Rodent Tumor Cell Research Articles

Retroviral Expression of Transforming Growth Factor-Alpha Does Not Transform Fibroblasts or Keratinocytes

Transforming growth factor alpha (TGF alpha) is a peptide so named because it helps to impart anchorage-independent growth to normal rat kidney (NRK) cells in vitro and is secreted by many rodent and human tumor cells. To directly investigate the transforming properties of this factor, we constructed a replication-defective murine retrovirus that expresses the human sequence coding for TGF alpha. Infection of NIH/3T3 cells with the TGF alpha retrovirus led to the integration of a transcriptionally active provirus and overexpression of biologically active TGF alpha, but failed to induce morphologic transformation. Similarly, the TGF alpha retrovirus failed to induce morphologic transformation of five other types of rodent fibroblasts. We also investigated the effect of TGF alpha expression on the growth of BALB/MK mouse keratinocytes, which require epidermal growth factor (EGF) for proliferation. We show that exogenously added TGF alpha is an extremely potent mitogen for BALB/MK cells. However, retroviral expression of TGF alpha in BALB/MK cells failed to relieve dependence on exogenously added EGF (or TGF alpha) for cell growth. These results suggest that overexpression of TGF alpha does not, by itself, transform rodent fibroblasts or keratinocytes.

Polyamine biosynthesis inhibitors combined with systemic hyperthermia in cancer therapy

A Phase I clinical trial has been initiated at the University of Arizona Cancer Center which combines escalating oral doses of the polyamine biosynthesis inhibitor a-difluoromethylornithine (DFMO), with systemic hyperthermia (∼-41.5°C) in the treatment of metastatic melanoma. The rationale for the combination of hyperthermia and polyamine biosynthesis inhibitors in the treatment of human cancers includes studies which show that depletion of endogenous polyamines, as a result of treatment with DFMO, sensitizes both rodent and human tumor cells to the cytotoxic effects of hyperthermia. Heat shock induces the first enzyme in polyamine catabolism, spermidine/spermine N 1-acetyltransferase (N 1-SAT). The consequently acetylated forms of spermidine and spermine are then constitutively oxidized by the enzyme polyamine oxidase (PAO). Both CHO and human A549 lung cancer cells exhibit heat-inducible polyamine acetylation, exhibit heat-inducible polyamine acetylation, display potent heat sensition after polyamine depletion, and ultimately reveal prolonged expression of thermotolerance. Conversely, HeLa cells do not demonstrate heat-inducible polyamine catabolism, are not sensitized to polyamine catabolism, are not sensitized to heat with DFMO, and display more rapid kinetics of thermotolerance decay. These laboratory studies suggest that enhancement of the cytotoxic action of hyperthermia by DFMO occurs as a consequence of the inhibition of polyamine catabolism, a heat-inducible process that affords some form of protection to cells undergoing heat stress. Human melanoma cultures demonstrated heat-inducible polyamine catabolism and are sensitized to hyperthermic cytotoxicity by DFMO. To date, 24 systemic hyperthermia treatments have been delivered to nine patients with metastatic melanoma in conjunction with DFMO under this Phase I clinical trial.

Transforming growth factor-α messenger RNA localization in the developing adult rat and human mammary gland by in situ hybridization

Transforming growth factor-alpha (TGF alpha) has been implicated in the autocrine growth control of a number of different rodent and human tumor cells, including breast cancer cells. Although TGF alpha has been detected in a limited number of normal tissues, its distribution and physiological function in the mammary gland are relatively unknown. TGF alpha mRNA expression was detected by in situ hybridization with a labeled TGF alpha antisense RNA probe and quantitated by application of computer-assisted digital image processing in both the ductal and alveolar epithelial cells in the virgin rat and nulliparous and parous human mammary glands. During pregnancy and lactation, the level of TGF alpha mRNA expression in the ductal and alveolar epithelial cells increased two- to threefold, while a heterogeneous yet strong expression of TGF alpha mRNA could also be detected in approximately 10-15% of the surrounding stromal cells in the pregnant mammary gland.

Purification of a human milk protein closely similar to tumor-secreted phosphoproteins and osteopontin.

