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M C Simon

Publications and source records attributed to M C Simon.

At least 73 records · Page 4Linked to original sources
PubMed1989

Multiple sequence elements in the c-fos promoter mediate induction by cAMP.

Induction of c-fos by cyclic AMP in NIH-3T3 cells is distinct from induction by serum. Whereas induction by serum is mediated by the serum response element (SRE), induction by cAMP does not require this element. In fact, no single sequence element in the c-fos promoter/enhancer is stringently required for the cAMP response. Rather, multiple sequence elements in the c-fos promoter/enhancer can mediate induction by cAMP independently. These elements are: (1) the region from -72 to -54, which contains a binding site for a cellular activating transcription factor (ATF); (2) the region from -225 to -99; (3) the region from -303 to -281, which is homologous to the consensus binding site for the transcription factor AP1; and (4) the region from -317 to -298, which contains the SRE. These sequence elements convey cAMP inducibility when fused to the cAMP-unresponsive 'minimal' fos promoter (-53 to +42). In addition, the c-fos regions from -700 to -63 and from -71 to -48 can confer cAMP inducibility to a heterologous promoter.

Blood↗
PubMed1989

The adenovirus E4 gene, in addition to the E1A gene, is important for trans-activation of E2 transcription and for E2F activation.

Previous experiments have demonstrated that adenovirus infection of human and mouse cells leads to an E1A-dependent activation of the DNA-binding capacity of a cellular transcription factor termed E2F. E2F binds to two sites in the adenovirus E2 early promoter which have been shown to be critical for E1A-dependent E2 early transcription, and the E2F-binding sites can confer E1A-induced transcription to a heterologous promoter. In addition, under a variety of circumstances, the increase in E2F-binding activity coincides with the activation of E2 transcription. We now find that, in addition to the E1A gene, another early viral gene, the E4 gene, is necessary for the activation of E2F-binding activity. Extracts prepared from human 293 cells, which express the E1A and E1B genes, had low levels of E2F activity, whereas infection of 293 cells with the E1A mutant dl312 increased E2F activity. This increase did not occur when 293 cells were infected with dl366, an E4 deletion mutant, nor was there an increase in E2F activity in HeLa cells infected with either dl366 or dl312; however, a coinfection with the two mutants yielded the normal wild-type increase in E2F. Furthermore, infection of HeLa cells with a high multiplicity of dl312, conditions that allow E4 gene expression in the absence of E1A, did not yield an increase in E2F activity. Thus, it appears that both the E1A gene and the E4 gene are directly involved in E2F activation. Measurements of E2 RNA production in a dl366 infection as compared with a wild-type or dl312 infection demonstrate that the E4 gene is essential for full E2 transcription. Furthermore, transfection assays of the E2 promoter demonstrate that, although E1A alone can trans-activate the E2 promoter, it is not as effective as the combination of E1A and E4 in the induction of the E2 promoter. We therefore conclude that the activation of the E2F factor leading to the activation of E2 transcription requires the combined action of both the E1A 289-amino-acid protein and an E4 product.

Adenoviridae↗
PubMed1988

Definition of multiple, functionally distinct TATA elements, one of which is a target in the hsp70 promoter for E1A regulation.

We have dissected the human hsp70 promoter to define sequence elements allowing response to E1A. Alterations of sequence upstream of the TATA element, either with Bal 31 nuclease or by site-directed mutagenesis, had little or no effect on the response of the promoter to E1A. In general, the basal level was reduced, indicating that these sites interact with factors important for transcription, but regulation persisted. Although a CAT gene driven by just the hsp70 TATA (void of upstream sequences) could be stimulated by E1A, a similar construct containing the early SV40 TATA element was not. Analysis of several additional such constructions indicated that the specific sequence TATAA was crucial. Substitution of the TATAA sequence with the SV40 TATTTAT element in the context of the wild-type hsp70 promoter resulted in loss of E1A inducibility, but maintenance of heat inducibility. Replacement of this element with sequences not related to any TATA element resulted in loss of activity and inducibility. Thus, the SV40 TATA equivalent is functional in the context of the hsp70 promoter but cannot be induced by E1A. We conclude that the target for E1A induction of the hsp70 promoter is TATAA, and that multiple functionally distinct TATA elements, and presumably cognate transcription factors, can be distinguished in eukaryotic cells.

