TIP47 Background Information Tail-interacting 47kDa protein (TIP47), known also as human placental tissue protein 17b (PP17b), binds to cytoplasmic domains of the cation-dependent (CD) and cation-independent (CI) mannose 6-phosphate receptors (MPRs) and facilitates their transport from endosomes to the golgi complex (1). The inability of TIP47 to bind several proteins also transported from endosomes to the trans golgi network indicates that TIP47 associates with a very select set of cargo molecules (2). In CD-MPR, TIP47 recognizes a phenylalanine/tryptophan signal sequence essential for proper sorting within the endosomal pathway (1). For CI-MPR binding, TIP47 requires cytoplasmic residues 48-74 of CI-MPR for high-affinity binding while residues 75-163 of CI-MPR aid in the presentation of the higher-affinity residues (3). Additionally, TIP47 competes with AP-2 clathrin adaptor for binding residues 24-29 of CI-MPR (3). In tissue extracts of cervical carcinoma patients, TIP47 is overexpressed (4). Dysplastic cells in high grade dysplasias express more TIP47 than dysplastic cells in low grade dysplasias, and both cytoplasmic types of dysplasias express more TIP47 than normal cervical epithelial cells (5). The gene encoding human TIP47 maps to chromosome 19pter-19p13.3 (1).
