Mir-15a/16-1 Cluster Is Frequently Deleted In Primary Hodgkin Lymphoma and Modulates Multiple Survival Pathways Including AP-1

Abstract 746

Classical Hodgkin Lymphoma (cHL) Reed-Sternberg (RS) cells have crippling mutations of their rearranged Ig genes and lack B-cell receptor-mediated survival signals. As a consequence, cHLs rely on alternative survival and proliferation pathways including AP-1. Although cHL RS cells express high levels of the AP-1 components, cJun and JunB, and depend on AP-1-mediated proliferation signals, the mechanism of constitutive AP-1 activation in cHL remains undefined. In a screen for genetic abnormalities in cHL, we integrated microRNA (miR) expression profiles with high resolution copy number data and identified single copy loss of the miR-15a/16-1 locus (chromosome 13q14) and decreased miR-15a/16 expression in 75% of examined HL cell lines. We isolated primary Hodgkin RS cells using laser-capture microdissection and confirmed frequent single copy loss of the miR-15a/16-1 locus by quantitative PCR and associated decreased miR-15a/16 abundance by RT-PCR in 10/23 (43%) of primary tumors. Using retroviral vectors containing miR-15a and miR-16, we reconstituted miR-15a/16 expression in HL cell lines with single copy loss of chromosome 13q14. In these HL lines, miR-15a/16 reconstitution was associated with cell cycle arrest, significantly decreased cellular proliferation and induction of apoptosis (88% apoptotic cells at 48 hours). In addition, miR-15a/16 reconstitution resulted in significant downregulation of multiple survival pathway components and known miR-15a/16 targets including panAKT, BCL2 and cyclin D1. Using a stand-alone miRanda algorithm with direct sequence entry, we also identified a candidate miR-15a/16 binding site in the AP-1 component, cJun. In multiple HL cell lines, miR-15a/16 reconstitution decreased the expression of cJun and additional known AP-1 targets such as galectin-1. Therefore, miR-15a/16-1 deletion is a frequent genetic abnormality in HL cell lines and primary tumors, a candidate mechanism of AP-1 activation in HL and a modulator of multiple critical survival pathways in this disease.