Characterization of the Promoter Region of the Human Peroxisomal Multifunctional Enzyme Type 2 Gene

A novel two-promoter-one-gene system of the chorionic gonadotropin β gene enables tissue-specific expression

The New World monkey (NWM), Callithrix jacchus, a preferred model in medical research, displays an interesting endocrine regulation of reproduction: LH, the heterodimeric glycoprotein hormone, is functionally replaced by the chorionic gonadotropin (CG), a hormone indispensable for establishment of pregnancy in humans and normally expressed in the placenta. In the marmoset pituitary, the expression of the β-subunit (CGB) gene is regulated similar to human LH β-subunit, but its placental regulation is unknown. This study intended to decipher the underlying mechanism of tissue-specific expression of CGB in the marmoset placenta. We identified a new placental transcriptional start site, described a new, previously undiscovered exon, and define a novel placental core promoter in the marmoset CGB gene. This promoter contains a TATA box and binding sites for activating protein 2 and selective promoter factor 1, the latter acting synergistically by forming a regulation cassette. Differential first exon usage directed the tissue-specific expression. Methylation analyses revealed a tissue-specific pattern in the placental promoter indicating additional epigenetic regulation of gene expression. Our findings point toward a hitherto unknown evolutionary plasticity in the LH/CG hormonal system in NWM, which could be used as a model to study human CGB regulation in clinical pathologies.

Induction of dystrophin Dp71 expression during neuronal differentiation: opposite roles of Sp1 and AP2alpha in Dp71 promoter activity

In this study, we delineated the molecular mechanisms that modulate Dp71 expression during neuronal differentiation, using the N1E-115 cell line. We demonstrated that Dp71 expression is up-regulated in response to cAMP-mediated neuronal differentiation of these cells, and that this induction is controlled at promoter level. Functional deletion analysis of the Dp71 promoter revealed that a 5'-flanking 159-bp DNA fragment that contains Sp1 and AP2 binding sites is necessary and sufficient for basal expression of this TATA-less promoter, as well as for its induction during neuronal differentiation. Electrophoretic mobility shift and chromatin immunoprecipitation assays revealed that Sp1 and AP2alpha bind to their respective DNA elements within the Dp71 basal promoter. Overall, mutagenesis assays on the Sp1 and AP2 binding sites, over-expression of Sp1 and AP2alpha, as well as knock-down experiments on Sp1 and AP2alpha gene expression established that Dp71 basal expression is controlled by the combined action of Sp1 and AP2alpha, which act as activator and repressor, respectively. Furthermore, we demonstrated that induction of Dp71 expression in differentiated cells is the result of the maintenance of positive regulation exerted by Sp1, as well as of the loss of AP2alpha binding, which ultimately releases the promoter from repression.

Peroxisomal multifunctional protein-2: the enzyme, the patients and the knockout mouse model

The mammalian multifunctional protein-2 (MFP-2, also called multifunctional enzyme 2, D-bifunctional enzyme or 17-beta-estradiol dehydrogenase type IV) was identified by several groups about a decade ago. It plays a central role in peroxisomal beta-oxidation as it handles most, if not all, peroxisomal beta-oxidation substrates. Deficiency of this enzyme in man causes a severe developmental syndrome with abnormalities in several organs but in particular in the brain, leading to death within the first year of life. Accumulation of branched-long-chain fatty acids and very-long-chain fatty acids and a disturbed synthesis of bile acids were documented in these patients. A mouse model with MFP-2 deficiency only partly phenocopies the human disease. Although the expected metabolic abnormalities are present, no neurodevelopmental aberrations are observed. However, the survival of these mice into adulthood allowed to document the importance of this enzyme for the normal functioning of the brain, eyes and testis. In the present review, the identification and biochemical characteristics of MFP-2, and the consequences of MFP-2 dysfunction in humans and in mice will be discussed.

Sp1 and AP2 enhance promoter activity of the mouse GM3-synthase gene

Promoters of the glycosyltransferase genes for ganglioside synthesis are TATA-less and often have multiple binding sites for transcription factors Sp1 and AP2 in their proximal regions. However, the function of Sp1 and AP2 in the promoters has not yet been defined. Here, we cloned 5'-flanking fragments of the mouse GM3-synthase gene and assessed the promoter activity of these fragments in mouse Neuro-2a cells. This promoter is TATA-less and contains a number of potential transcription factor-binding sites. Multiple putative transcriptional initiation sites for this gene were identified, including several downstream initiation sites. We then set out to dissect the regulatory elements important for GM3-synthase promoter function. We found that a 5'-flanking 254-bp DNA fragment of the gene contained regulatory elements including two Sp1-binding and six AP2-binding sites that were essential for the basal activity of the promoter in mouse Neuro-2a cells. The effects of the individual Sp1- and AP2-binding sites on basal activity of the GM3-synthase gene were investigated. Mutations in the juxtaposed Sp1/AP2-binding site and in an AP2-binding site decreased the activity of the proximal promoter to approximately 50%. In vitro and in vivo interactions between transcription factors Sp1 and AP2 and these regulatory elements were confirmed by EMSA and the chromatin immunoprecipitation approach, respectively. Therefore, our results demonstrate that Sp1 and AP2 enhance the basal activity of the TATA-less mouse GM3-synthase promoter.

Sp1 and AP2 regulate but do not constitute TATA-less human TAF(II)55 core promoter activity

Human TAF(II)55 (hTAF(II)55), a component of the general transcription factor TFIID, is the only general transcription factor encoded by an intronless gene identified thus far. Analysis of the TATA-less hTAF(II)55 promoter-proximal sequence reveals putative binding sites for STAT-1, MEF2, E2F, Sp1, AP2, AREB6 and E47. Using chromatin immunoprecipitation, DNase I footprinting and electrophoretic mobility shift assays, we demonstrate that Sp1 and AP2 can bind simultaneously to juxtaposed Sp1- and AP2-binding sites in the hTAF(II)55 promoter-proximal region and functionally modulate hTAF(II)55 promoter activity, as evidenced by reporter gene assays performed in transiently transfected human C-33A and insect SL2 cell lines. Interestingly, removal of all the promoter-proximal Sp1-binding sites does not impair the function of the hTAF(II)55 core promoter. Moreover, a 52-bp DNA fragment containing only the hTAF(II)55 initiator (Inr) and downstream promoter element (DPE) is able to support Gal4-VP16-mediated activation in vivo and in vitro. Our data suggest that Sp1, although it plays an enhancing role in hTAF(II)55 gene expression, is not essential for hTAF(II)55 core promoter activity. Interestingly, mutations introduced at the Inr and DPE differentially affect the selection of transcription start sites, suggesting that these two core promoter elements play a non-redundant role in the function of TATA-less promoters.