Abnormal Expression of TRAF Adapter Proteins in Waldenstrom’s Macroglobulinemia.

Background: Waldenström’s Macroglobulinemia (WM) is an incurable low-grade lymphoplasmacytic lymphoma with as yet unknown genetic basis for its pathogenesis. Several TNF family members (CD40L, APRIL and BAFF/BLYS) are known to regulate WM growth and survival. TRAFs are a novel family of adapter proteins that facilitate pro-apoptotic (TACI) or pro-survival/differentiation (CD40, BAFFR, BCMA) receptor signaling mediated by TNF family ligands. Therefore, understanding the TRAF system in WM may yield important clues about WM growth and survival.

Methods: WM cell lines (BCWM.1 and WSU-WM), IgM secreting low-grade lymphoma cell lines (MEK1, RL, Namalwa), and primary bone marrow CD19⁺ selected lymphoplasmacytic cells (LPC) from 20 WM patients and 6 healthy donors were evaluated for TRAF (TRAF 2, 3, 5, 6) expression using semi quantitative RT-PCR and/or western blot analysis.

Results: The TNF familiy receptors CD40, BAFFR, BCMA, and TACI were expressed in all cell lines tested as well as in CD19+ selected LPC from WM patients and healthy donors. Moreover, TRAF 2, 3, 5, 6 were expressed in all cell lines by both RT-PCR and western blot analysis. In contrast, we observed loss or abnormally low expression of both TRAF 2 and 5 in 6/20 (30%) patients, whilst TRAF 3 was absent or abnormally low in 3/30 (15%) patients. TRAF 6 was expressed in all patients. Among healthy donors, we observed expression of all TRAF adapter proteins.

Conclusion: Up to one third of WM patients demonstrate loss of TRAF 2 and 5 adapter proteins which facilitate signaling through the pro-apoptotic receptor TACI. Ongoing studies including gene sequencing and siRNA knockdown models are delineating a role for TRAF loss in the pathogenesis of WM.