title: Polypyrimidine tract-binding protein enhances the internal ribosomal entry site-dependent translation of p27Kip1 mRNA and modulates transition from G1 to S phase.
abstract: The p27(Kip1) protein plays a critical role in the regulation of cell proliferation through the inhibition of cyclin-dependent kinase activity. Translation of p27(Kip1) is directed by an internal ribosomal entry site (IRES) in the 5' nontranslated region of p27(Kip1) mRNA. Here, we report that polypyrimidine tract-binding protein (PTB) specifically enhances the IRES activity of p27(Kip1) mRNA through an interaction with the IRES element. We found that addition of PTB to an in vitro translation system and overexpression of PTB in 293T cells augmented the IRES activity of p27(Kip1) mRNA but that knockdown of PTB by introduction of PTB-specific small interfering RNAs (siRNAs) diminished the IRES activity of p27(Kip1) mRNA. Moreover, the G(1) phase in the cell cycle (which is maintained in part by p27(Kip1)) was shortened in cells depleted of PTB by siRNA knockdown. 12-O-Tetradecanoylphorbol-13-acetate (TPA)-induced differentiation in HL60 cells was used to examine PTB-induced modulation of p27(Kip1) protein synthesis during differentiation. The IRES activity of p27(Kip1) mRNA in HL60 cells was increased by TPA treatment (with a concomitant increase in PTB protein levels), but the levels of p27(Kip1) mRNA remained unchanged. Together, these data suggest that PTB modulates cell cycle and differentiation, at least in part, by enhancing the IRES activity of p27(Kip1) mRNA.
authors.affiliation: PBC, Division of Molecular and Life Science, Pohang University of Science and Technology, San 31, Hyoja Dong, Pohang, Kyungbuk 790-784, South Korea. sungkey@postech.ac.kr
authors.forename: Sungchan
authors.initials: S
authors.lastname: Cho
authors.forename: Jong Heon
authors.initials: JH
authors.lastname: Kim
authors.forename: Sung Hoon
authors.initials: SH
authors.lastname: Back
authors.forename: Sung Key
authors.initials: SK
authors.lastname: Jang
mesh_terms: D018797:Cell Cycle Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology*; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D010442:Peptide Chain Initiation, Translational / Q000187:drug effects / Q000502:physiology; D010703:Phorbol Esters / Q000494:pharmacology; D038941:Polypyrimidine Tract-Binding Protein / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D016196:S Phase / Q000187:drug effects / Q000502:physiology*; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D010703:Phorbol Esters; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; D038941:Polypyrimidine Tract-Binding Protein; D050760:Cyclin-Dependent Kinase Inhibitor p27