MRG1 Expression in Fibroblasts Is Regulated by Sp1/Sp3 and an Ets Transcription Factor (2001)

MRG1 (melanocyte-specific gene 1 (MSG1)-related gene), a ubiquitously expressed transcription factor that interacts with p300/CBP, TATA-binding protein and Lhx2, is the founding member of a new family of transcription factors. Initial characterization of this newly discovered transcription factor has underscored its potential involvement in many important cellular processes through transcriptional modulation. We previously demonstrated that MRG1 can be induced by various biological stimuli (Sun, H. B., Zhu, Y. X., Yin, T., Sledge, G., and Yang, Y. C. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 13555–13560). As a first step in understanding its role in different biological processes, we investigated mechanisms that regulate transcription of the mouse MRG1 gene in fibroblasts. Transient transfection of Rat1 fibroblast cells with sequential 5′-deletions of mouse MRG1 promoter-luciferase fusion constructs indicated that the −104 to +121 region contains the full promoter activity. Deletion and site-directed mutations within this region revealed that the Ets-1 site at −97 to −94 and the Sp1 site at −51 to −46 are critical for MRG1 expression in fibroblasts. Gel mobility shift and supershift assays performed with Rat1 nuclear extracts identified nucleoprotein complexes binding to the Ets-1 site and the Sp1 site. In Drosophila SL2 cells, which lack the Sp and Ets family of transcription factors, expression of Sp1, Sp3, and Ets-1 or Elf-1 functionally stimulated MRG1 promoter activity in a synergistic manner. These results suggest that multiple transcription factors acting in synergy are responsible for MRG1 expression and the responsiveness of cells to different biological stimuli. MRG1 (melanocyte-specific gene 1 (MSG1)-related gene), a ubiquitously expressed transcription factor that interacts with p300/CBP, TATA-binding protein and Lhx2, is the founding member of a new family of transcription factors. Initial characterization of this newly discovered transcription factor has underscored its potential involvement in many important cellular processes through transcriptional modulation. We previously demonstrated that MRG1 can be induced by various biological stimuli (Sun, H. B., Zhu, Y. X., Yin, T., Sledge, G., and Yang, Y. C. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 13555–13560). As a first step in understanding its role in different biological processes, we investigated mechanisms that regulate transcription of the mouse MRG1 gene in fibroblasts. Transient transfection of Rat1 fibroblast cells with sequential 5′-deletions of mouse MRG1 promoter-luciferase fusion constructs indicated that the −104 to +121 region contains the full promoter activity. Deletion and site-directed mutations within this region revealed that the Ets-1 site at −97 to −94 and the Sp1 site at −51 to −46 are critical for MRG1 expression in fibroblasts. Gel mobility shift and supershift assays performed with Rat1 nuclear extracts identified nucleoprotein complexes binding to the Ets-1 site and the Sp1 site. In Drosophila SL2 cells, which lack the Sp and Ets family of transcription factors, expression of Sp1, Sp3, and Ets-1 or Elf-1 functionally stimulated MRG1 promoter activity in a synergistic manner. These results suggest that multiple transcription factors acting in synergy are responsible for MRG1 expression and the responsiveness of cells to different biological stimuli. MSG1-related gene melanocyte-specific gene 1 signal transducers and activators of transcription 3 cAMP response element-binding protein electrophoretic mobility shift assay Schneider'sDrosophila cell line 2 kilobase(s) polymerase chain reactin sis-interacting element cytomegalovirus mitogen-activated protein kinase GA-binding protein MRG11 and MSG1 are the members of a new family of transcription factors, which share a conserved C-terminal acidic domain (the CR2 domain) that accounts for their transcriptional activity. Through CR2 (1Shioda T. Fenner M.H. Isselbacher K.J. