Endoplasmic reticulum is a target of cadmium toxicity in the calcisponge Clathrina clathrus

"Heavy metals are among the most dangerous and abundant inorganic environmental pollutants, arising from industrial discharges and mining practices. Unlike organic compounds, they cannot be degraded but accumulate throughout the trophic web, producing potential human health risks and ecological disturbance. Marine benthic filter-feeders are particularly vulnerable to waterborne metals because they are able to process large amounts of water. We used the calcisponge Clathrina clahtrus as experimental model to study the effects of exposure to sublethal cadmium (Cd2+) concentrations on the expression of GADD153, an endoplasmic reticulum (ER) stress marker. The presence of GADD153 immunoanalogue in C. clathrus was evidenced using Western blotting and confocal laser scanning microscopy. After 24 h of Cd2+ exposure (1 and 5 µM), GADD153 was upregulated. Consistent with immunofluorescence staining, predominant protein bands appeared in the immunoblotting of treated cells in a dose-dependent manner whereas the corresponding labelled protein bands were only barely detectable in control cells. An increased expression of the ER molecular chaperone GRP78, followed by activation of ER-specific caspase-12, was also associated with increased GADD153. Results indicate that ER is one of the primary target organelles in Cd2+-induced apoptosis and, therefore, ER stress proteins are key biomarkers of Cd2+ toxicity in sponge cells."