A wide variety of rodent and human tumor cells secrete antigenically related phosphoproteins with molecular weights (Mr) of approximately 58,000 (hamster), 62,000 (rat, mouse), 67,000 (human) (Senger, D.R. and Perruzzi, C.A. (1985) Cancer Res. 45, 5818-5823). Expression of these phosphoproteins is transformation-related; tumor cells produce at least 10-fold or more of this protein as compared to their normal or untransformed counterparts. N-terminal and internal sequences derived from the rat tumor-secreted phosphoprotein indicate that it is identical to rat osteopontin, a bone protein with an Arg-Gly-Asp cell-binding sequence (Oldberg, A., Franzen, A. and Heinegard, D. (1986) Proc. Natl. Acad. Sci. USA 83, 8819-8823). Antibody raised to the Mr 62,000 rat tumor-secreted phosphoprotein was found to bind Mr 75,000 and Mr 35,000 components of human milk, indicating that milk contains antigenically related proteins. The Mr 75,000 protein, which is present in human milk at concentrations ranging from 3 to 10 micrograms/ml, has been purified to homogeneity. The Mr 35,000 component is apparently derived from the Mr 75,000 protein by proteolytic cleavage, and this cleavage also occurs in vitro in the presence of thrombin. N-terminal and internal amino acid sequences were derived from the Mr 75,000 milk protein and found to be similar (12/21 residues) to N-terminal and internal sequences derived from the rat tumor-secreted phosphoprotein and osteopontin. Moreover, sequence derived from the N-terminus of the human milk protein is identical to that of human bone sialoprotein I (the likely human homolog of rat osteopontin) (Fisher, L.W., Hawkins, G.R., Tuross, N. and Termine, J.D. (1987) J. Biol. Chem. 262, 9702-9708).

Developmentally regulated expression of a human "finger"-containing gene encoded by the 5' half of the ret transforming gene.

We isolated and sequenced a cDNA clone of the human gene encoded by the 5' half of the ret transforming gene. The nucleotide sequence indicates that it encodes a protein with "finger" structures which represent putative metal- and nucleic acid-binding domains. Transcription of this gene was detected at high levels in a variety of human and rodent tumor cell lines, mouse testis, and embryos. In addition, a unique transcript was observed in testis RNA. When the expression of the unique transcript was examined at different stages of spermatogenesis, a striking increase in mRNA levels accompanied progression from meiotic prophase pachytene spermatocytes to postmeiotic round spermatids. This finger-containing gene may thus function in male germ cell development.

Developmentally regulated expression of a human "finger"-containing gene encoded by the 5' half of the ret transforming gene.

We isolated and sequenced a cDNA clone of the human gene encoded by the 5' half of the ret transforming gene. The nucleotide sequence indicates that it encodes a protein with "finger" structures which represent putative metal- and nucleic acid-binding domains. Transcription of this gene was detected at high levels in a variety of human and rodent tumor cell lines, mouse testis, and embryos. In addition, a unique transcript was observed in testis RNA. When the expression of the unique transcript was examined at different stages of spermatogenesis, a striking increase in mRNA levels accompanied progression from meiotic prophase pachytene spermatocytes to postmeiotic round spermatids. This finger-containing gene may thus function in male germ cell development.

Dietary Restriction of Tyrosine and Phenylalanine: Inhibition of Metastasis of Three Rodent Tumors<xref ref-type="fn" rid="FN2">2</xref>

The effects of a combined dietary restriction of tyrosine and phenylalanine on metastasis were investigated with the use of 3 rodent tumor cell lines: B16-bladder 6 (BL6) melanoma inoculated into (C57BL/6 X DBA/2)F1 mice, Lewis lung (3LL) carcinoma inoculated into C57BL/6 mice, and RT7-4bs hepatocarcinoma inoculated into BD-IV rats. When examined for effects on spontaneous metastasis, dietary restriction of tyrosine and phenylalanine had no effect on metastasis to draining lymph nodes in either BL6 or 3LL tumors. However, the restriction did reduce metastasis of RT7-4bs cells to draining lymph nodes by 60%. In all tumor systems, the dietary restriction effectively inhibited the subsequent growth of lymph node tumors. The most marked effect of the dietary restriction was on spontaneous hematogenous metastasis, which was almost totally blocked for BL6 cells and was reduced by 85% for RT7-4bs cells. Tumor-associated splenomegaly also was completely inhibited in 3LL tumor-bearing mice. The selective dietary amino acid restriction failed to reduce initial lung colonization in the experimental metastasis assay but clearly inhibited subsequent tumor outgrowth in the lungs. These findings demonstrate that modification of host nutritional status by restriction of the dietary intake of tyrosine and phenylalanine exerts a dramatic antimetastatic effect directed particularly on spontaneous hematogenous metastasis. Although the preliminary data suggest a primary modulating effect on tumor cell populations growing in diet-restricted animals to reduce inherent metastatic ability, the actual mechanisms remain to be defined.

