromosome Maintenance Complex Component 2”

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PubMed2006

The Chk1-mediated S-phase checkpoint targets initiation factor Cdc45 via a Cdc25A/Cdk2-independent mechanism.

DNA damage induced by the carcinogen benzo[a]pyrene dihydrodiol epoxide (BPDE) induces a Chk1-dependent S-phase checkpoint. Here, we have investigated the molecular basis of BPDE-induced S-phase arrest. Chk1-dependent inhibition of DNA synthesis in BPDE-treated cells occurred without detectable changes in Cdc25A levels, Cdk2 activity, or Cdc7/Dbf4 interaction. Overexpression studies showed that Cdc25A, cyclin A/Cdk2, and Cdc7/Dbf4 were not rate-limiting for DNA synthesis when the BPDE-induced S-phase checkpoint was active. To investigate other potential targets of the S-phase checkpoint, we tested the effects of BPDE on the chromatin association of DNA replication factors. The levels of chromatin-associated Cdc45 (but not soluble Cdc45) were reduced concomitantly with BPDE-induced Chk1 activation and inhibition of DNA synthesis. The chromatin association of Mcm7, Mcm10, and proliferating cell nuclear antigen was unaffected by BPDE treatment. However, the association between Mcm7 and Cdc45 in the chromatin fraction was inhibited in BPDE-treated cells. Chromatin immunoprecipitation analyses demonstrated reduced association of Cdc45 with the beta-globin origin of replication in BPDE-treated cells. The inhibitory effects of BPDE on DNA synthesis, Cdc45/Mcm7 associations, and interactions between Cdc45 and the beta-globin locus were abrogated by the Chk1 inhibitor UCN-01. Taken together, our results show that the association between Cdc45 and Mcm7 at origins of replication is negatively regulated by Chk1 in a Cdk2-independent manner. Therefore, Cdc45 is likely to be an important target of the Chk1-mediated S-phase checkpoint.

Cell Cycle Proteins↗

PubMed1997

HsMCM6: a new member of the human MCM/P1 family encodes a protein homologous to fission yeast Mis5.

BACKGROUND: The tight regulatory mechanism that prevents more than one round of chromosomal DNA replication per cell cycle is thought to require the function of Mcm/P1 proteins. We report here the structural and functional analyses of HsMcm6, a human homologue of the Mis5 of Schizosaccharomyces pombe. RESULTS: We demonstrate here that the transcription of the HsMCM6 gene was repressed in quiescent cells but was rapidly induced at the G1/S phase by growth factor stimulation. The 5' regulatory region of the HsMCM6 gene was found to harbour four putative E2F binding motifs, and these were responsible for the promoter activity. The HsMcm6 protein level oscillated during the cell cycle, with a peak at the G1/S phase. We also showed that the cell-cycle dependent change of subcellular localization of HsMcm6 resembles those of other Mcm/P1 proteins. HsMcm6 consists of two forms, a form extractable by Nonidet P-40 and the nucleus-bound form. A demonstration of the association of HsMcm6 with HsMcm2 and HsMcm7 in vivo supports the idea that they behave as a heteromeric complex. We mapped the HsMCM6 gene at 2q12-14. CONCLUSION: The results indicate that the behaviour of HsMcm6 is reminiscent of replication licensing factor like other Mcm/P1 family members.

Amino Acid Sequence↗

PubMed2002

MCM3-binding GANP DNA-primase is associated with a novel phosphatase component G5PR.

BACKGROUND: GANP, carrying DNA-primase and MCM3-binding domains, is up-regulated in germinal centre B cells. To understand the regulatory function of GANP upon MCM complex, we searched for GANP-associated molecules by yeast two-hybrid screening. RESULTS: Using the 1 kb fragment (G5) of the ganp cDNA, we identified a clone named G5PR that is structurally homologous to known regulatory subunits of protein phosphatases (PPases) and determined the association of G5PR with GANP in vivo in the DNA transfectant. G5PR is associated with protein phosphatase 5 (PP5) through its tetratricopeptide-repeat (TPR) domain. Pull-down assays demonstrated that G5PR is also associated with protein phosphatase 2A (PP2A), the complex of A subunit (PR65) and the catalytic (C) subunit (PP2Ac), similar to the B" subunit. The G5PR-associated complex had phosphatase activity on casein, histone H1 and MCM3 in vitro, but the addition of G5PR did not stimulate or inhibit the phosphatase activities of PP5 and PP2A. The cellular localization of G5PR in transfected cells varies during cell cycling, appearing in the nucleus during prophase, in the peri-chromatin during mitotic phase, and in the cytoplasm after cell division. CONCLUSION: G5PR is capable of recruiting two kinds of PPases, PP5 and PP2A, into the GANP/MCM3 complex, which might regulate its phosphorylation state during cell cycle progression.

