The cyanotoxin cylindrospermopsin slows down cell cycle progression and extends metaphase duration in immortalised human airway epithelial cells.

Cylindrospermopsin (CYN) is a cyanobacterial toxin that occurs worldwide in aquatic environments. It is known for its delayed effects upon oral uptake in animals and humans. A less well studied route of CYN internalisation is the inhalation of CYN-contaminated aerosols. We analyzed potential effects of different CYN concentrations (1, 2.5 and 5 µmol/l) on cultures of immortalised human bronchial epithelial cells (16HBE14o-). Impedance, a proxi for cell attachment to the culture support, cell spreading, cell growth and cell proliferation, was measured using an Acea iCELLigence device. Cell division rate and metaphase duration were determined using time lapse movies (Nikon Biostation II) of CYN-exposed cell cultures. Western blot studies were used to determine expression levels of cell cycle regulator proteins, the cyclins B1, D1 and A2. Our investigations revealed that exposure of cells to CYN concentrations of 1 µmol/l or higher led to a concentration- and time-dependent attenuation of impedance development as well as cell proliferation rate, and an extension of the metaphase of the cell cycle. CYN-mediated downregulation of cyclins B1 and D1 may be part of the underlying cell physiological mechanism. These results indicate that exposure of airways in humans and animals to aerosolised CYN over longer periods may be harmful.

Target Mechanisms of the Cyanotoxin Cylindrospermopsin in Immortalized Human Airway Epithelial Cells.

Cylindrospermopsin (CYN) is a cyanobacterial toxin that occurs in aquatic environments worldwide. It is known for its delayed effects in animals and humans such as inhibition of protein synthesis or genotoxicity. The molecular targets and the cell physiological mechanisms of CYN, however, are not well studied. As inhalation of CYN-containing aerosols has been identified as a relevant route of CYN uptake, we analyzed the effects of CYN on protein expression in cultures of immortalized human bronchial epithelial cells (16HBE14o-) using a proteomic approach. Proteins whose expression levels were affected by CYN belonged to several functional clusters, mainly regulation of protein stability, cellular adhesion and integration in the extracellular matrix, cell proliferation, cell cycle regulation, and completion of cytokinesis. With a few exceptions of upregulated proteins (e.g., ITI inhibitor of serine endopeptidases and mRNA stabilizer PABPC1), CYN mediated the downregulation of many proteins. Among these, centrosomal protein 55 (CEP55) and osteonectin (SPARC) were significantly reduced in their abundance. Results of the detailed semi-quantitative Western blot analyses of SPARC, claudin-6, and CEP55 supported the findings from the proteomic study that epithelial cell adhesion, attenuation of cell proliferation, delayed completion of mitosis, as well as induction of genomic instability are major effects of CYN in eukaryotic cells.