Cylindrospermopsin induced transcriptional responses in human hepatoma HepG2 cells

Abstract

The newly emerging cyanotoxin cylindrospermopsin (CYN) is showing genotoxic effects in a range of test systems. However, the knowledge on the mechanisms involved is limited. To get insight into the cellular responses to CYN a toxicogenomic analysis of selected genes commonly affected by genotoxic stress was performed on HepG2 cells exposed to a non-cytotoxic but genotoxic concentration of CYN (0.5 μg/ml for 12 and 24h). CYN increased expression of the immediate-early response genes from the FOS and JUN gene families and there was strong evidence for the involvement of P53 and NF-κB signaling. Strong up-regulation of the growth arrest and DNA damage inducible genes (GADD45A and GADD45B), cyclin-dependent kinase inhibitors (CDKN1A and CDKN2B), checkpoint kinase 1 (CHEK1), and genes involved in DNA damage repair (XPC, ERCC4 and others) indicated cell-cycle arrest and induction of nucleotide excision and double strand break repair. Up-regulation of metabolic enzyme genes provided evidence for the involvement of phase I (CYP1A1, CYP1B1, ALDH1A2 and CES2) and phase II (UGT1A6, UGT1A1, NAT1 and GSTM3) enzymes in the detoxification response and potential activation of CYN. The obtained transcriptional patterns after exposure of HepG2 cells to CYN provide valuable new information on the cellular response to CYN.

Keywords: AP-1; Apoptosis; BER; CDK; CDKI; CYN; CYP450; Cell-cycle; Cylindrospermopsin; DNA damage repair; DNA double-strand break; DSB; Detoxification response; ER; GST; HPBLs; HRR; Immediate-early response; MMR; NER; NF-κB; NHEJ; PCNA; TGF-B; TNFα; activator protein; base excision repair; cyclin-dependant kinase; cyclin-dependant kinase inhibitor; cylindrospermopsin; cytochrome P450; endoplasmic reticulum; glutathione S-transferase; homologous recombination repair; human peripheral blood lymphocytes; mismatch repair; none-homologous end joining; nuclear factor kappa B; nucleotide excision repair; proliferating cell nuclear antigen; transforming growth factor B; tumor necrosis factor α.