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J M Croop

Publications and source records attributed to J M Croop.

29 records · Page 2Linked to original sources
PubMed1989

P-glycoproteins encoded by mdr 1b in murine gravid uterus and multidrug resistant tumor cell lines are differentially glycosylated.

There are 3 members of the multidrug-resistance gene family expressed in mouse. Only one of these, mdr 1b, and its gene product P-glycoprotein are induced to high levels in the mouse endometrium during pregnancy. It is shown here that P-glycoprotein in the gravid uterus is significantly larger (Mr 155,000) compared to P-glycoprotein encoded by mdr 1b in a murine multidrug-resistant cell line (Mr 140,000). However, both species co-migrate after enzymatic removal of N-linked sugars (Mr 125,000). These results demonstrate that differential glycosylation of the mdr 1b gene product contributes to molecular heterogeneity found in P-glycoprotein from normal and multidrug-resistant cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

The three mouse multidrug resistance (mdr) genes are expressed in a tissue-specific manner in normal mouse tissues.

The gene responsible for multidrug resistance (mdr), which encodes the P-glycoprotein, is a member of a multigene family. We have identified distinct mdr gene transcripts encoded by three separate mdr genes in the mouse. Expression levels of each mdr gene are dramatically different in various mouse tissues. Specific mdr RNA transcripts of approximately 4.5, 5, and 6 kilobases have been detected. Each of the mdr genes has a specific RNA transcript pattern. These results should be considered in relation to understanding the normal physiological function of the mdr multigene family.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1988

The gene encoding multidrug resistance is induced and expressed at high levels during pregnancy in the secretory epithelium of the uterus.

A survey of the expression of the multidrug-resistance gene (mdr) in mouse tissues revealed that a mdr mRNA species is expressed at extremely high levels in the gravid uterus. mdr mRNA expression levels increase dramatically during pregnancy compared to the relatively low levels of expression observed in the nongravid uterus. In situ hybridization experiments revealed that the increased expression of the mdr mRNA is specifically localized to the secretory epithelial cells of the endometrium. Immunocytochemistry studies with a mdr glycoprotein-specific antiserum demonstrate that the mdr glycoprotein is predominantly localized to the luminal surface of the secretory epithelial cells. These results indicate that the mdr gene expression in the uterus is controlled by the physiologic changes associated with pregnancy. Our data are consistent with a potential role for the mdr glycoprotein in the transport of substrate across the secretory epithelium of the gravid uterus.

Animals↗
PubMed1987

Genetics of multidrug resistance: relationship of a cloned gene to the complete multidrug resistant phenotype.

Resistance to multiple chemotherapeutic agents remains the major cause of failure in cancer chemotherapy. Multidrug resistant cell lines developed in vitro have provided a useful model for analyzing this phenomenon. We describe a complementary DNA, lambda DR11, which is present in normal cells and overexpressed in multidrug resistant cell lines. We have placed this complementary DNA in an expression vector which uses the beta-actin promoter to drive transcription and introduced this vector via transfection into drug sensitive cells. Cells expressing increased levels of lambda DR11 are resistant to the same broad spectrum of chemotherapeutic agents which characterize the multidrug resistant phenotype. The expression of this complementary DNA in transfected clones is dependent upon the number of copies of lambda DR11 integrated in the genome as well as the amount of selective pressure placed on the clone during selection of the clone. Furthermore, the number of copies of lambda DR11 in the genome and the expression of lambda DR11 can be modulated by releasing an individual clone from selective pressure or by increasing the selective pressure on the clone. The endogenous sequences encoding the multidrug resistance gene are not amplified in transfected drug resistant clones. Finally, the drug resistant phenotype is reversed in the transfected clones by verapamil just as drug resistance is reversed in multidrug resistant cell lines.

Animals↗
PubMed1986

Chromosome-mediated gene transfer of multidrug resistance.

