title: Phosphomimetic substitution of heterogeneous nuclear ribonucleoprotein A1 at serine 199 abolishes AKT-dependent internal ribosome entry site-transacting factor (ITAF) function via effects on strand annealing and results in mammalian target of rapamycin complex 1 (mTORC1) inhibitor sensitivity.
abstract: The relative activity of the AKT kinase has been demonstrated to be a major determinant of sensitivity of tumor cells to mammalian target of rapamycin (mTOR) complex 1 inhibitors. Our previous studies have shown that the multifunctional RNA-binding protein heterogeneous nuclear ribonucleoprotein (hnRNP) A1 regulates a salvage pathway facilitating internal ribosome entry site (IRES)-dependent mRNA translation of critical cellular determinants in an AKT-dependent manner following mTOR inhibitor exposure. This pathway functions by stimulating IRES-dependent translation in cells with relatively quiescent AKT, resulting in resistance to rapamycin. However, the pathway is repressed in cells with elevated AKT activity, rendering them sensitive to rapamycin-induced G(1) arrest as a result of the inhibition of global eIF-4E-mediated translation. AKT phosphorylation of hnRNP A1 at serine 199 has been demonstrated to inhibit IRES-mediated translation initiation. Here we describe a phosphomimetic mutant of hnRNP A1 (S199E) that is capable of binding both the cyclin D1 and c-MYC IRES RNAs in vitro but lacks nucleic acid annealing activity, resulting in inhibition of IRES function in dicistronic mRNA reporter assays. Utilizing cells in which AKT is conditionally active, we demonstrate that overexpression of this mutant renders quiescent AKT-containing cells sensitive to rapamycin in vitro and in xenografts. We also demonstrate that activated AKT is strongly correlated with elevated Ser(P)(199)-hnRNP A1 levels in a panel of 22 glioblastomas. These data demonstrate that the phosphorylation status of hnRNP A1 serine 199 regulates the AKT-dependent sensitivity of cells to rapamycin and functionally links IRES-transacting factor annealing activity to cellular responses to mTOR complex 1 inhibition.
authors: Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, California 91343, USA.
authors: Jheralyn
authors: J
authors: Martin
authors: Janine
authors: J
authors: Masri
authors: Cheri
authors: C
authors: Cloninger
authors: Brent
authors: B
authors: Holmes
authors: Nicholas
authors: N
authors: Artinian
authors: Alexander
authors: A
authors: Funk
authors: Teresa
authors: T
authors: Ruegg
authors: Lauren
authors: L
authors: Anderson
authors: Tariq
authors: T
authors: Bashir
authors: Andrew
authors: A
authors: Bernath
authors: Alan
authors: A
authors: Lichtenstein
authors: Joseph
authors: J
authors: Gera
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism*; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes; D020125:Mutation, Missense; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D014176:Protein Biosynthesis / Q000187:drug effects / Q000235:genetics; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases
chemical_list: D000903:Antibiotics, Antineoplastic; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; C000619657:Hnrnpa1 protein, mouse; D046912:Multiprotein Complexes; D011506:Proteins; D012333:RNA, Messenger; C000619656:hnRNPA1 protein, human; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus