We have previously reported that c‐myc protein may promote cellular DNA replication by binding to initiation sites of replication. Here we report that a putative origin of human cellular DNA replication (ori) is present at approximately 2 kb upstream of the coding region of the c‐myc gene itself. The c‐myc protein, or protein(s) complexed with c‐myc protein, bind to the upstream region (approximately 200 bp in length) which has transcriptional enhancer activity as well as autonomously replicating activity in human cells, suggesting that the c‐myc protein may be an enhancer binding protein as well as a DNA replication protein. Results with deletion mutants suggest that the sequence essential to the origin of DNA replication may be adjacent to, but cannot be clearly separated from, the sequence responsible for enhancer activity. Furthermore, when cloned DNA containing putative c‐myc protein binding sequences was transfected as competitor into HL‐60 cells, expression of c‐myc was inhibited, suggesting that c‐myc protein itself may be necessary for c‐myc expression.

We have recently cloned a plasmid, pARS65, containing the sequences derived from mouse liver DNA which can autonomously replicate in mouse and human cells (Ariga et al., 1987). In this report, we show that replication of pARS65 in HL‐60 cells can be inhibited by co‐transfection with anti‐c‐myc antibody. In an in‐vitro replication system using HL‐60 nuclear extract, pARS65 functioned as a template. This in‐vitro replication was also blocked by addition of anti‐c‐myc antibody. Specific binding activity of the c‐myc product to pARS65 was detected by an immunobinding assay, suggesting that the c‐myc protein promotes DNA replication through binding to the initiation site of replication. This has been substantiated using the antibody to help isolate a human DNA segment that can autonomously replicate in the cells.

SummaryPrevious studies on recombinant human soluble thrombomodulin (rsTM) from Chinese hamster ovary cells revealed that rsTM was expressed as two proteins that differed functionally in vitro due to the presence (rsTMp) or absence (rsTMa) of chondroitin-4-sulfate. The current study evaluates the in vivo behavior of rsTM in rats and in a rat model of tissue factor-induced disseminated intravascular coagulation (DIC). rsTMp was more potent than rsTMa for prolongation of the activated partial thromboplastin time (APTT) and their in vivo half-lives determined by ELISA were 20 min for rsTMp and 5.0 h for rsTMa. Injection of a tissue factor suspension (5 mg/kg) resulted in DIC as judged by decreased platelet counts and fibrinogen concentrations, prolonged APTT, and increased fibrin and fibrinogen degradation products (FDP) levels. A bolus injection of either rsTM (0.2 mg/kg) 1 min before induction of DIC essentially neutralized effects on platelets, fibrinogen, and FDP levels, and had only a moderate effect on APTT prolongation. The dose of anticoagulant to inhibit the drop in platelet counts by 50% (ED50) was 0.2 mg/kg rsTMa, 0.07 mg/kg rsTMp, and 7 U/ kg heparin. The effect of increasing concentrations of rsTM and heparin on bleeding times were compared in experiments involving incision of the rat tail. Doubling of the bleeding times occurred at 5 mg/kg rsTMa, 3 mg/kg rsTMp or 90 U/kg heparin. These values represent a 25-fold increase over the ED50 for rsTMa, 43-fold for rsTMp and 13-fold for heparin. These results suggest that rsTMp is a potent anticoagulant to inhibit the platelet reduction when injected prior to the induction of DIC in rats.

Replicating activity of SV40 origin-containing plasmid was tested in human cells as well as in monkey CosI cells. All the plasmids possessing SV40 ori sequences could replicate, even in the absence of SV40 T antigen, in human HL-60 and Raji cells which are expressing c-myc gene at high level. The copy numbers of the replicated plasmids in these human cells were 1/100 as high as in monkey CosI cells which express SV40 T antigen constitutively. Exactly the same plasmids as the transfected original ones were recovered from the Hirt supernatant of the transfected HL-60 cells. Furthermore, replication of the SV40 ori-containing plasmids in HL-60 cells was inhibited by anti-c-myc antibody co-transfected into the cells. These results indicate that the c-myc protein can be substituted for SV40 T antigen in SV40 DNA replication.

We have already reported that the cloned mouse DNA fragment (pMU65) could replicate in a simian virus 40 T antigen-dependent system in vivo and in vitro (H. Ariga, Z. Tsuchihashi, M. Naruto, and M. Yamada, Mol. Cell. Biol. 5:563-568, 1985). The plasmid p65-tk, containing the thymidine kinase (tk) gene of herpes simplex virus and the BgllI-EcoRI region of pMU65 homologous to the simian virus 40 origin of DNA replication, was constructed. The p65-tk persisted episomally in tk+ transformants after the transfection of p65-tk into mouse FM3Ak-cells. The copy numbers of p65-tk in FM3Atk+ cells were 100 to 200 copies per cell. Furthermore, the p65-tk replicated semiconservatively, and the initiation of DNA replication started from the mouse DNA sequences when the replicating activity of p65-tk was tested in the in vitro DNA replication system developed from the FM3A cells. These results show that a 2.5-kilobase fragment of mouse DNA contains the autonomously replicating sequences.The replication of eucaryotic DNA occurs by initiation at many chromosomal sites which are usually clustered in a specific region characteristic of the cell type and the stage of the cell cycle (18). Recently, several investigators have tried to isolate replication origins by using in vitro recombination techniques (6). Another approach to the isolation of replication origin is to search autonomous replicating sequences (ARSs). Many ARSs of Saccharomyces cerevisiae, as well as those of other eucaryotic organisms, have been described (7, 9, 13-15, 17, 20, 22-24). These sequences from higher organisms may act as initiators of replication in S. cerevisiae cells. However, there is no evidence that these cloned eucaryotic DNA segments can also act as replicators in the cells of their original higher organisms. We have already reported that the cloned mouse DNA fragment pMU65 can replicate in a simian virus 40 (SV40) T antigen-dependent system in vivo and in vitro (5). The 2.5-kilobase (kb) mouse DNA fragment of pMU65 hybridized to half of a 27-nucleotide perfect palindrome present in the origin of SV40 DNA replication, and the initiation of DNA replication started from this fragment in an SV40 DNA replication system in vitro (5).We constructed the chimeric plasmid (p65-tk) containing 2.5 kb of mouse DNA, the thymidine kinase (tk) gene of herpes simplex virus type 1, and plasmid pKB111. The p65-tk plasmid persisted episomally in transfected mouse FM3A cells and had a good template activity in an in vitro DNA replication system that we have developed from FM3A cells. MATERIALS AND METHODSPlasmid and recombinant DNA constructions. Plasmid pMU65 harboring the mouse genomic DNA was reported previously (5) and is shown in Fig. 1. The 2.5-kb EcoRI-BglIll fragment of pMU65 was inserted into the EcoRI-BglII region of pKSV10, and the tk gene of herpes simplex virus type 1 (10) was further inserted into the BamHI site of the above plasmid. This was named p65-tk (Fig. 1) (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid) (pH 7.5), 5 mM KCl, 0.5 mM MgCl2, 0....