Polypeptide composition and an immunological analysis of DNA methyltransferases from different species.

The cross-reactivity of the monoclonal anti-human placental DNA methyltransferase antibody M2B10 with DNA methyltransferases isolated from other species was investigated. This antibody immunoprecipitates DNA methyltransferases from mammalian cells, i.e., human placenta, mouse P815 cells, and rat liver cells. No cross-reactivity is observed with DNA methyltransferases from wheat germ and with bacterial DNA methyltransferases HpaII and EcoRI. The mammalian enzymes are characterized by polypeptides of molecular mass 150-190 kDa. Polypeptides smaller than 190 kDa are presumably generated by proteolysis of the native 190-kDa DNA methyltransferase. Trypsin digestion of the 190-kDa polypeptide isolated from mouse cells results in progressive appearance of DNA methyltransferase polypeptides of 150-190, 110, 100, and 52-60 kDa.

A rapid method for the determination of human CEA/mouse anti-CEA immune complexes in patients undergoing immunoscintigraphy.

We report here on a new and quick procedure to isolate human (hu) CEA mouse anti CEA immune complexes of sera from patients admitted for immunoscintigraphy with radiolabeled monoclonal anti CEA antibody. This method employs rabbit anti mouse IgG immune affinity chromatography together with a commercial CEA-IRMA kit for the specific isolation of immune complexes. By applying this procedure we were able to show that immune complex formation increased in parallel to CEA serum concentration. The formation of immune complexes did not significantly affect tumor detection by immunoscintigraphy.

Proliferation-associated expression of DNA methyltransferase in human embryonic lung cells.

The cell cycle-dependent and proliferation-associated expression of the enzyme DNA methyltransferase has been evaluated immunocytochemically in synchronized L-132 human embryonic lung cells, using the anti-DNA methyltransferase monoclonal antibody M1F6D7/5C10. DNA methyltransferase-reactivity was firstly seen in mid-G1 cells. An intense and granular reaction in the cell nuclei with a sparing of the nucleoli was observed in addition to a homogenous and faint cytoplasmic staining. The staining intensity in the cell nuclei increased progressively up to mitosis. In early mitotic cells an intense perichromosomal staining was observed in addition to a homogenous staining of cyto- and karyoplasm after the resolving of the core membrane. In late mitosis the staining intensity decreased rapidly. Early G1 cells and density inhibited, resting G0 cells showed no DNA methyltransferase reactivity at all. Our results indicate that anti-DNA methyltransferase monoclonal antibodies could become valuable tools to detect proliferating cells in cell cultures and tissues.

Isolation and characterization of proteins that stimulate the activity of mammalian DNA methyltransferase.

Previously, the purification of DNA methyltransferase from murine P815 mastocytoma cells by immunoaffinity chromatography was described (Pfeifer, G.P., Grünwald, S., Palitti, F., Kaul, S., Boehm, T.L.J., Hirth, H.P. and Drahovsky, D. (1985) J. Biol. Chem. 260, 13787-13793). Proteins that stimulate the enzymatic activity of DNA methyltransferase have been purified from the same cells. These proteins, which partially coelute with DNA methyltransferase from DEAE-cellulose and heparin-agarose, are separated from the enzyme during the immunoaffinity purification step. A further purification of the stimulating proteins was achieved by butanol extraction, DEAE-cellulose chromatography and gel filtration on Superose 12. Two DNA methyltransferase-stimulating protein fractions were obtained. SDS-polyacrylamide gel electrophoresis of one fraction showed a single polypeptide with a molecular mass of 29 kDa. The second fraction consisted of 5 or 6 polypeptides with molecular masses 78-82 and 51-54 kDa. The proteins stimulate both de novo and maintenance activity of DNA methyltransferase about 3-fold. They enhance the methylation of any natural DNA and of poly[(dI-dC).(dI-dC)] but inhibit the methylation of poly[(dG-dC).(dG-dC)]. The purified proteins do not form a tight complex with DNA methyltransferase; however, they bind both to double-stranded and single-stranded DNA. The sequence specificity of DNA methyltransferase is obviously altered in presence of these proteins.

Reduced methyl group acceptance of 1-beta-D-arabinofuranosylcytosine-containing DNA polymers.

