Increased growth of NIH/3T3 cells by transfection with human p120 complementary DNA and inhibition by a p120 antisense construct.

The human nucleolar antigen p120 was detected with an anti-p120 monoclonal antibody in most human malignant tumors but not in most resting human tissues (J. W. Freeman et al., Cancer Res., 48: 1244-1251, 1988) and has been used as a prognostic tumor marker in breast cancer patients (J. W. Freeman et al., Cancer Res., 51: 1973-1978, 1991). After the complementary DNA and gene for the human p120 protein were isolated and sequenced (review: H. Busch, Cancer Res., 50: 4830-4838, 1990), constructs were prepared to study the expression of the sense p120 and its antisense, p021 message. NIH/3T3 cells were transfected by electroporation with pSVX plasmids containing either the p120 complementary DNA (pSVX120) or the antisense, p021 DNA (pSVX021), and clones containing these constructs were selected. The expression of p120 or p021 in these constructs was regulated by Moloney murine leukemia virus long terminal repeats. In pSVX120-transfected NIH/3T3 cells, the expressed human p120 protein was localized to the nucleoli as shown by anti-p120 monoclonal antibody immunofluorescence. Expression of the p120 message and protein was confirmed by Northern (mRNA) and Western (protein) blots. Transfection of the p120 complementary DNA in sense orientation caused malignant transformation of NIH/3T3 cells in vitro and produced rapidly growing tumors in nude mice. Transfection of the antisense p120 constructs markedly delayed the growth of these tumors in vitro and in vivo (L. Perlaky et al., Proc. Am. Assoc. Cancer Res., 32: 1682, 1991). When transformed 3T3/pSVX120 cells were transfected with an inducible antisense p120 construct (pMSG021), dexamethasone induction decreased the growth rate by 62%, and the cell line returned to its normal phenotype. Northern blot analysis showed a decreased level of p120 mRNA, and the immunofluorescence was also markedly reduced.     

Isolation and characterization of cDNA and genomic sequences for mouse O6-methylguanine-DNA methyltransferase.

An enzyme, O6-methylguanine-DNA methyltransferase, is present in various organisms and plays an important role in repair of DNA damaged by alkylating agents. The enzyme transfers methyl groups from O6-methylguanine and other methylated moieties of the DNA to its own molecule. As a first step to construct animal models with altered levels of the enzyme activity, we cloned cDNA and genomic DNA sequences for mouse methyltransferase and elucidated their structures. The nucleotide sequence of the cDNA revealed an open reading frame comprising 211 amino acid residues. The mol. wt of mouse O6-methylguanine-DNA methyltransferase, calculated from the predicted amino acid sequence, was 22,400, and the methyltransferase protein of this size was present when the cDNA was expressed in methyltransferase-deficient human cells. The predicted amino acid sequence of the mouse methyltransferase exhibits an intense homology with those of human and bacterial counterparts. Using the cDNA as a probe, part of the mouse gene for methyltransferase was isolated. The gene consisted of at least four exons and spanned greater than 145 kb. Sequences around the exon/intron junctions for the mouse gene are almost the same as those for the human species.     

PDGF, CSF-1, and EGF induce tyrosine phosphorylation of p120, a pp60src transformation-associated substrate.

Transformation by activated pp60c-src has been correlated by genetic analysis with the tyrosine phosphorylation of a 120 kilodalton (kDa) protein, p120. We now demonstrate tyrosine phosphorylation of p120 following stimulation of cells by growth factors whose receptors have intrinsic tyrosine-specific protein kinase activity. Stimulation of quiescent NIH3T3 cells with platelet-derived growth factor (PDGF) resulted in the tyrosine phosphorylation of p120 that was maximal by 5 min and returned to background levels by 30 min. p120 was also phosphorylated on tyrosine after addition of colony-stimulating factor 1 (CSF-1) or epidermal growth factor (EGF) to NIH3T3 cells engineered to express high levels of their respective receptors. Two additional src substrates, p110 and p85, were analysed under identical assay conditions. PDGF, CSF-1, and EGF induced only a minimal increase in the tyrosine phosphorylation of p85 and no change in the phosphorylation of p110. Thus, the marked ligand-induced tyrosine phosphorylation of p120 was a property not shared by the other src substrates examined. Immunoblotting with antibodies to p120 and the ras GTPase activating protein, GAP, suggests that p120 and GAP are unrelated. In addition, the amino acid sequences of four cyanogen bromide peptides derived from p120 showed no homology to GAP or to sequences in either the PIR or Swiss-Prot databases. These data suggest that tyrosine phosphorylation of p120 may contribute to both signal transduction through growth factor receptors and pp60src induced transformation.     

