RESUMEN
Ribosomal protein (RP) expression in higher eukaryotes is regulated translationally through the 5'TOP sequence. This mechanism evolved to more rapidly produce RPs on demand in different tissues. Here we show that 40S ribosomes, in a complex with the mRNA binding protein LARP1, selectively stabilize 5'TOP mRNAs, with disruption of this complex leading to induction of the impaired ribosome biogenesis checkpoint (IRBC) and p53 stabilization. The importance of this mechanism is underscored in 5q− syndrome, a macrocytic anemia caused by a large monoallelic deletion, which we found to also encompass the LARP1 gene. Critically, depletion of LARP1 alone in human adult CD34+ bone marrow precursor cells leads to a reduction in 5'TOP mRNAs and the induction of p53. These studies identify a 40S ribosome function independent of those in translation that, with LARP1, mediates the autogenous control of 5'TOP mRNA stability, whose disruption is implicated in the pathophysiology of 5q− syndrome.
Asunto(s)
Autoantígenos/metabolismo , Biosíntesis de Proteínas , Secuencia de Oligopirimidina en la Región 5' Terminal del ARN , Estabilidad del ARN , ARN Mensajero/metabolismo , Ribonucleoproteínas/metabolismo , Proteínas Ribosómicas/metabolismo , Ribosomas/metabolismo , Anemia Macrocítica/genética , Anemia Macrocítica/metabolismo , Autoantígenos/genética , Células de la Médula Ósea/metabolismo , Deleción Cromosómica , Cromosomas Humanos Par 5/genética , Cromosomas Humanos Par 5/metabolismo , Células HCT116 , Humanos , Complejos Multiproteicos , Unión Proteica , Interferencia de ARN , ARN Mensajero/genética , Ribonucleoproteínas/genética , Proteínas Ribosómicas/genética , Ribosomas/genética , Factores de Tiempo , Transfección , Proteína p53 Supresora de Tumor/genética , Proteína p53 Supresora de Tumor/metabolismo , Antígeno SS-BRESUMEN
Many oncogenes enhance nucleotide usage to increase ribosome content, DNA replication, and cell proliferation, but in parallel trigger p53 activation. Both the impaired ribosome biogenesis checkpoint (IRBC) and the DNA damage response (DDR) have been implicated in p53 activation following nucleotide depletion. However, it is difficult to reconcile the two checkpoints operating together, as the IRBC induces p21-mediated G1 arrest, whereas the DDR requires that cells enter S phase. Gradual inhibition of inosine monophosphate dehydrogenase (IMPDH), an enzyme required for de novo GMP synthesis, reveals a hierarchical organization of these two checkpoints. We find that the IRBC is the primary nucleotide sensor, but increased IMPDH inhibition leads to p21 degradation, compromising IRBC-mediated G1 arrest and allowing S phase entry and DDR activation. Disruption of the IRBC alone is sufficient to elicit the DDR, which is strongly enhanced by IMPDH inhibition, suggesting that the IRBC acts as a barrier against genomic instability.