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 12298-12303Crossref PubMed Scopus (80) Google Scholar, 2Dunwoodie S.L. Rodriguez T.A. Beddington R.S.P. Mech. Dev. 1998; 72: 27-40Crossref PubMed Scopus (141) Google Scholar, 3Bhattacharya S. Michels C.L. Leung M.K. Arany Z.P. Kung A.L. Livingston D.M. Genes Dev. 1999; 13: 64-75Crossref PubMed Scopus (315) Google Scholar, 4Yahata T. Caestecker M.P. Lechleider R.J. Andriole S. Roberts A.B. Isselbacher K.J. Shioda T.J. J. Biol. Chem. 2000; 275: 8825-8834Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar), MRG1 and MSG1 interact with the CH1 domain of the p300/cAMP response element-binding protein (CBP) complex, nuclear proteins that function as coactivators for basal transcription complexes (5Janknecht R. Hunter T. Curr. Biol. 1996; 6: 951-954Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar, 6Goldman P.S. Tran V.K. Goodman R.H. Recent Prog. Horm. Res. 1997; 52: 103-119PubMed Google Scholar, 7Shikama N. Lyon J. La Thangue N.B. Trends Cell. Biol. 1997; 7: 230-237Abstract Full Text PDF PubMed Scopus (424) Google Scholar). MRG1 also interacts with a LIM homeodomain transcription factor, Lhx2, to enhance Lhx2-dependent transcription possibly through recruitment of p300/CBP and TATA-binding proteins (8Glenn D.J. Maurer R.A. J. Biol. Chem. 1999; 274: 36159-36167Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar). The interaction of MRG1 with Lhx2 is dependent on the N-terminal region of MRG1, a region not conserved in MSG1. MSG1 interacts with Smad4 and enhances Smad-mediated transcription in a p300/CBP-dependent manner (4Yahata T. Caestecker M.P. Lechleider R.J. Andriole S. Roberts A.B. Isselbacher K.J. Shioda T.J. J. Biol. Chem. 2000; 275: 8825-8834Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar, 9Shioda T. Lechleider R.J. Dunwoodie S.L. Li H. Yahata T. de Caestecker M.P. Fenner M.H. Roberts A.B. Isselbacher K.J. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 9785-9790Crossref PubMed Scopus (100) Google Scholar). The Smad interaction domain resides in the N terminus of MSG1 and thus is unique to MSG1. Based upon these findings, it has been speculated that MRG1 family proteins bind p300/CBP through their conserved C-terminal regions (the CR2 region) while interacting with DNA-binding proteins through the unique N-terminal regions, thus regulating the p300/CBP-dependent transcriptional activation of different target genes (4Yahata T. Caestecker M.P. Lechleider R.J. Andriole S. Roberts A.B. Isselbacher K.J. Shioda T.J. J. Biol. Chem. 2000; 275: 8825-8834Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar). Besides their structural differences, MRG1 and MSG1 show a distinct pattern of expression that may also determine their functional specificity (1Shioda T. Fenner M.H. Isselbacher K.J. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 12298-12303Crossref PubMed Scopus (80) Google Scholar, 2Dunwoodie S.L. Rodriguez T.A. Beddington R.S.P. Mech. Dev. 1998; 72: 27-40Crossref PubMed Scopus (141) Google Scholar, 3Bhattacharya S. Michels C.L. Leung M.K. Arany Z.P. Kung A.L. Livingston D.M. Genes Dev. 1999; 13: 64-75Crossref PubMed Scopus (315) Google Scholar, 10Sun H.B. Zhu Y.X. Yin T. Sledge G. Yang Y.C. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13555-13560Crossref PubMed Scopus (90) Google Scholar). MSG1 transcripts are predominantly expressed in cultured human and mouse epidermal melanocytes, whereas MRG1 transcripts are detected in all of the human and mouse cell lines and adult tissues examined (1Shioda T. Fenner M.H. Isselbacher K.J. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 12298-12303Crossref PubMed Scopus (80) Google Scholar, 2Dunwoodie S.L. Rodriguez T.A. Beddington R.S.P. Mech. Dev. 1998; 72: 27-40Crossref PubMed Scopus (141) Google Scholar, 3Bhattacharya S. Michels C.L. Leung M.K. Arany Z.P. Kung A.L. Livingston D.M. Genes Dev. 1999; 13: 64-75Crossref PubMed Scopus (315) Google Scholar, 10Sun H.B. Zhu Y.X. Yin T. Sledge G. Yang Y.C. