Transcription Factor ZBP-89 Regulates the Activity of the Ornithine Decarboxylase Promoter

Abstract

Appropriate cellular levels of polyamines are required for cell growth and differentiation. Ornithine decarboxylase is a key regulatory enzyme in the biosynthesis of polyamines, and precise regulation of the expression of this enzyme is required, according to cellular growth state. A variety of mitogens increase the level of ornithine decarboxylase activity, and, in most cases, this elevation is due to increased levels of mRNA. A GC box in the proximal promoter of the ornithine decarboxylase gene is required for basal and induced transcriptional activity, and two proteins, Sp1 and NF-ODC 1 , bind to this region in a mutually exclusive manner. Polyamines are essential cations for normal cell growth and differentiation (1, 2). Increased synthesis of these compounds is closely associated with, and necessary for, stimulated cell proliferation and tumor promotion. Tight regulation of polyamine biosynthesis is important as overproduction of these compounds can be toxic to cells (3, 4). Ornithine decarboxylase (ODC) 1 catalyzes a key regulated step in polyamine synthesis, and regulation of ODC activity is a major mechanism for controlling polyamine concentrations within cells. The activity of this enzyme is tightly regulated during normal cell growth and differentiation. An increase in ODC activity is required for reentry of quiescent cells into the cell cycle (2, 5-7). Deregulated expression of ODC and the subsequent changes in polyamine concentrations have been associated with several types of tumors (4, 8 -10). Recent studies indicate that overexpression of oncogenes such as myc (11-13), ras (14), fos (15), and mos (16) result in elevated levels of ODC expression. Importantly, two studies have shown that overexpression of ODC in fibroblasts induces neoplastic transformation and suggest a direct link between deregulation of ODC expression and oncogenesis (17,18).Both activation and inhibition of ODC activity is required for precise regulation of ODC levels. A broad spectrum of stimuli, including hormones, growth factors, tumor promoters and oncogenes elevates ODC activity in the cell. In most cases, these increases in activity result from enhanced levels of ODC mRNA (6, 7). Several of the DNA elements and protein factors involved in both basal and stimulated activity of the ODC promoter have been identified, including several binding sites for transcription factor Sp1, two binding sites for members of the CREB/ ATF family of transcription factors, and binding sites for transcription factors related to c-myc (7). Little is known about DNA elements or protein factors that are involved in repressing ODC transcription. A GC-rich region located at Ϫ123 to Ϫ91 relative to the transcriptional start site of the ODC promoter seems to be such an element. We have demonstrated that two proteins bind this site in a mutually exclusive manner, Sp1 and NF-ODC 1 (19). Sp1 is a well characterized transcription factor that is found in most eukaryotic cell and is directly involved in both basal and induced expression of many genes. NF-O...

The Zinc Finger Repressor, ZBP-89, Binds to the Silencer Element of the Human Vimentin Gene and Complexes with the Transcriptional Activator, Sp1

“…Results are an average from 4 -6 separate transfections of at least two different plasmid preparations, and error bars represent the S.E. tor, o-phenanthroline (47). We also observed this result for vimentin's repressor from HeLa NE (Fig.…”

“…The first possibility was that only ZBP-89 can bind to the PS element and that Sp1 is held in this complex via proteinprotein interaction with ZBP-89. The second possibility was that, since the PS element is a GC-rich sequence, a binding site for Sp1 is located close to or overlapping ZBP's binding site as has been suggested for other ZBP-regulated genes (47). There-fore, Sp1 would be able to bind to the PS element along with, but independent from, ZBP-89.…”

“…In all of these cases, ZBP-89 appears to compete with another protein, like Sp1, Sp2, Sp3, Sp4, or WT1, for binding to an overlapping site in DNA (47). For example, ZBP-89 is involved in regulation of the ornithine decarboxylase gene together with the transcriptional activator Sp1, and its DNA binding site overlaps that of Sp1.…”

Activation of Myelin Genes during Transdifferentiation from Melanoma to Glial Cell Phenotype

“…ZBP-99 had been isolated previously as binding a long CACC box from the gastrin gene promoter and shown to belong to a novel family of proteins defined by an array of four Kruppel-type zinc fingers (51). ZBP-99 was reported to inhibit transcription of the Ornithine decarboxylase gene similarly to its homologous factor ZBP-89/BFCOL1 (51,61). However, ZBP-89 has also been shown to activate transcription of the p21/waf1 gene through cooperation with histone acetyltransferase p300 in HT29 cells (51).…”

Identification and Characterization of a Transcriptional Regulator for the lck Proximal Promoter

“…During this study, several cDNAs that have identical sequences with mt␤ have been reported: BFCOL1 that binds to the proximal promoters of the type I collagen genes (27) and BERF-1, a 89-kDa protein that binds to a muscle-specific enhancer of the ␤-enolase gene (28). In addition, the rat and human homologue of the protein, ZBP-89, has been shown to bind to promoter regions of the gastrin gene (29) and the ornithine decarboxylase promoter (30). It has subsequently been reported that the same zinc finger protein also binds to the p21WAF1 gene (31), the matrix metalloproteinase-3 gene (32), the pT␣ gene (33), and the vimentin gene (34).…”