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Biomedical subjects

H Varmus

Publications and source records attributed to H Varmus.

At least 19 recordsLinked to original sources
PubMed1989

Transgenic mice and host cell mutants resistant to transformation as model systems for identifying multiple components in oncogenesis.

Tumorigenesis appears to be a multistep process involving mutations of conventional, dominantly acting proto-oncogenes, mutations of other genes that may act in a recessive manner, and interactions (or a lack of interactions) between the products of mutant and wild-type genes. Our laboratory is using a few well-established, dominant oncogenes to pose experimental questions that could lead to a better understanding of the more elusive genetic interactions which occur during tumour development. Two such situations are described: (1) We have created a line of transgenic mice that carry the int-1 proto-oncogene under the control of the enhancer element in the mouse mammary tumour virus long terminal repeat. Such mice express the transgene in mammary glands, salivary glands and male reproductive tract; mammary glands from both male and female animals are grossly hyperplastic, yet tumours arise rarely in the males and sporadically in the females (80% of female mice have one or a few tumours by six months of age). Thus expression of int-1 in these mice appears to place a large number of mammary cells at risk for secondary events that lead to carcinogenesis, providing a provocative experimental context for identifying such secondary events. (2) We have isolated a rat cell line that lacks most of the characteristics of transformed cells, despite the expression of two wild-type copies of the v-src gene of Rous sarcoma virus. This line harbours what appears to be a dominant mutation in an unidentified gene that renders the cell resistant to transformation by v-src and several other oncogenes. Isolation of the mutant gene responsible for suppressing transformation in this line should provide new insights into the interactions between oncoproteins and other cellular proteins.

Animals↗
PubMed1989

Detection of antibodies against hepatitis B virus polymerase antigen in hepatitis B virus-infected patients.

By the use of a truncated recombinant hepatitis B virus polymerase antigen, we have characterized a series of patient sera for anti-hepatitis B virus polymerase antibodies. Seven of 54 (13%) had antipolymerase antibodies detectable by Western blot analysis, and no close correlation was apparent between the disease status and patient's immune response against hepatitis B virus polymerase antigen. Our results indicate that serologic responses to the viral polymerase are demonstrable but suggest that such antibodies are not likely to be clinically useful as diagnostic or prognostic markers of infection.

Blotting, Western↗
PubMed1989

Identification of genes from pattern formation, tyrosine kinase, and potassium channel families by DNA amplification.

The study of gene family members has been aided by the isolation of related genes on the basis of DNA homology. We have adapted the polymerase chain reaction to screen animal genomes very rapidly and reliably for likely gene family members. Using conserved amino acid sequences to design degenerate oligonucleotide primers, we have shown that the genome of the nematode Caenorhabditis elegans contains sequences homologous to many Drosophila genes involved in pattern formation, including the segment polarity gene wingless (vertebrate int-1), and homeobox sequences characteristic of the Antennapedia, engrailed, and paired families. In addition, we have used this method to show that C. elegans contains at least five different sequences homologous to genes in the tyrosine kinase family. Lastly, we have isolated six potassium channel sequences from humans, a result that validates the utility of the method with large genomes and suggests that human potassium channel gene diversity may be extensive.

Amino Acid Sequence↗
PubMed1989

Function, location, and regulation of the src protein-tyrosine kinase.

The physiological roles, precise locations, and relevant targets of the 60 kD protein-tyrosine kinase encoded by viral and cellular src genes p60src are not known, despite intensive study. We describe recent work that bears upon these unresolved problems: (i) p60c-src is phosphorylated during mitosis on threonine and serine residues by the protein kinase encoded by the mammalian homologue of cdc2, suggesting that c-src may contribute to the phenotype of mitotic cells; (ii) multiple regions in the amino-terminal portion of p60src are required for its proper intracellular localization--a short signal for myristylation and signals for association with cytoplasmic granules and with perinuclear and plasma membranes; and (iii) regions (called SH3 and SH2) upstream of the kinase domain modulate the behavior of p60src in complex ways, with some mutations in SH2 rendering p60 host-dependent for transformation. The latter mutants may prove to be powerful tools for identifying proteins that modify or serve as targets for src-encoded protein-tyrosine kinases.

Amino Acid Sequence↗
PubMed1988

Retroviruses.

First brought to scientific attention as infectious cancer-causing agents nearly 80 years ago, retroviruses are popular in contemporary biology for many reasons. (i) The virus life cycle includes several events--in particular, reverse transcription of the viral RNA genome into DNA, orderly integration of viral DNA into host chromosomes, and utilization of host mechanisms for gene expression in response to viral signals--which are broadly informative about eukaryotic cells and viruses. (ii) Retroviral oncogenesis usually depends on transduction or insertional activation of cellular genes, and isolation of those genes has provided the scientific community with many of the molecular components now implicated in the control of normal growth and in human cancer. (iii) Retroviruses include many important veterinary pathogens and two recently discovered human pathogens, the causative agents of the acquired immunodeficiency syndrome (AIDS) and adult T cell leukemia/lymphoma. (iv) Retroviruses are genetic vectors in nature and can be modified to serve as genetic vectors for both experimental and therapeutic purposes. (v) Insertion of retroviral DNA into host chromosomes can be used to mark cell lineages and to make developmental mutants. Progress in these and other areas of retrovirus-related biology has been enormous during the past two decades, but many practical and theoretical problems remain to be solved.

