Negative transcriptional regulatory element that functions in embryonal carcinoma cells

AP-1, ETS, and transcriptional silencers regulate retinoic acid-dependent induction of keratin 18 in embryonic cells

The differentiation of both embryonal carcinoma (EC) and embryonic stem (ES) cells can be triggered in culture by exposure to retinoic acid and results in the transcriptional induction of both the endogenous mouse keratin 18 (mK18) intermediate filament gene and an experimentally introduced human keratin 18 (K18) gene as well as a variety of other markers characteristic of extraembryonic endoderm. The induction of K18 in EC cells is limited, in part, by low levels of ETS and AP-1 transcription factor activities which bind to sites within a complex enhancer element located within the first intron of K18. RNA levels of ETS-2, c-Jun, and JunB increase upon the differentiation of ES cells and correlate with increased expression of K18. Occupancy of the ETS site, detected by in vivo footprinting methods, correlates with K18 induction in ES cells. In somatic cells, the ETS and AP-1 elements mediate induction by a variety of oncogenes associated with the ras signal transduction pathway. In EC cells, in addition to the induction by these limiting transcription factors, relief from negative regulation is mediated by three silencer elements located within the first intron of the K18 gene. These silencer elements function in F9 EC cells but not their differentiated derivatives, and their activity is correlated with proteins in F9 EC nuclei which bind to the silencers and are reduced in the nuclei of differentiated F9 cells. The induction of K18, associated with the differentiation of EC cells to extraembryonic endoderm, is due to a combination of relief from negative regulation and activation by members of the ETS and AP-1 transcription factor families.

AP-1, ETS, and transcriptional silencers regulate retinoic acid-dependent induction of keratin 18 in embryonic cells

The differentiation of both embryonal carcinoma (EC) and embryonic stem (ES) cells can be triggered in culture by exposure to retinoic acid and results in the transcriptional induction of both the endogenous mouse keratin 18 (mK18) intermediate filament gene and an experimentally introduced human keratin 18 (K18) gene as well as a variety of other markers characteristic of extraembryonic endoderm. The induction of K18 in EC cells is limited, in part, by low levels of ETS and AP-1 transcription factor activities which bind to sites within a complex enhancer element located within the first intron of K18. RNA levels of ETS-2, c-Jun, and JunB increase upon the differentiation of ES cells and correlate with increased expression of K18. Occupancy of the ETS site, detected by in vivo footprinting methods, correlates with K18 induction in ES cells. In somatic cells, the ETS and AP-1 elements mediate induction by a variety of oncogenes associated with the ras signal transduction pathway. In EC cells, in addition to the induction by these limiting transcription factors, relief from negative regulation is mediated by three silencer elements located within the first intron of the K18 gene. These silencer elements function in F9 EC cells but not their differentiated derivatives, and their activity is correlated with proteins in F9 EC nuclei which bind to the silencers and are reduced in the nuclei of differentiated F9 cells. The induction of K18, associated with the differentiation of EC cells to extraembryonic endoderm, is due to a combination of relief from negative regulation and activation by members of the ETS and AP-1 transcription factor families.

BOX DNA: a novel regulatory element related to embryonal carcinoma cell differentiation

BOX DNA was previously isolated from the DNA sequence inserted in the enhancer B domain of mutant polyomavirus (fPyF9) DNA. We also reported that BOX DNA functioned negatively on DNA replication and transcription of another polyomavirus mutant (PyhrN2) in F9-28 cells, a subclone of mouse F9 embryonal carcinoma (EC) cells expressing the polyomavirus large T antigen. In this study, we demonstrate that BOX DNA enhances transcription from the thymidine kinase (TK) promoter in various EC cells. One or three copies of BOX DNA, linked to the bacterial chloramphenicol acetyltransferase gene under the control of the herpes simplex virus TK promoter, activated promoter activity in F9, P19, and ECA2 cells. Band shift assays using BOX DNA as a probe revealed that specific binding proteins were present in all EC cells examined; the patterns of BOX DNA-protein complexes were the same among them. A mutation introduced within BOX DNA abolished enhancer activity as well as the formation of specific DNA-protein complexes. In non-EC cells, including L and BALB/3T3 cells, the enhancer activity of BOX DNA on the TK promoter was not observed, although binding proteins specific to the sequence exist. In band shift assays, the patterns of the DNA-protein complexes of either L or BALB/3T3 cells were different from those of EC cells. Furthermore, the enhancer activity of BOX DNA decreased upon differentiation induction in all EC cells examined, of different origins and distinct differentiation ability. In parallel with the loss of enhancer activity, the binding proteins specific for BOX DNA decreased in these cells. Moreover, we cloned a genomic DNA of F9, termed BOXF1, containing BOX DNA sequence approximately 400 bp upstream from the RNA start site of the gene. BOXF1, containing a TATA-like motif and the binding elements for Sp1 and Oct in addition to BOX DNA, possessed promoter activity deduced by a BOXF1-chloramphenicol acetyltransferase construct. Deletion analyses of the construct revealed that the transcription of BOXF1 gene is regulated by BOX DNA, preferentially in undifferentiated EC cells versus differentiated cells. Hence, BOX DNA is probably a novel transcriptional element related to EC cell differentiation.