Acetyltransferases↗

PubMed2006

Site-specific phosphorylation of MCM4 during the cell cycle in mammalian cells.

MCM4, a subunit of a putative replicative helicase, is phosphorylated during the cell cycle, at least in part by cyclin-dependent kinases (CDK), which play a central role in the regulation of DNA replication. However, detailed characterization of the phosphorylation of MCM4 remains to be performed. We examined the phosphorylation of human MCM4 at Ser3, Thr7, Thr19, Ser32, Ser54, Ser88 and Thr110 using anti-phosphoMCM4 sera. Western blot analysis of HeLa cells indicated that phosphorylation of MCM4 at these seven sites can be classified into two groups: (a) phosphorylation that is greatly enhanced in the G2 and M phases (Thr7, Thr19, Ser32, Ser54, Ser88 and Thr110), and (b) phosphorylation that is firmly detected during interphase (Ser3). We present data indicating that phosphorylation at Thr7, Thr19, Ser32, Ser88 and Thr110 in the M phase requires CDK1, using a temperature-sensitive mutant of mouse CDK1, and phosphorylation at sites 3 and 32 during interphase requires CDK2, using a dominant-negative mutant of human CDK2. Based on these results and those from in vitro phosphorylation of MCM4 with CDK2/cyclin A, we discuss the kinases responsible for MCM4 phosphorylation. Phosphorylated MCM4 detected using anti-phospho sera exhibited different affinities for chromatin. Studies on the nuclear localization of chromatin-bound MCM4 phosphorylated at sites 3 and 32 suggested that they are not generally colocalized with replicating DNA. Unexpectedly, MCM4 phosphorylated at site 32 was enriched in the nucleolus through the cell cycle. These results suggest that phosphorylation of MCM4 has several distinct and site-specific roles in the function of MCM during the mammalian cell cycle.

Amino Acid Sequence↗

PubMed2000

Cdk2-dependent and -independent pathways in E2F-mediated S phase induction.

The transcription factor E2F plays an important role in G(1) to S phase transition in the higher eukaryotic cell cycle. Although a number of E2F-inducible genes have been identified, the biochemical cascades from E2F to the S phase entry remain to be investigated. In this study, we generated stably transfected mouse NIH3T3 cells that express exogenous human E2F-1 under the control of a heavy metal-inducible metallothionein promoter and analyzed the molecular mechanism of the E2F-1-mediated initiation of chromosomal DNA replication. Ectopic E2F-1 expression in cells arrested in G(0)/G(1) by serum deprivation enabled them to progress through G(1) and to enter S phase. During the G(1) progression, mouse cyclin E, but little of cyclin D1, was induced to express, which subsequently activated Cdk2. Experiments using the Cdk inhibitory proteins p27, p18, and p19 proved that the activity of Cdk2, but not of Cdk4, was required for S phase entry mediated by E2F-1. Minichromosome maintenance proteins (MCM) 4 and 7, the components of the DNA-replication initiation complex (RC), were constitutively expressed during the cell cycle, although the MCM genes are well known E2F-inducible genes. However, tight association of these two proteins with chromatin depended upon ectopic E2F-1 expression. In contrast, the Cdc45 protein, another RC component, which turned out to be a transcriptional target of E2Fs, was induced to express and subsequently bound to chromatin in response to E2F-1. Experiments utilizing a chemical Cdk-specific inhibitor, butyrolactone I, revealed that Cdk2 activity was required only for chromatin binding of the Cdc45 proteins, and not for the expression of Cdc45 or chromatin binding of MCM4 and -7. These results indicate that at least two separate pathways function downstream of E2F to initiate S phase; one depends upon the activity of Cdk2 and the other does not.

