Tubulin posttranslational modifications induced by cadmium in the sponge Clathrina clathrus

As sessile filter feeders, sponges are exposed to environmental stress due to pollutants of both anthropogenic and natural origins and are able to accumulate harmful substances. Thus, sponges are considered a good tool for the biomonitoring of coastal areas. In this study, we used biochemical and immunocytochemical analyses to provide new data on the cadmium-related changes in sponge cells. In particular, we analyzed the effects of different concentrations of cadmium on the microtubule network in the calcisponge Clathrina clathrus. Quantitative densitometry of the immunoblots showed that, while the levels of alpha- and beta-tubulin remained relatively constant in C. clathrus when exposed to 1 and 5 mu M CdCl2, there were progressive shifts in the levels of some tubulin isoforms. Exposure for 24 h to sublethal concentrations of cadmium reduced the level of tyrosinated alpha-tubulin and enhanced the levels of acetylated and detyrosinated alpha-tubulin relative to the levels in controls. Confocal microscopy analysis of immunolabeled tissue sections showed that the inhibitory effect of cadmium was associated with a decrease in the labeling of the cells with a monoclonal antibody that recognizes tyrosinated alpha-tubulin. By contrast, the reactivity with a monoclonal antibody that recognizes acetylated alpha-tubulin and with a polyclonal antibody specific for detyrosinated alpha-tubulin was enhanced at the same time points. Because the acetylation and detyrosination of alpha-tubulin occur on stable microtubules, the marked enhancement of alpha-tubulin acetylation and detyrosination in Cd2+-treated cells indicates that divalent Cd ions stabilize microtubules. The possibility that Cd2+ may increase the stability of cytoplasmic microtubules was tested by exposing Cd2+-treated cells to a cold temperature (0 degrees C). As shown, the microtubule bundles induced by Cd2+, which were labeled by the monoclonal antibodies against acetylated and detyrosinated a-tubulin, were resistant to cold. (C) 2013 Elsevier B.V. All rights reserved.