Isolation and cell-free translation of messenger ribonucleic acids specifying thymus-leukemia antigens

Messenger ribonucleic acid (mRNA) for thymus-leukemia antigens, membrane-associated glycoproteins of murine leukemia cells, was obtained from polysomes of murine leukemia cells forming thymus-leukemia antigens. Polysomes forming thymus-leukemia antigens were recovered by immunoprecipitation using alloantibodies specific for the 1,2,3 determinants of the thymus-leukemia antigen complex before they were extracted with phenol-detergent. Poly(adenylic acid)-containing RNA [poly(A)-RNA] was fractionated by oligo[deoxythymidylate] [oligo(dT)]-cellulose chromatography. The mRNA obtained had a sedimentation coefficient of approximately 17 S in agreement with the predicted size necessary for forming proteins specifying thymus-leukemia antigens. In a wheat germ system, the polypeptides formed upon addition of mRNA for thymus-leukemia antigens consisted of a major product with a molecular weight of 42,000. It was larger than the nonglycosylated heavy chain molecule of 40,000 daltons formed by the cells themselves. On the cell surface thymus-leukemia antigens exist as glycosylated molecules of 47,000 daltons associated with a light-chain equivalent to beta 2-microglobulin. Molecules of 40,000 daltons were isolated from the cells cultured in the presence of tunicamycin, an inhibitor of de novo glycosylation, and by treating thymus-leukemia heavy chains with endo-beta-N-acetylglucosaminidase H.

Control of simian virus 40 gene expression at the levels of RNA synthesis and processing: thermally induced changes in the ratio of the simian virus 40 early mRNA's and proteins

Examination of the simian virus 40 early mRNA's from infected AGMK or CV-1 cells showed that the ratio of large T- to small t-antigen mRNA's increased with an increased incubation temperature. In tsA58 mutant-infected cells, an increased incubation temperature resulted in the overproduction of early RNAs'; however, the ratio of the early mRNA's was the same, at any temperature, in both wild-type- and tsA58-infected cells. Thus, the thermally induced alteration in the early mRNA ratios was apparently not affected by the tsA mutation or by the overproduction of early RNA in tsA mutant-infected cells. Time course studies at various temperatures showed that, although the ratio of large T- to small t-antigen mRNA's increased with temperature, at any one temperature it was consistent from early to late times of infection. Furthermore, the ratio of the early mRNA's adjusted in temperature shift experiments. Thus, the ratio of the early mRNA's appeared to be intrinsic to the thermodynamic environment of the cell. The thermally induced alterations in the early mRNA's were reflected at the protein level by parallel changes in the ratio of large T- to small t-antigens. These data suggest a level of gene expression control which may function at the stage of splicing.

Replication of Chinese hamster embryo cells transformed by temperature-sensitive T-antigen mutants of simian virus 40

Chinese hamster embryo cells transformed by simian virus 40 temperature-sensitive T-antigen mutants replicated when confluent at 40.5 degrees C, regardless of the selection method, selection temperature, or virus strain used.

Inhibition of AKR leukemogenesis by SMX-1, a dualtropic murine leukemia virus

Intrathymic injection of SMX-1, a dualtropic murine leukemia virus (MuLV) originally derived from Moloney murine leukemia virus stocks, protects AKR mice from developing MuLV-accelerated leukemia and spontaneous leukemia. Thymuses of SMX-1-injected mice show no change in weight, morphology, or thymocyte size, and quantitative expression of Thy-1 and Lyt-2 differentiation antigens is identical to control mice. The amplified thymic expression of MuLV-related antigens that occurs spontaneously in 6-month-old preleukemic AKR mice or that can be induced in young AKR mice by leukemogenic AKR dualtropic MuLV is prevented by SMX-1. It appears unlikely that the protective effect of SMX-1 is explicable in terms of cross-immunogenicity with transforming MuLV or transformed cells. As SMX-1 persists for long periods after intrathymic injection and does not alter levels of thymic ecotropic MuLV, SMX-1 may interfere with the generation, spread, or leukemogenicity of dualtropic MuLV that form de novo in AKR thymus during the late preleukemic phase. SMX-1 provides a way to probe the events leading to cell transformation in AKR mice.