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13555-13560Crossref PubMed Scopus (90) Google Scholar). Similarly, MRG1 and MSG1 expression profiles during early development are distinct from each other (2Dunwoodie S.L. Rodriguez T.A. Beddington R.S.P. Mech. Dev. 1998; 72: 27-40Crossref PubMed Scopus (141) Google Scholar). MSG1 is predominantly expressed in a subset of mesoderm derivatives, whereas MRG1 transcripts are restricted to anterior visceral endoderm prior to gastrulation. Interestingly, MRG1 is expressed during heart development and its expression can be detected throughout embryogenesis from 8.5 days post-conception, which is consistent with the ubiquitous expression of this gene in adult tissues. These results suggested that MRG1 and MSG1 might play different roles during mouse embryogenesis. MRG1 was cloned in our laboratory as part of an effort to isolate cytokine-inducible genes. Overexpression in Rat1 cells results in loss of cell contact inhibition, anchorage-independent growth in soft agar, and tumor formation in nude mice, suggesting that MRG1 is a transforming gene (10Sun H.B. Zhu Y.X. Yin T. Sledge G. Yang Y.C. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13555-13560Crossref PubMed Scopus (90) Google Scholar). Bhattacharya et al. demonstrated that MRG1 is up-regulated by hypoxia and deferoxamine (3Bhattacharya S. Michels C.L. Leung M.K. Arany Z.P. Kung A.L. Livingston D.M. Genes Dev. 1999; 13: 64-75Crossref PubMed Scopus (315) Google Scholar), and represses HIF-1α-mediated transactivation through competitive interaction with the CH1 domain of p300/CBP. Elevated expression of MRG1 in hypoxic cells has been postulated to negatively regulate the cellular response to hypoxia, which is cytokine-regulated. The promoter region of human MRG1 has been reported but not analyzed in detail (11Leung M.-K. Jones T. Michels C.L. Livingston D.M. Bhattacharya S. Genomics. 1999; 61: 307-313Crossref PubMed Scopus (44) Google Scholar), and the transcription factors that regulate it have not been identified. We have now isolated the mouse MRG1 genomic sequence and analyzed the promoter activity by deletion mapping and transient expression in cells. The basal mouse MRG1 promoter maps to region to −104 to +121, which is highly conserved in the human and mouse genes. Deletion analysis in conjunction with site-directed mutagenesis shows that an Ets-1 site at −97 to −94 and an Sp1 site at −51 to −46 are critical for MRG1 promoter activity. Electrophoretic mobility shift assays (EMSA) show that Sp1 and Sp3 bind the Sp1 element, whereas transcription factors binding to the Ets-1 element are yet to be identified. Cotransfection in insect cells that lack Sp and Ets factors demonstrates that Sp1, Sp3, Ets-1, or Elf-1 are important for MRG1 gene expression and therefore for the responses of cells to different biological stimuli. NIH3T3, Rat1, and HepG2 cells were maintained in Dulbecco's modified Eagle's medium with 10% fetal calf serum. Schneider's Drosophila cell line 2 (SL2) was maintained in Schneider's Drosophila medium supplemented with 10% fetal bovine serum at room temperature with atmospheric CO2. Cell culture reagents were obtained from Life Technologies Inc. (Gaithersburg, MD). Antibodies to nuclear proteins Sp1, Sp3, and STAT3 were purchased from Santa Cruz Biotechnology (Santa Cruz, CA). A 129/SvJ mouse liver genomic library in Lambda FIXII (Stratagene) was screened using the 2.1-kb MRG1 cDNA as the probe. The probe was random-labeled with [α-32P]dCTP using the Prime-It kit (Stratagene). A 5-kbHindIII fragment from one of the positive clones was subcloned into the HindIII site of a cloning vector, pUC19, resulting in plasmid pUCHi. Sequence analysis showed that the fragment contains a 2.7-kb 5′-flanking region, the first and the second the and of the 1 of the mouse MRG1 gene 5′-flanking region was analyzed with the H. T. Res. PubMed Scopus Google Scholar). The transcription site was by the promoter for and Hunter Scholar). The to +121 region to the transcription site was using and The was and and in a 6: Google Scholar), resulting in plasmid a fragment from genomic and fragment from was and and site of were by of and were by using as and the by were by and were by using as and the as for the Sp1 site in the region was by using as were The first one or as a and as a the second one as a and as a from each were and to a second of using or with The was into and by The MRG1 promoter fragment was by and and into and of prior to or Rat1 cells were at 2 were with 1 of plasmid and of using cell extracts were and activity was with assay assays were performed as previously by et al. J. T. a Scholar). transfection of HepG2 cells, cells were at and with of the plasmid and of using the as previously J. T. a Scholar). The medium was cell extracts were and and assays were performed as transfection of SL2 cells, 1 prior to cells were at and by the as J. G. J. 1996; PubMed Scopus Google Scholar). of of indicated and of expression plasmid as R. Cell. Full Text PDF PubMed Scopus Google Scholar), J. G. J. 1996; PubMed Scopus Google Scholar), or H. G. C. Y. J. Y. