Biomedical subjects
J Imbert
Publications and source records attributed to J Imbert.
Permanent expression of p53 in FR 3T3 rat cells but cell cycle-dependent association with large-T antigen in simian virus 40 transformants.
The p53 oncogene is thought to play a role in the proliferation of normal and transformed cells and its expression was postulated to be cell cycle dependent. Using flow cytofluorimetry sorting of populations of exponentially growing cells, coupled to a radioimmune assay, we have investigated the accumulation of p53 along the cell cycle in normal FR 3T3 rat cells as well as in two types of SV40-transformed derivatives, one of which only expresses the large-T protein during the G2 phase of the cell cycle. p53 was accumulated at a constant level throughout the cell cycle in FR 3T3 cells. Its level and stability increased to different extents in the two types of transformants. However, the formation of complexes between p53 and large-T was modulated by the G2-restricted accumulation of large-T, thus leading to a differential increase in the levels of p53 both in exponentially growing cells and along the cell cycle. This increase in the levels of p53 appeared to be regulated at a post-transcriptional level.
Cell cycle-dependent expression of early viral genes in one group of simian virus 40-transformed rat cells.
SV40-transformed FR 3T3 rat cells were previously shown to exhibit different patterns of accumulation of the virus-coded T-antigen. One group of transformants accumulates T-antigen throughout the cell cycle, whereas in another group, only the cells in the G2 phase of the cell cycle are stained by immunofluorescence with anti-T antigen antibodies. We investigated the mechanism involved by determining the amounts of early SV40 RNA during the cell cycle. Cells in the various phases of the cell cycle were sorted from an asynchronously growing population using a flow cytofluorimeter. Determination of the amounts of viral RNA in the different nuclear and cytoplasmic RNA fractions showed that in transformants with a G2-restricted accumulation of T-antigen, viral RNA was present in G2, to some extent in S, but could not be detected in cells in G1. In contrast, equivalent amounts of viral RNA were detected in all the phases of the cell cycle in the other group of transformants. Cell sorting, performed after pulse-labeling the cells for 2 h with [35S]methionine, confirmed that translation of the viral mRNAs occurred only in G2 in the first group of transformants, and throughout the cell cycle in the second group.
Cell lines derived from tumors induced in syngeneic rats by FR 3T3 SV40 transformants no longer synthesize the early viral proteins.
Several SV40-transformed FR 3T3 rat cell lines formed tumors upon inoculation to syngeneic immunocompetent Fisher rats. These tumors, which appeared only after a long latency period, showed a fast rate of growth. Tumor-derived (TD) cell lines were established in culture from several tumors induced by independent transformants, and their properties were analyzed. Though TD cells were highly tumorigenic, their level of transformation in culture was similar to that of the original transformants. They did not synthesize detectable amounts of the two early viral gene products, the large-T and small-T polypeptides. However, the transformation-associated cellular p53 protein was detected in all of them by [35S]methionine labeling and immune precipitation with monoclonal antibodies directed against the mouse p53. Growth in the animal apparently counterselected the cells expressing the early viral proteins, and hence, possibly, the tumor-specific transplantation antigen. This selection was mediated at least in part by the T-cell immune response, as the tumors induced by the same transformants in nu/nu mice still expressed the nuclear T-antigen. Absence of expression of the early viral region was frequently correlated with the loss of the integrated SV40 DNA. Some tumors, however, still contained early viral DNA sequences, which were, in even fewer cases, transcribed into RNA. These results altogether suggest that tumor formation by the FR 3T3-SV40 transformed cells in immunocompetent rats requires two events, the selection for the acquisition of a high tumorigenic potential, and against the expression of the early viral genes. Only the first of these two events was observed upon tumor formation in nude mice.
Simian virus 40 T antigen is detected only in cells in the G2 phase of the cell cycle in one group of rat transformants.
The relationship between the cell cycle and the presence of the nuclear T antigen in simian virus 40-transformed rat cells independently derived from FR 3T3 cells has been investigated using a fluorescence-activated cell sorter and a combination of stainings for cellular DNA (4',6-diamidine-2-phenylindole dihydrochloride, DAPI) and for the viral T antigen (fluorescein-labeled IgG). Such an analysis revealed that in three out of six lines, T antigen could be detected only in the G2 phase of the cell cycle. In the other three lines, the accumulation of T antigen appeared to be independent of the position of the cell in the cycle. The emergence of either phenotype was strictly correlated with the physiological state of the cell (growing versus resting, respectively) at the time the transformants were established.
