Disease relevance of CDT1

• The Cul4A gene is amplified in human breast and liver cancers, and loss-of-function of Cul4 results in the accumulation of the replication licensing factor CDT1 in Caenorhabditis elegans embryos and ultraviolet (UV)-irradiated human cells [1].
• Constitutive expression of Cdt1 causes DNA re-replication and is associated with the development of a subset of human non-small cell-lung carcinomas [2].
• Expression of the licensing factors, Cdt1 and Geminin, in human colon cancer [3].
• In the latent state, the EBV genomic DNA, which exists as a closed circular plasmid, appears to behave just like host chromosomal DNA and it has been demonstrated recently that replication of OriP-containing plasmids is indeed dependent on the chromosomal initiation factors, ORC2 and Cdt1 [4].
• Thus, our study indicates that DUP is more reproducible and more accurate than SD in identifying patients with CAD and LV dyskinesia [5].

Psychiatry related information on CDT1

• For patients first presenting with a non-affective psychotic disorder, the duration of untreated psychosis (DUP; the time between the onset of positive psychotic symptoms and the initiation of appropriate treatment) varies widely, from a few weeks to several years [6].
• 5. DUP 996-induced EEG-changes over time were most pronounced over temporo-occipital, temporo-frontal, parietal and frontal regions, e.g. over brain areas afflicted most by Alzheimer's disease [7].
• It would appear that as years of chronic, refractory illness accrue, psychomotor poverty becomes more sharply delineated and dominant within the overall structure of psychopathology, and its prominence is predicted enduringly by DUP [8].
• The specificity at the same level of alcohol consumption, markedly differed between the two methods: 92%, 76% and 90% for CDTect, AX CDT 1 and AX CDT 2, respectively [9].
• There were significant associations between internal locus of control score and short DUP, and between external locus of control score and a positive attitude to medication as measured by the Drug Attitudes Inventory [10].

High impact information on CDT1

• Both Cdc18 and Cdt1 are required to load the MCM protein Cdc21 onto chromatin at the end of mitosis and this is necessary to initiate DNA replication [11].
• Cdt1 cooperates with Cdc18 to promote DNA replication, interacts with Cdc18, is located in the nucleus, and its concentration peaks as cells finish mitosis and proceed to S phase [11].
• Inhibition of eukaryotic DNA replication by geminin binding to Cdt1 [12].
• CDT1 is degraded in S phase to prevent rereplication, and following DNA damage to prevent origin firing [13].
• We show that DTL associates with the CUL4-DDB1 E3 ubiquitin ligase and is required for CDT1 down-regulation in unperturbed cells and following DNA damage [13].

Chemical compound and disease context of CDT1

• We examined the influence of exposure time to DUP 785 on its growth-inhibitory effects in L1210 murine leukemia and WiDR human adenocarcinoma cells and the effects of pyrimidine (deoxy) nucleosides on reversal of growth-inhibition [14].
• 1. In a double-blind, placebo-controlled study the encephalotropic effects of DUP 996, a novel phenylindolinone derivative for Alzheimer's disease enhancing the release of acetylcholine in cholinergic nerve terminals in the brain only when its release is triggered, were studied with special consideration of the pharmacodynamic time-course [7].

Biological context of CDT1

• Our study reveals an evolutionarily conserved and uncharacterized G1 checkpoint that induces CDT1 proteolysis by the CUL4-ROC1 ubiquitin E3 ligase and CSN complexes in response to DNA damage [15].
• We show that radiation-mediated CDT1 proteolysis is independent of ATM and CHK2 and can occur in G1-phase cells [15].
• Geminin is an unstable inhibitor of DNA replication that negatively regulates the licensing factor CDT1 and inhibits pre-replicative complex (pre-RC) formation in Xenopus egg extracts [16].
• Human geminin promotes pre-RC formation and DNA replication by stabilizing CDT1 in mitosis [16].
• The current concept regarding cell cycle regulation of DNA replication is that Cdt1, together with origin recognition complex and CDC6 proteins, constitutes the machinery that loads the minichromosome maintenance complex, a candidate replicative helicase, onto chromatin during the G(1) phase [17].

