The role of the NFAT signalling pathway on diffuse large B-cell lymphoma

Abstract

Diffuse Large B-Cell Lymphomas (DLBCL) are common, aggressive malignancies of mature B-lymphocytes that represent ~40% of lymphomas. Despite the widespread use of combined immunochemotherapy, approximately 50% of patients with DLBCL die from their disease. The two main DLBCL subgroups resemble activated B cells (ABC) or germinal centre B cells (GCB), where patients with ABC-DLBCL have significantly worse outcome. There is urgent need for novel therapeutic strategies in the treatment of DLBCL, which requires a better understanding of the molecular pathways upon which tumours depend. Accumulating evidence suggests that the signalling networks promoting and sustaining DLBCL derive from dysregulation of the normal pathways controlling B-lymphocyte activation and differentiation. There is increasing evidence indicating important roles for the NFAT family of transcription factors in DLBCL. Constitutively-active nuclear NFAT2 has been demonstrated in approximately 40% of primary DLBCL samples and NFAT has been shown to regulate a small number of genes associated with DLBCL growth/survival. This project investigated the role of NFAT in DLBCL. Nuclear localisation and activation of NFAT family members were characterised in a panel of DLBCL cell lines and chemical inhibition of calcineurin/NFAT, using Cyclosporin A (CsA), indicated dependency on the calcineurin/NFAT pathway for survival. Gene expression microarray analysis performed in DLBCL cell lines treated with CsA revealed potential NFAT target genes involved in the tumour microenvironment and anergy. These data revealed that the cytokine TNFα was downregulated by CsA in ABC, but not GCB cell lines. TNFα expression has recently been reported a significant prognostic factor for OS and PFS in DLBCL and evidence suggests dependency of some DLBCL on autocrine TNFα signalling for survival. Biologically active TNFα was produced by DLBCL cell lines, however inhibition of TNFα signalling using Infliximab and Etanercept had no effect on cell viability, suggesting that TNFα may be functionally important in DLBCL by other mechanisms.