Biomedical subjects
Publications and source records attributed to H Lubon.
The promoter sequences from -175 to +10 of the mouse whey acidic protein (WAP) gene are a target for sequence-specific binding of nuclear proteins [(1987) Nucleic Acids Res. 15, 2103-2121]. Using in vitro transcription assays based on nuclear extracts, transcription factors were shown to bind to these sequences and promoter upstream sequences were found to stimulate transcription.
In this paper we demonstrate that modulator sequences upstream of the enhancer of the major immediate-early promoter of human cytomegalovirus exert a differential effect on the level of transcription in a variety of cells and that this region has the capacity to interact with specific nuclear protein. Depending on the cell type, these modulator sequences increased or decreased transcriptional activation from the IE1 gene promoter-enhancer. The cell lines identified in this report should be useful to study the molecular mechanism of cell-specific transcriptional repression and activation exerted by the major immediate-early promoter upstream region.
Nuclear extracts from mammary glands of lactating rats contain DNA binding protein(s) with high affinity to the region -125 to -85 of the rat alpha-lactalbumin promoter. The protected sequence is part of a mammary conserved sequence described by Hall et al. [(1987) Biochem. J. 242, 735-742]. Comparison of the DNA protein-binding sites in the 5' flanking sequence of the rat alpha-lactalbumin and mouse whey acidic protein genes suggests that the consensus sequence 5'-TGGCARNNWCKKC-3' is the protein(s) recognition site. This binding site is part of a highly conserved region [consensus sequence, TGGCAGSCTCGGCST(G)YTCTCTCT(NTG)TGGCARA] present in the promoter of four whey protein genes.
The binding of nuclear proteins and the functional activity of the HIV-LTR enhancer repeats in different cell lines (Jurkat, CEM, H9, U937, Raji, B cells, T47D, HeLa, 293, and HepG2 cells) was investigated in vitro. Five distinct complexes formed with the enhancer repeat have been identified by an electrophoretic mobility shift assay. The distribution of these complexes varied qualitatively and quantitatively between nuclear proteins from different sources. In the extracts tested, transcription of the HIV-LTR 5' deletion mutants (-453/80, -176/80, -117/80, -103/80, -65/80, and -48/80) was initiated correctly. Transcriptional stimulation dependent upon the presence of the enhancer repeat sequences was observed in all nuclear extracts and was highest in Jurkat, Raji, and B cell extracts. The presence of specific factors and the functional activity of the enhancer repeats as well as other regulatory units in a variety of cells indicates limited host-cell restriction of HIV transcription initiation in vitro.
Repeat sequence motifs as well as unique sequences between nucleotides -150 and -22 of the human cytomegalovirus immediate-early 1 gene interact in vitro with nuclear proteins. We show that a transcriptional element between nucleotides -91 and -65 stimulated promoter activity in vivo and in vitro by binding specific cellular transcription factors. Finally, a common sequence motif, (T)TGG/AC, present in 15 of the determined binding sites suggests a particular class of nuclear factors associated with the immediate-early 1 gene.
The possibility of DNA-binding proteins interacting in vitro with the polymerase II transcriptional machinery was explored by using a competition assay with individual target sequences for enhancer-binding factors. Transcription factors binding to at least five specific enhancer sequences mediate the activity of the human cytomegalovirus immediate-early 1 gene in vitro. Furthermore, our data suggest that individual DNA-bound enhancer factors can interact with the promoter transcription complex.
The gene for the whey acidic protein (WAP) is expressed specifically in the lactating mammary glands of rodents. We present evidence that nuclear proteins from mammary epithelial cells form a multiple nucleoprotein complex with the WAP gene promoter/upstream region. As monitored by mobility shifts, nuclear proteins from lactating mammary glands and from the mammary cell line MCF-7 form four high affinity complexes with a fragment spanning the region between nucleotides -175 and -88. Nuclear proteins from liver and HeLa cells generate only three high affinity complexes. DNAaseI and ExonucleaseIII protection confirmed the binding of mammary nuclear proteins to specific sequences in the WAP gene upstream region. This is the first report to describe the interaction of nuclear proteins from lactating mammary glands with cognate binding sites in the promoter/upstream region of a milk protein gene. The possibility of the binding sites being candidates for cis-acting regulatory elements governing the regulated expression of the WAP gene is discussed.
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The effect of the human cytomegalovirus immediate early region 1 enhancer on transcription was studied in vitro with HeLa cell nuclear extract. Stimulation of in vitro transcription mediated by the enhancer element involves its recognition by specific trans-acting factors present in the nuclear extract. DNase I protection analysis was used to determine at the nucleotide level those enhancer sequences that interact with nuclear factors. At least nine sites of protein-DNA interaction were detected over approximately 400 base pairs of enhancer sequence. The regions of nuclease protection are associated with 21-, 19-, 18-, and 17-base-pair repeat elements as well as with a unique sequence, creating a large nucleoprotein complex. The relationship between the protein binding and the activity of the immediate early region 1 enhancer is discussed.
Recombinant human protein C (rhPC) secreted in the milk of transgenic pigs was studied. Transgenes having different regulatory elements of the murine milk protein, whey acidic protein, were used with cDNA and genomic human protein C (hPC) DNA sequences to obtain lower and higher expressing animals. The cDNA pigs had a range of expression of about 0.1-0.5 g/l milk. Two different genomic hPC pig lines have expressed 0.3 and 1-2 g/l, respectively. The rhPC was first purified at yields greater than 60 per cent using a monoclonal antibody (mAb) to the activation site on the heavy chain of hPC. Subsequent immunopurification with a calcium-dependent mAb directed to the gamma-carboxyglutamic acid domain of the light chain of hPC was used to fractionate a population having a higher specific anticoagulant activity in vitro. The higher percentages of Ca(2+)-dependent conformers isolated from the total rhPC by immunopurification correlated well with higher specific activity and lower expression. A rate limitation in gamma-carboxylation of rhPC was clearly identified for the higher expressing animals. Thus, transgenic animals with high expression levels of complex recombinant proteins produced a lower percentage of biologically active protein.
Milk of transgenic pigs secreting recombinant human Protein C (rHPC) was used as a model system to determine the utility of aqueous two-phase extraction systems (ATPS) for the initial step in the purification of proteins from milk. The major challenges in purification of recombinant proteins from milk are removal of casein micelles (that foul processing equipment) and elimination of the host milk proteins from the final product. When milk was partitioned in ATPS composed of polyethylene glycol (PEG) and ammonium sulfate (AS), the phases were clarified and most of the caseins precipitated at the interphase. The partition coefficients of the major milk proteins and rHPC were dependent upon the molecular weight of the PEG used in the ATPS. Higher-partition coefficients of the major whey proteins, beta-lactoglobulin, and alpha-lactalbumin were observed in ATPS made up of lower molecular-weight PEG (1000 or 1450) as compared to systems using higher molecular-weight PEG. Lowering the pH of the ATPS from 7.5 to 6.0 resulted in increased precipitation of the caseins and decreased their concentration in both phases. rHPC had a partition coefficient of 0.04 in a system composed of AS and PEG 1450. The rHPC in pig milk was shown to be highly heterogenous by two-dimensional gel electrophoresis. The heterogeneity was owing to inefficient proteolytic processing of the single chain to the heterodimeric form and differences in glycosylation and other post-translational processing. Differential partitioning of the multiple forms of purified rHPC in the ATPS was not observed. rHPC after processing in ATPS was recovered in a clear phase free of most major milk proteins. ATPS are useful as the initial processing step in the purification of recombinant proteins from milk because clarification and enrichment in combined in a single step.