New alternative splicing BCR/ABL-OOF shows an oncogenic role by lack of inhibition of BCR GTPase activity and an increased of persistence of Rac activation in chronic myeloid leukemia

Cristina Panuzzo1, Gisella Volpe1, Elisa Cibrario Rocchietti2, Claudia Casnici3, Katia Crotta3, Sabrina Crivellaro1, Giovanna Carrà1, Roberta Lorenzatti1, Barbara Peracino1, Davide Torti1, Alessandro Morotti1, Maria Pilar Camacho-Leal4, Paola Defilippi4, Ornella Marelli3 and Giuseppe Saglio1

1 Department of Clinical and Biological Sciences, San Luigi Hospital, Orbassano - Turin. University of Turin, Italy

2 Department of Oncology, San Luigi Hospital, Orbassano - Turin. University of Turin, Italy

3 Department of Medical Biotechnologies and Translational Medicine, School of Medicine - Milan, University of Milan, Italy

4 Department of Molecular Biotechnology and Health Sciences, University of Turin, Turin, Italy


Cristina Panuzzo, email:

Keywords: BCR-ABL, Chronic Myeloid Leukemia, Rac GTPase, alternative splicing

Received: June 29, 2015 Accepted: November 09, 2015 Published: November 11, 2015


In Chronic Myeloid Leukemia 80% of patients present alternative splice variants involving BCR exons 1, 13 or 14 and ABL exon 4, with a consequent impairment in the reading frame of the ABL gene. Therefore BCR/ABL fusion proteins (BCR/ABL-OOF) are characterized by an in-frame BCR portion followed by an amino acids sequence arising from the out of frame (OOF) reading of the ABL gene. The product of this new transcript contains the characteristic BCR domains while lacking the COOH-terminal Rho GTPase GAP domain. The present work aims to characterize the protein functionality in terms of cytoskeleton (re-)modelling, adhesion and activation of canonical oncogenic signalling pathways. Here, we show that BCR/ABL-OOF has a peculiar endosomal localization which affects EGF receptor activation and turnover. Moreover, we demonstrate that BCR/ABL-OOF expression leads to aberrant cellular adhesion due to the activation of Rac GTPase, increase in cellular proliferation, migration and survival. When overexpressed in a BCR/ABL positive cell line, BCR/ABL-OOF induces hyperactivation of Rac signaling axis offering a therapeutic window for Rac-targeted therapy. Our data support a critical role of BCR/ABL-OOF in leukemogenesis and identify a subset of patients that may benefit from Rac-targeted therapies.

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