Activation of ERK and JNK signaling pathways by mycotoxin citrinin in human cells

Mycotoxin citrinin (CFN) is commonly found in foods and feeds that are contaminated/inoculated with Penicillium, Aspergillus and Monascus species. The exposure of human embryonic kidney (HEK293) and HeLa cells to CTN resulted in a dose-dependent increase in the phosphorylation of two major mitogen-activated protein kinases (MAPKs), ERK1/2 and JNK. In HEK293 Cultures, the administering of CTN increased both the mRNA and protein levels of egr-1, c-fos and c-jun genes; additionally, the ERK1/2 pathway contributed to the upregulation of Egr-1 and c-Fos protein expression. CTN treatment also induced the transcription activity of Egr-1 and AP-1 proteins, as evidenced by luciferase reporter assays. Bioinformatic analyses indicated two genes Gadd45 beta and MMP3 have Egr-1 and AP-1 response elements in their promoters, respectively. Furthermore, co-exposure of HEK293 cells to CFN and MAPK pathway inhibitors demonstrated that CTN increased the levels of Gudd45 beta mRNA through ERK1/2 signaling pathway and up-regulated the MMP3 transcripts majorly via JNK pathway. Finally, CTN-triggered caspase 3 activity was significantly reduced in the presence of MAPK inhibitors. Our results Suggest that CTN positively regulates ERK1/2 and JNK pathways as well as their downstream effectors in human cells; activated MAPK pathways are also involved in CTN-induced apoptosis. (C) 2009 Elsevier Inc. All rights reserved.