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar). of the expression were with the plasmid The medium was of and the cells were for assays were protein by protein assay extracts from Rat1 cells were as Res. PubMed Scopus Google Scholar). were with and of the was to of nuclear extracts in a of 1 of 1 and 1 and for at room the complexes were from the probe by through a were and to in the of at supershift 1 of was with nuclear extracts at for 1 in binding by an for at room temperature with was with nuclear extracts at for the of the probe. The as were prior to The of the of the were as MRG1 Sp1 MRG1 Ets-1 The were for MRG1 Sp1 1 Ets-1 (Santa Cruz MRG1 and J. PubMed Scopus Google Scholar). the for the ubiquitous expression of MRG1, we analyzed its promoter activity. A 5-kbHindIII fragment from a mouse MRG1 genomic which contains sequence from the transcription site and all of the regions, was subcloned into the to the human MRG1 gene (11Leung M.-K. Jones T. Michels C.L. Livingston D.M. Bhattacharya S. Genomics. 1999; 61: 307-313Crossref PubMed Scopus (44) Google Scholar), the mouse gene of by not The transcription site was to the promoter for and Hunter Scholar). have been identified through the H. T. Res. PubMed Scopus Google Scholar). These at and Sp1 at and site at site at Ets binding at and site at and an at 1 (the for mouse MRG1 gene is mouse and human promoter regions 1 and not that the MRG1 gene is conserved during As in 1 is an mouse and human MRG1 genes in the promoter region and are suggesting to +121 may play an important role in MRG1 the promoter activity of the MRG1 5′-flanking region, deletion were using the vector, 6: Google Scholar). resulting plasmid was into Rat1 with to transfection the constructs the full promoter whereas of the promoter activity that the region −104 and contains critical for MRG1 region contains an Sp1 site at an Ets-1 site at and an site at Rat1 cells were we previously this cell line to that MRG1 expression can be induced by and growth factor (10Sun H.B. Zhu Y.X. Yin T. Sledge G. Yang Y.C. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13555-13560Crossref PubMed Scopus (90) Google Scholar). The were also performed in NIH3T3, and HepG2 cells, and the results were consistent with the ubiquitous expression of MRG1 in different cell not We within this region As with with sequence at the a promoter activity. region contains an Ets-1 binding site. promoter activity of deletion of from which contains the Sp1 binding the promoter activity. Similarly, mutations of the Sp1 site in from to the promoter activity to the of 2 also be that deletion of the region and also in a in the promoter activity. region contains an binding site sequence at to These results demonstrated that the Ets-1 Sp1 and the region and are important for the mouse MRG1 promoter activity. the in the −104 region that to the promoter we a of MRG1 promoter constructs with mutations in Ets-1 and Sp1 from Ets-1 was to whereas Sp1 was to transfection into Rat1 cells, constructs a of Sp1 or Ets-1 element in and in the promoter The results were in the fibroblast cell In of the Sp1 site of the promoter activity. In all mutations of in a loss of the promoter activity that Ets-1 and Sp1 are important for the MRG1 promoter activity. determine the of protein complexes binding to the Sp1 or Ets-1 element of the MRG1 nuclear extracts from Rat1 fibroblast cells were analyzed by using a Sp1 or Ets-1 probe. As in complexes and were detected using Sp1 probe These complexes were in the of of Sp1 3 and and of an of Sp1 not the formation of these complexes members of the Sp1 family share the binding sequence or G. 1999; PubMed Scopus Google Scholar), we performed supershift to determine the of the As in A formation whereas complexes and were in the of