Nucleolar localization of cirhin, the protein mutated in North American Indian childhood cirrhosis.
Cirhin (NP_116219), the product of the CIRH1A gene is mutated in North American Indian childhood cirrhosis (NAIC/CIRH1A, OMIM 604901), a severe autosomal recessive intrahepatic cholestasis. It is a 686-amino-acid WD40-repeat containing protein of unknown function that is predicted to contain multiple targeting signals, including an N-terminal mitochondrial targeting signal, a C-terminal monopartite nuclear localization signal (NLS) and a bipartite nuclear localization signal (BNLS). We performed the direct determination of subcellular localization of cirhin as a crucial first step in unraveling its biological function. Using EGFP and His-tagged cirhin fusion proteins expressed in HeLa and HepG2, cells we show that cirhin is a nucleolar protein and that the R565W mutation, for which all NAIC patients are homozygous, has no effect on subcellular localization. Cirhin has an active C-terminal monopartite nuclear localization signal (NLS) and a unique nucleolar localization signal (NrLS) between residues 315 and 432. The nucleolus is not known to be important specifically for intrahepatic cholestasis. These observations provide a new dimension in the study of hereditary cholestasis.
Yu
Bin
B
Service de Génétique médicale, Centre de recherche, Hôpital Sainte-Justine, Université de Montréal, 3175 Côte Sainte-Catherine, Québec, Canada H3T1C5.
Mitchell
Grant A
GA
Richter
Andrea
A
D000293:Adolescent; D000595:Amino Acid Sequence; D002466:Cell Nucleolus / Q000737:chemistry* / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D002875:Chromosomes / Q000737:chemistry; D066246:ErbB Receptors / Q000032:analysis / Q000378:metabolism; D006801:Humans; D007198:Indians, North American / Q000235:genetics*; D007223:Infant; D007231:Infant, Newborn; D008105:Liver Cirrhosis, Biliary / Q000235:genetics* / Q000378:metabolism; D008938:Mitosis; D019913:Nuclear Localization Signals / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D010750:Phosphoproteins / Q000032:analysis / Q000378:metabolism; D017354:Point Mutation; D011506:Proteins / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000032:analysis / Q000378:metabolism; D012261:Ribonucleoproteins; D017384:Sequence Deletion; D000097796:Nucleolin
D066246:ErbB Receptors; D019913:Nuclear Localization Signals; D010750:Phosphoproteins; D011506:Proteins; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D000097796:Nucleolin; C470475:UTP4 protein, human