Interferon production and action in mouse, hamster and somatic hybrid mouse-hamster cells

A hybrid mouse-hamster cell line was developed from a mouse cell line which produces a high titer of interferon and is sensitive to its action, and a hamster cell line which produces little interferon and is relatively insensitive to its action. Parental cell lines demonstrated complete species specificity with respect to interferon production and action. The hybrid cells produced interferon (or interferons) effective when tested on the mouse cell line and primary hamster cells; the hybrids were sensitive to the action of both mouse and hamster interferons. Hybrid cells produced ten times more hamster interferon than the parent hamster cell line and were eight times more sensitive to hamster interferon than the parent hamster cell line.     

Potentiation of bleomycin lethality by anticalmodulin drugs: a role for calmodulin in DNA repair

Treatment of exponentially growing Chinese hamster ovary cells with bleomycin causes a dose-dependent decrease in cell survival due to DNA damage. This lethal effect can be potentiated by the addition of a nonlethal dose of the anticalmodulin drug N-(4-aminobutyl)-5-chloro-2-naphthalenesulfonamide ( W13 ) but not its inactive analog N-(4-aminobutyl)-2-naphthalenesulfonamide ( W12 ). By preventing the repair of damaged DNA, W13 also inhibits recovery from potentially lethal damage induced by bleomycin. These data suggest a role for calmodulin in the DNA repair pathway.     

Senescence of nickel-transformed cells by an X chromosome: possible epigenetic control

Transfer of a normal Chinese hamster X chromosome (carried in a mouse A9 donor cell line) to a nickel-transformed Chinese hamster cell line with an Xq chromosome deletion resulted in senescense of these previously immortal cells. At early passages of the A9/CX donor cells, the hamster X chromosome was highly active, inducing senescence in 100% of the colonies obtained after its transfer into the nickel-transformed cells. However, senescence was reduced to 50% when Chinese hamster X chromosomes were transferred from later passage A9 cells. Full senescing activity of the intact hamster X chromosome was restored by treatment of the donor mouse cells with 5-azacytidine, which induced demethylation of DNA. These results suggest that a senescence gene or genes, which may be located on the Chinese hamster X chromosome, can be regulated by DNA methylation, and that escape from senescence and possibly loss of tumor suppressor gene activity can occur by epigenetic mechanisms.     

Immunologic manipulation of metastases due to herpesvirus transformed cells

Herpes simplex virus type 1 (HSV-1), type 2 (HSV-2), and simian virus 40 (SV40) fail to induce immunity in weanling Syrian hamsters to transplant of hamster cells transformed by HSV-2. However, the development of metastatic tumors is markedly enhanced by prior immunization with HSV-1. Immunization with SV40, ultraviolet-irradiated tumor cells, or ultraviolet-irradiated normal hamster embryo cells inhibits the development of metastases. The HSV-hamster system appears a good one for the study of development, prevention, and control of metastases by mammalian cells transformed by a common human virus.     

Brown and white fats: development in the hamster

Sites occupied by multilocular brown fat in the adult hamster are occupied by unilocular cells in very young animals. Immature brown fat cells are laid down in the unilocular cell matrix at 3 to 5 days of age. White fat in the hamster does not develop from cells closely resembling mature brown fat.     

Histone synthesis in vitro by cytoplasmic microsomes from HeLa cells

HeLa cell microsomes incorporate labeled amino acids in vitro into acid-soluble proteins which have the same electrophoretic mobility as histones isolated from tile purified HeLa cell nuclei. The capacity to Svnthesize histones in vitro is dependent on deoxyribonucleic acid synthesis in the cells from which the microsonal fraction is prepared.     

Insulin receptor of fat cells in insulin-resistant metabolic states

A diminished response to insulin is exhibited by isolated fat cells obtained from rats that have been either starved, or treated with prednisone, or made diabetic by administration of streptozotocin. This decrease in response is not accompanied by changes in the quantity of insulin receptor of these cells or in the affinity of these receptors for insulin. Similarly, the decreased responsiveness to insulin of fat cells obtained from certain species (hamster, rabbit, mouse, guinea pig) is not explainable in terms of alterations of the insulin receptor.     

Hepatic drug metabolism in rats: impairment in a dirty environment

Reduction of aniline hydroxylase activity, ethylmorphine N-dementhylase activity, and cytochrome P-450 content occurred in hepatic microsomes of rats kept under dirty conditions, defined as accumulation for 1 week of urine and feces in pans under the wire mesh cages. In comparison with rats that had urine and feces removed twice daily from such pans, rats kept over Kimpak bedding or over Litter Green, changed twice daily, also showed reduced drug-metabolizing activity in hepatic microsomes, but to a lesser degree than the dirty rats. Placement of a filter top on cages for 1 week also decreased drug-metabolizing activity. These experiments suggest that the relative cleanliness of an animal's environment can influence hepatic microsomal drug metabolism.     

Temporal coordination of DNA replication with enzyme synthesis in diploid and heteroploid cells

The rate of DNA synthesis in the S phase of growth of synchronized diploid Chinese hamster cells shows two maximums, while in heteroploid hamster cells the DNA replication rate is constant. In diploid cells a reciprocal relationship exists between maximum DNA synthetic rates and maximum lactate dyhydrogenase and thymidine kinase enzyme levels. Enzyme activity in heteroploid cells increases continuously through the cell cycle with no evidence of oscillations. It seems possible that these differences in molecular organization may accompany or precede the transition to heteroploidy.     

