Transcriptional Repression from the c-myc P2 Promoter by the Zinc Finger Protein ZF87/MAZ

Abstract

ZF87/MAZ is a zinc finger-containing transcription factor that was cloned based on its ability to bind to a site within the c-myc P2 promoter. However, its role in the control of c-myc transcription has not yet been well established. Here we have analyzed the effect of ZF87/ MAZ overexpression on transcription from the murine c-myc P2 promoter. It was found that when overexpressed in COS cells, ZF87/MAZ significantly represses transcription from P2. The repression is mediated through the ME1a2 element, located at position ؊86 relative to the P2 transcriptional start site, and is not mediated through either the E2F or the ME1a1 sites. ZF87/ MAZ functions as a true transcriptional repressor since it can repress transcription independently of the c-myc promoter, as part of a fusion with the GAL4 protein. The repressive domain within ZF87/MAZ is located in the amino-terminal half of the protein, a region rich in proline and alanine residues. ZF87/MAZ therefore shares features (i.e. a Pro/Ala-rich region) with those of known transcriptional repressor proteins.The c-myc proto-oncogene is known as a critical factor in the control of both cell proliferation (1-5) and apoptosis (6). In particular, c-myc is known as a cooperating oncogene and is thought to be an important contributing factor to neoplastic transformation and the generation of many cancers (1-5). That c-myc plays such a key role in regulating cell proliferation and cell death is consistent with the observations that its expression is tightly controlled in normal cells. Expression of both c-myc mRNA and protein is extremely low in quiescent cells, and it increases in proliferating cells (1-5). Since c-myc plays an important role in regulating cell proliferation, much effort has gone into understanding how its expression is modulated.c-myc gene expression is controlled at least in part at the level of transcription initiation, and extensive research has gone into identifying the transcriptional control regions within the c-myc promoter. This has been complicated by the fact that c-myc has multiple promoters, which are termed P0, P1, P2, and P3 (4, 5). Yet in many normal and transformed cells, a majority of transcripts initiate at the P2 promoter (4, 5). A large number of cis-acting sequences exist both 5Ј and 3Ј to the P2 transcription start site (5, 7). These sequences, although some quite distant from P2, regulate transcription initiation from P2 and include binding sites for the FUSE factor (8, 9), Fos/Jun (10, 11), Cut (12), YY1 (13), v-Abl (14, 15), Blimp-1 (16), NF-B/Rel (17), CTCF (18), and CF1 (19). The expression of some of these factors are cell-and tissue-type specific. Additionally, some of these factors, such as Fos/Jun, Blimp-1, and CTCF, function to repress the transcription of c-myc.cis-Acting sequences more proximal to the P2 promoter are comprised of an initiator sequence at the start site, a well defined TATA sequence at position Ϫ29, and three elements termed ME1a1, E2F, and ME1a2 at positions Ϫ46, Ϫ64, and Ϫ85 relative to P2 (4, 20 -23). ...

p300 provides a corepressor function by cooperating with YY1 and HDAC3 to repress c-Myc

“…Region V was the only other promoter region that showed an increase in the p300 and HDAC3 occupancy levels (3.3-and 9-fold, respectively). Regions IV and V contain binding sites for transcription factors MAZ (Me1a2; Izzo et al, 1999), E2F (Albert et al, 2001), CTCF (Filippova et al, 1996) that function as repressors and also TBP (TATA box; see Figure 2b). …”

The amino-terminus of the E2F-1 transcription factor inhibits DNA replication of autonomously replicating plasmids in mammalian cells

“…Another cDNA with a high G/C content, the ZF87/ MAZ transcription factor (Izzo et al, 1999;Pyrc et al, 1992), was also used in this assay. Like the E2F1 cDNA, it also has an 80% G/C content within the ®rst 400 basepairs.…”

Tumor-specific adenoviral gene therapy: transcriptional repression of gene expression by utilizing p53-signal transduction pathways

“…[18][19][20][21][22][23][24][25][26]55,56 The KRAB-domain represses the activity of CMV-promoter through direct communications with TATA box-dependent basal transcription machinery, 18,55 whereas mSIN3B interacts with essential DNAbinding proteins that place it in a promoter context in which it can repress transcription by recruiting proteins that condense chromatin by histone deacetylation. 19 In contrast to KRAB-A or mSIN3B, the Zik1-repressor domain does not repress gene transcription from the CMV gal -promoter and some of the other repressor domains showed only weak repression of CMV galactivity.…”

“…Expression vectors for repressor fusion proteins of GAL4-DBD were kindly provided by: L Lania, Neaples, Italy (KRAB-A), 18 RA DePinho Boston, USA (m-SIN3B-SF and m-SIN3B-LF), 19 DJ Hall, Philadelphia, PA, USA (ZF87/MAZ), 20 K Bomsztyk, Seattle, USA (ZIK1), 21 LM Staudt, Bethesda, MD, USA (BCL-6), 22 C Bartholomew, Glasgow, Scotland (EVI-1), 23 Y Shi, Boston, USA (YY), 24 H-S Ro, Halifax Canada (AEBP2) 25 and A Bird, Edinburgh, UK (MeCP2 170-310 and MeCP2 209-492). 26 …”