Page 129 - 2019_02-Haematologica-web

JUNB, DUSP2, SGK1 and SOCS1 mutations in THRLBCL
A
BCD
Figure 1. Genes recurrently affected by mutations and their mutational load in nodular lymphocyte-predominant Hodgkin lymphoma and T-cell/histiocyte-rich large B-cell lymphoma. (A) Frequencies of recurrently mutated genes (≥2 cases) in six cases of NLPHL A/B (blue), 11 cases of NLPHL C/D/E (green) and nine cases of THRLBCL (red) sorted by overall recurrence. (B) Mutated genes per case in NLPHL A/B, NLPHL C/D/E and THRLBCL. (C) Number of SNVs per case in NLPHL A/B, NLPHL C/D/E and THRLBCL. (D) Scatter plot of SNVs per case and kbp of CCDS in the seven most recurrently mutated genes in NLPHL A/B, NLPHL C/D/E and THRL- BCL. In (B-D), horizontal lines correspond to medians; P-values by Kruskal-Wallis test are indicated in the case of statistical significance. *P<0.05, **P<0.01, ***P<0.001. NLPHL: nodular lymphocyte-predominant Hodgkin lymphoma; THRLBCL: T-cell/histiocyte-rich large B-cell lymphoma; SNVs: single nucleotide variants; CCDS: Consensus coding sequence.
ence in the mutational distribution between the three groups of lymphoma (Figure 2). Protein domains with functional relevance were affected by mutations, e.g. the SH2 domain of the negative regulator of JAK-STAT signal- ing SOCS1, the catalytic domain of the protein kinase SGK1 and the histone acetyltransferase domain of the chromatin modifier CREBBP, suggesting that mutations in these genes result in an alteration of the protein function. In the three relatively small genes (<2.5 kb) JUNB, DUSP2 and SOCS1, SNVs clustered to specific regions in the cod- ing sequence with an enrichment to the first 150 bp down- stream of the start codon in JUNB, to exon 2 in DUSP2 and to the first 80 bp of the coding sequence in SOCS1. In CREBBP, FN1 and TRRAP, which were the three larger genes (>75 kb), mutations tended to be diffusely scattered and localized further downstream of the transcriptional start site. Given the fact of ongoing SHM in NLPHL and THRLBCL,6,7 as well as aberrant activity of the SHM machinery in these entities,14 we explored whether muta- tions in the most recurrently mutated genes were caused by aberrant SHM. Criteria of SHM activity were investi- gated, as previously described in other reports.14–17 Mutations in the genes JUNB, DUSP2, SGK1 and SOCS1 were highly enriched in SHM hotspot sites (Figure 3A) and also met other SHM criteria in most SNVs (Figure 3B,C). Mutations in CREBBP, FN1 and TRRAP occasionally
occurred at C:G sites and showed a predominance of tran- sitions over transversions (Figure 3B,C). However, they were clearly located outside the SHM hotspot motifs WRCY/RGYW (Figure 3A). In line with these results of an active SHM machinery and consistent with previous data,13,18 expression of AICDA could be demonstrated in the tumor cells of typical and histopathological NLPHL variants (10/15 and 3/11 cases, respectively) (Figure 3D) as well as THRLBCL (10/12 cases) (Figure 3E) in an inde- pendent case series.
Discussion
In the present study, we performed ultra-deep targeted resequencing of a set of genes that had been previously identified to be mutated in two cases of composite lym- phoma of NLPHL with transformation into DLBCL.12 Four of these target genes, namely JUNB, DUSP2, SGK1 and SOCS1, were also found to be mutated in primary NLPHL cases without transformation. Since the relationship of NLPHL and THRLBCL has been long-discussed, we aimed to determine whether these four genes, among others, are also mutated in THRLBCL. Here, we confirm that muta- tions in these genes also occur at comparable frequencies in THRLBCL.
haematologica | 2019; 104(2)
333