Characterization of the human mitochondrial thiamine pyrophosphate transporter SLC25A19 minimal promoter: a role for NF-Y in regulating basal transcription.

Transcriptional regulation of expression of the human mitochondrial thiamine pyrophosphate transporter (the product of the SLC25A19 gene) is unknown. To understand this regulation, we cloned and characterized the 5'-regulatory region of the SLC25A19 gene (1,080 bp). The cloned fragment was found to possess promoter activity in transiently transfected human-derived liver HepG2 cells. 5'- and 3'-deletion analysis has identified the minimal region required for basal SLC25A19 promoter activity to be between -131 and +20 (using the distal transcriptional start site as +1). The minimal promoter lacks typical TATA motif and contains two inverted CCAAT boxes (binding sites for NF-Y transcriptional factor). By means of mutational analysis, the critical role of both the upstream and downstream CCAAT boxes in basal SLC25A19 promoter activity was established; however, each of these boxes alone was found to be unable to support promoter activity. EMSA and supershift EMSA (with the use of specific antibodies against NF-Y subunits) studies, as well as chromatin immunoprecipitation assay, demonstrated the binding of NF-Y to both CCAAT boxes in vitro and in vivo, respectively. The requirement for NF-Y in SLC25A19 promoter activity in vivo was directly confirmed by the use of a dominant negative NF-YA mutant in transiently transfected HepG2 cells. These studies report for the first time the characterization of the SLC25A19 promoter and demonstrate an essential role for NF-Y in its basal activity.

HOXB7 expression is regulated by the transcription factors NF-Y, YY1, Sp1 and USF-1.

Products of HOX genes are transcription factors responsible for developmental regulation and postnatal tissue homeostasis. Besides their well-established function played during embryonic development, we had previously demonstrated the direct role of HOXB7 in tumor progression through transactivation of several genes involved in the proliferative and angiogenic processes. This role is at first exerted through the deregulated, constitutive expression of this gene. To define the factors possibly responsible for such activation, we studied the molecular regulation of HOXB7 in embryonic and neoplastic cells. In a 1.9-kb 5' promoter region, we identified and functionally tested, at least in vitro, different regulatory sequences showing a direct binding by the NF-Y, YY1, Sp1/Sp3 and upstream stimulatory factor 1 (USF-1) transcription factors. Cell transfection and site-specific mutagenesis demonstrated Sp1/Sp3, NF-Y, YY1 and USF-1 binding to be functional and fundamental in driving HOXB7 expression. Disruption of the corresponding sites reduces gene expression of 65%, 78% and 55%, respectively. Because HOXB7 seems to play an important role in tumor proliferation and progression, the analysis of its regulatory sequences might represent an important step for gene targeting according to a new therapeutic strategy.