3T3 Cells↗

PubMed2004

Interaction between human MCM7 and Rad17 proteins is required for replication checkpoint signaling.

Human Rad17 (hRad17) is centrally involved in the activation of cell-cycle checkpoints by genotoxic agents or replication stress. Here we identify hMCM7, a core component of the DNA replication apparatus, as a novel hRad17-interacting protein. In HeLa cells, depletion of either hRad17 or hMCM7 with small-interfering RNA suppressed ultraviolet (UV) light- or aphidicolin-induced hChk1 phosphorylation, and abolished UV-induced S-phase checkpoint activation. Similar results were obtained after transfection of these cells with a fusion protein containing the hMCM7-binding region of hRad17. The hMCM7-depleted cells were also defective for the formation of ATR-containing nuclear foci after UV irradiation, suggesting that hMCM7 is required for stable recruitment of ATR to damaged DNA. These results demonstrate that hMCM7 plays a direct role in the transmission of DNA damage signals from active replication forks to the S-phase checkpoint machinery in human cells.

Aphidicolin↗

PubMed2003

Intra-G1 arrest in response to UV irradiation in fission yeast.

G1 is a crucial phase of cell growth because the decision to begin another mitotic cycle is made during this period. Occurrence of DNA damage in G1 poses a particular challenge, because replication of damaged DNA can be deleterious and because no sister chromatid is present to provide a template for recombinational repair. We therefore have studied the response of Schizosaccharomyces pombe cells to UV irradiation in early G1 phase. We find that irradiation results in delayed progression through G1, as manifested most critically in the delayed formation of the pre-replication complex. This delay does not have the molecular hallmarks of known checkpoint responses: it is independent of the checkpoint proteins Rad3, Cds1, and Chk1 and does not elicit inhibitory phosphorylation of Cdc2. Irradiated cells eventually progress into S phase and arrest in early S by a rad3- and cds1-dependent mechanism, most likely the intra-S checkpoint. Caffeine alleviates both the intra-G1- and intra-S-phase delays. We suggest that intra-G1 delay may be widely conserved and discuss significance and possible mechanisms.

Adenosine Triphosphatases↗

PubMed2002

MCM2-7 complexes bind chromatin in a distributed pattern surrounding the origin recognition complex in Xenopus egg extracts.

The MCM2-7 complex is believed to function as the eukaryotic replicative DNA helicase. It is recruited to chromatin by the origin recognition complex (ORC), Cdc6, and Cdt1, and it is activated at the G(1)/S transition by Cdc45 and the protein kinases Cdc7 and Cdk2. Paradoxically, the number of chromatin-bound MCM complexes greatly exceeds the number of bound ORC complexes. To understand how the high MCM2-7:ORC ratio comes about, we examined the binding of these proteins to immobilized linear DNA fragments in Xenopus egg extracts. The minimum length of DNA required to recruit ORC and MCM2-7 was approximately 80 bp, and the MCM2-7:ORC ratio on this fragment was approximately 1:1. With longer DNA fragments, the MCM2-7:ORC ratio increased dramatically, indicating that MCM complexes normally become distributed over a large region of DNA surrounding ORC. Only a small subset of the chromatin-bound MCM2-7 complexes recruited Cdc45 at the onset of DNA replication, and unlike Cdc45, MCM2-7 was not limiting for DNA replication. However, all the chromatin-bound MCM complexes may be functional, because they were phosphorylated in a Cdc7-dependent fashion, and because they could be induced to support Cdk2-dependent Cdc45 loading. The data suggest that in Xenopus egg extracts, origins of replication contain multiple, distributed, initiation-competent MCM2-7 complexes.

Animals↗

PubMed2006

Phosphorylation of MCM4 at sites inactivating DNA helicase activity of the MCM4-MCM6-MCM7 complex during Epstein-Barr virus productive replication.

