title: Rapamycin induces binding activity to the terminal oligopyrimidine tract of ribosomal protein mRNA in rats.
abstract: The immunosuppressant rapamycin selectively suppresses the translation of mRNAs containing a terminal oligopyrimidine (TOP) tract adjacent to the cap structure. trans-Acting factors that bind to the 5'-untranslated region (5'-UTR) of TOP mRNAs may be involved in selective translational repression. Some of these factors are regulated by rapamycin-responsive signaling pathways. To identify candidates for the selective trans-acting factor, we examined whether administration of rapamycin alters the binding activity of proteins that bind to RNA containing the TOP element of mouse ribosomal protein (r-protein) L32 mRNA. Preadministration with Freund's complete adjuvant (FCA) prior to rapamycin treatment resulted in increased translational efficiency of r-protein L32 mRNA in submaxillary lymph node (SLN; 2.3-fold), thymus (1.5-fold), and parotid gland (PG; 1.6-fold). Translation of r-protein L32 or elongation factor 1A mRNAs in SLN and PG from FCA-pretreated rats were sensitive to rapamycin administration and the binding ability of p56 was generally increased in extracts from these tissues. On the other hand, in thymus, rapamycin had no effect on the translational efficiency of TOP mRNAs and no p56 binding was detected in the extracts from FCA-pretreated animals. Coadministration of FK506, another immunosuppressive macrolide, increased the p56 TOP-RNA-binding activity and induced selective translational repression of TOP mRNAs in a dose-dependent manner, even in thymus. These findings indicate that p56 is a plausible candidate for the trans-acting factor responsible for regulating the translation of TOP mRNA by a rapamycin-sensitive pathway and that TOP mRNA translational regulation may be responsible for the tissue specificity of rapamycin.
authors.affiliation: Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan. tomohito@p.chiba-u.ac.jp
authors.forename: Tomohito
authors.initials: T
authors.lastname: Kakegawa
authors.forename: Makoto
authors.initials: M
authors.lastname: Ito
authors.forename: Akiko
authors.initials: A
authors.lastname: Hayakawa
authors.forename: Megumi
authors.initials: M
authors.lastname: Matsuda
authors.forename: Sayoko
authors.initials: S
authors.lastname: Tamura
authors.forename: Hiromi
authors.initials: H
authors.lastname: Saito
authors.forename: Roger L
authors.initials: RL
authors.lastname: Kaspar
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kobayashi
mesh_terms: D020121:5' Untranslated Regions / Q000378:metabolism*; D000818:Animals; D008198:Lymph Nodes / Q000378:metabolism; D008297:Male; D009687:Nuclear Proteins / Q000378:metabolism; D010306:Parotid Gland / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D011743:Pyrimidines / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012269:Ribosomal Proteins / Q000235:genetics*; D020123:Sirolimus / Q000008:administration & dosage / Q000494:pharmacology*; D013056:Spectrophotometry, Ultraviolet; D016559:Tacrolimus / Q000008:administration & dosage / Q000494:pharmacology; D013950:Thymus Gland / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; D009687:Nuclear Proteins; D011743:Pyrimidines; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D012269:Ribosomal Proteins; D014157:Transcription Factors; C041806:ribosomal protein L32; D020123:Sirolimus; D016559:Tacrolimus