RPLP0

RPLP0 (uL10) is the core scaffold of the ribosomal P-stalk in the GTPase-associated center (GAC) of the large subunit, the platform that recruits translational GTPases for elongation and termination (PMID:9988728, PMID:1939187). In the archaeal and conserved organization, uL10 nucleates a pentameric (P-protein)4–uL10 factor-binding complex adjacent to the L7/L12 (P1/P2) homologs (PMID:1939187), and it sits at a ribosome-surface position accessible to exogenous ligands, as shown by direct cross-linking of ricin A chain to L10e on mammalian ribosomes (PMID:7759553). Functionally, uL10 is coupled to eEF2-driven translocation: mutations in a conserved region confer resistance to the eEF2 inhibitor sordarin by destabilizing the eEF2–nucleotide–ribosome complex (PMID:9988728), and a conserved 'hinge' around Phe183 in the extended protuberant (uL10ext) domain undergoes conformational rearrangement that gates factor binding, since hinge mutation increases in vitro polyphenylalanine synthesis (PMID:31419120). P-stalk assembly is regulated by phosphorylation within the N-terminal rRNA-binding domain, which introduces negative charge that impairs ribosome association and thereby tunes GAC activity (PMID:32668052). Beyond steady-state translation, uL10 is released from pre-existing ribosomes into a free cytoplasmic pool under nucleolar stress (PMID:28986221), and an alternatively spliced isoform (uL10β) localizes predominantly to the nucleus, associates with 60S/80S particles, and redistributes to mitochondria upon ER stress (PMID:36328276). Extra-ribosomal activities have also been reported: RPLP0 binds cathepsin X/Z (CTSX) and the tumor suppressor PLAAT4 to influence G1 progression and apoptosis through CDK2/p21 (PMID:25433997, PMID:31131438), and c-Myc directly activates RPLP0 transcription while RPLP0 sustains a JAK2/STAT3/c-Myc feedback loop in hepatocellular carcinoma (PMID:41312719).

1. 1991 Medium

   Establishing where uL10 sits in the ribosome was the first step in defining its function; cross-linking placed it as a near neighbor of the L12e (P1/P2) proteins within the conserved factor-binding domain.

   Evidence 2-iminothiolane cross-linking and N-terminal sequencing of the (L12e)4–L10e complex in archaeal ribosomes

   PMID:1939187

   Open questions at the time

   • Conservation to mammalian ribosomes inferred but not directly tested here
   • Does not establish how uL10 engages translational GTPases functionally
2. 1995 High

   Cross-linking of ricin A chain confirmed L10e/RPLP0 is a surface-exposed component of mammalian ribosomes, anchoring the archaeal organization in the mammalian context.

   Evidence Chemical cross-linking of 125I-ricin A chain on purified mammalian ribosomes with tryptic peptide sequencing and competition controls

   PMID:7759553

   Open questions at the time

   • Does not define the catalytic or factor-recruitment role of L10e
   • Functional consequence of the ricin-uL10 proximity not established
3. 1999 High

   Linking uL10 to translocation: sordarin-resistance mutations showed L10e is functionally coupled to eEF2-mediated elongation, not merely structural.

   Evidence Sordarin-resistant L10e allele sequencing and in vitro eEF2–ribosome–nucleotide complex stabilization assays in yeast

   PMID:9988728

   Open questions at the time

   • Does not resolve the structural mechanism of factor engagement
   • Limited to eEF2; other GTPases not addressed in this study
4. 2002 Medium

   A yeast genetic screen revealed an unexpected link between the uL10 ortholog and prion propagation via chaperone gene expression, hinting at functions beyond translation.

   Evidence Multicopy genomic library screen, prion-curing assays, and chaperone promoter-reporter assays in yeast

   PMID:11923285

   Open questions at the time

   • Mechanism connecting Rpp0 overexpression to chaperone promoters unresolved
   • Relevance to mammalian RPLP0 untested
5. 2010 Medium

   RPLP0 was identified at the cell surface acting as a receptor for a homing peptide, an unusual extra-ribosomal localization.