Induction of Epstein-Barr virus (EBV) lytic replication blocks chromosomal DNA replication notwithstanding an S-phase-like cellular environment with high cyclin-dependent kinase (CDK) activity. We report here that the phosphorylated form of MCM4, a subunit of the MCM complex essential for chromosomal DNA replication, increases with progression of lytic replication, Thr-19 and Thr-110 being CDK2/CDK1 targets whose phosphorylation inactivates MCM4-MCM6-MCM7 (MCM4-6-7) complex-associated DNA helicase. Expression of EBV-encoded protein kinase (EBV-PK) in HeLa cells caused phosphorylation of these sites on MCM4, leading to cell growth arrest. In vitro, the sites of MCM4 of the MCM4-6-7 hexamer were confirmed to be phosphorylated with EBV-PK, with the same loss of helicase activity as with CDK2/cyclin A. Introducing mutations in the N-terminal six Ser and Thr residues of MCM4 reduced the inhibition by CDK2/cyclin A, while EBV-PK inhibited the helicase activities of both wild-type and mutant MCM4-6-7 hexamers, probably since EBV-PK can phosphorylate MCM6 and another site(s) of MCM4 in addition to the N-terminal residues. Therefore, phosphorylation of the MCM complex by redundant actions of CDK and EBV-PK during lytic replication might provide one mechanism to block chromosomal DNA replication in the infected cells through inactivation of DNA unwinding by the MCM4-6-7 complex.

Amino Acid Substitution↗

PubMed1996

Characterisation of a human homologue of a yeast cell division cycle gene, MCM6, located adjacent to the 5' end of the lactase gene on chromosome 2q21.

Four exons of a human homologue of a yeast cell division cycle gene (MCM6/mis5, which is thought to encode a DNA replication licensing factor) have been identified 3.3 kb upstream from the start of transcription of the intestinal lactase gene on human chromosome 2q21, initially by similarity to a rat 'intestinal crypt-cell replication factor'. RT-PCR analysis shows, that unlike lactase, MCM6 is not restricted in its tissue distribution and does not show person-to-person variation in the level of expression in adult intestine.

Adult↗

PubMed2001

Phosphorylation of Mcm4 at specific sites by cyclin-dependent kinase leads to loss of Mcm4,6,7 helicase activity.

Mcm proteins that play an essential role in eukaryotic DNA replication are phosphorylated in vivo, and cyclin-dependent protein kinase is at least in part responsible for the phosphorylation of Mcm4. Our group reported that the DNA helicase activity of Mcm4,6,7 complex, which may be involved in initiation of DNA replication, is inhibited following phosphorylation by Cdk2/cyclin A in vitro. Here, we further examined the interplay between mouse Mcm4,6,7 complex and cyclin-dependent kinases and determined the sites required for the phosphorylation of Mcm4. Six Ser and Thr residues, in all, were required for the phosphorylation. Inhibition of Mcm4,6,7 helicase activity by Cdk2/cyclin A was largely relieved by introducing mutations in these residues of Mcm4. Anti-phosphothreonine antibodies raised against one of these sites reacted with Mcm4 prepared from HeLa cells at mitotic phase but did not bind to those at G(1) and G(1)/S, suggesting that this site is mainly phosphorylated in the mitotic phase. Mcm4,6,7 complex purified from HeLa cells at the mitotic phase exhibited a low level of DNA helicase activity, compared with the complexes prepared from cells at other phases. These results suggest that phosphorylation of Mcm4 at specific sites leads to loss of Mcm4,6,7 DNA helicase activity.

Amino Acid Sequence↗

PubMed1999

Involvement of cyclin D1-cdk5 overexpression and MCM3 cleavage in bax-associated spontaneous apoptosis and differentiation in an A253 human head and neck carcinoma xenograft model.

