References

Notes: A ts mutant clone, tsJT60, was isolated from Ficher rat cell line, 3Y1. During the exponential growth at both 34 and 39.5 C, tsJT60 did not appear as ts mutant cells. However, once entered resting state (G0) under serum deprivation at the confluent state, they could re-enter S phase at 34 C but could not at 39.5 C following the stimulation of cells either by the addition of fetal bovine serum or by trypsinization and replating. These and other results suggested that tsJT60 is a G0-specific ts mutant, i.e., the cells have ts defect(s) in the function which is required for the stimulation from the resting state to S phase but not for the progression of the cell cycle in an exponential growth phase.
Reference ID: 5026

Notes: We have investigated the expression of growth-regulated genes in tsJT60 cells, a temperature-sensitive (ts) mutant of Fischer rat cells, which, on the basis of its kinetic behavior, can be classified as a G0 mutant. It grows normally at 34 degrees C and also at 39.5 degrees C if shifted to the higher temperature during exponential growth. However, if the cell population is first made quiescent by serum deprivation, subsequent stimulation by serum induces the cells to enter S phase at 34 degrees C but not at 39.5 degrees C. A panel of growth-regulated genes was used that included three protooncogenes (c-fos, c-myc, and p53), several genes that are induced in G0 cells stimulated by growth factors (beta-actin, 2A9, 2F1, vimentin, JE-3, KC-1, and ornithine decarboxylase), and an S-phase gene (histone H3). The expression of these growth-regulated genes was studied in both tsJT60 cells and its parental cell line, rat 3Y1 cells. All the genes tested, except histone H3, are similarly induced when quiescent tsJT60 cells are stimulated by serum at either permissive or restrictive temperatures. These results raise intriguing questions on the nature of quiescence and the relationship between G0 and G1 in cells in culture
Reference ID: 5027

Notes: A temperature-sensitive mutant, tsJT60, grew exponentially at both 34 degrees and 39.5 degrees C, but when stimulated from the resting state it entered S phase at 34 degrees but not at 39.5 degrees C. The mutated function appeared to be a prerequisite throughout from 0 to 9 h following the stimulation, in order that G0-arrested cells would enter S phase. When the arrested cells were stimulated with serum, the amount of and synthesis of protein increased at 34 degrees but not at 39.5 degrees C. The amount of polysome fraction was much smaller in stimulated and unstimulated cells at 39.5 degrees C than in those stimulated at 34 degrees C. Of the events reported to increase shortly after the stimulation, uridine transport increased at both temperatures. Mutation in tsJT60 cells may be concerned with the function prerequisite to induce protein synthesis following serum stimulation, resulting in the blocking of cell cycle progression toward S phase at 39.5 degrees C
Reference ID: 5028

Notes: The purpose of this study is to distinguish two possibilities that the transformed cells are blocked to enter a resting state (G0) and that they enter but are persistently stimulated to return to a growing cycle, using SV40-transformed tsJT60 cells as a model system. tsJT60 is a temperature-sensitive (ts) mutant of a Fischer rat cell line (3Y1), which is classified as a G0 mutant; i.e., the ts defect is not expressed within the growing cell cycle but is expressed only between G0 and S phases. We assumed that if the former possibility were the case, the transformed cells would not show any ts phenotype; and if the latter case, they might be ts. All SV40-transformed tsJT60 clones grew at 34 degrees C as well as SV40-transformed 3Y1 cells did at both temperatures. At 39.5 degrees C, some SV40-transformed tsJT60 clones grew (not ts) but others did not (ts) under conditions adequate for growth of untransformed cells. When clones that grew at 39.5 degrees C were cultured under conditions inadequate for growth of untransformed cells such as serum restriction or high cell density, they were ts for growth or even cytocidal at 39.5 degrees C. These results indicate that all clones of SV40-transformed tsJT60 cells are ts and the latter possibility is the case
Reference ID: 5029

