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. 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. TMEM174 is comprised of 243 amino acids and contains two predicted transmembrane helices which determine its subcellular localization in the endoplasmic reticulum and influences its functions. Over-expression of TMME174 enhanced the transcriptional activity of AP-1 and promoted cell proliferation, whereas the truncated mutant TMEM174DeltaTM without the transmembrane regions did not retain these functions. The TMEM174 gene exhibited high expression levels in certain renal carcinomas, which may indicate that TMEM174 may have a significant role in the development and progression of these renal carcinomas.