Nuclear factor-κB inhibitors alleviate nivalenol-induced cytotoxicity in HL60 cells

Abstract

Tricothecene mycotoxins, such as nivalenol, are toxic to leukocytes. To elucidate the molecular mechanism of nivalenol toxicity, we investigated the involvement of nuclear factor-κB (NF-κB) in nivalenol-induced cytotoxicity in HL60 cells using the NF-κB inhibitors pyrrolidinedithiocarbamate (PDTC) and dexamethasone. Cells were treated with the chemicals for 24 h before assays were performed. Nivalenol elicited interleukin (IL)-8 secretion. IL-8 secretion was lower in cells concomitantly treated with nivalenol and NF-κB inhibitors than with nivalenol alone. Nivalenol reduced monocyte chemotactic protein (MCP)-1 secretion. MCP-1 secretion was higher in cells concomitantly treated with nivalenol and NF-κB inhibitors than with nivalenol alone. NF-κB inhibitors thus alleviated the effects of nivalenol, indicating that NF-κB is important for nivalenol-caused changes in cytokine secretion. Nivalenol hindered cell proliferation, and dexamethasone reduced this effect, suggesting that NF-κB contributes to cell proliferation. Thus, it appears that NF-κB is involved in nivalenol-induced toxicity in HL60 cells.

Introduction

Various Fusarium fungi produce a number of different mycotoxins of the trichothecene class as well as some other mycotoxins. More than 60 trichothecene mycotoxins are known. Trichothecene mycotoxins are extremely toxic to rapidly dividing cells, including leukocytes, and alimentary toxic aleukia, a type of leucopenia, is one of the leading symptoms of trichothecene toxicosis (Joffe, 1971). We have previously reported that nivalenol, one of the trichothecenes, hinders cell proliferation (Nagashima et al., 2006), induces apoptosis (Nagashima et al., 2009a) and interleukin-8 (IL-8) secretion (Nagashima et al., 2006), and decreases monocyte chemotactic protein-1 (MCP-1) secretion (Nagashima et al., 2009b) in the human promyelocytic leukemia cell line HL60. In addition, intracellular calcium ions (Nagashima et al., 2006, Nagashima et al., 2009b), presumably released from the endoplasmic reticulum calcium store by ryanodine receptor 1 (Nagashima et al., 2010), and stress-activated mitogen-activated protein (MAP) kinases (Nagashima et al., 2009c) are crucial for nivalenol-associated toxicity.

Nuclear factor-κB (NF-κB), a collective term for a family of transcription factors, was originally detected as a transcription-enhancing complex governing the immunoglobulin light chain gene enhancer. In unstimulated cells, NF-κB complexes are retained intent cytoplasmic form through binding to a member of IκB (inhibitor of NF-κB) proteins. NF-κB induction occurs following the phosphorylation and subsequent degradation of IκB. This switch liberates NF-κB complexes for nuclear translocation and target gene transcription. A diverse spectrum of stimuli can activate this pleiotropic transcription factor that is responsible for diverse biological phenomena including immune response, inflammation, cell proliferation, and cell death (Hayden and Ghosh, 2004, Brown et al., 2008). To our knowledge, there are no studies that report the involvement of NF-κB in nivalenol toxicity. In this study, therefore, to elucidate the molecular mechanism underlying the toxicity of nivalenol, we investigated the effects of NF-κB inhibitors on nivalenol-induced cytotoxicity in HL60 cells.