Tissue specific trans-acting factor interaction with proximal rat prolactin gene promoter sequences.

Using an exonuclease III protection assay, strong, reversible and tissue-specific binding of GH3 cell nuclear factors to proximal regions of the rat prolactin (rPrl) promoter (-31 to -77) has been detected. A second less prominent region of factor binding, that may have a correlate in HeLa cell extracts, was detected in the region (-155 to -180). The binding is eliminated in the presence of excess unlabelled rPrl promoter sequences (-423 to +38), excess unlabelled distal rPrl 5'-flanking sequences (-1960 to -1260) and SV40-enhancer/promoter sequences; it is largely unaffected by growth hormone (rGH) promoter and RSV-LTR sequences. A plasmid containing the proximal rPrl promoter sequences (-75 to +38) was also shown to be an avid inhibitor, at low concentrations, of rPrl promoter driven chloramphenicol acetyl transferase (CAT) gene expression in transient cotransfection competition studies; under these assay conditions distal rPrl 5'-flanking sequences and RSV and rGH promoter plasmids do not compete. The results emphasize the critical importance of proximal rPrl promoter sequences for prolactin gene expression in GH3 cells but recognize the related functional potential of more distal sequences.     

Identification of the promoter sequences involved in the cell specific expression of the rat somatostatin gene.

DNA sequences containing the 5' flanking region of the rat somatostatin gene were linked to the coding sequence of the bacterial chloramphenicol acetyl transferase gene. This recombinant plasmid is active in expressing CAT activity in the neuronally derived, somatostatin producing CA-77 cell line. Deletion analyses of the somatostatin promoter show that the sequences proximal to position -60, relative to the cap site are required for expression of this promoter. A 4 base pair deletion of residues -46 through -43 within the somatostatin promoter results in a down mutation in vivo suggesting the existence of an element critical for the expression of the promoter in CA-77 cells. In addition, the somatostatin recombinant and its 5' deletion constructs preferentially express CAT activity in CA-77 cells, whereas only basal level of expression is observed in HeLa, BSC40, and RIN-5F cell lines, pointing to the cell specific nature of this promoter.     

A cell surface receptor complex for collagen type I recognizes the Arg- Gly-Asp sequence

To isolate collagen-binding cell surface proteins, detergent extracts of surface-iodinated MG-63 human osteosarcoma cells were chromatographed on affinity matrices of either type I collagen-Sepharose or Sepharose carrying a collagen-like triple-helical peptide. The peptide was designed to be triple helical and to contain the sequence Arg-Gly-Asp, which has been implicated as the cell attachment site of fibronectin, vitronectin, fibrinogen, and von Willebrand factor, and is also present in type I collagen. Three radioactive polypeptides having apparent molecular masses of 250 kD, 70 kD, and 30 kD were distinguishable in that they showed affinity toward the collagen and collagen-like peptide affinity columns, and could be specifically eluted from these columns with a solution of an Arg-Gly-Asp-containing peptide, Gly-Arg-Gly-Asp-Thr-Pro. These collagen-binding polypeptides associated with phosphatidylcholine liposomes, and the resulting liposomes bound specifically to type I collagen or the collagen-like peptide but not to fibronectin or vitronectin or heat-denatured collagen. The binding of these liposomes to type I collagen could be inhibited with the peptide Gly-Arg-Gly-Asp-Thr-Pro and with EDTA, but not with a variant peptide Gly-Arg-Gly-Glu-Ser-Pro. We conclude from these data that these three polypeptides are membrane molecules that behave as a cell surface receptor (or receptor complex) for type I collagen by interacting with it through the Arg-Gly-Asp tripeptide adhesion signal. The lack of binding to denatured collagen suggests that the conformation of the Arg-Gly-Asp sequence is important in the recognition of collagen by the receptor complex.     

Characterization of a novel anti-peptide antibody that recognizes a specific conformation of the platelet-derived growth factor receptor.

Two site-specific anti-peptide antibodies (AbP1 and AbP2) were raised against the platelet-derived growth factor (PDGF) receptor. These two sites correspond to amino acid residues 977 through 988 (peptide 1) and 932 through 947 (peptide 2) of the murine PDGF receptor. Both antibodies recognized human and murine PDGF receptors in immunoprecipitation and immunoblotting analyses. None of the antibodies was directed to phosphotyrosine. One of the antibodies (AbP2) showed unusual antigen recognition specificity. This antibody specifically recognized the tyrosine-phosphorylated PDGF receptor and not the unphosphorylated native receptor, suggesting that recognition by this antibody requires a specific conformation that is induced by PDGF-stimulated autophosphorylation.     

Metal-dependent binding of a nuclear factor to the rat metallothionein-I promoter.

Genomic footprinting studies in vivo and experiments using synthetic metal regulatory elements (MREs) in vitro suggest protein binding to the MREs of the mouse and rat metallothionein I (MT-I) genes. Using gel-retardation assays of promoter fragments, we observe a cadmium-dependent binding factor for the rat MT-I promoter in rat hepatoma cells. This factor is present in extracts from both uninduced and cadmium-induced cells, but requires the presence of cadmium to bind to the promoter. The formation of a cadmium-dependent complex is competed by an oligonucleotide containing two MREs. This competition is lost when when one of the MREs is mutated, indicating a requirement for at least two MREs for binding of this factor. The cadmium-dependent factor dissociates more rapidly from the MT-I promoter than does a factor that binds to a consensus Sp1 site present on the same DNA fragment. UV crosslinking analysis using nuclear extracts from cadmium induced cells, in the presence of an oligonucleotide probe containing both 5-bromodeoxyuridine and 32P-deoxycytidine, identifies a 39 kDalton protein associated with the metal inducible complex.