Notes: tsJT60, a temperature-sensitive (ts) G0-mutant cell line from a Fischer rat, grows normally in the exponential growth phase at 34 degrees C and 39.5 degrees C, but when stimulated with fetal bovine serum (FBS), from the G0 phase they reenter the S phase at 34 degrees C but not at 39.5 degrees C. The ts-block was bypassed when G0-arrested tsJT60 cells were stimulated at 39.5 degrees C with FBS plus epidermal growth factor (EGF). The presence of EGF for the first 6 h after serum stimulation caused tsJT60 cells to enter the S phase in the presence of FBS at 39.5 degrees C. When EGF was added 6 h after serum stimulation, entrance into the S phase was delayed by about 6 h. The sequential presence of two growth factors, EGF without FBS for 6 h then FBS without EGF, or the reversed sequence, failed to initiate DNA synthesis at 39.5 degrees C. The binding of EGF was not temperature sensitive. The amounts of RNA and protein present doubled after stimulation with both FBS and EGF at 39.5 degrees C. These and other findings suggest that EGF bypasses only some specific event in the entire prereplicative process that operates operating in serum-stimulated cells at 39.5 degrees C
Reference ID: 5030

Notes: tsJT60 cells, a temperature-sensitive G0 mutant of a Fischer rat cell line, grew normally in an exponential growth phase at both permissive (34 degrees C) and nonpermissive (39.5 degrees C) temperatures, but when stimulated with fetal bovine serum in the growth-arrested state (G0 phase) they entered S phase at 34 degrees C but not at 39.5 degrees C. Infection of G0-arrested tsJT60 cells with SV40, adenovirus (Ad) 5 wild type and its E1B mutant dl313, and Ad12 wild type and its E1B mutants in205B, in205C, dl205, and in206B induced DNA synthesis at both temperatures. The DNA synthesized after virus infection was shown to be cellular by Hirt separation of DNA from SV40-infected cells and by CsCl equilibrium density gradient centrifugation of DNA from Ad5-infected cells
Reference ID: 5031

Notes: tsJT60 cells are G0-specific temperature-sensitive mutants of the cell cycle from Fischer rats i.e., they grow exponentially at both 34 degrees and 39.5 degrees C, but when stimulated with fetal bovine serum (FBS) from the resting state (G0) they enter S phase at 34 degrees C but not at 39.5 degrees C. Epidermal growth factor (EGF) also induced DNA synthesis, although weakly, in G0-arrested tsJT60 cells at 34 degrees C but failed at 39.5 degrees C. When G0-arrested tsJT60 cells were stimulated at 39.5 degrees C with FBS plus EGF, they entered S phase and divided. Somatomedin C, insulin, or transferrin had a weak effect in inducing DNA synthesis in G0-arrested cells when applied at 34 degrees C or with FBS at 39.5 degrees C. Fibroblast growth factor, platelet-derived growth factor, or 12-O-tetradecanoyl phorbol 13-acetate had no such stimulatory effect at 39.5 degrees C. Binding of 125I-somatomedin C was not temperature-sensitive. Several other ts mutant cells that were blocked at 39.5 degrees C from entering S phase from the resting state following FBS addition were stimulated by FBS plus EGF at 34 degrees C but not at 39.5 degrees C
Reference ID: 5032

Notes: tsJT60 is a nonlethal temperature-sensitive (ts) mutant of a Fischer rat cell line (3Y1) classified as a G0 mutant; i.e., the ts defect is not expressed within the cell growth cycle but is expressed only between the G0 and S phase. tsJT60 clones transformed with oncogenes such as adenovirus E1A, polyoma large T, polyoma middle T, v-Ki-ras, and LTR activated c-myc, or with a chemical carcinogen N-methyl-N'-nitro-N-nitrosoguanidine, grew well at 34 degrees C. However, most of these clones grew slowly at 40 degrees C, producing many floating dead cells, and some clones were killed at 40 degrees C. When they were cultured under conditions inadequate for growth of untransformed cells, such as high cell density or serum restriction, they were killed at 40 degrees C. These and previous results from SV40- and adenovirus-transformed tsJT60 clones favour the idea that transformed tsJT60 cells occasionally enter the G0 phase and are metabolically imbalanced at 40 degrees C during self-stimulation from the G0 to S phase. We propose that a drug which exclusively block, G0-G1 transition would be cytocidal to transformed cells but cytostatic to normal cells
Reference ID: 5033