Time-dependent ladder-type DNA fragmentation and morphological alterations consistent with apoptosis were observed among A253 human head and neck squamous cell carcinoma (HNSCC) cells in nude mice from 15 to 18 days after transplantation, without any drug treatment. No evidence of ladder-type DNA fragmentation was detected in A253 cells in vitro or in normal nude mouse tissues (skin and muscle). Our aim was to explore molecular factors associated with such spontaneous apoptosis. Bcl-2 protein expression decreased, while bax protein expression increased from day 9 after transplantation. Moreover, altered expression of bcl-2 and bax was accompanied by the increased proteolytic cleavage of poly(ADP-ribose) polymerase (PARP). Time-dependent dephosphorylation of Rb, followed by proteolytic cleavage, was also observed from day 9 after transplantation. The data indicate that the caspase-3 activation and cleavage of Rb protein may represent important steps in the regulation pathway of bax-mediated spontaneous apoptosis. Interestingly, the time-dependent activation of spontaneous apoptosis was almost simultaneous with the induction of differentiation and increased expression of several differentiation-associated regulatory proteins. An increased expression of cyclin D1 and cyclin-dependent kinase-5 (cdk5) was observed from day 9 after transplantation, whereas only slight alteration of cdk4 expression was found. The time-dependent activation of cyclin D1 and cdk5 preceded both the induction of ladder-type DNA fragmentation and increased keratin pearl formation. Furthermore, MCM3 was cleaved early in spontaneous apoptosis and differentiation. Our observations suggest the involvement of cyclin D1-cdk5 overexpression and MCM3 cleavage in bax-mediated spontaneous apoptosis and differentiation in A253 xenografts. P53 and WAF1 proteins were not expressed in the xenografts, indicating that the changes in the regulatory proteins during apoptosis and differentiation were not p53 or WAF1 dependent.

Animals↗

PubMed1998

E2F3 activity is regulated during the cell cycle and is required for the induction of S phase.

Previous work has demonstrated the important role of E2F transcription activity in the induction of S phase during the transition from quiescence to proliferation. In addition to the E2F-dependent activation of a number of genes encoding DNA replication activities such as DNA Pol alpha, we now show that the majority of genes encoding initiation proteins, including Cdc6 and the Mcm proteins, are activated following the stimulation of cell growth and are regulated by E2F. The transcription of a subset of these genes, which includes Cdc6, cyclin E, and cdk2, is also regulated during the cell cycle. Moreover, whereas overall E2F DNA-binding activity accumulates during the initial G1 following a growth stimulus, only E2F3-binding activity reaccumulates at subsequent G1/S transitions, coincident with the expression of the cell-cycle-regulated subset of E2F-target genes. Finally, we show that immunodepletion of E2F3 activity inhibits the induction of S phase in proliferating cells. We propose that E2F3 activity plays an important role during the cell cycle of proliferating cells, controlling the expression of genes whose products are rate limiting for initiation of DNA replication, thereby imparting a more dramatic control of entry into S phase than would otherwise be achieved by post-transcriptional control alone.

CDC2-CDC28 Kinases↗

PubMed1998

Association of RPA with chromosomal replication origins requires an Mcm protein, and is regulated by Rad53, and cyclin- and Dbf4-dependent kinases.

Eukaryotic cells use multiple replication origins to replicate their large genomes. Some origins fire early during S phase whereas others fire late. In Saccharomyces cerevisiae, initiator sequences (ARSs) are bound by the origin recognition complex (ORC). Cdc6p synthesized at the end of mitosis joins ORC and facilitates recruitment of Mcm proteins, which renders origins competent to fire. However, origins fire only upon the subsequent activation of S phase cyclin-dependent kinases (S-CDKs) and Dbf4/Cdc7 at the G1/S boundary. We have used a chromatin immunoprecipitation assay to measure the association with ARS sequences of DNA primase and the single-stranded DNA binding replication protein A (RPA) when fork movement is inhibited by hydroxyurea (HU). RPA's association with origins requires S-CDKs, Dbf4/Cdc7 kinase and an Mcm protein. The recruitment of DNA primase depends on RPA. Furthermore, early- and late-firing origins differ not in the timing of their recruitment of an Mcm protein, but in the timing of RPA's recruitment. RPA is recruited to early but not to late origins in HU. We also show that Rad53 kinase is required to prevent RPA association with a late origin in HU. Our data suggest that the origin unwinding accompanied by RPA association is a key step, regulated by S-CDKs, Dbf4/Cdc7 and Rad53p. Thus, in the presence of active S-CDKs and Dbf4/Cdc7, Mcms may open origins and thereby facilitate the loading of RPA.

Adenosine Triphosphatases↗

PubMed2004

Sir Antagonist 1 (San1) is a ubiquitin ligase.

