Abstract B05: Characterization of the pre-ribosomal complex, which mediates the p53 Impaired Ribosome Biogenesis Checkpoint (IRBC)

Abstract

Abstract Ribosome biogenesis is one of the most energy consuming anabolic processes in a growing tumor cell. For more than a century it has been recognized that the increased size and abnormal morphology of nucleoli, the sites of ribosome biogenesis, are markers of aggressive cancers, particularly sporadic colorectal cancers (sCRC). The TCGA has recently published that over 90% of sCRCs have a mutation in the WNT/APC signaling pathway, leading to persistent c-Myc activation in almost all cases. As c-Myc tumors are addicted to high rates of ribosome biogenesis, recent studies have suggested that impaired ribosome biogenesis, leading to the activation of p53 may serve as an Achilles' heel in the treatment of such tumors. Although a number of ribosomal proteins (RPs) have been implicated in inducing p53 stabilization following impaired ribosome biogenesis, our laboratory has shown that this response is mediated by a ribosomal precursor complex made-up of RPL5, RPL11 and non-coding 5S rRNA, which upon a lesion in ribosome biogenesis is redirected from assembly into nascent 60S ribosomal subunits to the binding and inhibition of Hdm2, leading to p53 stabilization, cell cycle arrest and apoptosis. We have termed this response the Impaired Ribosome Biogenesis Checkpoint (IRBC). However the sequence of molecular events that determine the transition of the RPL5/RPL11/5S rRNA-precursor complex upon impaired ribosome biogenesis into a tumor suppressor, the IRBC complex, are unknown. Here we present the use of a colon cancer cell line endogenously tagged by means of CRISPR/Cas9 with a GFP-fusion moiety placed at the eukaryotic-specific N-terminal extension of one copy of the gene coding for RPL11, which behaves as the wild type allele in terms of ribosome assembly and protein synthesis. We are using cells expressing this allele i) to follow by live imaging the endogenous IRBC complex localization over time under normal growing conditions or upon inducing lesions in ribosome biogenesis known to trigger the IRBC and p53 stabilization and (ii) to determine underlying molecular and biochemical alterations leading to the transition of the RPL5/RPL11/5S rRNA-precursor complex into of the IRBC complex. Citation Format: Sandra Menoyo, Antonio Gentilella, George Thomas. Characterization of the pre-ribosomal complex, which mediates the p53 Impaired Ribosome Biogenesis Checkpoint (IRBC). [abstract]. In: Proceedings of the AACR Special Conference on Translational Control of Cancer: A New Frontier in Cancer Biology and Therapy; 2016 Oct 27-30; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2017;77(6 Suppl):Abstract nr B05.