   Evidence In vivo phage display, peptide affinity pull-down, and endothelial internalization assay with competitive inhibition

   PMID:20863866

   Open questions at the time

   • Surface display of a classically cytoplasmic protein not mechanistically explained
   • No structural basis for peptide recognition
6. 2014 Medium

   Identification of RPLP0–cathepsin X/Z interaction and a CDK2/p21-linked cell-cycle phenotype framed RPLP0 as an anti-apoptotic, cell-cycle regulator in cancer cells.

   Evidence Yeast two-hybrid, reciprocal co-IP, co-localization, siRNA knockdown, and cell cycle analysis in gastric cancer cells

   PMID:25433997

   Open questions at the time

   • Whether the cell-cycle effect is ribosome-dependent or extra-ribosomal unclear
   • Direct biochemical mechanism linking RPLP0 to CDK2/p21 not defined
7. 2017 High

   Demonstrating stress-induced release answered whether uL10 is a static subunit: under nucleolar stress it exits ribosomes to form a free cytoplasmic pool.

   Evidence Biochemical fractionation and FRAP after photoconversion (FRAP-AC) in mammalian cells

   PMID:28986221

   Open questions at the time

   • Function of the free cytoplasmic pool not established
   • Trigger linking nucleolar stress to release mechanistically undefined
8. 2019 High

   Two studies refined uL10 mechanism: a conserved Phe183 'hinge' in the uL10ext domain gates translation-factor binding, and a PLAAT4 interaction tied RPLP0 to tumor-suppressor-induced apoptosis.

   Evidence NMR solution structure with 15N relaxation plus yeast F181A mutant and in vitro translation; and yeast two-hybrid/co-IP/knockdown phenocopy for PLAAT4

   PMID:31131438 PMID:31419120

   Open questions at the time

   • How hinge dynamics coordinate sequential eEF2/eRF1 binding not directly resolved
   • PLAAT4–RPLP0 mechanism (single-lab) lacks reciprocal in vivo validation
9. 2020 Medium

   Identifying N-terminal phosphorylation as a switch showed P-stalk assembly is actively regulated: negative charge in the rRNA-binding domain impairs ribosome association.

   Evidence Phosphosite mapping, phosphomimetic mutagenesis, and ribosome association assays

   PMID:32668052

   Open questions at the time

   • Kinase responsible not identified
   • Physiological conditions driving phosphorylation undefined
10. 2022 Medium

    Characterization of the uL10β splice isoform revealed a nuclear-localizing, ribosome-associating variant that relocates to mitochondria under ER stress, expanding the functional repertoire.

    Evidence Isoform RT-PCR/sequencing, subcellular fractionation, imaging, and ribosome sedimentation with ER stress induction

    PMID:36328276

    Open questions at the time

    • Function of mitochondrial relocalization unknown
    • Whether uL10β supports translation distinct from canonical uL10 untested
11. 2025 Medium

    Integration into a transcriptional circuit: c-Myc directly activates RPLP0, which sustains JAK2/STAT3 via ROS suppression to reinforce c-Myc, defining a feedback loop in HCC; related work tied RPLP0 to endothelial apoptosis and miR-450b-5p regulation.

    Evidence ChIP and dual-luciferase promoter assays with ROS measurement and pathway westerns; plus knockdown studies in HUVECs and HCC with luciferase 3'UTR targeting

    PMID:39110356 PMID:39383650 PMID:41312719

    Open questions at the time

    • Direct biochemical link between RPLP0 and JAK2/STAT3 not reconstituted
    • Whether the cancer roles depend on ribosomal vs extra-ribosomal RPLP0 unresolved

• How RPLP0's canonical P-stalk function mechanistically connects to its reported extra-ribosomal roles in cell-cycle control, apoptosis, and oncogenic signaling remains unresolved.
• No structural or biochemical bridge between the free/nuclear pool and signaling functions
• Kinases, recruitment factors, and stress sensors governing relocalization unidentified