In the of complexes and were and the of A was as a and was not to the mobility of these complexes The shift pattern was performed using nuclear extracts from cells not These results indicated that Sp1 is a of A and and Sp3, a shift pattern as previously for the Sp1 site G. 1999; PubMed Scopus Google Scholar). The potential interaction of the Ets-1 element with nuclear proteins was also by factors in the Ets family the sequence with a in the binding The sequence is for Ets family members to bind with the specificity different members by S.L. A. J. PubMed Scopus Google Scholar, A.L. Y. J. Cell Biol. 1997; PubMed Scopus Google Scholar). The region contains Ets one at −97 to Ets-1 and the other one at to MRG1 Ets-1 element as a complexes were and be by suggesting are a Ets-1 element to was to for binding the is critical for the formation of the element J. PubMed Scopus Google Scholar), a not for the formation suggesting that are also important for the formation of Interestingly, the other from the MRG1 promoter to for the formation of but not complexes and C. of the in region to not the promoter activity in Rat1 cells not the of a of binding the formation of all complexes as as These results suggested that contains an Ets-1 binding site. of various members of Ets factor family and not the shift pattern not The of proteins in each of the complexes therefore to be determine and proteins functionally MRG1 promoter Drosophila SL2 cells, which are in and proteins J. G. J. 1996; PubMed Scopus Google Scholar, R. Cell. Full Text PDF PubMed Scopus Google were The for using insect of cells is and factors are expressed in all cells, which the of We MRG1 promoter expression or SL2 cells. As in and stimulated promoter in a with the was with of Sp3 enhance transcriptional activation by Sp1, and were into Drosophila As in transcriptional activation by Sp1 be by the Sp1 binding site was was with Sp1, Sp3, or the of Sp1 and These results indicated that the Sp1 element is for the transactivation of Sp1 and Sp3 on the MRG1 promoter assay the functional of proteins on MRG1 or was SL2 cells with the for Ets factors, or showed that Ets-1 or Elf-1 activity of with Ets-1 Elf-1 on the Ets-1 suggesting the transactivation by Ets-1 or Elf-1 is dependent on the of the Ets-1 with these of the region have been to enhance the activity of a promoter in various cell lines and to the Ets-1 or Elf-1 transactivation in SL2 cells not to the functional the and we performed using or with different transcription factors. As in stimulated promoter activity by whereas of Sp1 with Ets-1 stimulated by Cotransfection of Elf-1 with Sp1 also in a functional interaction on MRG1 synergy was dependent upon the of the region and was not on promoter These results demonstrated synergistic activation of the MRG1 promoter by Sp1 and Ets transcription factors. MRG1 the founding member of a new family of transcription factors that may be in many processes through its with p300/CBP, binding proteins and DNA-binding transcription factors (1Shioda T. Fenner M.H. Isselbacher K.J. Proc. Natl. Acad. Sci. U. S. A. 1996; 93: 12298-12303Crossref PubMed Scopus (80) Google Scholar, 2Dunwoodie S.L. Rodriguez T.A. Beddington R.S.P. Mech. Dev. 1998; 72: 27-40Crossref PubMed Scopus (141) Google Scholar, 3Bhattacharya S. Michels C.L. Leung M.K. Arany Z.P. Kung A.L. Livingston D.M. Genes Dev. 1999; 13: 64-75Crossref PubMed Scopus (315) Google Scholar, 4Yahata T. Caestecker M.P. Lechleider R.J. Andriole S. Roberts A.B. Isselbacher K.J. Shioda T.J. J. Biol. Chem. 2000; 275: 8825-8834Abstract Full Text Full Text PDF PubMed Scopus (105) Google Scholar, D.J. Maurer R.A. J. Biol. Chem. 1999; 274: 36159-36167Abstract Full Text Full Text PDF PubMed Scopus (90) Google Scholar, 9Shioda T. Lechleider R.J. Dunwoodie S.L. Li H. Yahata T. de Caestecker M.P. Fenner M.H. Roberts A.B. Isselbacher K.J. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 9785-9790Crossref PubMed Scopus (100) Google Scholar, 10Sun H.B. Zhu Y.X. Yin T. Sledge G. Yang Y.C. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13555-13560Crossref PubMed Scopus (90) Google Scholar). Sequence of mouse and human (11Leung M.-K. Jones T. Michels C.L. Livingston D.M. Bhattacharya S. Genomics. 