The functions of the Betanodavirus non-structural protein B1 is still unknown. We examined B1 expression patterns and investigated novel cell death regulatory functions for this viral protein following RGNNV infection in fish cells. The B1 gene (336 nt) was cloned from the redspotted grouper nervous necrosis virus (RGNNV) genome. B1 mRNA was rapidly expressed in the fish cells from viral RNA3 at 12 h post-infection (p.i.). At the protein level, expression was low at 12 h p.i., and then increased rapidly between 24 h and 72 h p.i. In RGNNV-infected, B1-containing fish cells, over expression of RGNNV B1 reduced Annexin-V positive cells by 50% and 65% at 48 h and 72 h p.i., respectively, and decreased loss of mitochondrial membrane potential (MMP) by 20% and 70% at 48 h and 72 h p.i., respectively. Finally, B1 knockdown during RGNNV infection using anti-sense RNA increased necrotic cell death and reduced cell viability during the early replication cycle (24 h p.i.). Our results suggest that B1 is an early expression protein that has an anti-necrotic cell death function which reduces the MMP loss and enhances viral host cell viability. This finding provides new insights into RNA viral pathogenesis and disease control.

The molecular functions of betanodavirus non-structural protein B and its role in host cell survival remain unclear. In the present study, we examined the roles of specific nuclear targeting domains in B1 localization as well as the effect of B1 nuclear localization on the cell cycle and host cell survival. The B1 protein of the Red spotted grouper nervous necrosis virus (RGNNV) was detected in GF-1 grouper cells as early as 24 hours post-infection (hpi). Using an EYFP-B1 fusion construct, we observed nuclear localization of the B1 protein (up to 99%) in GF-1 cells at 48 hpi. The nuclear localization of B1 was mediated by two arginine-rich nuclear targeting domains (B domain: 46RRSRR51; C domain: 63RDKRPRR70) and domain C was more important than domain B in this process. B1 nuclear localization correlated with upregulation of p53 and p21(wef1/cip1); downregulation of Cyclin D1, CDK4 and Mdm2; and G1/S cell cycle arrest in GF-1 cells. In conclusion, nuclear targeting of the RGNNV B1 protein via two targeting domains causes cell cycle arrest by up-regulating p53/p21 and down-regulating Mdm2, thereby regulating host cell survival.

The antimetabolite mercaptopurine is commonly used as part of treatment regimens for acute lymphoblastic leukemia and as treatment for inflammatory bowel diseases. Adverse effects associated with mercaptopurine include myelosuppression, hepatotoxicity, and hyperpigmentation. We describe a 36-year-old man with Philadelphia chromosome-negative pre-B-cell acute lymphoblastic leukemia who experienced a serious mercaptopurine-induced hypersensitivity reaction requiring prolonged hospitalization and extensive laboratory testing and imaging. He was treated with a multiagent chemotherapy regimen. Mercaptopurine 60 mg/m(2)/day orally was started as part of his third course of chemotherapy. On day 9 of mercaptopurine therapy, the patient developed persistent fevers, skaking chills, and rigors that persisted in the absence of documented infection, consistent with drug fever. All symptoms and signs resolved after discontinuation of mercaptopurine. Use of the Naranjo adverse drug reaction probability scale indicated a probable relationship between the patient's development of fever and mercaptopurine therapy. Mercaptopurine-induced fever has been reported in patients with inflammatory bowel diseases, but this case report is the first, to our knowledge, in a patient with acute lymphoblastic leukemia. Health care professionals should be aware of the possible development of fever as a hypersensitivity reaction in patients with acute lymphoblastic leukemia treated with mercaptopurine.