Constitutive activation of distinct NF-κB signals in EBV-associated nasopharyngeal carcinoma.

As a distinct type of head and neck cancer, non-keratinizing nasopharyngeal carcinoma (NPC) is closely associated with EBV infection and massive lymphoid infiltration. The unique histological features suggest that local inflammation plays an important role in NPC tumourigenesis. We comprehensively characterized NF-κB signalling, a key inflammatory pathway which might contribute to the tumourigenesis of this EBV-associated cancer. By EMSA, western blotting, and immunohistochemical staining, constitutive activation of distinct NF-κB complexes, either p50/p50/Bcl3 or p50/RelB, was found in almost all EBV-positive NPC tumours. siRNA or chemical inhibition of NF-κB signalling significantly inhibited the growth of EBV-positive NPC cells C666-1. Gene expression profiling identified a number of NF-κB target genes involved in cell proliferation, apoptosis, immune response, and transcription. We further confirmed that p50 signals modulate the expression of multiple oncogenes (MYB, BCL2), chemokines, and chemokine receptors (CXCL9, CXCL10, CX3CL1, and CCL20). The findings support a crucial role of these constitutively activated NF-κB signals in NPC tumourigenesis and local inflammation. In addition to expression of the viral oncoprotein LMP1, genetic alteration of several NF-κB regulators (eg TRAF3, TRAF2, NFKBIA, A20) also contributes to the aberrant NF-κB activation in EBV-associated NPC. Except for LMP1-expressing C15 cells, all NPC tumour lines harbour at least one of these genetic alterations. Importantly, missense mutations of TRAF3, TRAF2, and A20 were also detected in 3/33 (9.1%) primary tumours. Taken together with the reported LTBR amplification in 7.3% of primary NPCs, genetic alterations in NF-κB pathways occurred in at least 16% of cases of this cancer. The findings indicate that distinct NF-κB signals are constitutively activated in EBV-positive NPC cells by either multiple genetic changes or EBV latent genes.

Clonality of oligoastrocytomas.

Oligoastrocytomas (OA) are mixed glial tumors that show morphologic features of both oligodendrogliomas and astrocytomas. The histogenesis of these tumors remains undefined. The aim of this study was to investigate the clonality of OA on the basis of tumor-dependent genetic alterations and tumor-independent X-chromosome inactivation. We microdissected 11 biphasic OA and subjected the oligodendroglial and astrocytic components to allelic loss analysis of chromosomes 1p, 9p21, 10q, 13q, 17p, and 19q; TP53 immunohistochemical and mutation analyses; and X-linked HUMARA gene methylation study. On the basis of the genetic findings, we categorized these tumors into 3 groups. Group 1 consisted of 4 tumors that showed identical genetic aberrations in the 2 histologic elements, characterized by allelic loss on 1p and 19q. These results suggest that group 1 tumors are of monoclonal origin and share a precursor cell with oligodendrogliomas. Group 2 consisted of 5 tumors characterized by losses on 1p and 19q, with additional allelic losses on chromosomes 9p, 10q, 13q and/or 17p. Four of these tumors were of the anaplastic type. Thus, group 2 tumors may be regarded as advanced variants of group 1 OA with heterogeneous genetic changes during clonal expansion. The X-chromosome inactivation analysis confirmed the monoclonality of groups 1 and 2 OA. Group 3 consisted of two tumors that showed divergent allelic loss patterns in the 2 histologic components. Mutation and overexpression of TP53 were detectable in the astrocytic components only. These findings raise the possibility that group 3 tumors have a biclonal origin. In conclusion, our results suggest that OA are predominantly of monoclonal origin but that a small subset of tumors may be derived from different precursors.