Bacteriophage lambda↗
PubMed1987

Proliferative fibromatosis in avian skeletal muscle caused by cloned recombinant avian leukosis viruses.

Two molecular recombinants (EU-8 and K-3) constructed from ring-necked pheasant virus and UR2AV, the helper virus associated with avian sarcoma virus UR2, caused a high incidence of a hitherto unreported pathological condition in chick skeletal muscle. A disease spectrum was observed in which muscle was infiltrated by proliferating fibroblasts and caused white streaks, white diffuse areas, or well-defined elongated tumors. Fibroblast proliferation was progressive, and the gross presentation depended on the rapidity and extent of proliferation. There was evidence of anaplasia but not frankly malignant disease or metastases. The disease was produced at a high frequency when 10-day-old embryos were infected. Breast muscle (pectoralis major and minor) was affected with variable severity in all birds, thigh muscles were affected occasionally, while other thoracic, external abdominal, and wing muscles were affected very rarely. Progression of proliferative muscle lesions was demonstrated by sequential necropsies and microscopic examination of muscle samples. The disease appeared before 2 weeks of age, and thin white streaks with minimal cellular proliferation were the earliest lesions observed. Elongated, spindle-shaped tumors were the most advanced form of proliferation observed. The advanced lesions showed cellular anaplasia and signs of rapid growth, and appeared most commonly at 6 weeks of age or later. Histologically, mild proliferation correlated with normal appearing fibroblasts producing collagen. Severe proliferation correlated with anaplastic, rapidly dividing cells producing little collagen and a high mitotic index. A decrease in the virus dose resulted in less severe fibromatosis, but at least one chicken infected with a low virus dose showed severe disease. When 10- or 35-day-old hatched chicks were injected in the breast muscle with EU-8 or K-3, a low incidence of lymphoid leukosis was observed, but no fibromatosis resulted during an observation period of 27 weeks. Infectious virus was extracted from the fibromatosis in the breast muscle, and extracted virus caused the same disease when injected in 10-day-old embryos. No transforming activity was observed on normal chick embryo fibroblast monolayers. Cell cultures were established from areas in the breast muscle affected by fibromatosis, and from discrete tumors. These cells did not show any signs of transformation in culture. Supernatants obtained from these cell cultures caused fibromatosis when injected into 10-day-old embryos, but did not transform normal chick embryo fibroblasts.

Animals↗
PubMed1987

Genetic determinants of neoplastic diseases induced by a subgroup F avian leukosis virus.

Two subgroup F avian leukosis viruses, ring-necked pheasant virus (RPV) and RAV-61, were previously shown to induce a high incidence of a fatal proliferative disorder in the lungs of infected chickens. These lung lesions, termed angiosarcomas, appear rapidly (4 to 5 weeks after infection), show no evidence of proto-oncogene activation by proviral integration, and are not induced by avian leukosis viruses belonging to other subgroups. To identify the viral sequences responsible for induction of these tumors, we constructed recombinant viruses by exchanging genomic segments of molecularly cloned RPV with those of a subgroup A leukosis virus, UR2AV. The ability to induce rapid lung tumors segregated only with the env sequences of RPV; the long terminal repeat of RPV was not required. However, recombinants carrying both env and long terminal repeat sequences of RPV induced lung tumors with a shorter latency. In several cases, recombinant viruses exhibited pathogenic properties differing from those of either parental virus. Recombinants carrying the gag-pol region of RPV and the env gene of UR2AV induced a high incidence of a muscle lesion termed infiltrative intramuscular fibromatosis. One recombinant, EU-8, which carries the gag-pol and LTR sequences of RPV, and the env gene of UR2AV, induced lymphoid leukosis after an unusually short latent period. The median time of death from lymphoid leukosis was 6 to 7 weeks after infection with EU-8 compared with approximately 5 months for UR2AV.

Animals↗
PubMed1987

Selective induction of human heat shock gene transcription by the adenovirus E1A gene products, including the 12S E1A product.

