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M Boshart

Publications and source records attributed to M Boshart.

29 records · Page 2Linked to original sources
PubMed1990

Two genetically defined trans-acting loci coordinately regulate overlapping sets of liver-specific genes.

Mice homozygous for deletions around the albino locus fail to activate expression of a set of neonatal liver functions and die shortly after birth. This phenotype is thought to result from the loss of a positive transacting factor, denoted alf, in deletion homozygotes. Using differential cDNA screening, we isolated and characterized genes whose cell type-specific transcription is affected by alf and found as a common feature that expression of these genes is induced by glucocorticoids and cAMP. Surprisingly, a subset of these alf-responsive genes is negatively controlled by the tissue-specific extinguisher locus Tse-1. Administration of glucocorticoids and cAMP leads to reversal of Tse-1-mediated extinction of these genes. These results show that two trans-acting factors coordinately regulate expression of overlapping sets of liver-specific genes. We suggest that both the lethal phenotype and the extinguished state result from interference with hormone signal transduction.

Animals↗
PubMed1990

A cyclic AMP response element mediates repression of tyrosine aminotransferase gene transcription by the tissue-specific extinguisher locus Tse-1.

Tyrosine aminotransferase (TAT) gene expression is liver specific and inducible by glucocorticoids and via the cAMP signaling pathway. In fibroblasts and other nonliver cells the gene is subject to negative control by the trans-dominant tissue-specific extinguisher locus Tse-1. We identified a hepatocyte-specific enhancer that is repressed by Tse-1. Two distinct sequence motifs are absolutely essential for function of this enhancer: a cAMP response element (CRE), which is the target for repression by Tse-1, and a hepatocyte-specific element. The specificity of the enhancer is generated by the combination of these two essential elements, which are fully interdependent. In vivo footprinting indicates that Tse-1 acts by affecting protein binding at the CRE. A direct antagonism between Tse-1 and the cAMP signaling pathway suggests that Tse-1 plays a role in control of developmental activation of the TAT gene.

Animals↗
PubMed1990

In vivo monitoring of a cAMP-stimulated DNA-binding activity.

The transcriptional activity of the tyrosine aminotransferase (TAT) gene is influenced by two major signal transduction pathways, by glucocorticoids and by glucagon acting via cAMP. We analyzed the effect of cAMP on protein-DNA interactions in vivo and on the transcription rate of the TAT gene. We demonstrate that a cAMP-responsive element (CRE) is located in a tissue-specific DNase I-hypersensitive region, 3.6 kb upstream of the start site of transcription. By using the genomic footprinting technique, we show that this sequence is occupied by protein in uninduced cells and that the in vivo footprint is transiently increased upon cAMP induction. Protein binding at the TAT-CRE correlates with the rate of transcription of the TAT gene. Cycloheximide treatment reveals that the genomic footprint is subject to rapid turnover; however, subsequent cAMP induction in the continued presence of cycloheximide restores the footprint partially. We conclude that as a part of the signal transduction pathway, a cAMP-dependent, post-translational modification increases the DNA-binding activity of a protein to the TAT-CRE and thereby stimulates the transcription rate of the TAT gene.

Base Sequence↗
PubMed1990

Chromatin structures of the rat tyrosine aminotransferase gene relate to the function of its cis-acting elements.

The relationship between DNase I-hypersensitive sites (HSs) and transcriptional enhancers of the rat tyrosine aminotransferase (TAT) gene was examined by comparing HSs in and around the TAT gene with the activity of the corresponding DNA sequences in transient transfection assays. In this manner, we identified two HSs as liver-specific enhancers. Of three hepatoma cell lines examined, only one sustained TAT mRNA levels comparable to those of liver. In this cell line, both enhancers were strongly active, and strong hypersensitivity in chromatin over the enhancers was evident. The other two hepatoma cell lines had reduced levels of TAT mRNA and no or altered hypersensitivity over either the enhancers or the promoter. One of these lines carried a negative regulator of the TAT gene, the tissue specific extinguisher Tse-1. This cell line exhibited all HSs characteristic of the strongly active gene except at the promoter; however, one enhancer was inactive even though hypersensitive in chromatin. In a TAT-nonexpressing cell line, inactivity of both enhancers correlated with absence of the respective HSs. We conclude that although hypersensitivity in chromatin necessarily accompanies cell-type-specific enhancer activity, the occurrence of cell-type-specific HSs does not imply that the underlying sequences harbor enhancers active in transient transfection assays.

Animals↗
PubMed1989

Glucocorticoid- and progesterone-specific effects are determined by differential expression of the respective hormone receptors.

Although glucocorticoids and progestins control vastly different physiological processes, the receptors mediating the effects of these hormones interact with the same DNA sequences. Transfer experiments involving synthetic genes and in vitro binding studies have shown that progesterone and glucocorticoid receptors both recognize the same 15-base pair DNA element (TGTACAGGATGTTCT), raising the question of how the two steroids affect gene expression selectively. We considered the possibility that their selectivity arises from either the differential expression of the receptors in target cells or the differential dependence of receptor function on additional transcription factors. To test these alternatives we introduced a progesterone-receptor expression plasmid into the rat hepatoma cell line Fto2B-3 which contains glucocorticoid receptor but is devoid of progesterone receptor. We report that expression of the progesterone receptor in Fto2B-3 cells renders endogenous glucocorticoid-regulated genes inducible by progestins. Our data show that the responsiveness of a cell to external stimuli can be reprogrammed by the expression of a single transcription factor and that differential expression of hormone receptors is at least one mechanism by which steroid-specific gene activation is achieved.

