ALK-Negative Anaplastic Large Cell Lymphomas with 6p25.3 Translocations Show a Histone-Modifying Gene Expression Signature

The biology and genetics of anaplastic large T-cell lymphomas (ALCLs) lacking ALK translocations remain poorly defined. We recently identified recurrent translocations involving the DUSP22-IRF4 locus on 6p25.3 in ALK-negative ALCL (Blood 2011;117:915–9). This translocation is present in about 20% of ALK-negative ALCLs and is absent in other T-cell lymphomas; however, the biologic consequences are unknown. In this study, we utilized gene expression profiling (GEP) to compare T-cell lymphomas with and without this translocation.

cDNA was prepared from total RNA extracted from frozen tissue from 25 T-cell lymphoma patients under a Mayo Clinic IRB-approved protocol as follows: 5 ALK-negative ALCLs with 6p25.3 translocations (2 systemic, 3 cutaneous), 12 ALK-negative ALCLs without 6p25.3 translocations (11 systemic, 3 cutaneous), 5 ALK-positive ALCLs, and 3 CD30-positive peripheral T-cell lymphomas (1 transformed mycosis fungoides and 2 not otherwise specified). Partner loci in cases with 6p25.3 translocations were 7p32.3 in 2, 9p24.3 in 1, and unknown in 2. GEP data (Affymetrix U133 plus 2.0) were analyzed by unsupervised clustering; in addition, a GEP signature was developed using genes with raw values >200 in at least 2 cases with at least 2-fold, statistically significantly different expression between 6p25.3-translocated and non-translocated cases (p<0.05 after Benjamini-Hochberg multiple testing correction). Representative overexpressed genes were confirmed by quantitative real-time (qRT-) PCR. Supervised pathway analysis was performed using signatures derived from other studies or curated from public pathway databases.

By unsupervised clustering, the 5 cases with 6p25.3 translocations clustered together (281 probe sets). A GEP signature segregating translocated from non-translocated cases included 283 genes (195 up- and 88 down-regulated). Key features of this signature included altered expression of histone-modifying genes (e.g. EZH2, SUZ12, MLLT3, MLL; HDAC4) and up-regulation of cancer-testis antigen (CTA) genes (e.g. SSX4, TEX14, MAGEA12, SSX1, CTAG2). The signature included down-regulation of DUSP22 but not of other genes on 6p25 in the signature. Additional overexpressed genes were validated by qRT-PCR (relative expression: TEX14, 2.9, p=0.01, t test; MAL, 6.5, p=0.003; CCR8, 7.6, p=0.0004). Supervised pathway analysis demonstrated a high proliferation signature in cases with 6p25.3 translocations (p=0.006 vs. untranslocated cases).

ALK-negative ALCLs with translocations involving the DUSP22-IRF4 locus on 6p25.3 have a distinct gene expression signature characterized by alterations of histone-modifying genes and CTA genes (which typically are regulated epigenetically, either through histone modifications or changes in methylation). This signature appears independent of anatomic site (systemic vs. cutaneous) and partner locus (7p32.3 vs. other). DUSP22, encoding a dual-specificity phosphatase involved in modulating mitogen-activated protein kinase (MAPK) signaling, is significantly down-regulated in translocated cases; however, pathway analysis did not show significant alterations in MAPK-associated genes. Other known genes in the region of the breakpoint on 6p25 were not affected substantially. These findings suggest the possibility of an unrecognized function of DUSP22. Contributions of the varying partner loci remain unclear. The distinct GEP signature associated with 6p25.3 translocations provides strong support for their biologic relevance. Finally, the genes involved in the histone-modifying signature show overlap with histone-modifying genes mutated in B-cell lymphomas, suggesting potential commonalities in the biology and possibly targeted treatment of B- and T-cell lymphomas.

No relevant conflicts of interest to declare.