Janet S. Butel

Bio: Janet S. Butel is an academic researcher from Baylor College of Medicine. The author has contributed to research in topics: Virus & Cell culture. The author has an hindex of 54, co-authored 234 publications receiving 15711 citations.

Mice deficient for p53 are developmentally normal but susceptible to spontaneous tumours

Abstract: Mutations in the p53 tumour-suppressor gene are the most frequently observed genetic lesions in human cancers. To investigate the role of the p53 gene in mammalian development and tumorigenesis, a null mutation was introduced into the gene by homologous recombination in murine embryonic stem cells. Mice homozygous for the null allele appear normal but are prone to the spontaneous development of a variety of neoplasms by 6 months of age. These observations indicate that a normal p53 gene is dispensable for embryonic development, that its absence predisposes the animal to neoplastic disease, and that an oncogenic mutant form of p53 is not obligatory for the genesis of many types of tumours.

Spontaneous and carcinogen−induced tumorigenesis in p53−deficient mice

Abstract: Using gene targeting techniques, mice that have been generated with two germ–line p53 null alleles (homozygotes) develop normally but are highly susceptible to early onset spontaneous tumours. Here, we show that mice with a single null p53 allele (heterozygotes) produced in the same way are also susceptible to spontaneous tumours, but with a delayed onset compared to homozygotes. The most frequent tumour type in homozygotes was malignant lymphoma; in heterozygotes, osteosarcomas and soft tissue sarcomas predominated. Heterozygous mice treated with a liver carcinogen, dimethylnitrosamine, showed a decreased survival time in comparison to treated wild type mice, suggesting that the p53–deficient mice may be useful for some in vivo carcinogenesis assays.

DNA sequences similar to those of simian virus 40 in ependymomas and choroid plexus tumors of childhood.

Abstract: Background. Ependymomas and papillomas of the choroid plexus occur in early childhood. The ubiquitous human polyomaviruses, BK virus and JC virus, have been associated with the induction of these neoplasms in animal models. A related monkey polyomavirus, simian virus 40 (SV40), is highly tumorigenic in rodents and also induces choroid plexus papillomas. Methods. We tested the possibility that polyomaviruses were associated with these tumors in humans. Tumors from 31 children — 20 with choroid plexus neoplasms and 11 with ependymomas — were evaluated for the presence of polyomavirus T-antigen gene sequences by means of amplification with the polymerase chain reaction. Results. Ten of the 20 choroid plexus tumors and 10 of the 11 ependymomas contained amplification products that preferentially hybridized to probes specific for SV40 viral DNA rather than BK or JC viral DNA. In two specimens, DNA sequencing demonstrated that the amplified sequence was identical to the sequence of that region of the S...

Cell and Molecular Biology of Simian Virus 40: Implications for Human Infections and Disease

Abstract: Simian virus 40 (SV40), a polyomavirus of rhesus macaque origin, was discovered in 1960 as a contaminant of polio vaccines that were distributed to millions of people from 1955 through early 1963. SV40 is a potent DNA tumor virus that induces tumors in rodents and transforms many types of cells in culture, including those of human origin. This virus has been a favored laboratory model for mechanistic studies of molecular processes in eukaryotic cells and of cellular transformation. The viral replication protein, named large T antigen (T-ag), is also the viral oncoprotein. There is a single serotype of SV40, but multiple strains of virus exist that are distinguishable by nucleotide differences in the regulatory region of the viral genome and in the part of the T-ag gene that encodes the protein's carboxyl terminus. Natural infections in monkeys by SV40 are usually benign but may become pathogenic in immunocompromised animals, and multiple tissues can be infected. SV40 can replicate in certain types of simian and human cells. SV40-neutralizing antibodies have been detected in individuals not exposed to contaminated polio vaccines. SV40 DNA has been identified in some normal human tissues, and there are accumulating reports of detection of SV40 DNA and/or T-ag in a variety of human tumors. This review presents aspects of replication and cell transformation by SV40 and considers their implications for human infections and disease pathogenesis by the virus. Critical assessment of virologic and epidemiologic data suggests a probable causative role for SV40 in certain human cancers, but additional studies are necessary to prove etiology.

Cancer Cell Cycles

Abstract: Uncontrolled cell proliferation is the hallmark of cancer, and tumor cells have typically acquired damage to genes that directly regulate their cell cycles. Genetic alterations affecting p16(INK4a) and cyclin D1, proteins that govern phosphorylation of the retinoblastoma protein (RB) and control exit from the G1 phase of the cell cycle, are so frequent in human cancers that inactivation of this pathway may well be necessary for tumor development. Like the tumor suppressor protein p53, components of this "RB pathway," although not essential for the cell cycle per se, may participate in checkpoint functions that regulate homeostatic tissue renewal throughout life.

Lipofection: a highly efficient, lipid-mediated DNA-transfection procedure

Abstract: A DNA-transfection protocol has been developed that makes use of a synthetic cationic lipid, N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA). Small unilamellar liposomes containing DOTMA interact spontaneously with DNA to form lipid-DNA complexes with 100% entrapment of the DNA, DOTMA facilitates fusion of the complex with the plasma membrane of tissue culture cells, resulting in both uptake and expression of the DNA. The technique is simple, highly reproducible, and effective for both transient and stable expression of transfected DNA. Depending upon the cell line, lipofection is from 5- to greater than 100-fold more effective than either the calcium phosphate or the DEAE-dextran transfection technique.