A Proteomic Approach to Discovery of Candidate Proteins Involved in the Transformation of Follicular Lymphoma.

Abstract

Background: Follicular lymphoma (FL) undergoes transformation to a high grade diffuse large B-cell lymphoma (tr-DLBCL) in about 50% of patients. During transformation, a more virulent subclone of tumor cells emerges, leading to a rapidly progressive clinical course and resistance to therapy. The identification of proteins involved in transformation is critical for understanding the mechanism of transformation and developing molecularly targeted therapy. In this study, we compared protein expression between grade 1- FL (G1-FL) and tr-DLBCL using 2D-gel electrophoresis and Western blot analysis. Design: Frozen tissue and frozen cells were obtained from the Department of Pathology, Oregon Health and Science University tumor bank. The protein expression profiles of 3 G1-FL and 3 tr-DLBCL were compared using 2D-gel electrophoresis. Protein identification was done using a MALDI mass spectrometer. Frozen cells of an additional 11 non-paired GI-FL and 11 non-paired tr-DLBCL, and 2 pairs of G1-FL and tr-DLBCL specimens were used for Western blot confirmation of the initial 2D-gel findings. Results: 2D-gel analysis and MALDI protein identification revealed 14 differentially expressed proteins between G1-FL and tr-DLBCL (figure 1), all of which are known to play important roles in cellular energy/metabolic pathways, signal transduction pathways, and protein and nuclear synthesis. The two most differentially expressed proteins on 2D-gel analysis were superoxide dismutase (MnSOD2) and growth factor receptor bound protein 2 (Grb2). Western blot analysis of MnSOD2 and Grb2 confirmed their relative over- or under-expression in frozen cells from multiple additional clinical lymphoma samples, including 2 paired- and 22 non-paired G1-FL and tr-DLBCL. Both 2D-gel analysis and Western Blot showed a significantly higher level of expression of MnSOD2 and a lower expression of Grb2 expression in tr-DLBCL (figure 2). Summary: Using proteomic profiling, confirmed by Western blot analysis of clinical G1-FL and tr-DLBCL samples, we have confirmed 2 proteins (MnSOD2 and Grb2) that are expressed at significantly different levels in G1-FL and DLBCL. MnSOD2 is capable of protecting cells from reactive oxygen species and regulating signal transduction pathways to influence cell growth and apoptosis. Inhibition of MnSOD2 has been shown in studies of several cancer cell lines to render cancer cells more susceptible to apoptosis. Grb2 is a member of a critical signaling pathway leading to Ras activation in hematopoietic cells. Both proteins may play a critical role in FL transformation. These proteins have the potential to be therapeutic drug targets, diagnostic and/or prognostic markers, or biomarkers for monitoring therapeutic response. Summary of Differentially Expressed Spots Summary of Differentially Expressed Spots Figure Figure