Epstein-Barr virus (EBV) activates NKL homeobox gene HLX in DLBCL

NKL homeobox genes encode developmental transcription factors regulating basic processes in cell differentiation. According to their physiological expression pattern in early hematopoiesis and lymphopoiesis, particular members of this homeobox gene subclass constitute an NKL-code. B-cell specific NKL-code genes generate a regulatory network and their deregulation is implicated in B-cell lymphomagenesis. Epstein-Barr virus (EBV) infects B-cells and influences the activity of signalling pathways including JAK/STAT and several genes encoding developmental regulators. Therefore, EBV-infection impacts the pathogenesis and the outcome of B-cell malignancies including Hodgkin lymphoma and diffuse large B-cell lymphoma (DLBCL). Here, we isolated EBV-positive and EBV-negative subclones from the DLBCL derived cell line DOHH-2. These subclones served as models to investigate the role of EBV in deregulation of the B-cell specific NKL-code members HHEX, HLX, MSX1 and NKX6-3. We showed that the EBV-encoded factors LMP1 and LMP2A activated the expression of HLX via STAT3. HLX in turn repressed NKX6-3, SPIB and IL4R which normally mediate plasma cell differentiation. In addition, HLX repressed the pro-apoptotic factor BCL2L11/BIM and hence supported cell survival. Thus, EBV aberrantly activated HLX in DLBCL, thereby disturbing both B-cell differentiation and apoptosis. The results of our study appreciate the pathogenic role of EBV in NKL homeobox gene deregulation and B-cell malignancies.

NKL同源框基因（NKL homeobox genes）编码发育类转录因子，调控细胞分化的基本进程。根据其在早期造血与淋巴细胞生成中的生理表达模式，该同源框基因亚家族的特定成员共同构成NKL编码（NKL-code）。B细胞特异性的NKL编码基因可形成调控网络，其表达失调与B细胞淋巴瘤发生密切相关。EB病毒（Epstein-Barr virus, EBV）感染B细胞后，可影响包括JAK/STAT在内的多条信号通路活性，以及若干发育调控因子编码基因的表达。因此，EB病毒感染会影响B细胞恶性肿瘤的发病进程与预后，涵盖霍奇金淋巴瘤与弥漫大B细胞淋巴瘤（diffuse large B-cell lymphoma, DLBCL）。本研究从弥漫大B细胞淋巴瘤来源的细胞系DOHH-2中分离出EB病毒阳性与EB病毒阴性的亚克隆株。这些亚克隆株作为模型，用于探究EB病毒在B细胞特异性NKL编码成员HHEX、HLX、MSX1及NKX6-3表达失调中的作用。研究发现，EB病毒编码的LMP1与LMP2A可通过STAT3激活HLX的表达。HLX进而可抑制通常介导浆细胞分化的NKX6-3、SPIB及IL4R的表达。此外，HLX还可抑制促凋亡因子BCL2L11/BIM的表达，从而促进细胞存活。综上，EB病毒在弥漫大B细胞淋巴瘤中异常激活HLX，进而干扰B细胞分化与细胞凋亡过程。本研究结果明确了EB病毒在NKL同源框基因失调与B细胞恶性肿瘤中的致病作用。