Multidrug resistance can be transferred from drug-resistant LZ Chinese hamster cells to drug-susceptible mouse LTA cells by chromosome-mediated gene transfer. Analysis of genomic DNA demonstrated the transfer of multiple copies of a DNA domain which is amplified in the donor multidrug-resistant cells. The transfer of 10 to 15 copies of the Chinese hamster gene was sufficient to produce a multidrug-resistant phenotype. Chromosome transferents exhibited overexpression of an mRNA of approximately 5 kilobases which has previously been demonstrated to be encoded by the amplified DNA domain of the donor LZ cells. Phenotypic analysis of individual clones selected in adriamycin showed the resistance to be pleiotropic. All clones tested demonstrated similar levels of cross-resistance to the drugs daunorubicin and colchicine. These results indicate that the DNA sequences transferred confer the complete multidrug-resistant phenotype on recipient cells and suggest that multidrug resistance is due to overexpression of the protein encoded by the 5-kilobase mRNA.

Animals↗
PubMed1978

Differences among 100-A filamentilament subunits from different cell types.

The protein subunit of 100-A filaments constitutes approximately 50% of the cytoskeleton protein of chick fibroblasts. In addition to the 43,000-dalton protein (constitutive actin) common to all cell types, fibroblast cytoskeletons contain a 58,000-dalton protein likely to be the 100-A filament subunit, whereas smooth muscle contains, instead, a 55,000-dalton protein. Additional differences among 100-A filaments are shown by immunofluorescence using antibodies angainst chick fibroblast 58,000-dalton component (anti-F58K) and against chick brain 100-A filament subunits (anti-BF). Anti-F58K binds to 100-A filaments in chick fibroblasts, presumptive myoblasts, chondroblasts, pigment cells, and neurons, but not to 100-A filaments in mouse or human fibroblasts. This antibody stains cables of 100-A filaments induced by sequentially treating cells with cytochalasin B and Colcemid. Anti-BF binds only to neurofilaments and not to 100-A filaments of other cell types studied. Absorption or antibodies with purified subunits from gizzard 100-A filaments eliminates binding of anti-F58K to the filaments of all cell types but does not diminish binding of anti-BF to neurofilaments. Various IgGs also bind nonspecifically to induced cables of 100-A filaments. The problem of nonspecific binding of labeled antibodies, as well as the problem of cell and species specificity of the 100-A filaments, is discussed.

Actins↗
PubMedDate not supplied

Isolation and expression of a complementary DNA that confers multidrug resistance.

The emergence and outgrowth of a population of tumour cells resistant to multiple drugs is a major problem in the chemotherapeutic treatment of cancer. We have used highly drug-resistant cell lines developed in vitro to study the molecular basis of multidrug resistance. In these cell lines high levels of resistance are frequently associated with amplification and overexpression of a small group of genes termed mdr or gp170. Direct evaluation of the role of these genes in multidrug resistance has awaited the isolation of a member of this gene family in a biologically active form. Here we report the isolation of DNA clones complementary to the cellular messenger RNA transcripts of mdr genes and show that high-level expression of a full-length complementary DNA clone in an otherwise drug-sensitive cell confers a complete multidrug-resistant phenotype. Our results demonstrate that overexpression of a single member of the mdr group is sufficient to confer drug resistance. Furthermore, because the cDNA was isolated from a drug-sensitive cell, mutations in the primary sequence of mdr are not required to produce a multidrug-resistance phenotype.

Animals↗
PubMedDate not supplied

Gene therapy with B7.1 and GM-CSF vaccines in a murine AML model.

PURPOSE: Characterization of B7.1 and GM-CSF vaccines on the induction of anti-tumor immunity in a murine AML model. MATERIALS AND METHODS: Primary AML cells were retrovirally transduced with the murine costimulatory molecule B7.1, a natural ligand for the T-cell receptors CD28 and CTLA-4, or the cytokine GM-CSF. Mice were vaccinated with irradiated AML cells expressing B7.1 or GM-CSF before or after inoculation of wild type AML cells. RESULTS: Intravenous injection of irradiated B7.1 or GM-CSF expressing AML cells can provide long lasting systemic immunity against a subsequent challenge of wild type AML cells. Vaccination with irradiated B7.1 or GM-CSF expressing AML cells results in rejection of established leukemia when the vaccination occurs in the early stages of the disease. However, when the vaccines are administered > 2 weeks after leukemic inoculation, only mice which receive the GM-CSF vaccine are cured of leukemia. CONCLUSIONS: These results suggest that tumor burden and vaccine efficiency are most likely to be the limiting factors in the curative potential of tumor vaccines. Novel approaches such as this experiment could provide improved therapeutic outcomes in patients with AML and other cancers.

Animals↗