Showing papers by "Michael Karin published in 1987"

Activation of transcription by two factors that bind promoter and enhancer sequences of the human metallothionein gene and SV40

Abstract: Genetic analysis of eukaryotic transcriptional promoters has revealed that protein-coding genes often contain a complex array of cis-control elements consisting of upstream activator sequences and enhancer elements1–5. The metallothionein genes provide a useful example for dissecting the action of multiple interspersed control elements that govern both basal level and regulated expression in animal cells6–8. The human metallothionein (hMTIIA) promoter has been analysed in detail and found to contain no less than five distinct control elements in the 5' flanking regions of the gene that mediate specificity and regulation of transcription9,10 (Fig. 1). These different control elements can be functionally subdivided into two categories: basal and induced elements. There are several distinct basal recognition sequences, which include a TATA-box, a GC-box, and at least two basal level enhancer (BLE) sequences, that function like classical enhancer elements10–12. The hMTIIA gene also responds to induction by heavy metals and by steroid hormones through the action of metal regulatory elements (MRE) and glucocorticoid responsive elements (GRE)9. Here we report the identification of two cellular DNA-binding proteins that interact selectively with sequences governing the basal level expression of hMTIIA. One of these factors is a novel activator protein (API) that interacts with sequences in the BLE of hMTIIA and also binds to a site within the 72-base pair (bp) repeats of the simian virus 40 (SV40) enhancer region. The second protein has been purified to homogeneity and shown to be transcription factor Sp1 which recognizes and binds to a single GC-box element within the hMTIIA promoter.

Multiple cis- and trans-acting elements mediate the transcriptional response to phorbol esters.

Abstract: Protein kinase C is important in the transduction of signals generated at the plasma membrane. The physiological activators of protein kinase C are diacylglycerols1, and the tumour-promoting phorbol esters, such as 12-O-tetradecanoyI-phorbol-14 acetate (TPA), constitute another group of specific activators1,2. Many cellular substrates for phosphorylation by protein kinase C have been described1,3, but proteins that directly control transcription in response to protein kinase C activation are yet to be identified. TPA treatment leads to induction of various proto-oncogenes4–7, growth factor genes7,8, and genes encoding secreted proteases9. In addition. TPA increases the activity of viral enhancer elements10–13. To identify trans-acting factors that mediate the transcriptional response to TPA we chose the simian virus 40 (SV40) enhancer14 as a model, because it is known to be composed of several discrete cis-acting elements15–18 which are recognized by multiple trans-acting factors19–21. We report here that the SV40 enhancer contains at least four different TPA responsive elements whose activity is dependent on cell-type. The induction response is likely to involve at least two distinct post-translational steps which modulate the activity of the proteins that recognize these elements.

Tissue-specific expression of the human growth hormone gene is conferred in part by the binding of a specific trans-acting factor.

Abstract: The molecular basis for the pituitary-specific expression of the human growth hormone (hGH) gene was investigated, by gene transfer and protein footprinting experiments. Plasmid constructs in which CAT or Neo transcription units are fused to a 0.5 kb fragment of the hGH 5' sequences were efficiently expressed in GC and GH3 cells, derived from a pituitary tumor, but not in cell lines of other origins, indicating the presence of a tissue-specific promoter. DNaseI footprinting experiments have identified at least three factors that specifically bind to the hGH 5' region. While two of these factors were also detected in extracts of non-expressing cells, the third factor, GHF-1, was detected only in extracts of GH expressing pituitary tumor cells. Mutagenesis experiments suggest that binding of GHF-1 and some of the other more ubiquitous factors is required for optimal hGH promoter activity in vivo. Tissue specificity of the hGH promoter therefore seems to be determined by the binding of at least one tissue-specific trans-acting factor, acting in concert with several other more ubiquitous, yet specific, DNA binding proteins.