Description
MUC-1 (Mucin-1) is a type 1 transmembrane glycoprotein that is normally expressed on the apical surface of most epithelial cells (1-2). It is known to be overexpressed by various human carcinomas and is shed into circulation (2). The extracellular domain is made up of tandem repeats (TRs) of 20 amino acid (aa) each, with each TR containing five potential O-glycosylation sites (3). The number of TRs vary between 25-100, depending on the allele (3). Within the mature region including 16 TRs (residues 24-380), human MUC-1 shares 30% aa sequence identity with mouse and rat MUC-1. It has been reported that high expression level of MUC-1 generally correlates with increased mortality rates (4). In addition, MUC-1 is aberrantly underglycosylated on cancer cells with short and sialylated O-linked glycans in contrast to the long, branched chain seen in normal epithelial cells (4-7). It has been demonstrated that MUC-1 can interact with E-selectin and ICAM-1 to mediate firm adhesion of circulating tumor cells and subsequent extravasation in the metastatic adhesion cascade (4). Furthermore, MUC-1 can modulate the tumor immunological microenvironment through engagement of Siglec-9 by inducing the recruitment of beta-catenin to the cytoplasmic tail of MUC-1, increasing the expression of PD-L1 by macrophages, and activating the MEK-ERK pathway (5,6). MUC-1 can also interact with Galectin-3 to promote EGFR activation thus regulating EGFR-associated tumorigenesis and cancer progression (7). Our Avi-tag Biotinylated human MUC-1 features biotinylation at a single site contained within the Avi-tag, a unique 15 amino acid peptide. Protein orientation will be uniform when bound to streptavidin-coated surface due to the precise control of biotinylation and the rest of the protein is unchanged so there is no interference in the protein's bioactivity