TM4SF1Transmembrane 4 L6 family member 1 is a protein that in humans is encoded by the TM4SF1 gene.FunctionThe protein encoded by this gene is a member of the transmembrane 4 superfamily, also known as the tetraspanin family. Most of these members are cell-surface proteins that are characterized by the presence of four hydrophobic domains. The proteins mediate signal transduction events that play a role in the regulation of cell development, activation, growth and motility. This encoded protein is a cell surface antigen and is highly expressed in different carcinomas.Marker gene for alveolar epithelial progenitorsTM4SF1 has been identified as a marker of Wnt-responsive alveolar epithelial progenitor cells, and a marker of alveolar repair in injured regions of the lungs. It has also been found hypomethylated and upregulated in asthma, with potential prognostic value.