Mouse Monoclonal Antibody to Embryonic Antigen: Development, Cross-Reactivity With Rodent and Human Tumors, and Preliminary Polypeptide Characterization<xref ref-type="fn" rid="FN2">2</xref>

Hybridomas producing IgM and IgG monoclonal antibodies (MoAb) to embryonic or fetal antigens (EA) were obtained in a completely syngeneic system. Lethally irradiated, 13-day-gestation, C57BL/6N mouse fetal cells or KCI extracts of these fetal cells obtained from primaparous donors were used as immunogens in several regimens to induce splenocytes in C57BL/6N mice that were utilized to form the hybridomas following fusion with a mouse myeloma line. Successful growth and cloning of the IgM-producing hybridomas required supplementation with factor(s) produced in the growth medium of the macrophage cell line RAW 264.7. An enzyme-linked immunosorbent assay (ELISA) was employed to screen the primary fusion hybridomas for antibody directed against fetal cell or adult cell determinants with the use of freshly explanted tissues. Glutaraldehyde-fixed fetal cells as well as crude fetal cell membranes were used as EA+ target cells (i.e., cell lines known to activate T-lymphocyte-mediated tumor resistance) in a solid-phase ELISA to perform quantitative ELISA adsorption tests of the MoAb. The anti-EA monoclonal IgM and the IgG detected common, embryo-specific antigen(s) on mouse, hamster, and human fetuses. Term fetal cells and adult normal tissues of the mouse, hamster, and human did not express cross-reactive determinants for the MoAb by absorption analysis and/or by direct binding in ELISA. EA expression as oncofetal antigens could also be detected with the monoclones on several rodent tumor cell lines tested as well as on a variety of human carcinomas but not on a spectrum of normal human tissues with the use of indirect ELISA absorption and affinity gel and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses. Fluorescence analysis with the monoclones demonstrated specific reactivity with the surface of EA+ tumor cells in the FACS IV flow cytometer. The responsible antigen was carried on a 44- and a 200-kilodalton polypeptide.

Fibroblast immortality is a prerequisite for transformation by EJ c-Ha-ras oncogene.

The established mouse cell line NIH 3T3 has been used with considerable success over the past three years as the basis of an in vitro transformation assay for demonstrating the presence of transfectable transforming genes in the DNA of certain human and rodent tumour cells (for review see ref. 1). In the case of the human bladder carcinoma cell lines EJ and T24, this approach has led to the molecular cloning of a transforming gene which is closely related to the rat-derived Harvey sarcoma virus oncogene, v-Ha-ras. A single point mutation, which distinguishes these genes from their normal human homologue (c-Ha-ras1), is thought to be solely responsible for their transforming potential. However, carcinogenesis in both humans and laboratory rodents is a multi-stage process (reviewed in ref. 11) of which the NIH 3T3 cell, already partly transformed, may represent only the penultimate stage. We therefore chose to examine the transforming effects of the EJ oncogene in a hamster fibroblast system originally developed in our laboratory to study stages in carcinogen-induced malignant transformation of normal diploid cells. We show here that EJ c-Ha-ras-1 lacks complete transforming activity when transfected into normal fibroblasts which have a limited lifespan, but can fully transform fibroblasts that have been newly 'immortalized' by carcinogens.

Polypeptide inhibitors of DNA synthesis and cellular proliferation produced by cultured BRL-3A rat liver cells

Variants of the NIL8 hamster cell line have been isolated by a procedure that selects against cells that incorporate [ 3H]thymidine into DNA in response to stimulation with multiplication-stimulating activity (MSA, an insulin-like growth factor produced by cultured BRL-3A rat liver cells). Some of the variant clones proved to be hypersensitive to two inhibitors of [ 3H]thymidine incorporation that were present in partially purified MSA preparations. The inhibitors have been found to be heat-labile polypeptides. The inhibitors copurify with MSA through ion exchange chromatography on Dowex 50, but are separable from MSA by gel filtration on Sephadex G-75. One of these factors (IN I) has been shown to inhibit DNA synthesis (as determined by autoradiography) and proliferation of the variant cells. Among several other rodent tumor cell lines tested for sensitivity to inhibition by INI, Reuber H-35 rat hepatoma cells and HSV-transformed hamster fibroblasts were not inhibited by the factor, whereas PG19 mouse melanoma cells were slightly inhibited.