Phosphorylation of hUPF1 induces formation of mRNA surveillance complexes containing hSMG-5 and hSMG-7.
Eukaryotic mRNAs containing premature termination codons (PTCs) are degraded by a process known as nonsense-mediated mRNA decay (NMD). NMD has been suggested to require the recognition of PTC by an mRNA surveillance complex containing UPF1/SMG-2. In multicellular organisms, UPF1/SMG-2 is a phosphoprotein, and its phosphorylation contributes to NMD. Here we show that phosphorylated hUPF1, the human ortholog of UPF1/SMG-2, forms a complex with human orthologs of the C. elegans NMD proteins SMG-5 and SMG-7. The complex also associates with protein phosphatase 2A (PP2A), resulting in dephosphorylation of hUPF1. Overexpression of hSMG-5 mutants that retain interaction with P-hUPF1 but which cannot induce its dephosphorylation impair NMD, suggesting that NMD requires P-hUPF1 dephosphorylation. We also show that P-hUPF1 forms distinct complexes containing different isoforms of hUPF3A. We propose that sequential phosphorylation and dephosphorylation of hUPF1 by hSMG-1 and PP2A, respectively, contribute to the remodeling of the mRNA surveillance complex.
Ohnishi
Tetsuo
T
Department of Molecular Biology, Yokohama City University School of Medicine, Yokohama 236-0004, Japan.
Yamashita
Akio
A
Kashima
Isao
I
Schell
Thomas
T
Anders
Kirk R
KR
Grimson
Andrew
A
Hachiya
Takahisa
T
Hentze
Matthias W
MW
Anderson
Philip
P
Ohno
Shigeo
S
D000595:Amino Acid Sequence; D000818:Animals; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002458:Cell Fractionation; D018389:Codon, Nonsense; D006367:HeLa Cells; D006801:Humans; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D054648:Protein Phosphatase 2; D020365:RNA Helicases; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D018389:Codon, Nonsense; D046911:Macromolecular Substances; D012333:RNA, Messenger; C472410:SMG-5 protein, C elegans; C117551:SMG-7 protein, C elegans; D015534:Trans-Activators; D014157:Transcription Factors; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D020365:RNA Helicases; C101828:UPF1 protein, human