Coding capacity of a 35 percent fragment of the polyoma virus genome is sufficient to initiate and maintain cellular transformation

Rat-1 cells were transfected with the restriction enzyme fragment of polyoma virus DNA that extends clockwise from the Bcl I site ((65.4 map units) to the EcoRI site (0/100 map units). Six transformed cell lines were obtained and one of them (BE-1) has been investigated in detail. The viral DNA that is integrated into host DNA in this line appeared to consist of two fragments arranged in a "head-to-tail" tandem with no detectable intervening host sequences. BE-1 cells contained polyoma virus small and middle tumor antigens that were indistinguishable from the corresponding tumor antigens from lytically infected cells. No large tumor antigen was detected but a "new" Mr 34,000 protein, which proved to be a truncated version of large tumor antigen, was immunoprecipitated by anti-tumor-antigen antiserum. After injection of 10(6) BE-1 cells into young syngeneic Fischer rats, tumors appeared within 3--4 weeks. Thus, the coding capacity of the Bcl I/EcoRI fragment of polyoma virus DNA is sufficient to enable the cells to produce all of small and middle tumor antigens and about a third of large tumor antigen, to transform cells stably in culture, and to produce tumors in vivo.

Simian virus 40 and polyoma virus stimulate overall cellular RNA and protein synthesis

In lytic infection with simian virus 40 and polyoma virus of monkey and mouse cells in tissue culture, synthesis of the viral tumor (T) antigens (T antigens) is rapidly followed by a mitogenic response of the host cell. The latter begins with virus-induced stimulation of overall cellular RNA and protein synthesis, leading to a substantial increase in cytoplasmic and nuclear RNA and protein. Stimulation begins within 1 hr after onset of T-antigen synthesis and also occurs if virus-induced DNA synthesis is blocked by metabolic inhibitors. The broad spectrum of biological and molecular effects induced by simian virus 40 and polyoma virus is, at least phenotypically, reminescent of the pleiotropic impact exerted on target cells by nonviral mitogens and by certain growth-promoting steroid and polypeptide hormones.

Association of endogenous retroviruses with radiation-induced leukemias of BALB/c mice

X-irradiation of BALB/c mice in the second month of life induced a high incidence of generalized lymphatic leukemia of T-cell origin, beginning at 7 months of age. Infectious ecotropic murine leukemia virus (B-tropic predominant over N-tropic) was isolable from all tumor extracts but exhibited a wide titer range among individual leukemias. Detection of infectious xenotropic virus usually required extensive amplification on indicator cells. Dual-tropic (mink cell focus-forming) virus has not been found in the leukemias. Expression of ecotropic virus in tail extracts prepared at 6.5 months of age, although greatly enhanced compared with unirradiated controls, was not found to be prognostic of tumor development in individual mice. We conclude that leukemogenesis does not show a simple dependence on infectious murine leukemia virus expression in these mice.

Production of two recognins related to malignin: recognin M from mammary MCF-7 carcinoma cells and recognin L from lymphoma P3G cells

From the first two non-brain cancer cell types examined, mammary cancer cells (MCF-7) and lymphoma cells (P3G), two new acidic polypeptides of approximately 10,000 M.W. each have been produced, called recognin M and recognin L, respectively. These are very closely related in amino acid composition and in immunological reactions to the first two cancer recognins, astrocytin from human gliomas in vivo and malignin from malignant glial cells grown in vivo. Together with earlier findings, these observations suggest that the cancer polypeptide recognins may be produced from members of a closely related family of substances characteristic of malignant cells.

The effect of specific antiserum on the metabolism of three membrane-associated antigens of ASL-1 x LM(TK)- hybrid cells

Fusion of ASL-1 cells, a murine leukemia forming thymus leukemia (TL) antigens, with LM(TK)- cells, a TL(--) murine cell line, resulted in a stable hybrid forming TL antigens. The hybrids failed to undergo modulation, the reversible dissappearance of TL antigens from the surfaces of the cells, stimulated by TL antiserum. Unlike ASL-1 cells, the rate of disappearance of the antigens from modulation negative hydrid cells was unaffected by TL antiserum. The t 1/2 of TL antigens of the hybrid was approximately 30 h. The t 1/2 of TL antigens of ASL-1 cells was 10 h in the presence of TL antiserum, 18 h in the absence of TL antiserum. The rate of metabolism of a putative tumor-associated antigen of ASL-1 cells formed by the hybrid was unaffected by exposure to specific antiserum, as was the metabolism of H-2 antigens formed by the cell types.

