title: Protein kinase A phosphorylation modulates transport of the polypyrimidine tract-binding protein.
abstract: The heterogeneous nuclear ribonucleoprotein particle (hnRNP) proteins play important roles in mRNA processing in eukaryotes, but little is known about how they are regulated by cellular signaling pathways. The polypyrimidine-tract binding protein (PTB, or hnRNP I) is an important regulator of alternative pre-mRNA splicing, of viral RNA translation, and of mRNA localization. Here we show that the nucleo-cytoplasmic transport of PTB is regulated by the 3',5'-cAMP-dependent protein kinase (PKA). PKA directly phosphorylates PTB on conserved Ser-16, and PKA activation in PC12 cells induces Ser-16 phosphorylation. PTB carrying a Ser-16 to alanine mutation accumulates normally in the nucleus. However, export of this mutant protein from the nucleus is greatly reduced in heterokaryon shuttling assays. Conversely, hyperphosphorylation of PTB by coexpression with the catalytic subunit of PKA results in the accumulation of PTB in the cytoplasm. This accumulation is again specifically blocked by the S16A mutation. Similarly, in Xenopus oocytes, the phospho-Ser-16-PTB is restricted to the cytoplasm, whereas the non-Ser-16-phosphorylated PTB is nuclear. Thus, direct PKA phosphorylation of PTB at Ser-16 modulates the nucleo-cytoplasmic distribution of PTB. This phosphorylation likely plays a role in the cytoplasmic function of PTB.
authors.affiliation: Howard Hughes Medical Institute, Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, CA 90095-1662, USA.
authors.forename: Jiuyong
authors.initials: J
authors.lastname: Xie
authors.forename: Ji-Ann
authors.initials: JA
authors.lastname: Lee
authors.forename: Tracy L
authors.initials: TL
authors.lastname: Kress
authors.forename: Kimberly L
authors.initials: KL
authors.lastname: Mowry
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Black
mesh_terms: D016475:3T3 Cells; D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D010766:Phosphorylation; D038941:Polypyrimidine Tract-Binding Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D014982:Xenopus laevis
chemical_list: D011994:Recombinant Proteins; D038941:Polypyrimidine Tract-Binding Protein; D012694:Serine; D017868:Cyclic AMP-Dependent Protein Kinases