The heat-shock protein 90 inhibitor, geldanamycin, induces apoptotic cell death in Epstein-Barr virus-positive NK/T-cell lymphoma by Akt down-regulation.

NK/T-cell lymphoma (NKTL) is strongly associated with latent Epstein-Barr virus (EBV) infection. Recently, latent membrane protein 1 (LMP1), an EBV oncoprotein, was reported to activate the phosphatidylinositol-3 kinase (PI3K)/Akt pathway for cell survival. Because geldanamycin (GA) and its derivative, 17-allylamino-17-demethoxygeldanamycin (17-AAG), exhibit anti-tumour activity by degrading HSP90 client proteins, including Akt, we investigated the effect of GA and 17-AAG on the survival of NKTL cell lines. EBV-positive NKTL cell lines, Hank-1 and NK-YS, and an EBV-negative NK leukaemia cell line, NK-L, were treated with PI3K and Akt inhibitors, GA, and 17-AAG, and were subjected to apoptosis and cell viability assays, and immunoblot analysis. EBV-positive B-lymphoblastoid cell lines IM9 and LMP1-transfected IM9 (IM9-LMP1) were also included. Hank-1 and NK-YS cell viability was compromised and apoptosis was induced by LY294002 (PI3K inhibitor) or Akt inhibitor II. GA or 17-AAG administration resulted in the apoptosis of NKTL cells, accompanied by Akt and pAkt down-regulation, caspase 3 activation, and mitochondrial membrane potential disruption. The intrinsic level of pAkt was higher in EBV-positive NKTL cells than in EBV-negative NK-L, and GA or 17-AAG decreased the viability of NKTL cells more efficiently than NK-L. Moreover, IM9-LMP1 was more sensitive to Akt inhibitor II or HSP90 inhibitors than IM9. Importantly, GA showed little effect on the viability of normal peripheral NK cells as non-neoplastic counterparts for comparison. In conclusion, this study suggests that the PI3K/Akt pathway is frequently activated in EBV-positive NKTL and that therapeutic modalities based on targeting the PI3K/Akt pathway with HSP90 inhibitors could be useful for achieving NKTL control.

Early B-cell factor-associated zinc-finger gene is a frequent target of retroviral integration in murine B-cell lymphomas.

The early B-cell factor (EBF)-associated zinc-finger protein (EBFAZ) binds to and negatively regulates EBF, a basic helix-loop-helix transcription factor required for B-cell lineage commitment and development of the olfactory epithelium. It also binds to SMA- and MAD-related protein 1 (SMAD1) and SMAD4 in response to bone morphogenic protein 2 (BMP2) signaling. It is highly related to ecotropic viral integration site 3 (EVI3), a protein that, like EBFAZ, contains 30 Krüppel-like zinc-finger repeats. In previous studies, we showed that Evi3 is a frequent target of retroviral integration in AKXD27 B-cell lymphomas. Here, we show that EBFAZ is also a frequent target. Integrations at Ebfaz and Evi3 are mutually exclusive, suggesting that they function in the same tumor pathway. Lymphomas with integrations at Ebfaz or Evi3 express the pre-B-cell-specific marker immunoglobulin lambda chain 5, and contain immunoglobulin heavy-chain rearrangements, suggesting that they are blocked at an early B-cell stage. Unlike Evi3, which is expressed at low levels in normal B cells, or Ebfaz, which is not expressed in B cells, both genes are highly expressed following viral integration. Collectively, our results suggest that ectopic expression of Ebfaz can substitute for the upregulated expression of Evi3 in B-cell disease and highlight the importance of this gene family in hematopoietic cancer.