PubMed Health⌕ Search

Biomedical subjects

B H Cochran

Publications and source records attributed to B H Cochran.

32 records · Page 2Linked to original sources
PubMed1988

The human c-fos serum response factor and the yeast factors GRM/PRTF have related DNA-binding specificities.

One of the elements that mediates growth factor and serum inducibility of the human c-fos gene is a region of dyad symmetry that lies between nucleotides -320 and -299 of the human gene. A mammalian protein specifically binds to this sequence element and has been termed the serum response factor (SRF). Gel-shift analysis and competition experiments demonstrate that there is a factor in the yeast Saccharomyces cerevisiae that binds specifically to the human c-fos SRE. The methylation interference pattern of the yeast factor is identical to that of the mammalian SRF. Regulatory elements of cell-type-specific genes in yeast have homologies to the c-fos SRE and complete for binding of both the mammalian and yeast factors to the SRE. Antisera to the gene product of the MCM1 locus react with the yeast SRE-binding factor. These data suggest that this yeast protein is closely related or identical to the factors [general regulator of mating type (GRM) and pheromone/receptor transcription factor (PRTF)] that are required for the regulation of cell-type-specific genes in yeast.

Cloning, Molecular↗
PubMed1987

A rapidly inducible DNA-binding activity which binds upstream of the c-fos proto-oncogene.

The c-fos proto-oncogene is rapidly inducible by a variety of extracellular stimuli. In order to dissect the intracellular signalling pathways responsible for c-fos induction, we have used a gel electrophoresis DNA-binding assay to identify trans-acting factors that bind to c-fos regulatory regions. We have identified a factor in Balb/c-3T3 cells that binds to an oligonucleotide, containing sequences -351 to -337 of the human c-fos gene. This factor is inducible in quiescent cells within 30 min of addition of conditioned medium from v-sis transformed cells. Cycloheximide fails to block this induction. This result suggests that the factor is present in an inactive form in quiescent cells and is activated only in response to the appropriate inducer. Fibroblast growth factor (FGF) and the tumor promoter phorbol myristate acetate (TPA) induce the c-fos gene but not this DNA-binding activity. We propose from this that there are multiple regulatory regions upstream of c-fos each capable of responding to a different set of stimuli.

Animals↗
PubMed1987

Inducible binding of a factor to the c-fos regulatory region.

The c-fos gene is rapidly and transiently activated in quiescent BALB/c-3T3 cells in response to serum, platelet-derived growth factor or conditioned medium from v-sis-transformed cells. This activation occurs at the level of transcription and in the absence of new protein synthesis. Using a gel electrophoresis DNA-binding assay, we have found a DNA-binding activity in BALB/c-3T3 cells that is induced within 20 min of treatment with conditioned medium from v-sis-transformed cells. A DNA methylation interference assay has shown that this factor binds to a sequence approximately 346 base pairs upstream of the transcription initiation site of the human c-fos gene. Insulin, epidermal growth factor, and phorbol 12-myristate 13-acetate fail to induce this DNA-binding factor. Protein synthesis inhibitors do not block the induction of this activity. We propose that this factor preexists in an inactive form in quiescent cells and that its binding activity is activated in response to appropriate extracellular inducers.

Animals↗
PubMed1985

The PDGF-inducible 'competence genes': intracellular mediators of the mitogenic response.

We have described a new gene family within mammalian cells. Transcription of this gene family is coordinately induced when BALB/c-3T3 cells are exposed to platelet-derived growth factor. At least two cellular proto-oncogenes (c-myc and c-fos) are members of this gene family, which we term 'competence'. At least one competence gene, c-myc, functions as an intracellular mediator of the mitogenic response to PDGF. Expression of the competence gene family may be a central component of the mitogenic response in fibroblasts, lymphocytes and regenerating liver.

Animals↗
PubMed1985

Platelet-derived growth factor and double-stranded ribonucleic acids stimulate expression of the same genes in 3T3 cells.

Platelet-derived growth factor (PDGF) stimulates expression of a "competence" gene family in Balb/c-3T3 cells. The competence family contains the c-myc and c-fos genes together with several functionally uncharacterized genes (JE, KC, and r-fos) that have been isolated as cDNA clones. We show that double-stranded ribonucleic acid is a potent inducer of the competence gene family. Infection with vesicular stomatitis virus also induces expression of this gene family. Conversely, PDGF stimulates expression of genes hitherto characterized as responsive to double-stranded ribonucleic acids, including the beta-fibroblast interferon and (2'-5')-oligoadenylate synthetase genes. These PDGF-inducible genes could conceivably function in a feedback loop to control 3T3 cell growth. Some of the genes, such as c-fos and c-myc, are induced quickly by PDGF and may initiate a round of cell division. Others, such as beta-fibroblast interferon and (2'-5')-oligoadenylate synthetase, are induced more slowly and may function as feedback inhibitors of the growth response to PDGF.