Previous studies have shown that 1-beta-D-arabinofuranosylcytosine (ara-C) can induce differentiation of various malignant cells and that DNA methylation patterns become altered under ara-C treatment of those cells. The aim of this study was to investigate whether this influence on DNA methylation is caused by a direct effect of DNA-incorporated ara-C molecules on nuclear DNA methylase. For this reason, we constructed various ara-C-substituted DNA polymers and used them as substrates for highly purified eukaryotic DNA methylase isolated from murine P815 mastocytoma cells. The ara-C incorporation into DNA polymers was measured by either an ara-C-specific radioimmunoassay or by use of radioactive-labelled ara-C during the synthesis of those polymers. We found an inverse correlation between the level of ara-C substitution of the DNA polymers and their methyl group acceptance. Kinetic experiments performed with ara-C-modified DNA polymers pointed out that the mode of action of DNA methylase remains unaltered. DNA methylase is neither detached nor fixed at an ara-C site, but is somehow hindered in its enzymatic activity, probably by slowing down the walking mechanism. Hence, the previously observed hypermethylation of DNA of some eukaryotic cells, propagated in the presence of ara-C, is apparently not due to a direct effect of DNA-incorporated ara-C molecules on endogenous DNA methylase.

Intracellular distribution of DNA methyltransferase during the cell cycle.

The intracellular distribution of DNA methyltransferase has been analyzed in synchronously proliferating human cells. The localization of DNA methyltransferase was determined immunocytochemically using monoclonal antibodies directed against this enzyme. DNA methyltransferase was found to accumulate predominantly in nuclei with weak cytoplasmic staining. The DNA methyltransferase antigen was absent in early G1 phase, appeared in late G1 prior to the onset of DNA synthesis and persisted throughout S and G2 phases of the cell cycle. Mitotic cells showed a particularly strong staining intensity. These results show that DNA methyltransferase levels fluctuate during the cell cycle. This has possible implications on the stability of the DNA methylation pattern.

DNA methylation levels in acute human leukemia.

We have studied the overall 5-methylcytosine content and the percentage of methylated CpG-dinucleotides in 25 cases of untreated human acute leukemias. For comparison, normal leucocyte subpopulations were similarly analyzed. The methylation levels in normal white blood cell DNA varied in the same range as those in leukemia cells with no apparent hypomethylation in tumor cell DNA. Such hypomethylation, however, was found in a patient studied in first and second relapses of the disease. These data suggest that genome-wide demethylation, a characteristic of other tumors, does not accompany leukemic transformation.

Immunocytochemical staining of different cell types in vaginal smears by monoclonal anti-DNA methylase antibodies.

Enzymatic methylation of mammalian DNA is closely related to the replication process; also, the synthesis of DNA methylase, an enzyme that is responsible for this process, is cell cycle related. A monoclonal antibody against DNA methylase recognizes proliferatively active cells in the heterogeneous population. We used this antibody to identify the proliferative state of different cell types in normal vaginal smears and in smears of patients with precancerous lesions and cervical cancer. In all preparations, the normal epithelial cells remained unstained. The majority of cancer cells gave a positive immunocytochemical signal indicating the presence of DNA methylase antigen and the proliferative state. Staining was also observed in dyskaryotic cells, particularly in nuclei of parabasal-type cells.

Inactivation of de novo DNA methyltransferase activity by high concentrations of double-stranded DNA.

The activity of eukaryotic DNA methyltransferase diminishes with time when the enzyme is incubated with high concentrations (200-300 micrograms/ml) of unmethylated double-stranded Micrococcus luteus DNA. Under similar conditions, single-stranded DNA induces only a limited decrease of enzyme activity. The inactivation process is apparently due to a slowly progressive interaction of the enzyme with double-stranded DNA that is independent of the presence of S-adenosyl-L-methionine. The inhibited enzyme cannot be reactivated either by high salt dissociation of the DNA-enzyme complex or by extensive digestion of the DNA. Among synthetic polydeoxyribonucleotides both poly(dG-dC).poly(dG-dC) and poly(dA-dT).poly(dA-dT), but not poly(dI-dC).poly(dI-dC), cause inactivation of DNA methyltransferase. This inactivation process may be of interest in regulating the 'de novo' activity of the enzyme.

A rapid and efficient screening method for DNA restriction fragment length polymorphisms.

Genomic loci displaying DNA sequence polymorphisms represent useful landmarks on the genetic linkage map. We describe an integrated experimental approach to facilitate the detection of DNA restriction fragment length polymorphisms (RFLP) with useful allelic frequencies at loci covered by cloned DNA sequences. The essential feature of the screening method presented is the pooling of DNA from unrelated individuals for Southern blot hybridization analyses using non-repetitive DNA sequences identified in and preparatively isolated from genomic lambda phage clones. This procedure results in the detection of RFLP with maximal values of heterozygosity while counterselecting for RFLP with unfavourable allelic frequencies. The described experimental protocol should therefore facilitate the identification and characterization of polymorphic loci with frequent heterozygosity.