Stabilization of the large T protein in temperature-independent (type A) FR 3T3 rat cells transformed with the simian virus 40 tsA30 mutant.
The stabilities of in vivo [35S]methionine-labeled large T and small t proteins, synthesized in temperature-sensitive (type N) and temperature-insensitive (type A) FR 3T3 rat cells transformed by an early temperature-sensitive mutant of simian virus 40 (SV40), tsA30, were analyzed at the permissive and restrictive temperatures. The two polypeptides, detected in greatly reduced amounts in cells of the N type at the restrictive temperature, were also unstable at the permissive temperature. However, both were made in similar amounts and were apparently stable in cells of the A type, irrespective of the temperature. The structures of the viral RNAs present at the permissive temperature were analyzed for transformants representative of each type, and containing a single integration of viral DNA. The two cell lines synthesized transcripts identical to the large T and small t mRNAs identified in SV40-infected monkey cells. Similar amounts of viral RNA were found in A and N transformants in active growth at the permissive and restrictive temperatures, which argued against a control at a transcriptional level. Assay of a defined function of the protein, namely, the binding of nucleotide detected by affinity labeling with periodate-oxidized [alpha-32P]ATP, clearly showed that the large T proteins from both types of transformants exhibited, at least for that particular biochemical function, the same in vitro temperature sensitivity. In transformants of the A type only could a reduced binding activity be detected in extracts from cells grown at the restrictive temperature. Thus, the temperature-independent behavior of the A transformants may result from an in vivo partial stabilization of the newly synthesized large T protein, probably through interaction with a cellular component(s).
Studies of the immune response against a polyoma virus-induced fibrosarcoma in BALB mice using the Winn's tumor neutralization assay.
Rejection of a polyoma-virus induced fibrosarcoma was studied by the adoptive tumor neutralization assay. This assay showed that polyoma immune spleen cells had a specific growth inhibiting effect on admixed polyoma tumor cells; they only delayed the tumor growth of an irrelevant cell line. We provide evidence both for the role of T-cells in this rejection and for a possible participation of macrophages. T-cells action was not strictly H-2 restricted but H-2 preference was observed. Adoptive protection of nude mice showed that T-cells of the recipient did not participate in the reaction.
[Different sensitivities to ultraviolet rays of various functions of the polyoma virus. Stimulation of the synthesis of cellular DNA].
Peritoneal Mouse macrophage were used to study the stimulation of cell DNA synthesis by polyoma virus. Using ultraviolet-irradiated polyoma virus, it was possible to show a difference between the inactivations of infectivity and of induction of DNA synthesis. By statistically analysis of these two phenomena it was found that 39% of the viral genome is necessary for the induction of cell DNA synthesis.
[Prognostical factors of breast neoplasms without metastasis. Synthesis by a multifactoral analysis].
Multifactorial analysis by dichotomous split was applied to a consecutive series of 541 female breast cancer patients without detectable metastasis at onset of treatment. These patients were entirely treated in the same institution (Fondation Bergonié), in the years 1960-1974. This multifactorial analysis sets a hierarchical order among the different prognostic factors and defines groups of patients homogeneous for metastatic risks. The significant prognostic factors in these series are : number of malignant axillary nodes; location and size of tumour; state of adjacent skin; relations with thoracic wall; pre or post-menopausal status; inflammatory signs; thermographic and mammographic data.
Bioassay of 2, 4, 5-trichlorophenoxyacetic acid for carcinogenicity in mice.
Adult mice of strains C3Hf and XVII/G received 2, 4, 5-T by continuous oral administration (80 ppm in the diet). The 2, 4, 5-T preparation contained less than 0-05 ppm of dioxins. In 2, 4, 5-T -treated C3Hf mice a significant increase in the incidence of neoplastic lesions was found. No significant difference was found in the XVII/G strain between the treated and control mice. Rare forms of tumours, which were not observed in the controls, were present in the 2, 4, 5-t -treated C3Hf mice.
[Immunological surveillance of otorhinolaryngological cancers].
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["Suppletive" transplantation of the liver on the regimen of the portal vein].
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[Liver involvement in typhoid fever. A prospective study of 60 patients (author's transl)].
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Interleukin-7, a major T-lymphocyte cytokine.
IL-7 is a single-chain 25 kDa protein first identified in bone marrow cultures through its pre-B cell growth factor properties, then also described as a potent T-lymphocyte growth factor. This review relates to the molecular and functional aspects of interleukin-7 (IL-7) and its receptor (IL-7R). We focused on the role of IL-7 in T-cell activation, cytotoxicity generation, leukemic cell growth and immunotherapy.