Identification and characterization of survival-related gene, a novel cell survival gene controlling apoptosis and tumorigenesis

Apoptosis plays a critical role in cellular homeostasis during development, immune responses, and tumorigenesis. Recent studies have identified a number of genes that control this process. We report here our identification of a novel cell survival-related gene (SRG) from a human expression cDNA library by functional cloning. SRG shows no significant nucleotide sequence homology to any known genes in the Genbank. Our fluorescence in situ hybridization analysis has estimated that SRG is located at 1p36, agreeing with the location at 1p36.22 in the human genome sequence. SRG encodes a putative protein of 172 amino acids, which is mainly located in the perinuclear region. Northern blotting analysis indicates that SRG is highly expressed in many human cancer cell lines although it is low in most tissues except liver and placenta. To investigate the function of SRG in apoptosis, we transfected SRG cDNA into BAF/BO3 and B16/F0 cells and induced apoptosis by cytokine/serum deprivation. We found that SRG-transfected cells are resistant to apoptosis induced by cytokine/serum deprivation. In addition, mice bearing SRG-transfected melanoma had more tumor formation and larger tumor growth. Melanoma transfected with antisense SRG showed significantly less tumor formation and smaller tumor growth. Interestingly, mouse SRG gene was also identified on chromosome 4 and blocking SRG expression with small interfering RNA promoted serum deprivation-induced apoptosis of NIH3T3 cells. Our results show that SRG is a novel cell survival gene that critically controls apoptosis and tumor formation.     

Human hst-2 (FGF-6) oncogene: cDNA cloning and characterization.

The hst-2 gene was previously identified by its close homology to the hst-1 gene. Cosmid clones containing the hst-2 gene were cloned from a normal human genomic library. Focus-forming activity was observed for the hst-2 cosmids when NIH3T3 transfection assay was performed in a serum-free medium, whereas induction of morphological transformation was difficult to detect in an ordinary serum-supplemented medium. The hst-2 cDNA was cloned from the NIH3T3 transformant. Nucleotide sequence analysis of the cDNA indicates that the hst-2 gene encodes a 198 amino acid transforming protein containing a signal peptide with the characteristics of a heparin-binding growth factor. The coding sequence was almost identical to the published portion of the exon sequence of the FGF-6 gene, indicating that hst-2 is identical to FGF-6. The hst-2 cDNA fragment, when inserted into an expression vector, was able to transform NIH3T3 cells effectively, and the resulting transformant formed a well-vascularized tumor in nude mice, thus suggesting an angiogenic property similar to some other members of the family. RNA blot analysis revealed the expression of the hst-2 gene in human leukemia cell lines with platelet/megakaryocytic differentiation potential.     

The MEL gene: a new member of the RAB/YPT class of RAS-related genes

The MEL gene was identified following transfection of NIH3T3 mouse fibroblasts with DNA from a human melanoma cell line. The human MEL gene has been localized to 19cen-p13.2, a region in which translocation breakpoints occur in a number of malignancies. We have identified and sequenced human and mouse MEL cDNA clones which show homology of 92% and 96% at the nucleotide and amino acid levels respectively. The predicted human MEL protein shows only six amino acid differences between it and the recently described dog RAB8 protein. All of these changes occur in the 30 amino acids at the C-terminal of these proteins. MEL is similar to the RAB/YPT proteins in the region corresponding to the putative effector domain, suggesting that they may interact with the same cellular substrates. However, MEL contains a C-terminal CAAX motif in common with the majority of the RAS superfamily, unlike YPT1 and the majority of the RAB proteins.     