T cell receptor gamma chain variable gene rearrangements in acute lymphoblastic leukemias of T and B lineage.

The status of immunoglobulin and T cell receptor genes in acute lymphoblastic leukemia (ALL) of T and B lineage has been studied. Our data indicate that illegitimate gene rearrangements at immunoglobulin heavy chain (in T cell ALL), and T cell receptor beta chain (in pre-B ALL) genes are only rarely found (2 out of 30 patients). In contrast, T cell receptor gamma chain gene rearrangements, characteristically found in T-ALL, are also present in 7 of 18 patients with pre-B ALL. Several features distinguish these illegitimate T cell receptor gamma chain gene rearrangements from those in normal and leukemic T cells. V gamma genes located far upstream of the J gamma/C gamma complexes (V gamma 2, V gamma 3, V gamma 4, V gamma 5) appear to be preferentially used in normal adult peripheral blood T cells. In contrast, V gamma genes located immediately 5' to the J gamma/C gamma complexes (V gamma 8, V gamma 9, V gamma 10, V gamma 11) predominate in V gamma -J gamma recombinations observed in T-ALL and pre-B ALL. Whereas the J gamma 2 region is primarily used in T cell receptor gamma gene rearrangements observed in T-ALL, those in pre-B ALL are confined mostly to the J gamma 1 region. These data suggest a limited accessibility of the T cell receptor gamma chain gene locus for recombination processes in early stages of B cell differentiation.

In vitro differentiation of a null-acute leukemia: T-lymphoid surface antigen expression associated with rearrangement in T-cell receptor beta chain variable genes.

We describe a human acute unclassified leukemia with a unique t(4;17) translocation that coexpresses T-lymphoid and myeloid surface antigens after in vitro culture in the presence of the tumor promoter, TPA. Under these conditions, the joining regions of the immunoglobulin heavy chain and T-cell receptor gamma and beta chain complexes remained in germ line configuration. A T-cell receptor beta chain variable gene probe, however, revealed the presence of rearrangements in the V beta M3-2 gene region after bilineage differentiation. These results may be pertinent to the interrelationship of T-cell receptor gene rearrangements and the control of T-cell antigen surface expression.

Oncogene amplifications, rearrangements, and restriction fragment length polymorphisms in human leukaemia.

We have determined the prevalence of amplification and rearrangements for c-myc, c-myb, c-mos, bcr, c-abl, c-Ha-ras-1, c-N-ras, and c-K-ras-2 in a total of 51 cases of human leukaemia (19 patients with AML, 13 cases with CML, 14 cases with ALL, and 5 cases with CLL). Amplifications at a level of more than 2 two copies per haploid genome are apparently very rare and were found only once for c-myb in a c-ALL patient. Oncogene rearrangements were not found except for bcr, which was rearranged in all cases of CML, and 5 cases of ALL studied. Restriction fragment lengths polymorphisms (RFLPs) were also analysed. A previously described rare 5 kb EcoRI allele at the c-mos locus was absent in our patients. Rare alleles at the c-Ha-ras-1 locus were found to be significantly more prevalent in our patients than in a control group. Transfection experiments revealed no dominant transforming oncogenes in the tumour DNA of 3 patients carrying such rare alleles.

Immunoglobulin heavy chain and T-cell receptor gamma and beta chain gene rearrangements in acute myeloid leukemias.

Somatic rearrangements of immunoglobulin (Ig) and T-cell receptor (TCR) genes are the basis for the production of receptors for antigen in B-cells and T-cells, respectively. Here, we have studied the extent and pattern of rearrangements at Ig and TCR loci in 17 patients presenting with acute myeloid leukemia (AML). Our data demonstrate illegitimate clonal rearrangements at Ig heavy and/or TCR beta chain genes in 5 of 17 AML patients. In four of these five patients, rearrangements at the TCR beta chain gene locus were also observed. Seven patients displayed clonal TCR gamma chain gene rearrangements as the only abnormality. Rearrangements at Ig light chain and TCR alpha chain gene loci were not detected. Illegitimate TCR gamma chain gene rearrangements in AML involve recombinations of only a subset of V gamma genes, predominantly with the J gamma 1 region. Rearrangements at the TCR beta chain gene locus are characterized by both D-J and V-D-J recombinations, with predominant use of the J beta 1 region. The absence or presence of illegitimate antigen receptor gene rearrangements in AML may constitute a prognostic marker. In addition, these alterations can be used to establish clonality in AML with direct applications in the monitoring of disease. Finally, the present data relate to the problem of lineage assignment of acute leukemias based on Ig and TCR gene rearrangements and strongly suggest that the latter cannot be regarded as unequivocal evidence for the B-cell or T-cell lineage, respectively.