We have previously shown that the human 70-kilodalton heat shock protein gene (hsp70) is induced by the adenovirus E1A gene product and during the S-G2 phase of the cell cycle. In this study, we investigated the effect of E1A on the expression of other human hsp genes. A gene encoding one form of the hsp89 protein (hsp89 alpha) was activated during an adenovirus infection with kinetics similar to those of activation of hsp70. The induction required a functional E1A gene. However, the hsp89 transcript was not cell cycle regulated. Genes encoding another form of hsp89 and the hsp27 protein were not induced by E1A or during the cell cycle. Further examination of hsp70 expression revealed a greater complexity than previously seen. S1 nuclease analysis using an hsp70 cDNA as well as a distinct hsp70 genomic clone demonstrated three related hsp70 transcripts; two were induced by E1A, and one was not. Both of the E1A-inducible genes were regulated during the cell cycle. All three were induced by heat shock. These results suggest common aspects of control among certain members of this family of cellular genes distinct from heat shock control. Finally, using viruses that express the individual E1A proteins, we found that the hsp70 gene is induced by the 12S and the 13S E1A products. The efficiency of induction by the 12S product was somewhat less than that by the 13S product but only by a factor of less than 2. This is in contrast to the induction of early viral genes, for which the 13S product is considerably more efficient than the 12S product.

Adenovirus Early Proteins↗
PubMed1986

Isolation of chicken cellular DNA sequences with homology to the region of viral oncogenes that encodes the tyrosine kinase domain.

A library of chicken genomic DNA was screened for sequences that could hybridize to a cloned DNA fragment containing the transforming gene (v-fps) of Fujinami sarcoma virus. In addition to c-fps, two unique chicken cellular DNA sequences were isolated that hybridized weakly to v-fps. These sequences hybridized with many other viral oncogenes encoding tyrosine kinases. Sequence analysis of the region where homology was detected revealed a region that is highly conserved among the tyrosine kinases both at the nucleotide and amino acid levels. Although we were unable to detect expression of either chicken cellular DNA sequence in a variety of avian tissues, the data suggest the existence of additional members of the tyrosine kinase gene family. Screening genomic libraries for sequences that hybridize weakly to functional regions of other genes may prove useful for the isolation and characterization of additional members of other gene families.

Animals↗
PubMed1984

Mechanisms of oncogenesis by subgroup F avian leukosis viruses.

Subgroup F avian leukosis viruses, such as RAV-61 and ring-necked pheasant virus, are recombinants between exogenous chicken retroviruses and endogenous pheasant viruses and contain new envelope (env) genes. Chickens infected as 10-day-old embryos with subgroup F viruses develop fibrosarcomas, nephroblastomas, osteopetrosis, B-cell lymphomas, and a high incidence of a proliferative disorder involving the lung. Fibrosarcomas, nephroblastomas, and lymphomas appear after long latent periods (3 to 12 months). They contain discrete virus-cell junction fragments and are therefore clonal outgrowths of a single infected cell. Two ring-necked pheasant virus-induced B-cell lymphomas and an adenocarcinoma of the abdomen contained proviruses integrated at the c-myc locus and elevated levels of myc mRNA. At least four of the fibrosarcomas appeared to contain proviruses integrated at a common site, suggesting that a specific cellular gene may be involved in these tumors. The host gene has not been identified, however; 16 different oncogene probes failed to hybridize to fibrosarcoma junction fragments. In contrast to these neoplasms, lung lesions appeared rapidly (4 to 5 weeks), showed no evidence of clonality, and lacked long terminal repeat-initiated transcripts other than viral 35S and 21S mRNA. We conclude, therefore, that subgroup F retroviruses induce the proliferative disorder of the lung by a different mechanism.

Animals↗
PubMed1982

Kinetics of fast haemoglobin in diabetic rats.

This study was designed to examine the appearance and disappearance kinetics of glycosylated haemoglobin during abrupt changes of blood glucose in the rat. The concentration of the fast haemoglobin component, which has similar chromatographic and electrophoretic profiles to human haemoglobin A1, was measured after the induction of diabetes by streptozotocin and its cure by syngeneic intraportal islet transplantation. Fast haemoglobin was increased in 12 diabetic rats compared with 22 controls (15.8 +/- 0.8 versus 8.2 +/- 0.3%, mean +/- SEM). In a group with mild diabetes (n = 8, blood glucose less than 22 mmol/l), fast haemoglobin rose to 13.7 +/- 1.0% by week 8. In a group with severe diabetes (n = 4, blood glucose greater than 22 mmol/l), fast haemoglobin rose more quickly (in 3 weeks) to a higher level (18.2 +/- 3.3%) and changed little thereafter. This suggests a saturable system in which the rate of increase and final value depend upon the degree of hyperglycaemia. After islet transplantation, fast haemoglobin returned to normal in 4 weeks (n = 5, 17.6 +/- 1.4 to 9.4 +/- 0.9%). This delay is shorter than expected from the red cell lifespan (around 60 days), suggesting that haemoglobin glycosylation may be partly reversible. These results suggest that in unstable diabetes the interpretation of haemoglobin A1 levels is not as simple as was supposed previously.

