Multiple protein complexes, including AP2 and Sp1, interact with a specific site within the rat preprotachykinin-A promoter

Regulatory mechanisms in the differential expression of Hemokinin-1

Hemokinin-1, encoded by the TAC4 gene, is the most recent addition to the tachykinin family. Although most closely related to the neuropeptide Substance P, Hemokinin-1 distinguishes itself from other tachykinins by its predominantly non-neuronal expression pattern. Its expression in T and B lymphocytes, macrophages, and dendritic cells points to an important role for Hemokinin-1 in the immune system. To seek reasons for its preferential expression in the immune system and ultimately to provide clues to its function, we investigated the molecular mechanisms driving the differential expression pattern of this unique tachykinin. Our study provides the first analysis of the promoter region of the TAC4 gene, which reveals regulatory mechanism different from the Substance P promoter. We demonstrate for the first time that Hemokinin-1 initiates transcription from multiple start sites through a TATA-less promoter. Conservation of the 5' non-coding region indicates the importance of the upstream regulatory region in directing expression of Hemokinin-1 in specific cell types, during cell differentiation and activation. Furthermore, NFkappaB, a transcription factor important in the activation of immune cells was shown to be involved in promoting increased TAC4 transcription during PMA induction of a T cell line. Our studies reveal that Hemokinin-1 is regulated by a unique transcription regulation system that likely governs its differential expression pattern and suggests a role for Hemokinin-1 distinct from Substance P.

Regulation of sphingosine kinase 1 gene expression by protein kinase C in a human leukemia cell line, MEG-O1

The prolonged treatment with phorbol 12-myristate 13-acetate (PMA) of a human megakaryoblastic leukemia cell line, MEG-O1, induced increase of sphingosine kinase (SPHK) enzyme activity and SPHK1 protein expression as well as SPHK1 message. Protein kinase C (PKC) inhibitor prevented the PMA-induced SPHK1 gene expression. To elucidate the regulatory mechanism of this gene expression, we examined the promoter area (distal to the first exon) and its binding proteins. Luciferase analyses showed that the area of 300 bp from the first exon was sufficient for PMA-responsiveness, and that specificity protein 1 (Sp1)- and two activator protein 2 (AP-2)-binding motifs within this area were necessary for responsiveness. Inhibitors for PKC and MEK1 decreased this PMA-induced promoter activity. Electrophoresis mobility shift assay (EMSA) showed that Sp1 protein was originally bound to the Sp1 site and that two additional bands bound to the two AP-2 motifs were observed only when stimulated with PMA in MEG-O1 cells. The appearance of these bands resulted from binding to an unknown protein rather than AP-2. These results indicated that PMA up-regulates SPHK1 gene expression through PMA-responsive elements of the 5' promoter area of the gene, and suggested that PMA-mediated SPHK1 gene expression would be mediated via PKC- and ERK-dependent signal transduction pathway by binding the transcription factor to AP-2 motifs.

Molecular cloning and functional analysis of the human Na(+)/H(+) exchanger NHE3 promoter

Na(+)/H(+) exchanger (NHE) isoforms NHE2 and NHE3, colocalized to the brush border membrane of the epithelial cells, exhibit differences in their pattern of tissue expression and regulation by various molecular signals. To investigate the mechanisms involved in regulation of NHE3 gene expression, the human NHE3 promoter region was cloned and characterized. Primer extension experiments located the transcription start site to a position 116 nucleotides upstream from the translation start codon. The 5'-flanking region lacked a CCAAT box but contained a TATA-like sequence. Nucleotide sequencing of the 5'-flanking region revealed the presence of a number of cis elements including Sp1, AP-2, MZF-1, CdxA, Cdx-2, steroid and nonsteroid hormone receptor half sites, and a phorbol 12-myristate 13-acetate-response element. Transient transfection experiments using C2/bbe cell line defined a maximal promoter activity in -95/+5 region. The regulatory response elements clustered within this region include a potential transcription factor IID (TF IID), a CACCC, two Sp1, and two AP-2 motifs. Deletion of a fragment containing the AP-2 and Sp1 motifs resulted in a drastic decrease in promoter activity. In gel mobility shift assays, an oligonucleotide spanning from -78 to -56 bp bound a recombinant AP-2, and the corresponding binding activity in nuclear extracts was supershifted with anti-AP2alpha antibody. Our studies suggest that the NHE3 expression is regulated by a combination of cis elements and their cognate transcription factors that include the AP-2 and Sp1 family members.

The human preprotachykinin-A gene promoter has been highly conserved and can drive human-like marker gene expression in the adult mouse CNS

Toward an understanding of the mechanisms controlling Preprotachykinin-A (PPTA) transcription, we introduced a 380-kb human yeast artificial chromosome containing the PPTA gene tagged with the beta-galactosidase gene into transgenic mice. This resulted in a pattern of LacZ expression in the central nervous system (CNS) remarkably similar to that reported for PPTA mRNA in the rat. However, the human gene drove expression in areas of the mouse CNS not associated with strong PPTA expression in rodents but which have been shown to express PPTA in the human. This study clearly demonstrates the high degree of conservation of the mechanisms involved in PPTA transcription that has occurred throughout 100 million of divergent human and rodent evolution. This study also defines the maximum linear extent of the human PPT-A promoter. We believe these findings constitute the removal of a significant obstacle in studying the transcriptional regulation of the human PPTA gene in vivo.

