title: Keratin 20 serine 13 phosphorylation is a stress and intestinal goblet cell marker.
abstract: Keratin polypeptide 20 (K20) is an intermediate filament protein with preferential expression in epithelia of the stomach, intestine, uterus, and bladder and in Merkel cells of the skin. K20 expression is used as a marker to distinguish metastatic tumor origin, but nothing is known regarding its regulation and function. We studied K20 phosphorylation as a first step toward understanding its physiologic role. K20 phosphorylation occurs preferentially on serine, with a high stoichiometry as compared with keratin polypeptides 18 and 19. Mass spectrometry analysis predicted that either K20 Ser(13) or Ser(14) was a likely phosphorylation site, and Ser(13) was confirmed as the phospho-moiety using mutation and transfection analysis and generation of an anti-K20-phospho-Ser(13) antibody. K20 Ser(13) phosphorylation increases after protein kinase C activation, and Ser(13)-to-Ala mutation interferes with keratin filament reorganization in transfected cells. In physiological contexts, K20 degradation and associated Ser(13) hyperphosphorylation occur during apoptosis, and chemically induced mouse colitis also promotes Ser(13) phosphorylation. Among mouse small intestinal enterocytes, K20 Ser(13) is preferentially phosphorylated in goblet cells and undergoes dramatic hyperphosphorylation after starvation and mucin secretion. Therefore, K20 Ser(13) is a highly dynamic protein kinase C-related phosphorylation site that is induced during apoptosis and tissue injury. K20 Ser(13) phosphorylation also serves as a unique marker of small intestinal goblet cells.
authors.affiliation: Department of Medicine, Veterans Affairs Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA. qzhou@stanford.edu
authors.forename: Qin
authors.initials: Q
authors.lastname: Zhou
authors.forename: Monique
authors.initials: M
authors.lastname: Cadrin
authors.forename: Harald
authors.initials: H
authors.lastname: Herrmann
authors.forename: Che-Hong
authors.initials: CH
authors.lastname: Chen
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Chalkley
authors.forename: Alma L
authors.initials: AL
authors.lastname: Burlingame
authors.forename: M Bishr
authors.initials: MB
authors.lastname: Omary
mesh_terms: D000818:Animals; D017209:Apoptosis; D006224:Cricetinae; D020895:Enterocytes / Q000378:metabolism; D020397:Goblet Cells / Q000166:cytology*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000166:cytology*; D053554:Keratin-20; D007633:Keratins / Q000737:chemistry*; D051379:Mice; D008807:Mice, Inbred BALB C; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D012694:Serine / Q000737:chemistry*
chemical_list: C507499:KRT20 protein, human; D053554:Keratin-20; D012694:Serine; D007633:Keratins