2',5'-Oligoadenylate Synthetase↗
PubMed1984

Expression of the c-fos gene and of an fos-related gene is stimulated by platelet-derived growth factor.

Complementary DNA clones of genes induced by platelet-derived growth factor (PDGF) in BALB/c-3T3 cells were isolated; one such clone contains a domain having nucleotide sequence homology with the third exon of c-fos. This nucleotide sequence homology is reflected in the predicted amino acid sequences of the gene products. Under low stringency conditions, the mouse v-fos gene cross-hybridizes with the PDGF-inducible complementary DNA clone. However, the messenger RNA transcripts of mouse c-fos and the new fos-related gene can be distinguished by gel electrophoresis and by S1 nuclease analysis. Expression of the authentic c-fos gene is induced by PDGF and superinduced by the combination of PDGF and cycloheximide.

Amino Acid Sequence↗
PubMed1983

Molecular cloning of gene sequences regulated by platelet-derived growth factor.

We have screened a cDNA library for gene sequences that are regulated by platelet-derived growth factor (PDGF) in BALB/c-3T3 cells. Of 8000 clones screened, less than 14 independent PDGF-inducible sequences were found. Two of these (KC and JE) were studied in detail. By hybrid-selection and translation the KC and JE mRNAs encode 10,000 and 19,000 dalton polypeptides, respectively. In the absence of PDGF, the JE and KC sequences correspond to low abundance mRNAs. One hour after addition of PDGF their abundance level can be increased 10- to 20-fold. Within 4 hr, a 60-fold induction of JE can be attained. Nanogram per ml quantities of pure PDGF regulate these sequences whereas microgram/ml quantities of chemically unrelated mitogens (EGF, insulin, or platelet-poor plasma) have either a weak or an undetectable effect. Inhibitors of protein synthesis block the progression of quiescent 3T3 cells through G1 into S phase; however these drugs do not block the induction of KC and JE by PDGF. This result indicates that these sequences correspond to "early genes" which are not induced as a consequence of cell growth, but rather are directly regulated by PDGF.

Animals↗
PubMed1983

Cell-specific regulation of the c-myc gene by lymphocyte mitogens and platelet-derived growth factor.

We show that c-myc is an inducible gene that is regulated by specific growth signals in a cell-cycle-dependent manner. Specifically, agents that initiate the first phase of a proliferative response in lymphocytes (lipopolysaccharide or Concanavalin A) and fibroblasts (platelet-derived growth factor) induce c-myc mRNA. Within one to three hr after the addition of these mitogens to the appropriate cells, c-myc mRNA concentration is increased between 10- and 40-fold. This induction of c-myc mRNA occurs in the presence of cycloheximide and, therefore, does not require the synthesis of new protein species. Consequently, the induction of c-myc mRNA is not secondary to growth. In addition, c-myc mRNA is "superinduced" by the combination of cycloheximide and mitogen, a finding consistent with a model that a labile protein may regulate c-myc levels in these cells. Further, this work suggests a regulatory linkage between the function of two oncogenes--c-myc and c-sis--the latter being the putative structural gene for PDGF.

Animals↗
PubMed1981

Post-transcriptional control of protein synthesis in Balb/c-3T3 cells by platelet-derived growth factor and platelet-poor plasma.

Platelet-derived growth factor (PDGF) and platelet-poor plasma, which lacks PDGF, both induce a rapid increase in the rate of total protein synthesis within quiescent, density-arrested Balb/c-3T3 cells. This stimulation of protein synthesis is associated with an increased aggregation of ribosomes into polyribosomes. Nuclear functions are not required for this response, as demonstrated by the observation that this stimulation of protein synthesis occurs in cells pretreated with actinomycin D and in enucleated cells (cytoplasts). The response to PDGF persists even after PDGF has been removed from the culture medium, but in contrast, when plasma is removed from the medium, polysomes disaggregate and protein synthesis declines. PDGF and plasma do not function synergistically to increase protein synthesis, whereas they do to induce optimum DNA synthesis. Thus stimulation of the translational apparatus may be necessary for the mitogenic response of Balb/c-3T3 cells to growth factors, but it is not by itself sufficient.

Animals↗
PubMedDate not supplied

Functional role for c-myc in mitogenic response to platelet-derived growth factor.

In BALB/c-3T3 cells, expression of the c-myc gene is stimulated by platelet-derived growth factor (PDGF). Using mouse mammary tumour virus promoter: c-myc recombinant plasmids, 3T3 sublines were constructed in which hydrocortisone was the primary determinant of myc mRNA content. The c-myc gene product is an intracellular mediator of the growth response to PDGF though probably not the only one. Both the human and the mouse c-myc genes stimulate clonal growth of 3T3 cells in PDGF-free medium suggesting new strategies for analysis of oncogenes which do not function in focus formation assays.

Animals↗