Finding of TRE (TPA responsive element) in the sequence of human taurine transporter promoter

Activity of the taurine transporter (TAUT) is regulated by signal transduction in response to diverse stimuli including tumor promoters such as phobol ester. Regulation of the transcription rate of TAUT appears to play an important role in exerting biological roles of taurine in mammalian tissues in adverse environments. Although cDNA of human TAUT has been cloned and sequenced in placenta, thyroid cells, and retinal pigment epithelial cells, the promoter region of TAUT has never been reported. In order to clone the upstream region of the human TAUT promoter, we have compared TAUT cDNA sequences with the entire human genome sequence. Polymerase chain reaction (PCR) was performed from genomic DNA prepared from a SK-Hep-1 cell line for the amplification of the TAUT promoter region including the partial exon (150 bp) and the 5' untranslated region (UTR, 380 bp). The PCR product of the promoter region, which was 1800 bp long, was ligated into the pGEM-T vector, and sequenced. The 5' flanking region of the TAUT promoter was analysed for the identification of enhancer and regulation motifs. Surprisingly we found the consensus TPA responsive element (TGAGTCAG) which is responsible for gene regulation by the protein kinase C (PKC)-mediated signal transduction pathway. The well known fact that proto-oncogene AP1 (cFos/cJun heterodimer or cJun/cJun homodimer) binds to TRE implies that TAUT expression might be closely linked to tumor promotion. Since AP1 activity is also tightly regulated in nerve cells, AP1-regulated TAUT transcription might be an important step in nerve cell function. Furthermore, the TFIID binding site, cap signal for transcription initiation, PEA3 motif, heat shock factor binding motif, and many other motifs were found in the TAUT promoter region, and require characterization.