BOX DNA: a novel regulatory element related to embryonal carcinoma cell differentiation

BOX DNA was previously isolated from the DNA sequence inserted in the enhancer B domain of mutant polyomavirus (fPyF9) DNA. We also reported that BOX DNA functioned negatively on DNA replication and transcription of another polyomavirus mutant (PyhrN2) in F9-28 cells, a subclone of mouse F9 embryonal carcinoma (EC) cells expressing the polyomavirus large T antigen. In this study, we demonstrate that BOX DNA enhances transcription from the thymidine kinase (TK) promoter in various EC cells. One or three copies of BOX DNA, linked to the bacterial chloramphenicol acetyltransferase gene under the control of the herpes simplex virus TK promoter, activated promoter activity in F9, P19, and ECA2 cells. Band shift assays using BOX DNA as a probe revealed that specific binding proteins were present in all EC cells examined; the patterns of BOX DNA-protein complexes were the same among them. A mutation introduced within BOX DNA abolished enhancer activity as well as the formation of specific DNA-protein complexes. In non-EC cells, including L and BALB/3T3 cells, the enhancer activity of BOX DNA on the TK promoter was not observed, although binding proteins specific to the sequence exist. In band shift assays, the patterns of the DNA-protein complexes of either L or BALB/3T3 cells were different from those of EC cells. Furthermore, the enhancer activity of BOX DNA decreased upon differentiation induction in all EC cells examined, of different origins and distinct differentiation ability. In parallel with the loss of enhancer activity, the binding proteins specific for BOX DNA decreased in these cells. Moreover, we cloned a genomic DNA of F9, termed BOXF1, containing BOX DNA sequence approximately 400 bp upstream from the RNA start site of the gene. BOXF1, containing a TATA-like motif and the binding elements for Sp1 and Oct in addition to BOX DNA, possessed promoter activity deduced by a BOXF1-chloramphenicol acetyltransferase construct. Deletion analyses of the construct revealed that the transcription of BOXF1 gene is regulated by BOX DNA, preferentially in undifferentiated EC cells versus differentiated cells. Hence, BOX DNA is probably a novel transcriptional element related to EC cell differentiation.

Organization of mouse DNA polymerase beta gene silencer elements and identification of the silencer-binding factor(s)

Different portions of the 5'-upstream region of the mouse DNA polymerase beta gene were combined with bacterial chloramphenicol acetyltransferase (CAT) gene of the CAT vector. Transfection of these recombinant plasmids into mouse NIH/3T3 cells has revealed that each of the previously identified two negatively acting regions (silencers I and II) of this gene consists of multiple sub-domains. The distal silencer (silencer I) at around -1.5 kb consists of four sub-domains (-1852 to -1667, -1663 to -1616, -1564 to -1525 and -1355 to -1257). The promoter-proximal silencer (silencer II) at around -0.5 kb consists of two functional domains (-681 to -523 and -490 to -447) separated by a neutral region of 33 base pairs. Silencer II functioned efficiently when silencer I was deleted. Conversely, the distal silencer I functioned efficiently when silencer II was deleted. Thus, these silencers functioned redundantly to each other in NIH/3T3 cells. Nucleotide sequence analysis revealed no extensive sequence similarity between these two silencers. Significant sequence similarity is present between a distal portion of silencer II and the c-myc gene silencer, and also between a proximal portion of silencer II and the mouse F9 cell-specific silencer. A protein factor(s) that specifically bound to the silencer elements was detected in nuclear extracts of NIH/3T3 cells and mouse liver in which DNA polymerase beta was expressed at a rather low level. The same binding factor(s) can bind to both silencer I and II regions, although its affinity for silencer II is much higher than that for silencer I.

