title: Insulin receptor substrate-1 associates with small nucleolar RNA which contributes to ribosome biogenesis.
abstract: Insulin receptor substrates (IRSs) are well known to play crucial roles in mediating intracellular signals of insulin-like growth factors (IGFs)/insulin. Previously, we showed that IRS-1 forms high molecular mass complexes containing RNAs. To identify RNAs in IRS-1 complexes, we performed ultraviolet (UV) cross-linking and immunoprecipitation analysis using HEK293 cells expressing FLAG-IRS-1 and FLAG-IRS-2. We detected the radioactive signals in the immunoprecipitates of FLAG-IRS-1 proportional to the UV irradiation, but not in the immunoprecipitates of FLAG-IRS-2, suggesting the direct contact of RNAs with IRS-1. RNAs cross-linked to IRS-1 were then amplified by RT-PCR, followed by sequence analysis. We isolated sequence tags attributed to 25 messenger RNAs and 8 non-coding RNAs, including small nucleolar RNAs (snoRNAs). We focused on the interaction of IRS-1 with U96A snoRNA (U96A) and its host Rack1 (receptor for activated C kinase 1) pre-mRNA. We confirmed the interaction of IRS-1 with U96A, and with RACK1 pre-mRNA by immunoprecipitation with IRS-1 followed by Northern blotting or RT-PCR analyses. Mature U96A in IRS-1(-/-) mouse embryonic fibroblasts was quantitatively less than WT. We also found that a part of nuclear IRS-1 is localized in the Cajal body, a nuclear subcompartment where snoRNA mature. The unanticipated function of IRS-1 in snoRNA biogenesis highlights the potential of RNA-associated IRS-1 complex to open a new line of investigation to dissect the novel mechanisms regulating IGFs/insulin-mediated biological events.
authors.affiliation: Graduate School of Agriculture and Life Sciences, The University of Tokyo , Tokyo , Japan.
authors.forename: Atsufumi
authors.initials: A
authors.lastname: Ozoe
authors.affiliation: Graduate School of Agriculture and Life Sciences, The University of Tokyo , Tokyo , Japan.
authors.forename: Meri
authors.initials: M
authors.lastname: Sone
authors.affiliation: Graduate School of Agriculture and Life Sciences, The University of Tokyo , Tokyo , Japan ; Institute of Biomedical and Health Sciences, Hiroshima University , Hiroshima , Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Fukushima
authors.affiliation: Laboratory for Malignancy Control Research, Medical Innovation Center, Graduate School of Medicine, Kyoto University , Kyoto , Japan.
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Kataoka
authors.affiliation: Graduate School of Agriculture and Life Sciences, The University of Tokyo , Tokyo , Japan.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Chida
authors.affiliation: Institute of Biomedical and Health Sciences, Hiroshima University , Hiroshima , Japan.
authors.forename: Tomoichiro
authors.initials: T
authors.lastname: Asano
authors.affiliation: Graduate School of Agriculture and Life Sciences, The University of Tokyo , Tokyo , Japan.
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Hakuno
authors.affiliation: Graduate School of Agriculture and Life Sciences, The University of Tokyo , Tokyo , Japan.
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Takahashi
keywords: RACK1; U96A; insulin receptor substrate; insulin-like growth factor; snoRNA