Functional Domains of c-myc Promoter Binding Protein 1 Involved in Transcriptional Repression and Cell Growth Regulation

Abstract

c-myc promoter binding protein 1 (MBP-1), initially identified from a human cervical carcinoma (HeLa) cell expression library, binds to the TATA box sequences of the c-myc P2 promoter and negatively regulates both human and mouse c-myc promoter activities (6,25,26). The c-myc proto-oncogene can promote cell proliferation, differentiation, and oncogenic transformation (7,36) or apoptosis under certain conditions (9, 35). Regulation of c-myc occurs at multiple levels, such as the initiation or termination of transcription and the attenuation of transcription (20,25). Recent studies have shown that MBP-1 and TATA binding protein bind simultaneously in the minor groove of the c-myc P2 promoter (6). It is possible that MBP-1 negatively regulates c-myc expression by preventing formation of a transcription initiation complex with a general transcriptional factor(s).MBP-1 is expressed ubiquitously in normal human tissues (27) and localized at human chromosome 1p35-ter (38). Ectopic expression of MBP-1 in murine fibroblasts (NIH 3T3 cells) induces massive cell death, DNA fragmentation, and reduction of c-myc expression (26). Bcl2, a cell survival gene, protects against MBP-1-mediated cell death. Complementation of exogenous deregulated c-myc (without an MBP-1 binding site) also prevents MBP-1-induced cell death. Since MBP-1 negatively regulates c-myc transcription, downregulation of endogenous c-myc expression, which is compensated for by exogenous deregulated c-myc, may be a possible mechanism of protection from apoptotic cell death (26). However, the protective role of Bcl2 in MBP-1-mediated cell death suggests the involvement of another cell regulatory factor(s) in the mediation of biological activity of MBP-1. Thus, in addition to c-myc regulation, MBP-1 appears to exert a regulatory effect on cell growth through another, unknown, mechanism. Exogenous expression of MBP-1 in human breast carcinoma cells results in reduced invasiveness, loss of anchorage-independent growth, and suppression of tumor formation in athymic nude mice (28). Recent studies suggest that the C-terminal half of MBP-1 does not bind to the c-myc promoter (29). However, the Cterminal half of MBP-1 suppressed c-myc transcription and reduced cell growth. The mechanism by which MBP-1 exerts its biological activity is unknown. However, one reasonable explanation is that MBP-1 directly or indirectly modulates the expression of other genes necessary for cell proliferation. In this study, we embarked on a detailed analysis of MBP-1-related functional activities. We have used a number of MBP-1 deletion mutant proteins fused to the DNA binding domain of GAL4 to map its transcriptional regulatory activity. The repressor domains identified in the context of the GAL4 system correlated with the biological activities of MBP-1. MATERIALS AND METHODSCells. NIH Swiss mouse embryo (NIH 3T3) cells, human cervical carcinoma (HeLa) cells, and African monkey kidney (COS7) cells were obtained from the American Type Culture Collection. Cells were grown in Dulbecco's modif...

c-myc Promoter-binding Protein 1 (MBP-1) Regulates Prostate Cancer Cell Growth by Inhibiting MAPK Pathway

“…CMVGFP-MEK5␤ fusion construct, a gift from J.-I. Abe (University of Rochester Medical Center, Rochester, NY), and CMV MBP-1 (14) were included in this study.…”

“…MBP-1, ubiquitously expressed in different human tissues (9), is located at human chromosome 1p35-pter (10). MBP-1, an ϳ37-kDa cellular protein, has many intriguing properties such as transcriptional repressor activity, induction of apoptosis, and regression of tumor growth (8,(11)(12)(13)(14)(15). Sequence analysis suggests that MBP-1 has a high homology with Eno1 cDNA (8), designated as human ␣-enolase cDNA (16).…”

BMI-1 is important in bufalin-induced apoptosis of K562 cells

“…It was demonstrated that the expression levels of ING3 are decreased in melanoma and head and neck squamous cell carcinoma, and predict a poor prognosis (34). DENND4A, also known as C-myc promoter-binding protein MBP-1, acts as a general transcriptional repressor (35). It binds to c-myc promoter sequences and transcriptionally represses the c-myc gene (36)(37)(38).…”

Proteome analysis of proliferative response of bystander cells adjacent to cells exposed to ionizing radiation

“…NPM/ B23 and enolase-α), which play such different functional roles in the cell, interrelate in the promitogenic/prosurvival bystander response? It has been reported that enolase-α also plays an important role in the regulation of c-myc promoter activity in the form of alternative translation product MBP-1 (37-40 kDa), which is distinct from its role as a glycolytic enzyme [59][60][61][62]. The c-myc proto-oncogene is known as an essential part of normal cell proliferative machinery [63,64].…”

“…The c-myc proto-oncogene is known as an essential part of normal cell proliferative machinery [63,64]. MPB-1, structurally very similar to enolase-α, binds to the c-myc P2 promoter and down-regulates c-myc expression, and therefore, suppresses cell proliferation [60][61][62]. Unlike enolase-α, which is mainly localized in the cytoplasm, MPB-1 has been primarily found in the cell nuclei [61].…”