Animals↗
PubMed1980

Efficient production of mammalian RNA tumor viruses in serum-free culture medium allows rapid RNA subunit purification.

A wide variety of infected mammalian cell cultures were observed to produce high levels of RNA tumor virus particles in the absence of serum for at least 12 h. Virus production was measured by yields of 50-70 S virus RNAs isolated directly from serum-free culture media by chromatography on oligo(dT)-cellulose. Yields of RNAs from viruses produced in serum-free medium were comparable to yields obtained from purified viruses produced in serum-containing medium. Subunits of viral RNAs were thermally dissociated and separated by a new sedimentation system using sucrose gradients with resolving power (in the relevant size range) equivalent to that obtained with electrophoresis in polyacrylamide gels. RNA subunits isolated directly from serum-free medium appeared to be intact as judged by poly(A) content and resedimentation. The overall approach developed here represents dramatic savings in time and effort over previous ways of producing purified RNA subunits from tumor viruses.

Animals↗
PubMed1980

Toward a model for the molecular genetics of carcinogenesis in rats.

Cultured rat embryo cells are resistant to neoplastic transformation by chemical carcinogens unless they are extensively subcultured or infected with a murine leukemia virus (MuLV) first. We found that, in normal cultured cells, MuLV activates expression of rat genes that are the progenitors of sarcoma virus genes, but not those of endogenous "leukemia" virus. Elevated levels of sarcoma virus-related RNA in normal cells infected with MuLV were indistinguishable from the levels in cells transformed spontaneously or by a carcinogen or a sarcoma virus. Because of previous reports that some carcinomas in rats also contain elevated levels of sarcoma virus-related RNA, we believe these events can be explained by a molecular genetic model which may be generally valid for initiation of carcinogenesis. The basic elements of the model are: transcriptional activation of all the multiple copies of normal rat progenitors of sarcoma virus genes is required before cellular transformation can be initiated, and initiation occurs when a spontaneous or induced mutation in any one active copy of these same genes generates a dominant transforming function.

Animals↗
PubMed1980

Low plasma levels of pancreatic polypeptide in obesity.

Plasma levels of pancreatic polypeptide (PP) were studied in a group of 22 normal and 22 obese subjects after an overnight fast. In a second group of 10 normal and 13 obese adults, PP secretion was stimulated by a protein-rich meal. The results indicate lower fasting PP values in the obese subjects and a decreased response during the second phase of the meal-induced secretion. This could suggest a possible role of PP in obesity.

Adult↗
PubMed1977

[Initiation of transcription and translation in E. coli nucleoids].

The initiation of both transcription and translation occurs in membrane-associated nucleoid of E. coli without the addition of cytoplasmic fraction. Initiation of translation, however, is stimulated by adjunction of S 165. Our results suggest that the system is limited in synthesizing F-met-tRNA. The capacity of nucleoid-extracted ribosomes to form initiation complexes is only slightly higher than that of supernatant ribosomes. RNA synthesis is partially rifampicin-sensitive, which implies that initiation of new chains takes place in our system.

Cell Membrane↗
PubMed1977

[Synthesis of specific proteins by the nucleoid of Escherichia coli].

The induction of beta-galactosidase and alkaline phosphatase by the nucleoid of Escherichia coli was studied. Only the membrane-associated form was active in the presence of S 30. The induction of beta-galactosidase showed an absolute requirement for the inducer and was enhanced by cyclic AMP and cyclic GMP. Further-more, in our hands, the synthetic activity of the membrane-associated nucleoid proved to be far higher than that of the soluble system described by Zubay. Our results suggest that membrane shield the structure which is necessary for the integrity of the initiation step of both transcription and translation.

Alkaline Phosphatase↗