Effects of 3-methylcholanthrene and phenobarbital on amino acid incorporation into protein

Treatment of rats with methylcholanthrene and phenobarbital, two compounds known to enhance microsomal enzyme activity, stimulates the incorporation of free or soluble ribonucleic acid bound amino acid into proteins of cell-free liver preparations. Mitochondria, microsomes, and cell sap all contribute to the methylcholanthrene effect on the incorporation of free amino acid.     

Adenovirus tumorigenesis: role of the viral genome in determining tumor morphology

Adenovirus type 12 transforms the fibroblastic BHK21 (baby hamster kidney) cell line into rounded or cuboidal cells that give rise in hamsters to undifferentiated small cell sarcomas indistinguishable from those induced in newborn hamsters by inoculation of the virus itself. In contrast. cells from this line transformed by polyoma virus retain their fibroblastic morphology and induce fibrosarcomas in hamsters. This suggests that the morphology of tumors induced by the adenovirus-transformed cells from this line may be determined by the viral genome and that such mechanism may also explain the remarkably uniform microscopic appearance which seems to characterize tumors induced in hamsters by direct inoculation of adenovirus type 12.     

Carbon tetrachloride poisoning in rats: alteration in ribosomes of the liver

Microsomes from livers of albino rats treated with carbon tetrachloride were compared with those from normal rats with respect to their ability to incorporate amino acid. Acute carbon tetrachloride poisoning results in depressed capacity of microsomes to incorporate amino acid. From ultracentrifugal data, there is an apparent dissociation of 79S ribosomes into 54S components.     

Saccharin-induced sister chromatid exchanges in Chinese hamster and human cells

Since the induction of sister chromatid exchanges in cultured cells has been shown to be the most sensitive mammalian system to detect the effects of mutagenic carcinogens, Chinese hamster ovary cells and human lymphocytes were exposed to the sodium saccharin found to induce bladder cancer in rats. Both that saccharin and a highly purified extract of it increased the yield of sister chromatid exchanges in both types of cells. The results, which were repeatable and statistically highly significant, indicated that the weak carcinogen, saccharin, is also mutagenic in the sense that it induces cytogenetic changes.     

Tumor formation dependent on proteoglycan biosynthesis

The role proteoglycans play in tumor formation was examined by measuring the tumorigenicity of proteoglycan-deficient Chinese hamster ovary cell mutants in nude mice. When 10(7) cells were injected subcutaneously, mutants with less than about 15% of the wild-type level of proteoglycan synthesis did not produce tumors. Mutants defective in the synthesis of heparan sulfate proteoglycans also did not form tumors, whereas mutants with altered chondroitin sulfate proteoglycans were tumorigenic. Tumors arose from mixtures of wild-type and nontumorigenic mutant cells and contained both cell types, suggesting that wild-type cell proteoglycans enabled mutant cells to survive. The failure of heparan sulfate-deficient mutants to form tumors depended on the ability of the host to mount a B cell-mediated immune reaction.     

Antireceptor antiserum causes specific inhibition of reactivity to rat histocompatibility antigens

The antigen receptor of lymphocytes destined to form antibody appears to have the characteristics of the immunoglobulin produced. Antibody directed against the combining region of this immunoglobulin should interact with the combining region of the cell receptor for the antigen. Purified Lewis rat alloantibody prepared against Brown Norway (BN) rat histocompatibility antigens was used to immunize L x BN F(1) hybrids. The resultant antiserum has anti-receptor activity because (i) it yields precipitin lines in gel diffusion when reacted against the immunizing alloantibody; (ii) it inhibits the hemagglutinin antibody response of Lewis rats to BN histocompatibility antigens; and (iii) it inhibits the local graft-versus-host response of Lewis lymphoid cells against BN antigens. This suggests that antireceptor antibody may inhibit cell-mediated responses as well as antibody responses to histocompatibility antigens and may play a role in the regulation of immune responses to such antigens.     

Salivary proline-rich protein genes on chromosome 8 of mouse

Endonuclease restriction (Hind III) fragments of DNA from Chinese hamster X mouse somatic cell hybrids hybridized with proline-rich protein complementary DNA clones only when the DNA was isolated from cells containing mouse chromosome 8, or a fragment of chromosome 8. The evidence suggests that proline-rich protein genes are located at the proximal portion of chromosome 8 toward the centromere.     

Cell surface P-glycoprotein associated with multidrug resistance in mammalian cell lines

The plasma membranes of hamster, mouse, and human tumor cell lines that display multiple resistance to drugs were examined by gel electrophoresis and immunoblotting. In every case, increased expression of a 170,000-dalton surface antigen was found to be correlated with multidrug resistance. This membrane component is of identical molecular size and shares some immunogenic homology with the previously characterized P-glycoprotein of colchicine-resistant Chinese hamster ovary cells. This finding may have application to cancer therapy.     

DNA synthesis and mitosis in well-differentiated mammalian cardiocytes

Incorporation of [(3)H]thymidine into nuclei of heart cells of 2-day-old rats indicates that neonatal cardiac cells containing well-aligned myofibrils synthesize DNA. In these highly differentiated cells, neither the presence of contractile proteins nor their organization into myofibrils inhibits either DNA synthesis or mitosis.