Animals↗
PubMed1987

Definition of regions in human c-myc that are involved in transformation and nuclear localization.

To study the relationship between the primary structure of the c-myc protein and some of its functional properties, we made in-frame insertion and deletion mutants of the normal human c-myc coding domain that was expressed from a retroviral promoter-enhancer. We assessed the effects of these mutations on the ability of c-myc protein to cotransform normal rat embryo cells with a mutant ras gene, induce foci in a Rat-1-derived cell line (Rat-1a), and localize in nuclei. Using the cotransformation assay, we found two regions of the protein (amino acids 105 to 143 and 321 to 439) where integrity was critical: one region (amino acids 1 to 104) that tolerated insertion and small deletion mutations, but not large deletions, and another region (amino acids 144) to 320) that was largely dispensable. Comparison with regions that were important for transformation of Rat-1a cells revealed that some are essential for both activities, but others are important for only one or the other, suggesting that the two assays require different properties of the c-myc protein. Deletion of each of three regions of the c-myc protein (amino acids 106 to 143, 320 to 368, and 370 to 412) resulted in partial cytoplasmic localization, as determined by immunofluorescence or immunoprecipitation following subcellular fractionation. Some abnormally located proteins retained transforming activity; most proteins lacking transforming activity appeared to be normally located.

Animals↗
PubMed1987

Identification of a human gene (HCK) that encodes a protein-tyrosine kinase and is expressed in hemopoietic cells.

We have isolated cDNAs representing a previously unrecognized human gene that apparently encodes a protein-tyrosine kinase. We have designated the gene as HCK (hemopoietic cell kinase) because its expression is prominent in the lymphoid and myeloid lineages of hemopoiesis. Expression in granulocytic and monocytic leukemia cells increases after the cells have been induced to differentiate. The 57-kilodalton protein encoded by HCK resembles the product of the proto-oncogene c-src and is therefore likely to be a peripheral membrane protein. HCK is located on human chromosome 20 at bands q11-12, a region that is affected by interstitial deletions in some acute myeloid leukemias and myeloproliferative disorders. Our findings add to the diversity of protein-tyrosine kinases that may serve specialized functions in hemopoietic cells, and they raise the possibility that damage to HCK may contribute to the pathogenesis of some human leukemias.

Amino Acid Sequence↗
PubMed1986

Rearrangement at the 5' end of amplified c-myc in human COLO 320 cells is associated with abnormal transcription.

The proto-oncogene c-myc is amplified in sublines of human COLO 320 cells carrying either homogeneously staining chromosomal regions or double minutes. COLO 320 cells carrying homogeneously staining chromosomal regions have 15 to 20 copies of an apparently normal c-myc allele and 1 to 2 copies of an abnormal c-myc allele lacking exon 1 and express high levels of a normal c-myc mRNA 2.5 kilobases in size. COLO 320 cells carrying double minutes have about 25 copies each of the normal allele and the abnormal allele but express preferentially an abnormal c-myc mRNA 2.2 kilobases in size. Nucleotide sequence analyses revealed that the break point of rearrangement resulting in the loss of exon 1 in the abnormal allele lies within a region frequently rearranged in human and murine B-cell tumors.

Alleles↗
PubMed1986

The int-1 proto-oncogene.

The int-1 proto-oncogene is the first cellular gene discovered and implicated in tumorigenesis solely on the basis of repeated insertional mutations that activate transcription of the gene. The gene is silent in most tissues but expressed in the embryonic central nervous system, in the late (post-meiotic) stages of spermatogenesis, and in a high proportion of mouse mammary tumor virus-induced carcinomas, when a provirus is inserted upstream or downstream of the coding domain. The functional significance of int-1 in the oncogenic process is supported by the demonstration that murine leukemia virus-based vectors carrying the gene can alter the morphology and growth properties of an established line of mammary epithelial cells. The predicted primary protein product of the int-1 gene is 370 amino acids in length and cysteine-rich; immunoprecipitation with anti-peptide antibodies reveals multiple species of int-1 protein, due to asparagine-linked glycosylations and probable cleavage of a signal peptide. However, the active product of the gene and its biochemical behavior during normal development and mammary tumorigenesis are not known.

Animals↗
PubMed1985

Mapping the major transcripts of ground squirrel hepatitis virus: the presumptive template for reverse transcriptase is terminally redundant.

The ground squirrel hepatitis virus (GSHV) belongs to a recently defined class of viruses with open circular DNA genomes that encode proteins in extensively overlapping reading frames and appear to replicate via RNA intermediates. We have determined the primary structure of the major GSHV transcripts in the livers of infected ground squirrels. Both major classes of transcripts, 2.3 kb and 3.5 kb, are plus-stranded, unspliced, polyadenylated at a common position, and display heterogeneous 5' ends that can encode proteins with different amino termini. The 2.3 kb transcripts, like their structural analogs transcribed from human hepatitis B virus DNA, are likely mRNAs for products of the major surface antigen and presurface coding domains. The 3.5 kb transcripts are likely mRNAs for one or more products of the core antigen reading frame; these transcripts also encompass the entire genome and contain terminal redundancies of 130-160 nucleotides that include a putative initiation site for reverse transcription.

Animals↗