protein_function: Cell surface glycoprotein receptor involved in thecostimulatory signal essential for T-cell receptor (TCR)-mediatedT-cell activation. Acts as a positive regulator of T-cellcoactivation, by binding at least ADA, CAV1, IGF2R, and PTPRC. Itsbinding to CAV1 and CARD11 induces T-cell proliferation and NF-kappa-B activation in a T-cell receptor,CD3-dependent manner. Itsinteraction with ADA also regulates lymphocyte-epithelial celladhesion. In association with FAP is involved in the pericellularproteolysis of the extracellular matrix (ECM), the migration andinvasion of endothelial cells into the ECM. May be involved in thepromotion of lymphatic endothelial cells adhesion, migration andtube formation. When overexpressed, enhanced cell proliferation, aprocess inhibited by GPC3. Acts also as a serine exopeptidase witha dipeptidyl peptidase activity that regulates variousphysiological processes by cleaving peptides in the circulation,including many chemokines, mitogenic growth factors, neuropeptidesand peptide hormones. Removes N-terminal dipeptides sequentiallyfrom polypeptides having unsubstituted N-termini provided that thepenultimate residue is proline..
Dipeptidyl peptidase-4(DPP4), also known as adenosine deaminase complexing protein 2 or CD26(cluster of differentiation 26) is a protein that, in humans, is encoded by the DPP4 gene. By fluorescence in situ hybridization, the CD26 gene was mapped to 2q24.3. DPP4 plays a major role in glucose metabolism. It is responsible for the degradation of incretins such as GLP-1. Furthermore, it appears to work as a suppressor in the development of cancer and tumours. CD26, DPP4 plays an important role in tumor biology, and is useful as a marker for various cancers, with its levels either on the cell surface or in the serum increased in some neoplasms and decreased in others.