Animals↗
PubMed1987

Cooperativity of glucocorticoid response elements located far upstream of the tyrosine aminotransferase gene.

Two glucocorticoid response elements (GREs) located 2.5 kb upstream of the transcription initiation site of the tyrosine aminotransferase gene were identified by gene transfer experiments and shown to bind to purified glucocorticoid receptor. Although the proximal GRE has no inherent capacity by itself to stimulate transcription, when present in conjunction with the distal GRE, this element synergistically enhances glucocorticoid induction of gene expression. Cooperativity of the two GREs is maintained when they are transposed upstream of a heterologous promoter. An oligonucleotide of 22 bp representing the distal GRE is sufficient to confer glucocorticoid inducibility. As evidenced by the mapping of DNAase I hypersensitive sites, local alterations in the structure of chromatin at the GREs take place as a consequence of hormonal treatment.

Base Sequence↗
PubMed1986

Human papillomaviruses in Buschke-Löwenstein tumors: physical state of the DNA and identification of a tandem duplication in the noncoding region of a human papillomavirus 6 subtype.

Six Buschke-Löwenstein tumors, i.e., highly differentiated squamous cell tumors of the genital region, were shown to contain human papillomavirus 6 (HPV 6) or HPV 11 genomes. The viral DNA was found in an episomal state, including a very small fraction of circular oligomers. HPV 6a and HPV 6d genomes were cloned from two of the tumors. Comparison with HPV 6b, cloned from a benign genital wart (E. -M. de Villiers, L. Gissmann, and H. zur Hausen, J. Virol. 40:932-935, 1981) by restriction mapping and partial sequence analysis, revealed a very high degree of homology with the different HPV 6 subtypes. A tandem duplication of 459 base pairs within the noncoding region of the genome was found in the new subtype HPV 6d. This structural rearrangement in a region containing the putative control elements for early gene transcription might influence the biological potential of that virus. No evidence for rearrangement of this region was found in the HPV DNA from the five other tumors.

Base Sequence↗
PubMed1985

A very strong enhancer is located upstream of an immediate early gene of human cytomegalovirus.

A strong transcription enhancer was identified in the genomic DNA (235 kb) of human cytomegalovirus (HCMV), a ubiquitous and severe pathogen of the herpesvirus group. Cotransfection of enhancerless SV40 DNA with randomly fragmented HCMV DNA yielded two SV40-HCMV recombinant viruses that had incorporated overlapping segments of HCMV DNA to substitute for the missing SV40 enhancer. Within HCMV, these enhancer sequences are located upstream of the transcription initiation site of the major immediate-early gene, between nucleotides -118 and -524. Deletion studies with the HCMV enhancer, which harbors a variety of repeated sequence motifs, show that different subsets of this enhancer can substitute for the SV40 enhancer. The HCMV enhancer, which seems to have little cell type or species preference, is severalfold more active than the SV40 enhancer. It is the strongest enhancer we have analyzed so far, a property that makes it a useful component of eukaryotic expression vectors.

Base Sequence↗
PubMed1984

A new type of papillomavirus DNA, its presence in genital cancer biopsies and in cell lines derived from cervical cancer.

DNA of a new papillomavirus type was cloned from a cervical carcinoma biopsy. Two EcoRI clones of 7.8 and 6.9 kb in length were obtained, the latter contained a 900-bp deletion. The BamHI fragments of both clones were used to characterize the DNA. It represents a distinct type of papillomavirus as determined by its size, its cross-hybridization with DNA of other papillomavirus types under conditions of low stringency only, the co-linear alignment of its genome with HPV 6 and HPV 16 prototypes and its occasional occurrence as oligomeric episomes. We tentatively propose to designate it as HPV 18. DNA hybridizing with HPV 18 under stringent conditions was detected in 9/36 cervical carcinomas from Africa and Brazil, in 2/13 cervical tumors from Germany and 1/10 penile carcinomas. Benign tumors (17 cervical dysplasias, 29 genital warts), eight carcinomata in situ and 15 biopsies of normal cervical tissue were devoid of detectable HPV 18 DNA. HPV 18-related DNA was found, however, in cells of the HeLa, KB and C4-1 lines all derived from cervical cancer. The state of the viral DNA was investigated in four cervical cancer biopsies. The data reveal that the DNA might be integrated into the host cell genome. One tumor provided evidence for head to tail tandem repeats some of which persisted as circular episomes.

Base Sequence↗
PubMed1984

Presence of human papillomavirus in genital tumors.

Human papillomavirus (HPV) types 16 and 18 have been identified in two different human cervical carcinomas. The viral DNAs were molecularly cloned and used as probes to screen a large number of genital tumors by Southern blot analysis. HPV-16 or HPV-18 sequences, respectively, were found in a high percentage of cervical carcinomas, but only in a small number of condylomata acuminata or flat condylomas. The majority of the latter lesions, however, contained HPV-6 or HPV-11 sequences, respectively, which in contrast were detected only rarely in carcinomas in situ or invasively growing carcinomas. A similar distribution of the different papillomaviruses was observed when cell swabs taken from the cervix were tested by in situ hybridization.

Animals↗