title: Clathrin mediates endocytosis of progastrin and activates MAPKs: role of cell surface annexin A2.
abstract: Cell-surface-associated annexin A2 (CS-ANXA2) is a nonconventional "receptor" for progastrin; expression levels of both are elevated in colon cancers, and downregulation of either reduces tumorigenic potential of cells. We recently reported internalization of progastrin in target cells. Here, mechanisms mediating internalization of progastrin were examined. Initially, we confirmed that cell-surface ANXA2 mediates binding and internalization of progastrin in intestinal cells. Progastrin, covalently linked to sepharose beads, failed to activate p38MAPK/ERKs, suggesting internalization of progastrin was required for eliciting biological effects; importantly annexin A2 expression and availability of CS-ANXA2 were required for internalization of progastrin. Clathrin expression and formation of clathrin-coated pits were critically required for endocytotic internalization of progastrin; in the absence of clathrin, progastrin failed to activate p38MAPK/ERKs. Downregulation of caveolin had no effect on binding or internalization of progastrin. We therefore demonstrate for the first time that progastrin binds CS-ANXA2 and is rapidly internalized via clathrin-mediated endocytotic pathway, resulting in activation of MAPKinases. Targeting clathrin-mediated endocytosis of progastrin may thus inhibit previously reported co-carcinogenic/tumorigenic effects of progastrin on intestinal cells.
authors.affiliation: Dept. of Neuroscience and Cell Biology, Univ. of Texas Medical Branch, Galveston, TX 77555-1043, USA.
authors.forename: Shubhashish
authors.initials: S
authors.lastname: Sarkar
authors.forename: Carla
authors.initials: C
authors.lastname: Kantara
authors.forename: Pomila
authors.initials: P
authors.lastname: Singh
mesh_terms: D000818:Animals; D017306:Annexin A2 / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002746:Chlorpromazine / Q000494:pharmacology; D002966:Clathrin / Q000235:genetics / Q000378:metabolism*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004705:Endocytosis / Q000502:physiology*; D004789:Enzyme Activation / Q000502:physiology; D005755:Gastrins / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D021381:Protein Transport; D051381:Rats; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism
chemical_list: D017306:Annexin A2; D002966:Clathrin; D018492:Dopamine Antagonists; D005755:Gastrins; D008565:Membrane Proteins; D011498:Protein Precursors; D051996:Transcription Factor RelA; C013706:big gastrin; D020929:Mitogen-Activated Protein Kinase Kinases; D002746:Chlorpromazine