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TORC1 phosphorylates and inhibits the ribosome preservation factor Stm1 to activate dormant ribosomes

ABSTRACT: Target of rapamycin complex 1 (TORC1) promotes biogenesis and inhibits degradation of ribosomes in response to nutrient availability. To ensure a basal supply of ribosomes, cells preserve a small pool of dormant ribosomes under nutrient-limited conditions. The regulation of dormant ribosomes is poorly characterized. Here, we show that upon inhibition of TORC1 by rapamycin or nitrogen starvation, Stm1 (suppressor of target of Myb protein 1) forms non-translating, dormant 80S ribosomes. Furthermore, Stm1-bound 80S ribosomes are protected from proteasomal degradation. Upon re-feeding, TORC1 directly phosphorylates and inhibits Stm1, thereby reactivating translation. Finally, SERBP1 (SERPINE1 mRNA binding protein), a mammalian ortholog of Stm1, forms dormant 80S ribosomes upon mTORC1 inhibition in mammalian cells. Thus, TORC1 regulates ribosomal dormancy in an evolutionarily conserved manner via a ribosome preservation factor.

INSTRUMENT(S): Orbitrap Fusion Lumos

ORGANISM(S): Homo Sapiens (human) Saccharomyces Cerevisiae (baker's Yeast)

SUBMITTER: Danilo Ritz

LAB HEAD: Alexander Schmidt

PROVIDER: PXD037117 | Pride | 2023-01-19

REPOSITORIES: Pride

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			Action	DRS
	001_Pilot_3ul.raw	Raw
	001_Pilot_3ul__F068277_.mzid.gz	Mzid
	001_Pilot_3ul__F068277_.mzid_001_Pilot_3ul__F068277_.MGF	Mzid
	001_ss_036_PO4_D22.raw	Raw
	001_ss_036_PO4_D22__F068242_.mzid.gz	Mzid

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Project description:Recent studies have revealed that the mRNA translation is punctuated by ribosomal pauses through the body of transcripts. However, little is known about its physiological significance and regulatory aspects. Here we present a multi-dimensional ribosome profiling approach to quantify the dynamics of initiation and elongation of 80S ribosomes across the entire transcriptome in mammalian cells. We show that a subset of transcripts have a significant pausing of 80S ribosome around the start codon, creating a major barrier to the commitment of translation elongation. Intriguingly, genes encoding ribosome proteins themselves exhibit an exceptionally high initiation pausing on their transcripts. Our studies also reveal that the initiation pausing is dependent on the 5’ untranslated region (5’ UTR) of mRNAs and subject to the regulation of mammalian target of rapamycin complex 1 (mTORC1). Thus, the initiation pausing of 80S ribosome represents a novel regulatory step in translational control mediated by nutrient signaling pathway. Untreated TSC2 WT MEFs, TSC2 KO MEFs and TSC2 WT MEFs, TSC2 KO MEFs treated with 20nM rapamycin for 30 minutes or 3hours were harvested for ribosme profiling. The fraction samples were pooled into three groups based on velocity sedimentation: single ribosome fraction (Small group), fractions with 2 ~ 4 ribosomes (Medium group), and the one with ≥5 ribosomes (Large group). RNA were extracted from the whole cell lysis and each fraction group.

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