Anatomical context of CDT1

• Geminin was downregulated, whereas cdt1 levels were maintained upon differentiation of both cell lines, independently of whether cells entered extra S-phases [18].
• Consistently, in HeLa cells cosilenced of Skp2 and Cul4, Cdt1 remained stable in S-G2 phases [19].
• Moreover, both Cdt1 and Geminin expression are severely downregulated upon differentiation of Caco-2 cells, an in vitro model of intestinal epithelial differentiation [3].
• Geminin interacts with a DNA replication initiation factor, Cdt1p, to suppress initiation of DNA replication in a Xenopus egg extract based cell-free system, leading to the expectation that the protein acts as an inhibitor of cell proliferation [20].
• Among these, Cdt1 is likely the most important target for regulating licensing in higher eukaryotic cells, since illegitimate accumulation of Cdt1 causes multiple rounds of DNA replication without an intervening mitosis [21].

Associations of CDT1 with chemical compounds

• However, threonine 29 and the Cy motif are not necessary for proteolysis of Cdt1 during S phase [22].
• An array of glutamic acid residues on the coiled-coil domain surface interacts with positive charges in the middle of Cdt1 [23].
• CONCLUSIONS: This is the first report of complete thyroxine-binding globulin deficiency (TBG-CDT1 and TBG-CDT2) due to TBG gene mutations in Taiwan [24].
• Based on T-DNA activation tagging, a gene (CDT-1) was isolated which encodes a signalling molecule in the ABA transduction pathway [25].
• In nonfailing hearts, 69 +/- 4% of binding sites were blocked by the subtype-2-specific inhibitor PD 123319 and were therefore classified as AT2; 33 +/- 5% were blocked by the subtype-1-specific inhibitor DUP 753 and thus classified as subtype 1 [26].
• In vitro, Cdt1 can be acetylated at its N terminus by the lysine acetyltransferases KAT2B and KAT3B [27].

Physical interactions of CDT1

• Our studies suggest that L2DTL and PCNA interact with CUL4/DDB1 complexes and are involved in CDT1 degradation after DNA damage [28].
• PCNA binds to Cdt1 through the six conserved N-terminal amino acids [19].
• We showed that the F-box protein Skp2 specifically interacted with human Cdt1 in a phosphorylation-dependent manner [29].
• The human licensing factor for DNA replication Cdt1 accumulates in G1 and is destabilized after initiation of S-phase [30].

Enzymatic interactions of CDT1

• Cyclin-dependent kinases phosphorylate human Cdt1 and induce its degradation [31].

Regulatory relationships of CDT1

• L2DTL/CDT2 interacts with the CUL4/DDB1 complex and PCNA and regulates CDT1 proteolysis in response to DNA damage [28].
• The most important finding in these studies is that deregulated Cdt1 induces chromosomal damage and activation of the ATM-Chk2 DNA damage checkpoint pathway even in quiescent cells [32].
• These Cdt1 activities are negatively regulated by cyclin A/Cdks, probably through modification by phosphorylation [32].
• These findings suggest that exogenous Cdt1 induces re-replication by de-repressing endogenous Cdt1 through the titration of PCNA and cyclin [33].

Other interactions of CDT1

• Once the origin recognition complex (ORC) binds to origins, CDC6 and CDT1 associate with ORC and promote loading of the MCM2-7 proteins onto chromatin, generating the preRC [15].
• Phosphorylated Cdt1 is subsequently recognized by the F-box protein Skp2 and targeted for proteasomal mediated degradation [22].
• Several mechanisms of pre-RC regulation are known, including ATP utilization, cyclin-dependent kinase levels, protein turnover, and Cdt1 binding by geminin [34].
• Regulation of Geminin and Cdt1 expression by E2F transcription factors [35].
• Geminin has been proposed to coordinate cell cycle and differentiation events through balanced interactions with the cell cycle regulator Cdt1 and with homeobox transcription factors and chromatin remodeling activities implicated in cell fate decisions [36].
• We show that human CDT1 associates with the CDC7 kinase and recruits CDC45 to chromatin [37].

Analytical, diagnostic and therapeutic context of CDT1

• In vivo soluble Cdt1 and PCNA co-elute by gel filtration and associate with each other physically [2].
• Under these conditions, nearly all Cdt1 and a major part of geminin are bound to chromatin and reside at the same or closely adjacent sites as shown here by chromatin immunoprecipitation [38].
• In situ hybridization and immunohistochemistry localize Cdt1 as well as geminin to the proliferative compartment of the developing mouse gut epithelium [39].
• Constitutive overexpression of CDT-1 leads to desiccation tolerance in the absence of ABA and to the constitutive expression of characteristic transcripts [25].
• We therefore studied the effect of a small (Mr = 497), highly effective (Ki = 41 pM), reversible tripeptide inhibitor of thrombin, DUP 714 (1 microM), in a well characterized model of simulated extracorporeal circulation [40].

References