Abstract

Constitutive activation of NF-κB signaling pathways has been identified in a variety of malignancies, however the molecular basis has remained largely unknown. Recently, we have shown mutations in 10 genes encoding positive and negative regulators of NF-κB signaling pathways in 20% of multiple myeloma (MM) patients, with TRAF3 being the most commonly affected gene. TRAF3 is a negative regulator of NF-κB signal and its inactivation results in the constitutive activation of the alternative or noncanonical NF-κB signaling pathway. With the exception of two recent studies in MM, there is no available data regarding the mechanisms that dysregulate NF-κB in other B-cell malignancies. The aim of this study was to analyze the TRAF3 status in a cohort of Waldenström’s macroglobulinemia (WM) patients. Forty-nine WM were analyzed by using a combination of array-based comparative genomic hybridization (aCGH) and cIgM-FISH. Genome sequencing from 28 of these patients was performed on all coding exons of TRAF3 and the adjacent intron-exon junctions. A NF-κB index, as a measure of NF-κB transcription activity, was calculated from 21 patients with gene expression data. The index is the mean expression level of four probe sets differentially expressed between human myeloma cell lines with identified mutations compared to those without identified NF-κB pathway mutations (CD74, IL2RG and 2x TNFAIP3). By performing aCGH we identified a small monoallelic deletion (∼460 Kb), including the TRAF3 locus in one of 22 patients. Genome sequencing identified a missense mutation (D483N) in the remaining allele. This substitution affects a highly conserved amino acid throughout vertebrate evolution, suggesting its functional relevance. We used cIgM-FISH to screen 27 patients with no available aCGH data and we found one biallelic TRAF3 deletion and one chromosome 14 monosomy. In the later case, no DNA was available to sequence the remaining allele. Both samples with biallelic inactivation of TRAF3 possess the two highest NFKB index values of our WM cohort, suggesting NF-κB transcription activity. Moreover, the case with biallelic deletion showed the lowest level of TRAF3 gene expression. Additionally, the entire TRAF3 coding region was sequenced in 28 of these 49 patients and one homozygous nonsense mutation (K286X) was identified. No GEP was available in this sample to calculate the NF-κB index. TRAF3 was only recently implicated in a malignant process, when inactivating mutations and biallelic deletions were reported in approximately 13% of MM patients, making it the most frequently inactivated tumor suppressor in MM. Our study has identified biallelic TRAF3 inactivation in at least 3 of 49 WM patients, suggesting that the constitutive activation of NF-κB signaling pathways may be involved in the pathogenesis of WM. Recent findings showing an association between TRAF3 loss of function and good response to bortezomib in MM patients suggest that proteasome inhibitor-based therapy may be an attractive option in the treatment of the WM patients with constitutive activation of NF-κB signaling pathways. Additional mutational screening of TRAF3 and other regulators of these pathways are ongoing to determine the extent of constitutive activation present in WM and other B-cell malignancies.

Author notes

Disclosure: No relevant conflicts of interest to declare.