Identification of the HeLa tumor-associated antigen, p75/150, as intestinal alkaline phosphatase and evidence for its transcriptional regulation

Prior studies identified a cell-surface antigen, p75/150, that exclusively associated with the tumorigenic phenotype of the HeLa parent and the tumorigenic phenotype of the HeLa parent and the tumorigenic segregants of suppressed, nontumorigenic HeLa x human fibroblast cell hybrids. Candidate p75/150 cDNA clones were isolated from a D98/AH.2 (HeLa) cDNA library using oligonucleotide probes derived from p75/150 partial peptide sequence data. A data base search revealed close similarity of p75/150 with intestinal alkaline phosphatase (IAP) [Berger, J., Garantini, E., Hua, J. C. & Udenfriend, S. (1987) Proc. Natl. Acad. Sci. USA 84, 695-698]. We demonstrate that p75/150 is identical to HeLa IAP by the following criteria: (i) 47/49 amino acid identity of p75 peptide sequence with IAP, (ii) restriction maps for the p75/150 candidate cDNA clone and IAP are identical, (iii) partial DNA sequence analysis of p75/150 candidate cDNA clones revealed complete nucleotide identity with IAP, except for a single nucleotide substitution in the 5' untranslated region, (iv) transfection of a p75/150 cDNA expression vector into the nontumorigenic hybrid, CGL1, yielded p75/150 antibody-positive transfectants that also expressed partially heat-resistant alkaline phosphatase activity. Northern blot analysis demonstrated that high levels of HeLa IAP mRNA were expressed in D98/AH.2 and the tumorigenic segregant CGL4; however, no mRNA was detected in CGL1. Nuclear run-on analyses indicate that HeLa IAP mRNA expression in the HeLa x fibroblast hybrids is regulated at the level of transcription initiation. Furthermore, evidence is discussed supporting the involvement of a chromosome 11 tumor suppressor locus in the regulation of HeLa IAP gene expression.

Effect of silencer on polyomavirus DNA replication

We have cloned the cellular sequence termed box DNA from the enhancer region of polyomavirus F9 mutant fPyF9. Box DNA functions as a negative transcriptional element (silencer) in undifferentiated F9 cells but not in differentiated L cells. Plasmid DNAs containing the origin and enhancer of polyomavirus were used to measure simultaneously transcriptional and replication activities in transfected cells. DNA replication activity was significantly reduced under conditions in which the silencer was able to reduce enhancer activity in F9 cells. On the other hand, when the silencer could not repress enhancer activity in MOP-8 cells, which are mouse NIH 3T3 cells producing polyomavirus T antigen constitutively, replication activity was still intact. The silencer itself had no effect on DNA replication or transcription in either type of cells. Furthermore, the insertion of a 6-base oligonucleotide within a consensus sequence of box DNA abolished the repressive effect of the silencer on DNA replication and enhancer activities. These results suggest that enhancer factors, interacting with silencer factors, may be closely associated with the mechanism of replication.

Effect of silencer on polyomavirus DNA replication

We have cloned the cellular sequence termed box DNA from the enhancer region of polyomavirus F9 mutant fPyF9. Box DNA functions as a negative transcriptional element (silencer) in undifferentiated F9 cells but not in differentiated L cells. Plasmid DNAs containing the origin and enhancer of polyomavirus were used to measure simultaneously transcriptional and replication activities in transfected cells. DNA replication activity was significantly reduced under conditions in which the silencer was able to reduce enhancer activity in F9 cells. On the other hand, when the silencer could not repress enhancer activity in MOP-8 cells, which are mouse NIH 3T3 cells producing polyomavirus T antigen constitutively, replication activity was still intact. The silencer itself had no effect on DNA replication or transcription in either type of cells. Furthermore, the insertion of a 6-base oligonucleotide within a consensus sequence of box DNA abolished the repressive effect of the silencer on DNA replication and enhancer activities. These results suggest that enhancer factors, interacting with silencer factors, may be closely associated with the mechanism of replication.