1999; 61: 307-313Crossref PubMed Scopus (44) Google MRG1 genes showed in promoter regions 1 and of MRG1 during of are suggesting the promoter region might play an important role in MRG1 gene with this we the promoter region of mouse MRG1 to We identified Sp1 element to and Ets binding site to within this region to be for the promoter activity. Sp1 is a DNA-binding protein that is important for transcription of many cellular and genes that in their R. Cell. Full Text PDF PubMed Scopus Google Scholar, G. 1999; PubMed Scopus Google Scholar). transcription factors Sp3, and have been not the sequence as Sp1, and expression is restricted to the Sp3, on the other is ubiquitously expressed and the sequence as Sp1 to be an transcription factor, Sp3 contains a transcriptional domain and can as a transcriptional or on the promoter and cell J. G. J. 1996; PubMed Scopus Google Scholar, J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). We have that Sp1 is part of whereas complexes and Sp3 In we have demonstrated that Sp1 and Sp3 MRG1 promoter in Drosophila SL2 cells. Interestingly, our also suggested that Sp1 and Sp3 function in a manner for MRG1 promoter activity Sp1 has been to with members of the basal transcription as and has been as a transcriptional that as a basal factor for and expression may for basal expression of MRG1 in various cell and tissues. In its role in transcription of Sp1 has been demonstrated to be in induced transcription of various genes to different biological stimuli H. T. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar, G. A. S. J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar, 2000; PubMed Scopus Google Scholar, J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google Scholar). 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Ets proteins in binding site in with many other transcription factor the homeodomain The the a Ets domain bind the site. family contains proteins in cell and We have identified Ets-1 site at and its binding proteins to be for MRG1 These binding proteins to be the Ets-1 element as an in Rat1, NIH3T3, and cell lines not we in our to Ets factors in formation through supershift is consistent with by in the of Ets family members H. G. C. Y. J. Y. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar), in part to the of binding in each of the Ets factors Cell. Biol. 1996; PubMed Scopus Google Scholar, T. PubMed Scopus Google Scholar, Sci. 1996; PubMed Scopus Google Scholar). of the Ets family Ets-1 and which have different expression tissues and cell transcription through the MRG1 Ets-1 element in SL2 cells These therefore the positive role of the MRG1 Ets-1 element in MRG1 the that cell multiple Ets proteins and these proteins can interact with or the of this functional Ets-1 site in MRG1 promoter may also for the ubiquitous of MRG1 Ets family transcription factors have been to be nuclear of the J. A. Sci. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar). In many of Ets proteins enhances their to transcription and of ubiquitous the transient of MRG1 we reported previously (10Sun H.B. Zhu Y.X. Yin T. Sledge G. Yang Y.C. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13555-13560Crossref PubMed Scopus (90) Google might in part be by the are to this is that Ets factors bind as for but can also with other transcription factors to their in the of the Ets binding site S.L. A. J. PubMed Scopus Google Scholar, A.L. Y. J. Cell Biol. 1997; PubMed Scopus Google Scholar). Ets-1 and Sp1 interact to the human A. R. R.A. J. J. PubMed Scopus Google Scholar). In Sp1 activity can be by factors that or a A. J. J. Biol. Chem. Full Text PDF PubMed Google Scholar, A.B. J. PubMed Scopus Google Scholar). In the of the mouse MRG1 the Ets-1 element is of the Sp1 element, which a for an factor and Sp1 to In this it is to that Sp1 and Ets factors the MRG1 promoter in SL2 cells In we cloned and functionally mouse MRG1 promoter and identified in the promoter We showed that Sp1, Sp3, and an transcription factor to the mouse MRG1 The of these and transcription factors the first for the ubiquitous expression of MRG1 in cells and the of its up-regulated expression by different biological stimuli. We are to and for Drosophila SL2 cells and and and to for We also for