Lenalidomide Induces A Ribosomal Stress Response In Multiple Myeloma (MM) Cells
Notice bibliographique
Résumé
Abstract Background Deregulation of ribosome biogenesis is associated with carcinogenesis and in MM two of the most common recurrent mutations (DIS3 and FAM46C) are implicated in ribosomal decay and translational control. Beside its role in the regulation of protein synthesis, the importance of ribosome biogenesis is underscored by the observation that the impairment of this process leads to a ribosomal stress response with induction of p53, inhibition of c-Myc and cell cycle arrest. These effects are mediated by the direct binding of ribosomal proteins (RPs), particularly RPL11 and RPL5 to Mdm2 and c-Myc. Immunomodulatory drugs (IMiDs) anti-MM effects require their binding to Cereblon (CRBN), an adaptor protein of the Cul4A-DDB1-ROC1 ubiquitin E3 ligase complex with an ensuing down-regulation of c-Myc and up-regulation of p21. In the present study, we delineated the mechanisms through which IMiDs mediate these effects in MM cells. Methods and Results In order to identify ubiquitylated substrates that are modified by lenalidomide (Len) treatment, we performed a ubiquitin-proteome pull-down using Tandem Ubiquitin Binding Entity (Lifesensors) coupled with quantitative mass-spectroscopy proteomics (iTRAQ) in OPM2 cells exposed to Len (10 μM). Several ribosomal proteins (RPs) - S25, S26, S20 & S28 - were increased in Len treated samples suggesting that the Cul4a-CRBN complex may regulate RPs stability and hence IMiDs binding to cereblon may trigger a ribosomal stress response. Immunoblot analysis of MM cells exposed to Len lead to a rapid decrease in c-Myc expression (within 30 min) that significantly preceded the downregulation of IRF4 consistent with an IRF4-independent mechanism for c-Myc down-regulation. Furthermore, Len treatment transiently stabilised and subsequently down-regulated MDM2 expression with up-regulation of p53 and its down-stream targets (p21, PUMA). Under ribosomal stress conditions, polysome-free RPs are released into the nucleoplasm where they bind Mdm2 and suppress its E3 ligase activity. Consistent with this effect, in Len treated cells MDM2 co-immunoprecipitated with RPL11 and RPL5 with p53 protein stabilization (no change in p53 mRNA). In addition, an increase in the interaction between RPL11 and c-Myc was also observed consistent with the reported role for RPL11 in the post-transcriptional regulation and suppression of c-Myc. Furthermore, treatment with Lenalidomide supressed ribosomal RNA (rRNA) transcription with inhibition of pre-rRNA (47S) processing. The examination of polysome fractions (sucrose gradients) in Len treated MM cells (OPM2 and MM1S) revealed a striking reduction of 60S and 80S as well as polysomes fractions, an effect similar to that Actinomycin D (5 nM), a known RNA PolI inhibitor and potent ribosome stress inducer. Furthermore Len treatment significant reduced RPL11 within the 60S and 80S ribosome fractions. Of note, CRBN knockdown abrogated all these effects suggesting that Len binding to CRBN is upstream of this ribosome stress response. In order to investigate whether the down-regulation of c-Myc is the primary event leading to the disruption of ribogenesis, we transiently and stably silenced RPL11 in MM cells. RPL11 silencing nearly fully protected MM cells from the effects of Len and importantly it completely reversed Len-induced Mdm2 E3 ligase inhibition with up-regulation of p53, p21 and suppression of c-Myc and IRF4. Conclusion Taken together our data indicate that treatment with lenalidomide suppresses ribogenesis and induces a ribosomal stress response downstream of Cul4a-CRBN but upstream of c-Myc suppression and p53 induction. These effects likely result from the IMiDs-induced modification of the Cul4a-CRBN ubiquitome and the regulation of RPs integration into ribosomal subunits. These findings also explain the observed clinical activity of IMiDs in other ribosomopathies like 5q- MDS and Diamond-Blackfan anemia Disclosures: No relevant conflicts of interest to declare.
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Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».