Cloning, characterisation and bacterial expression of full length cDNA for the mouse liver microsomal glutathione S-transferase

We have isolated a cDNA encoding full length microsomal glutathione S-transferase (MGST) from mouse liver. The cDNA was isolated by RT-PCR using primers designed from published cDNA sequence of rat MGST with the addition of 5' Nde-1 and 3' HindIII sites, and cloned into bacterial expression vector pSP19T7LT. Deduced amino acid sequence (155 amino acids, calculated mol.mass 17512 Dalton) confirmed the identity of microsomal GST from mouse liver which has sequence homology with that of rat and human liver MGST1. Recombinant GST cDNA (Genbank accession # 159050) was expressed in BL21(DE3) in the presence of 1 mM IPTG at 30 degrees C. The expressed GST protein was found to be localised in the bacterial membrane as determined by measuring catalytic activity using CDNB and cumene hydroperoxide substrates, SDS-PAGE and Western blot analysis. We have demonstrated the cloning and expression of full length cDNA for MGST from mouse liver and have characterised the functionally active product as MGST protein. These results should facilitate studies on the role of MGST in the regulation of chemical carcinogenesis and in the prevention of oxidative stress caused by endogenous and exogenous chemicals.     

Cloning of Mouse DAN cDNA and Its Down-regulation in Transformed Cells

Recently, we have demonstrated that DAN gene product exhibits a tumor-suppressive activity in vitro . We report here the cloning and sequencing of a mouse DAN cDNA that contains the entire coding region. Sequence analysis revealed that mouse DAN cDNA is 1691 nucleotides in length and contains an open reading frame of 178 amino acids. The deduced mouse DAN protein sequence shows 96% and 93% identity with the counterparts isolated from rat 3Y1 fibroblasts and normal human lung, respectively. Genomic Southern blot hybridization indicated that DAN gene exists as a single copy in the mouse genome. The expression of DAN gene was suppressed in a variety of transformed NIH3T3 cells when compared with that in the parental NIH3T3 cells.     

p53 Antisense Oligonucleotide Inhibits Growth of Human Colon Tumor and Normal Cell Lines

We examined the relationship between the expression of mutant p53 proteins and tumor cell growth using a p53 antisense oligonucleotide (5'-CCCTGCTCCCCCCTGGCTCC-3'). The oligonucleotide inhibited the growth of three human colon tumor cell lines (DLD-1, SW620 and WiDr), which produce only mutant p53 proteins with different mutation sites. Treatment of DLD-1 cells with the p53 antisense oligonucleotide caused a decrease in the level of p53 mutant protein. Synthesis of DNA in DLD-1 and SW620 cells was inhibited more potently than that of RNA or protein after antisense treatment. Furthermore, these cells were accumulated in the S phase when DNA synthesis was inhibited. Meanwhile, the antisense oligonucleotide also inhibited the growth of three human normal cell lines (WI-38, TIG-1 and Intestine 407). While treatment of WI-38 and TIG-1 cells with the antisense oligonucleotide inhibited synthesis of DNA more potently than that of RNA or protein, these normal cells were accumulated in the G0/G1 phase. These results suggest that p53 proteins, either with or without mutation, play a pivotal role in the growth of tumor and normal cells, but that mutant and wild-type p53 proteins may function differently in cell growth.     

Induction of the estrogen-regulated "24K" protein by heat shock

We have previously demonstrated an estrogen-regulated protein, termed 24K, in human breast cancer cell lines and human tumor biopsies. The presence of the protein correlates well with the presence of steroid hormone receptors. We have cloned a partial complementary DNA to 24K and show that the nucleotide and deduced amino acid sequence contains a striking homology to the low molecular weight heat shock proteins of Drosophila and the mammalian alpha-crystallins. Our complementary DNA is identical to that reported for the 3' region of human heat shock protein 27/28 with the mRNAs for the gene significantly induced by both heat shock and estradiol treatment in MCF-7 breast cancer cells. A variant polymorphism of the gene was detected in two estrogen-unresponsive cell lines, but not in other human breast cancer cell lines or human placenta; the polymorphism did not affect heat shock induction of the gene. The heat shock protein 27/28 model system in MCF-7 cells will afford a valuable tool to analyze the molecular events underlying the hormonal regulation of gene expression; heat shock may offer an approach to manipulate the hormonal regulation of the heat shock protein 27/28 gene.     