Mutations in Sir Antagonist 1 (SAN1) suppress defects in SIR4 and SPT16 in Saccharomyces cerevisiae. San1 contains a RING domain, suggesting that it functions by targeting mutant sir4 and spt16 proteins for degradation by a ubiquitin-mediated pathway. Consistent with this idea, mutant sir4 and spt16 proteins are unstable in SAN1 cells but are stabilized in san1Delta cells. We demonstrate that San1 possesses ubiquitin-protein isopeptide ligase activity in vitro, and the ubiquitin-protein isopeptide ligase activity of San1 is required for its function in vivo. Wild-type Sir4 has a half-life of about 21 min, and san1Delta increased Sir4 half-life to >90 min. In contrast, san1Delta did not affect the stability of wild-type Spt16, Sir3, Sir2, or the Spt16-associated proteins Pob3 and Nhp6. Loss of SAN1 also did not affect the stability of Ste6-166, a highly unstable protein in yeast. These results support the idea that San1 controls the turnover of a specific class of unstable nuclear proteins. Sir4 nucleates the assembly of silent chromatin at telomeres and the silent mating-type loci (HM) in S. cerevisiae. Sir4 can also affect silencing in the rDNA indirectly by sequestering limiting Sir2. Increasing the stability of wild-type Sir4 by deleting SAN1 had only subtle effects on silencing, suggesting that silent chromatin in yeast is robustly buffered against changes in Sir4 stability. Consistent with the idea that San1 participates as an accessory factor to regulate silent chromatin, including the silent mating-type loci, microarray analysis defined a small but statistically significant role for San1 in transcription of several mating pheromone-responsive genes.

Amino Acid Sequence↗

PubMed2000

Inhibition of Mcm4,6,7 helicase activity by phosphorylation with cyclin A/Cdk2.

A strong body of evidence indicates that cyclin-dependent protein kinases are required not only for the initiation of DNA replication but also for preventing over-replication in eukaryotic cells. Mcm proteins are one of the components of the replication licensing system that permits only a single round of DNA replication per cell cycle. It has been reported that Mcm proteins are phosphorylated by the cyclin-dependent kinases in vivo, suggesting that these two factors are cooperatively involved in the regulation of DNA replication. Our group has reported that a 600-kDa Mcm4,6,7 complex has a DNA helicase activity that is probably necessary for the initiation of DNA replication. Here, we examined the in vitro phosphorylation of the Mcm complexes with cyclin A/Cdk2 to understand the interplay between Mcm proteins and cyclin-dependent kinases. The cyclin A/Cdk2 mainly phosphorylated the amino-terminal region of Mcm4 in the Mcm4,6,7 complex. The phosphorylation was associated with the inactivation of its DNA helicase activity. These results raise the possibility that the inactivation of Mcm4,6,7 helicase activity by Cdk2 is a part of the system for regulating DNA replication.

Animals↗

PubMed2002

Visualization of replication initiation and elongation in Drosophila.

Chorion gene amplification in the ovaries of Drosophila melanogaster is a powerful system for the study of metazoan DNA replication in vivo. Using a combination of high-resolution confocal and deconvolution microscopy and quantitative realtime PCR, we found that initiation and elongation occur during separate developmental stages, thus permitting analysis of these two phases of replication in vivo. Bromodeoxyuridine, origin recognition complex, and the elongation factors minichromosome maintenance proteins (MCM)2-7 and proliferating cell nuclear antigen were precisely localized, and the DNA copy number along the third chromosome chorion amplicon was quantified during multiple developmental stages. These studies revealed that initiation takes place during stages 10B and 11 of egg chamber development, whereas only elongation of existing replication forks occurs during egg chamber stages 12 and 13. The ability to distinguish initiation from elongation makes this an outstanding model to decipher the roles of various replication factors during metazoan DNA replication. We utilized this system to demonstrate that the pre-replication complex component, double-parked protein/cell division cycle 10-dependent transcript 1, is not only necessary for proper MCM2-7 localization, but, unexpectedly, is present during elongation.

Animals↗

PubMed2006

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.

9,10-Dimethyl-1,2-benzanthracene↗