A Novel Translocation in MALT Lymphoma Involving a G-Protein Coupled Receptor (GPR34) and Immunoglobulin Heavy Chain Gene Activates NFB Pathway
ED Remstein, AJ Novak, T Akaska, M Manske, M Gupta, TE Witzig, MJS Dyer, SM Ansell, A Dogan. Mayo Clinic, Rochester, MN; University of Leicester, Leicester, United Kingdom
Background: In this study we present a new translocation in MALT lymphoma which targets an orphan G-protein coupled receptor (GPR34) and provide evidence that this may be a unique oncogenic mechanism leading to NFB mediated oncogenesis in MALT lymphoma.
Design: We used a long-distance inverse polymerase chain reaction (LDI-PCR) technique to clone the breakpoint involving IGH and an unknown partner in a case of parotid MALT lymphoma. The LDI-PCR results were confirmed by FISH and array-based comparative genomic hybridization (aCGH) analysis (Agilent 244A platform).The expression of genes at the breakpoint was investigated by quantitative RT-PCR, global gene expression profiling (GEP) (Affymetrix U133 Plus 2.0 platform). The ability of the genes identified as the target of the translocation to induce NFB activation was studied using a transient transfection system in HeLa cells. Genetic and GEP data from previously characterized MALT lymphoma cases and normal splenic B-ells were used for comparison purposes.
Results: LDI-PCR identified a novel breakpoint involving IGHSA2 on chromosome 14 and Xp11.4. The breakpoint on chromosome Xp11.4 was adjacent to two genes, GPR82 and GPR34, both of which code for orphan G-protein coupled receptors. The breakpoint also fell within and disrupted a larger gene called CASK. FISH and aCGH studies confirmed LDI-PCR findings on the original tumor specimen. 64 other MALT lymphomas lacked Xp11.4 region abnormalities by FISH and/or aGCH. Quantitative RT-PCR and GEP found that GPR34 RNA but not GPR82 or CASK was markedly overexpressed by the tumor, indicating that GPR34 gene is deregulated upon its translocation to the IGHSA2 switch region. Interestingly, to a lesser extent GPR34 mRNA was overexpressed in most MALT lymphomas compared to normal B-cells suggesting mechanisms other than the translocations may upregulate GPR34. Transient expression of GPR34 in HeLa cells resulted in increased phosphorylation of Ik-Ba indicating that GPR34 could activate NFB pathway.
Conclusions: 1. We identified a novel IGH translocation partner in MALT lymphoma, GPR34. 2. GPR34 is expressed by MALT lymphomas irrespective of the translocation. 3. In vitro, overexpression of GPR34 results in activation of the NFB pathway and may be a novel mechanism MALT lymphoma oncogenesis. 4. Targeting GPR34 may be a therapeutic option in MALT lymphoma.
Monday, March 9, 2009 11:00 AM
Platform Session: Section D, Monday Morning