[New possibilities of heterozygote detection of hemophilia A]. / Neue Möglichkeiten in der Konduktorinnendiagnostik der Hämophilie A.

Hemophilia A is the most common inherited bleeding disorder in man. The recent isolation of the hemophilia gene has led to the identification of an intragenic restriction fragment length polymorphism (RFLP) which can be used for segregation analysis in families at risk for carrying the disease. In addition, a tightly linked extragenic RFLP can also be used for these analyses. In this paper, we exemplify the usefulness of DNA analysis in genetic counseling of families at risk for hemophilia A. Although DNA analysis allows carrier detection in the majority of families, bioassays are still required for accurate diagnosis when DNA analysis is not informative.

Application of a bcr-specific probe in the classification of human leukaemia.

A genomic probe derived from the breakpoint cluster region (bcr) on chromosome 22q11 was used to assess whether Philadelphia (Ph) chromosome positive chronic myelogenous leukaemia patients have unique patterns of bcr rearrangements and whether this pattern is modified as the disease progresses from stable phase to blast crisis. The data indicated that bcr rearrangements are fairly unique to each patient and are not subject to additional modifications during the course of the disease. We have also found bcr rearrangements in acute lymphocytic leukaemia (ALL) patients, usually of the cALL phenotype. For the majority of Ph+ ALL patients, the breakpoint on 22q11 was in bcr. However, we describe a case of Ph+ ALL without bcr rearrangement, indicating heterogeneity of Ph chromosomes in ALL at the molecular level. Contrary to previous reports, a bcr rearrangement was also identified in a childhood cALL.

DNA methyltransferase polypeptides in mouse and human cells.

DNA methyltransferase was isolated as a single polypeptide of 190 kDa from mouse P815 mastocytoma cells by immunoaffinity chromatography. This polypeptide seems to be highly susceptible to proteolytic degradation resulting in additional polypeptides in the size range of 150 to 190 kDa. A polypeptide of 190 kDa was immunoprecipitated by monoclonal anti-DNA methyltransferase antibodies from extracts of two different human cell lines, Raji and K562. The 190 kDa polypeptide was synthesized in rapidly proliferating cells and, albeit at a much lower rate, also in cells grown to saturating density. DNA methyltransferase polypeptides smaller than 190 kDa were synthesized neither in log phase nor in stationary phase cells.

Use of a biotinylated DNA probe specific for the human Y chromosome for rapid antenatal sex determination.

We have cloned a male-specific 3.4 kb human DNA sequence which showed only little crosshybridisation to autosomal sequences. To further enhance the specificity of the probe, we subcloned an internal TaqI-fragment resulting in clone pH343T33. This clone was used to determine the presence of Y-chromosomal sequences in DNA extracted from amniotic cells and from chorionic villi by Southern and dot hybridisation assays, respectively. Using this clone, we correctly predicted fetal sex in all of 148 cases analysed. To facilitate the use of this clone in clinical practice, we simplified the dot hybridisation procedure so that it can be performed in less than 48 h. The procedure with 32P-labeled DNA probes requires less than 0.5 mL of amniotic fluid; when biotinylated DNA probes are used, 3-5 mL of amniotic fluid usually suffice. We have used this probe in genetic counseling of families at risk for X-linked disorders.

Preferential binding of DNA methyltransferase and increased de novo methylation of deoxyinosine containing DNA.

Mammalian DNA-cytosine 5-methyltransferases methylate cytosines in deoxyinosine containing DNA polymers more rapidly than in other synthetic or naturally occurring DNAs. The initial methylation rate of poly(dI-dC) X poly(dI-dC) is about 10-times higher than that of poly-(dG-dC) X poly(dG-dC) or of the native Micrococcus luteus DNA. In competitive binding experiments, DNA methyltransferase has about 10-fold higher affinity for the dI-containing alternating DNA polymer than for poly(dG-dC) X poly(dG-dC). The observed high methyl accepting capacity of poly(dI-dC) X poly(dI-dC) may be a useful methodological advance to determine de novo DNA methyltransferase activity in extracts of mammalian cells.