Release of tumor-associated antigens by murine melanoma cells

Synthesis and release of radiolabeled macromolecules and tumor-associated antigens (MAA) by murine B16 melanoma was studied by pulse labeling cells in culture with 3H-leucine. Approximately 36% of newly synthesized macromolecules and 44% of newly synthesized MAA were released in 48 hr. MAA release was slightly, but consistently, more rapid than the average release of other macromolecules. Release of MAA did not result solely from cell death since it was greater than that of 51Cr-labeled molecules and cell viability was over 98%. The rate of release of newly synthesized MAA was not significantly influenced by cell replication. However, synthesis of MAA was much greater during the logarithmic than the stationary phase of cell growth, suggesting a concomitant increase in the amount of MAA available for release. These findings indicate that antigens and other macromolecules can be rapidly released by viable tumor cells.

Production of melanoma-associated antigen(s) by a defined malignant melanoma cell strain grown in chemically defined medium

A human malignant melanoma cell strain, UCLA-SO-M14 (M14), was adapted to grow in serum-free, chemically defined medium (CDM). The 3 M KCl extract prepared from the CDM-grown cells (M-14-CDM) was assayed against leukocytes from melanoma patients, patients with other cancers, and normal donors by leukocyte migration inhibition (LMI). The leukocytes from 15 to 27 (56%) melanoma patients tested were LMI positive. In contrast, 4 of 18 (22%) other cancer patients and 5 of 30 (17%) normal donors leukocytes were LMI positive. One of 14 melanoma patients' leukocytes were LMI positive for a control 3 M KCI extract from autologous muscle. Comparative studies were performed with the M14-CDM extract and a 3 M KCI extract from a freshly biopsied tumor specimen from the donor of the M14 cell strain. Seven of 12 (58%) melanoma patients' leukocytes were LMI positive to the M14-CDM extract, but only 2 of 12 (17%) were LMI positive to the autologous melanoma tissue extract. Furthermore, only 100 to 300 mug protein of M14-CDM extract were required to educe delayed cutaneous hypersensitivity response in 6 of 8 (75%) melanoma patients and 0 of 5 lung cancer patients, but 500 mug protein from biopsied autologous melanoma tissue extract were needed to produce delayed cutaneous hypersensitivity response in 24 of 42 (57%) melanoma patients and 7 of 28 (25%) nonmelanoma cancer patients. These data suggest: (a) the M14-CDM cells synthesized melanoma-associated antigen(s) (MAA) in CDM; (B) the 3 M KCI extraction procedure effectively removed the MAA from the M14-CDM cells; (c) the M14-CDM cells were a more potent source of MAA than the surgical autologous melanoma specimen; and (d) the M14-CDM cells provided a continuous source of standard MAA.

Herpesvirus type 2-related antigens and their relevance to humoral and cell-mediated immunity in patients with cervical cancer

The central theme of this communication is the interaction of herpes simplex virus type 2 with its host. In addition to the productive infection, we are confronted by latency and, as suggested by recent studies, by cancer. The possible mechanisms of latency and the role it may play as a precursor of carcinogenesis are discussed. If virus is to coexist with its host, a defined level of molecular interaction between host and viral gene products must exist. The association of AG-4 with active tumor growth and its identification as a minor virion protein, also exposed on the surface of the infected cell, open new vistas in the understanding of the role virus-host cell interactions may play in tumor growth. The modulation of the host immune response by the results of this interaction may play a significant role in cancer control. In these terms, the observation that antibody to AG-4 is a macroglobulin and that, therefore, immunity to AG-4 may be T-cell independent, should be given further consideration.

Evidence for a DNA replicative genome for RNA-containing tumor viruses

The requirement for DNA synthesis in the reproduction of RNA tumor viruses was examined using 5-bromodeoxyuridine (BrdU). Addition of BrdU for the first 12 hr after exposure of cells to Rous sarcoma virus resulted in a large decrease in infectious progeny. However, incorporation of [(3)H]uridine into the viral RNA of virions was unaffected. Also, the numbers of virions visualized by electron microscopy were similar in BrdU-treated and untreated samples. Viral group-specific antigen was synthesized after BrdU treatment, and BrdU had little effect on transformation of cells by Rous sarcoma virus. The results support the hypothesis that the replicative genome of RNA-containing tumor viruses contains DNA.