TSPAN1 belongs to the transmembrane 4 superfamily, also known as the tetraspanin family. Tetraspanins have four hydrophobic domains, intracellular N- and C-termini and two extracellular domains. Tetraspanins act as scaffolding proteins, anchoring multiple proteins to one area of the cell membrane. They also mediate signal transduction events that play a role in the regulation of cell development, activation, growth and motility. TSPAN1 interacts with human thiamine transporter-1 (hTHTR-1). HTHTR-1 contributes to intestinal thiamine uptake, and its function is regulated at both the transcriptional and posttranscriptional levels. TSPAN1 and hTHTR-1 colocalize in human intestinal epithelial HuTu-80 cells. Coexpression of TSPAN1 in these cells led to a significant decrease in the rate of degradation of hTHTR-1 compared with cells expressing the hTHTR-1 alone; in fact the half-life of the TSPAN1 protein was twice longer in the former cell type compared with the latter cell type.