title: Molecular dissection of the importin beta1-recognized nuclear targeting signal of parathyroid hormone-related protein.
abstract: Produced by various types of solid tumors, parathyroid hormone-related protein (PTHrP) is the causative agent of humoral hypercalcemia of malignancy. The similarity of PTHrP's amino-terminus to that of parathyroid hormone enables it to share some of the latter's signalling properties, but its carboxy-terminus confers distinct functions including a role in the nucleus/nucleolus in reducing apoptosis and enhancing cell proliferation. PTHrP nuclear import occurs via a novel importin beta1-mediated pathway. The present study uses several different direct binding assays to map the interaction of PTHrP with importin beta using a series of alanine mutated PTHrP peptides and truncated human importin beta1 derivatives. Our results indicate that PTHrP amino acids 83-93 (KTPGKKKKGK) are absolutely essential for importin beta1 recognition with residues 71-82 (TNKVETYKEQPL) additionally required for high affinity binding; residues 380-643 of importin beta1 are required for the interaction. Binding of importin beta1 to PTHrP is reduced in the presence of the GTP-bound but not GDP-bound form of the guanine nucleotide binding protein Ran, consistent with the idea that RanGTP binding to importin beta is involved in the release of PTHrP into the nucleus following translocation across the nuclear envelope. This study represents the first detailed examination of a modular, non-arginine-rich importin beta1-recognized nuclear targeting signal.
authors.affiliation: Division for Biochemistry and Molecular Biology, John Curtin School of Medical Research, Canberra, Australia.
authors.forename: M H
authors.initials: MH
authors.lastname: Lam
authors.forename: W
authors.initials: W
authors.lastname: Hu
authors.forename: C Y
authors.initials: CY
authors.lastname: Xiao
authors.forename: M T
authors.initials: MT
authors.lastname: Gillespie
authors.forename: D A
authors.initials: DA
authors.lastname: Jans
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D028884:Karyopherins; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D019913:Nuclear Localization Signals / Q000235:genetics; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D044162:Parathyroid Hormone-Related Protein; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D020931:ran GTP-Binding Protein / Q000378:metabolism
chemical_list: D028884:Karyopherins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; C470121:PTHLH protein, human; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D011993:Recombinant Fusion Proteins; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020931:ran GTP-Binding Protein