Abstract B26: Role of ribosomal protein, Rpl22 in regulating leukemic transformation.

Inactivation of ribosomal proteins (RP) is known to cause diseases called ribosomopathies, which are often associated with abnormal hematopoiesis and an increased risk for development of leukemia. Our laboratory has recently reported an important link between inactivation of one such ribosomal protein, Rpl22, and poor survival in T cell acute lymphoblastic leukemia (T-ALL) patients. Preliminary bioinformatic analysis shows that RPL22 is lost in ~10% of pediatric T-ALL patients, who exhibit a more aggressive disease course. Deletion of the RPL22 locus is also enriched in the early T-cell precursor (ETP-ALL) subset of T-ALL patients, which exhibit a more aggressive disease course. Thus, RPL22 loss appears to be a marker for poor outcome in pediatric T-ALL patients. While RP inactivation has previously been linked to increased cancer risk, the mechanistic basis for this linkage remained unclear. We have recently demonstrated that inactivation of Rpl22 promotes leukemic transformation by activating NF-kB and inducing the stem cell gene, LIN28B. Nevertheless, the molecular link between Rpl22 inactivation and the induction of NF-kB activity remained unclear. We have now determined that inactivation of Rpl22 activates NF-kB signaling by exacerbating ER stress responses. Indeed, Rpl22 loss results in hyperactivation of the PERK-EIF2α-ATF4 stress pathway, which is known to activate NF-kB. We have demonstrated that knockdown of PERK using shRNA abrogates the activation of NF-kB in Rpl22 mutant cells and returns Lin28B expression levels to baseline. This reduction in Lin28B eliminates the predisposition to transformation exhibited by Rpl22 mutant cells, as evidenced by decreased formation of colonies in soft agar. Taken together, these data suggest that RPL22 inactivation may serve as a negative prognostic indicator in T-ALL and that pharmacologic targeting of ER stress pathways may represent a novel therapeutic alternative in this molecularly-defined subclass of T-ALL. Citation Format: Nehal Solanki Patel, Noa Greenberg, Suraj Peri, Shuyun Rao, Michele Rhodes, David Wiest. Role of ribosomal protein, Rpl22 in regulating leukemic transformation. [abstract]. In: Proceedings of the AACR Special Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(17 Suppl):Abstract nr B26.