Analysis of promoters and CREB/AP-1 binding sites of the human TMEM174 gene

Transmembrane protein 174 (TMEM174) is a type III transmembrane protein with no clear signal peptide. The N and C terminals are located inside the cell. Our previous study demonstrated high expression of TMEM174 in the kidney and its potential involvement in renal cancer based on its capacity to stimulate cell proliferation. However, the mechanism by which TMEM174 promotes proliferation at the transcriptional level remains to be elucidated. In the present study, the TMEM174 promoter region was amplified from whole blood DNA. Six different regions of the regulatory sequences of the TMEM174 promoter region including ~2.5 kb of the upstream region were cloned into the dual luciferase expression vector pGL3-basic. Comparison of the activity of these fragments in dual luciferase reporter assays revealed higher levels of activity for the fragments spanning -186 to +674, -700 to +674, -1,000 to +674 and -2,500 to +1 bp. Lower levels of activity were detected for the fragments spanning -466 to +674 and -890 to +674 bp. The highest activity was detected for the fragment spanning -186 to +674 bp. Electrophoretic mobility shift assay (EMSA) was performed to determine effective transcription factor binding sites. Specific binding of the cyclic-AMP response element binding (CREB) within the TMEM174 gene promoter region was demonstrated, although binding of the activator protein-1 (AP-1) was also detected in this region. In conclusion, these results suggest that the core promoter region of the human TMEM174 gene is located within the region spanning -186 to +674 bp and that the transcription factors CREB and AP-1 are involved in the transcriptional regulation of this gene.