The NKL-code for innate lymphoid cells reveals deregulated expression of NKL homeobox genes HHEX and HLX in anaplastic large cell lymphoma (ALCL).

Stefan Nagel,Hans G Drexler,Maren Kaufmann,Roderick A.F Macleod,Claudia Pommerenke,Corinna Meyer

doi:10.18632/oncotarget.27683

Abstract

NKL homeobox genes encode developmental transcription factors and display an NKL-code according to their physiological expression pattern in hematopoiesis. Here, we analyzed public transcriptome data from primary innate lymphoid cells (ILCs) for NKL homeobox gene activities and found that ILC3 expressed exclusively HHEX while in ILC1 and ILC2 these genes were silenced. Deregulation of the NKL-code promotes hematopoietic malignancies, including anaplastic large cell lymphoma (ALCL) which reportedly may derive from ILC3. Accordingly, we analyzed NKL homeobox gene activities in ALCL cell lines and investigated their role in this malignancy. Transcriptome analyses demonstrated low expression levels of HHEX but powerfully activated HLX. Forced expression of HHEX in ALCL cell lines induced genes involved in apoptosis and ILC3 differentiation, indicating tumor suppressor activity. ALCL associated NPM1-ALK and JAK-STAT3-signalling drove enhanced expression of HLX while discounting HHEX. Genomic profiling revealed copy number gains at the loci of HLX and STAT3 in addition to genes encoding both STAT3 regulators (AURKA, BCL3, JAK3, KPNB1, NAMPT, NFAT5, PIM3, ROCK1, SIX1, TPX2, WWOX) and targets (BATF3, IRF4, miR135b, miR21, RORC). Transcriptome data of ALCL cell lines showed absence of STAT3 mutations while MGA was mutated and downregulated, encoding a novel potential STAT3 repressor. Furthermore, enhanced IL17F-signalling activated HLX while TGFbeta-signalling inhibited HHEX expression. Taken together, our data extend the scope of the NKL-code for ILCs and spotlight aberrant expression of NKL homeobox gene HLX in ALCL. HLX represents a direct target of ALCL hallmark factor STAT3 and deregulates cell survival and differentiation in this malignancy.

Highlights

Lymphocytes are white blood cells and include those possessing adaptive immunity (B-cells and T-cells) and cells which lack this specificity and belong to the innate immune system (NK-cells and innate lymphoid cells: ILCs)
Among www.oncotarget.com innate lymphocytes NK-cells express MSX1 and ILC3 HHEX while ILC1 and ILC2 lack any activity of NKL homeobox genes [17]
Our data showed that HHEX operates as a tumor suppressor gene in anaplastic large cell lymphoma (ALCL), activating both apoptosis and differentiation (Figure 6)

Summary

INTRODUCTION

Lymphocytes are white blood cells and include those possessing adaptive immunity (B-cells and T-cells) and cells which lack this specificity and belong to the innate immune system (NK-cells and innate lymphoid cells: ILCs). Particular NKL homeobox genes including HHEX and HLX are expressed in the course of hematopoiesis, exerting major impacts on cell lineage decisions [11, 12] They are expressed in HSCs and progenitors of myeloid and lymphoid lineages and remain active in most mature myeloid cells. We have identified eleven members of the NKL homeobox gene subclass expressed in early hematopoiesis, lymphopoiesis and myelopoiesis and termed this signature NKL-code [13,14,15] Alterations of this code via ectopic activation of non-code members or deregulation of code-members have been described in both lymphoid and myeloid malignancies [13,14,15]. In addition we analyzed deregulated NKL homeobox genes HHEX and HLX in ALCL cell lines and their relation to ILC3/TH17 cell differentiation

RESULTS

DISCUSSION

MATERIALS AND METHODS