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Description

UL16-binding protein-like transcript 1 splicing variant (UniProt: Q330P3, also known as MULT1, MULT-1, ULBP1) is encoded by the Ulbp1 gene in murine species. MULT-1 is a MHC Class I-like molecule that serves as a high affinity ligand for natural Killer Group 2D (NKG2D) receptor. It is a type I transmembrane protein that is synthesized with a signal peptide (aa 1-25), which is subsequently cleaved off to generate the mature form. Its transmembrane domain is localized to amino acids 124 to 146 and its extracellular domain contains an alpha 1 and alpha 2 like domain with two intrachain disulfide bonds. MULT-1 expression is reported to be low or absent in normal adult tissues, however, under conditions of stress and in tumor cells its levels are elevated. Many tumor cells are shown to release soluble NKG2D ligands through proteolytic shedding, alternative splicing, or exosome secretion. In mice MULT-1 is shown to cause NK cell activation and tumor rejection. Mice subjected to cytomegalovirus (MCMV) infection display strong expression of Ulbp1 (Mult1) gene, but surface expression of MULT-1 is nevertheless completely abolished by the virus. Fc receptor fcr-1 is reported to down-regulate MULT-1 levels by interfering with surface MULT-1 and causing its subsequent degradation in lysosomes. This effect of Fcr-1 can be completely abolished by imipramine (Cat. No. I0899), which blocks AP2-mediated clathrin pathway. (Ref.: Lenac, T., et al. (2006). J. Exp. Med. 203(8), 1843 1850, Krmpotic, A., et al. (2005). J. Exp. Med. 201(2): 211-220, Deng, W., et al. (2015). Science. 348(6230), 136-139).