Notes: tsJT60, a temperature-sensitive (ts) cell-cycle mutant of Fischer rats, is viable at both the permissive (34 degrees C) and nonpermissive (40 degrees C) temperatures. The cells grow normally in exponential growth phase at both temperatures, but when stimulated with serum from G0 phase they enter S phase at 34 degrees C but not at 40 degrees C. tsJT60 cells transformed with human adenovirus (Ad) 12 dl205, which lacks the E1B 19-kDa polypeptide gene, were lethal at 40 degrees C, whereas tsJT60 cells transformed with Ad12 wt, dl207, which lacks E1B 58-kDa protein gene, or in206B, which produces 19- to 58- kDa fused protein, were viable. Degradation of cell DNA occurred in dl205-transformed tsJT60 cultured at both 34 degrees C and 40 degrees C. Neither cytocidal phenotype nor degradation of DNA occurred in 3Y1 cells (a parental line of tsJT60) transformed with dl205. These results suggest that the lethal phenotype and degradation of DNA are related to the ts mutation in tsJT60 and also to the lack of Ad12 E1B 19kDa polypeptide
Abstract: tsJT60, a temperature-sensitive (ts) cell-cycle mutant of Fischer rats, is viable at both the permissive (34 degrees C) and nonpermissive (40 degrees C) temperatures. The cells grow normally in exponential growth phase at both temperatures, but when stimulated with serum from G0 phase they enter S phase at 34 degrees C but not at 40 degrees C. tsJT60 cells transformed with human adenovirus (Ad) 12 dl205, which lacks the E1B 19-kDa polypeptide gene, were lethal at 40 degrees C, whereas tsJT60 cells transformed with Ad12 wt, dl207, which lacks E1B 58-kDa protein gene, or in206B, which produces 19- to 58- kDa fused protein, were viable. Degradation of cell DNA occurred in dl205-transformed tsJT60 cultured at both 34 degrees C and 40 degrees C. Neither cytocidal phenotype nor degradation of DNA occurred in 3Y1 cells (a parental line of tsJT60) transformed with dl205. These results suggest that the lethal phenotype and degradation of DNA are related to the ts mutation in tsJT60 and also to the lack of Ad12 E1B 19kDa polypeptide
Reference ID: 5034

Notes: tsJT60 is a temperature-sensitive (ts) mutant of the cell cycle isolated from a rat cell line. It does not enter the cell cycle from the G0 phase at a nonpermissive temperature (40 degrees C) but proliferates normally in log phase at both permissive (34 degrees C) and nonpermissive temperatures (G0-specific ts mutant). Here we examined whether tsJT60 fails to downregulate growth arrest-specific genes after growth stimulation from G0 phase at 40 degrees C. Among growth arrest-specific genes examined, an expression of gadd153, which decreased after serum stimulation at 34 degrees C as expected, increased markedly at 40 degrees C. It is plausible to assume that induction of gadd153 at 40 degrees C is correlated with inability of tsJT60 to enter S phase from G0 phase at 40 degrees C, because it also occurred in tsJT366 (another ts mutant clone in the same complementation group) but did not occur in parental 3Y1 and in other ts mutant lines of different complementation groups. However, gadd153 was also induced after the temperature upshift in tsJT60 cells growing in log phase or progressing S phase
Abstract: tsJT60 is a temperature-sensitive (ts) mutant of the cell cycle isolated from a rat cell line. It does not enter the cell cycle from the G0 phase at a nonpermissive temperature (40 degrees C) but proliferates normally in log phase at both permissive (34 degrees C) and nonpermissive temperatures (G0-specific ts mutant). Here we examined whether tsJT60 fails to downregulate growth arrest-specific genes after growth stimulation from G0 phase at 40 degrees C. Among growth arrest-specific genes examined, an expression of gadd153, which decreased after serum stimulation at 34 degrees C as expected, increased markedly at 40 degrees C. It is plausible to assume that induction of gadd153 at 40 degrees C is correlated with inability of tsJT60 to enter S phase from G0 phase at 40 degrees C, because it also occurred in tsJT366 (another ts mutant clone in the same complementation group) but did not occur in parental 3Y1 and in other ts mutant lines of different complementation groups. However, gadd153 was also induced after the temperature upshift in tsJT60 cells growing in log phase or progressing S phase
Reference ID: 5035