Molecular models to analyse preprotachykinin-A expression and function

Towards an understanding of the mechanisms controlling Preprotachykinin A (PPT) expression we have generated a variety of molecular models to determine the mechanisms regulating both the tissue-specific and stimulus-inducible expression of the PPT gene. The approaches used include transgenic and virus vector models complementing biochemical analysis of promoter interactions with transcription factors. We have identified and characterised a yeast artificial chromosome (YAC) containing the human PPT gene and generated transgenic mouse lines containing multiple copies of this chromosome on a normal mouse genetic background. This resulted in a pattern of expression in the nervous system remarkably similar to that reported for PPT mRNA in rodents. In addition, this transgenic model has been constructed in such a manner to allow for over expression of tachykinins based on the number of extra alleles in the transgenic mouse. These animals allow us to further examine the function of the tachykinins and acts as a useful complement to existing PPT ablated mice. In vitro we have introduced the proximal PPT promoter in reporter gene constructs into adult neurones in both DRG and the CNS by an adenoassociated virus (AAV) vector or by biolistic transfection respectively. Using the AAV vector we have demonstrated that the proximal promoter can mediate the effects of NGF in adult rat DRG. These models allow us to delineate transcriptional domains involved in the physiological and pathological expression of the PPT gene.

Tau promoter confers neuronal specificity and binds Sp1 and AP-2

Tau, a microtubule-associated protein, is encoded by a single gene, whose expression is primarily neuronal. In this work, we defined an 80-bp region of the tau promoter that confers tau protein with neuronal expression. This fragment works in conjunction with an endogenous initiation region to activate neuronal precursor-specific transcription of the tau promoter and works independently of this initiation region to confer nerve growth factor inducibility. Furthermore, this 80-bp fragment binds both Sp1 and AP-2 proteins. DNase I foot-print analysis revealed a third protein binding region at the center of this 80-bp fragment in neuronal cells. Mutation within any of these three protein binding sites decreases transcriptional activation of the tau gene. Comprehension of the interactions that occur between cis- and trans-regulatory elements of the tau promoter is important to understand the regulation of tau expression during normal development and changes that may occur in many cases of dementia, including Alzheimer's disease.

Perinatal regulation of the ClC-2 chloride channel in lung is mediated by Sp1 and Sp3

Mechanisms responsible for regulation of pulmonary epithelial chloride-channel expression in the perinatal period are under investigation to better understand normal lung development and airway disease pathogenesis. The ClC-2 epithelial chloride channel is regulated by changes in pH and volume and is most abundant in lung during fetal development. In this study, we identify and sequence the ClC-2 promoter, which is GC rich and lacks a TATA box. By construction of a series of promoter-luciferase constructs, a 67-bp GC box-containing sequence in the promoter is shown to be critical to ClC-2 expression in primary and immortalized fetal lung epithelial cells. Electrophoretic mobility shift assays and antibody supershifts demonstrate that the Sp1 and Sp3 transcription factors are expressed in fetal lung nuclei and interact with the GC box sequences in the promoter. Immunoblotting techniques demonstrate that Sp1 and Sp3 are perinatally downregulated in the lung with the same temporal sequence as ClC-2 downregulation. This work suggests that Sp1 and Sp3 activate ClC-2 gene transcription and that reduction in Sp1 and Sp3 at birth explains perinatal downregulation of ClC-2 in the lung.

Novel role for Sp1 in phorbol ester enhancement of human platelet thromboxane receptor gene expression

Expression of platelet thromboxane receptors is transcriptionally increased during megakaryocytic differentiation stimulated by phorbol 12-myristate 13-acetate (PMA). We previously cloned and characterized the promoter region of the human thromboxane receptor gene and localized PMA-responsive elements to a region between 1.84 and 1.95 kilobase pairs (kb) 5' of the transcription initiation site (D'Angelo, D. D., Davis, M. G., Houser, W. A., Eubank, J. J., Ritchie, M. E., and Dorn, G. W., II (1995) Circ. Res. 77, 466-474). Herein we report the localization of the PMA response element to a 14-nucleotide C-rich sequence, flanked by an octanucleotide inverted repeat, located -1.938 to -1.925 kb 5' of the transcription start site of this gene. We further identify the PMA-responsive enhancer factor that binds to this C-rich sequence as Sp1. Heterologous thromboxane receptor gene promoter/thymidilate kinase reporter constructs transfected into K562 cells exhibited PMA responsiveness when the C-rich element was included with additional 3' sequence from -1.924 to -1.84 kb. However, mutations of the C-rich element that disrupted a GC box located on the inverse strand eliminated PMA responsiveness and, in gel mobility shift assays, eliminated binding of Sp1. PMA treatment of K562 cells significantly increased, by 5-fold, Sp1 binding to the C-rich element and increased both phosphorylated and nonphosphorylated Sp1 protein levels by 2-fold. Furthermore, PMA treatment transiently increased Sp1 mRNA levels prior to increasing thromboxane receptor mRNA, suggesting that up-regulation of Sp1 contributes to up-regulation of thromboxane receptors. Finally, we have detected an unidentified K562 nuclear protein that binds specifically to the sense strand of the C-rich sequence overlapping the Sp1 binding site and that, by stabilizing a double stem-loop conformation of this DNA segment, may also play a role in Sp1 regulation of this gene. These studies are the first to describe regulatory and regulated roles for Sp1 in PMA-responsive gene expression and suggest that modulation of Sp1 levels controls thromboxane receptor expression during megakaryocytic differentiation.