黏附调节因子p120ctn 3A细胞核靶向表达质粒的构建及鉴定

目的：既往少数研究表明p120ctn存在核浆穿梭现象,为研究细胞核内p120ctn的功能,我们试图构建p120ctn 3A细胞核定向表达载体pCMV/p120ctn 3A。方法：采用PCR方法扩增人p120ctn 3A活性片段,将其插入细胞核定向表达载体pCMV/myc/nuc,构建重组体pCMV/p120ctn 3A,经脂质体介导转染肺癌细胞A549,用荧光显微镜观察绿色荧光信号,免疫细胞化学及Western blot鉴定其在肺癌细胞A549中的表达与定位。结果：限制性双酶切及DNA测序分析结果显示插入pCMV/p120ctn 3A的片段为2496bp左右,与预期p120ctn 3A基因片段大小相同。荧光显微镜观察到绿色荧光信号定位于细胞核内,免疫细胞化学结果显示表达的p120ctn 3A定位于A549细胞核。Western blot结果显示转染pCMV/p120ctn 3A的A549细胞p120ctn 3A蛋白表达量显著上调。结论：成功构建了p120ctn 3A细胞核定向表达载体pCMV/p120ctn 3A。     

黏附调节因子p120ctn3A细胞核靶向表达质粒的构建及鉴定

目的 既往少数研究表明p120ctn存在核浆穿梭现象,为研究细胞核内p120ctn的功能,我们试图构建p120ctn 3A细胞核定向表达载体pCMV/p120ctn 3A.方法 采用PCR方法扩增人p120ctn 3A活性片段,将其插入细胞核定向表达载体pCMV/myc/nuc,构建重组体pCMV/p120ctn 3A,经脂质体介导转染肺癌细胞A549,用荧光显微镜观察绿色荧光信号,免疫细胞化学及Western blot鉴定其在肺癌细胞A549中的表达与定位.结果 限制性双酶切及DNA测序分析结果显示插入pCMV/p120ctn 3A的片段为2496bp左右,与预期p120ctn 3A基因片段大小相同.荧光显微镜观察到绿色荧光信号定位于细胞核内,免疫细胞化学结果显示表达的p120ctn 3A定位于A549细胞核.Western blot结果显示转染pCMV/p120ctn 3A的A549细胞p120ctn 3A蛋白表达量显著上调.结论 成功构建了p120ctn 3A 细胞核定向表达载体pCMV/p120ctn 3A.     

Isolation and characterization of a complementary DNA clone for a Mr 32,000 protein which is induced with tumor promoters in BALB/c 3T3 cells

The synthesis of a protein of Mr 32,000 (p32) is enhanced by various tumor promoters, chemical carcinogens, metal salts, and heat shock in BALB/c 3T3 cells. We have isolated a complementary DNA (cDNA) clone for p32 from a lambda gt10 library of BALB/c 3T3 cells. The library was constructed from mRNA extracted from the cells treated with sodium arsenite, which stimulates the p32 expression most effectively among various agents so far tested. Having screened this library differentially with probes which represent induced and uninduced mRNA populations for p32, we first obtained a partial p32 cDNA clone and have subsequently succeeded in the isolation of a cDNA clone containing the entire coding sequence. RNA blot analysis has shown that p32 mRNA is induced as early as 0.5 h after the addition of 12-O-tetradecanoyl-phorbol-13-acetate or sodium arsenite. Computer-assisted comparison with GenBank data has revealed a striking similarity in the nucleotide sequences between cDNAs of p32 and rat heme oxygenase. These results strongly suggest that p32 is a mouse homolog of this enzyme.     

Substrate specificity of the p53-associated 3'-5' exonuclease

p53 exhibits 3'-5' exonuclease activity and the significance of this biochemical function is currently not defined. In order to gain information about the potential role(s) of this exonuclease activity, recombinant and wild-type human p53 was examined for excision of nucleotides from defined synthetic DNA substrates. p53 removes nucleotides threefold faster from single-strand DNA than from DNA duplexes, exhibits a 1.5-fold preference for 3'-terminals of DNA that contain a single nucleotide mispair (mismatch) as compared to correctly paired DNA and efficiently excises nucleotides from 3'-ends of blunt and cohesive (staggered) DNA double-strand breaks. The p53 exonuclease is predominantly non-processive on DNA which is 17 nucleotides long (or shorter) and processive on the longer 30-mers. The processivity of nucleotide excision is decreased in the presence of 50 mM potassium phosphate and eliminated when full-length p53 is replaced with the core domain, comprised of amino acids 82-292. Photoaffinity labeling indicates that (1) p53 monomers, rather than dimers, bind to single-strand forms of these oligomers; (2) complexes between p53 and 30-mers are more stable than those formed with 17-mers. The stability of these complexes determines processivity during nucleotide removal and modulates the 3'-5' exonuclease activity of p53. The relevance of substrate specificity of the p53 exonuclease to DNA repair is discussed.