Extensive Gene-Specific Translational Reprogramming in a Model of B Cell Differentiation and Abl-Dependent Transformation

Jamie G Bates,Martin Mcintosh,Gregory J Hogan,Patty B Garcia,Mark S Schlissel,Pat O Brown,Damon May,Julia Salzman,Wasif N Khan

doi:10.1371/journal.pone.0037108

Abstract

To what extent might the regulation of translation contribute to differentiation programs, or to the molecular pathogenesis of cancer? Pre-B cells transformed with the viral oncogene v-Abl are suspended in an immortalized, cycling state that mimics leukemias with a BCR-ABL1 translocation, such as Chronic Myelogenous Leukemia (CML) and Acute Lymphoblastic Leukemia (ALL). Inhibition of the oncogenic Abl kinase with imatinib reverses transformation, allowing progression to the next stage of B cell development. We employed a genome-wide polysome profiling assay called Gradient Encoding to investigate the extent and potential contribution of translational regulation to transformation and differentiation in v-Abl-transformed pre-B cells. Over half of the significantly translationally regulated genes did not change significantly at the level of mRNA abundance, revealing biology that might have been missed by measuring changes in transcript abundance alone. We found extensive, gene-specific changes in translation affecting genes with known roles in B cell signaling and differentiation, cancerous transformation, and cytoskeletal reorganization potentially affecting adhesion. These results highlight a major role for gene-specific translational regulation in remodeling the gene expression program in differentiation and malignant transformation.

Highlights

B cells are the antibody-producing lymphocytes of the immune system
We used a genome-wide polysome profiling technique, called Gradient Encoding, to identify genes translationally regulated by vAbl transformation, and to define the contribution of mTOR to this regulation
We assume that changes in the number of ribosomes bound to a particular transcript in response to treatment represent a change in the rate of translation of that transcript, provided that 1) the sedimentation rate is determined by the number of ribosomes bound to each transcript, 2) initiation is rate-limiting and the elongation rate is uniform, and 3) the ORF length remains constant

Summary

Introduction

Ex-vivo transduction of mouse bone marrow with the viral oncogene v-Abl, a constitutively active version of the cellular c-Abl protein tyrosine kinase, suspends B cell differentiation in a permanently proliferating state (at the pre-B cell stage) [1,2,3]. This transformed state is a model for Chronic Myelogenous Leukemia (CML) and Acute Lymphoblastic Leukemia (ALL), of which 95% and 30% of cases, respectively, harbor the BCR-ABL1 translocation (referred to as Ph+) that leads to a constitutively active Abl kinase [4,5,6]. Many initially sensitive cancers develop resistance to imatinib, emphasizing the need for a more complete understanding of the molecular mechanisms in BCR-ABL1 transformation [13]

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Results

Discussion

Conclusion