RPL15

RPL15 (eL15) is a large ribosomal subunit protein essential for early 60S subunit biogenesis, where it acts during pre-rRNA processing and pre-60S particle assembly (PMID:29599205, PMID:37865285). RPL15 is required for efficient cleavage of internal transcribed spacer 1 (ITS1) and for the 27SA3→27SB→25S/5.8S maturation steps of the large-subunit rRNA, and its loss causes turnover of nascent 27S pre-rRNAs and reduced 60S formation (PMID:23812780, PMID:29599205, PMID:37865285). Within the assembling particle, RPL15/eL15 incorporation is a prerequisite for shaping domain I of the 5.8S/25S rRNA, for the assembly of neighboring ribosomal proteins eL8 and eL36, for recruitment of A3- and B-factor assembly complexes, and for nucleocytoplasmic export of pre-60S particles (PMID:37865285). Disruption of RPL15 function triggers ribosomal stress: loss activates the RPs-MDM2-p53 pathway through RPL5/RPL11, stabilizing p53 to drive cell-cycle arrest and apoptosis, a response evident as severe proliferation defects and elevated TP53 activity in erythroblasts and as suppressed proliferation, invasion, and migration in hepatocellular carcinoma cells (PMID:29599205, PMID:35410346). Topotecan directly binds RPL15 and disrupts the RPL15–RPL4 interaction while inhibiting pre-ribosomal subunit formation, and depletion of RPL15 induces DAMP secretion that activates cGAS-STING-mediated antitumor immunity in a manner that is independent of TOP1 and dependent on STING (PMID:35725272, PMID:41276688).

1. 2013 Medium

   Established that RPL15 is needed for human large-subunit biogenesis by linking patient deletions to a specific pre-rRNA processing defect rather than a generic loss.

   Evidence Array-CGH deletion mapping and pre-rRNA processing analysis in patient-derived cells

   PMID:23812780

   Open questions at the time

   • Did not define which assembly factors or neighboring proteins depend on RPL15
   • Causal mechanism linking processing defect to disease phenotype not resolved
2. 2018 High

   Connected RPL15 loss-of-function mutations to the TP53 stress-response axis in hematopoietic cells, explaining how a biogenesis defect produces a proliferation/apoptosis phenotype.

   Evidence In vitro pre-rRNA processing, ribosome profiling, primary erythroblast culture, and flow cytometry for apoptosis and TP53 activity

   PMID:29599205

   Open questions at the time

   • Did not delineate the molecular bridge between RPL15 deficiency and p53 activation
   • Cell-type specificity of erythroid sensitivity not mechanistically explained
3. 2022 Medium

   Placed RPL15 in the canonical ribosomal-stress p53 circuit by showing its silencing alters p53/MDM2 engagement of RPL5/RPL11 to stabilize p53.

   Evidence RPL15 knockdown/overexpression with Co-IP of p53/MDM2/RPL5/RPL11, cycloheximide chase, and xenograft in HCC cells

   PMID:35410346

   Open questions at the time

   • Whether RPL15 acts upstream of free RPL5/RPL11 release versus directly on MDM2 not distinguished
   • Direct binding partners within the RPL5/RPL11-MDM2 complex not mapped
4. 2022 Medium

   Identified RPL15 as a direct drug target whose perturbation links ribosomal stress to innate antitumor immunity, separating this activity from topoisomerase inhibition.

   Evidence Drug-binding assay, reciprocal Co-IP of RPL15–RPL4, RPL15 knockdown in B16-F10 melanoma, DAMP secretion and immune-cell flow cytometry, CDK12 rescue

   PMID:35725272

   Open questions at the time

   • Structural basis of topotecan–RPL15 binding not defined
   • Mechanism linking RPL4 destabilization to DAMP secretion not resolved
5. 2023 High

   Defined the mechanistic role of eL15 in 60S assembly, showing it gates 27S pre-rRNA processing, neighboring protein incorporation, assembly factor recruitment, and pre-60S export.

   Evidence Yeast eL15 depletion with polysome profiling, Northern blot, MS analysis of pre-60S particle composition, and nucleocytoplasmic export assay

   PMID:37865285

   Open questions at the time

   • Conservation of every step in human cells not directly demonstrated
   • Order of eL15 incorporation relative to eL8/eL36 within the assembly hierarchy not fully resolved
6. 2025 Medium

   Confirmed via selective degradation that RPL15 itself, not TOP1, is the effector for DAMP secretion and cGAS-STING activation, and showed therapeutic synergy with anti-PD-1.

   Evidence SN38-PROTAC inducing ubiquitin-proteasomal RPL15 degradation, DAMP and cGAS-STING reporter assays in dendritic cells, and B16-F10 model with STING-deficient controls

   PMID:41276688

   Open questions at the time

   • The signaling intermediates between RPL15 degradation and STING activation are undefined
   • Whether immune activation requires the biogenesis defect or a separate RPL15 function is unclear
7. 2025 Low

   Identified free RPL15 as a major substrate of PARP1/PARP2 ADP-ribosylation, raising the possibility of a post-translational regulatory layer on ribosome-unbound RPL15.

   Evidence In vitro ADP-ribosylation assay with radiolabeled NAD+ comparing free versus ribosome-bound subunit proteins (preprint)

   PMID:bio_10.1101_2025.09.15.676193

   Open questions at the time

   • In vitro only; not confirmed in cells or peer-reviewed
   • Functional consequence of PARylation on RPL15 unknown
   • Modified residues not mapped

• It remains unknown how RPL15-dependent biogenesis defects mechanistically couple to the distinct downstream outputs of p53 stabilization versus cGAS-STING immune activation, and whether post-translational modification of free RPL15 regulates these branches.
• No unified model integrating biogenesis, p53 stress, and innate immune signaling
• No structural data on RPL15 within human pre-60S particles or drug complexes