Recovery from vanadium involves the elimination of cellular structures in the yeast Hansenula polymorpha

The mechanisms by which living organisms can protect themselves from vanadium toxicity are not completely understood. This is partly due to the multiplicity of possible targets for the metal which interferes with the phosphorylation state of enzymes and regulatory molecules. In vanadate-resistant mutants of Neurospora crassa and Candida albicans resistance to vanadium is due to the exclusion of the metal from the intracellular compartment through the inactivation of the phosphate transport system. Saccharomyces cerevisiae vanadate-resistant mutants show glycosylation defects and alterations in protein phosphorylation and growth control which suggest that resistance could be due to the alteration of sensitive target(s) in the secretory pathway and/or in the phosphorylation system. The vanadate-tolerant yeast Hansenula polymorpha greatly modifies its ultrastructural aspect when grown in the presence of the metal, showing an increase in cell vacuolation and in the number of cytoplasmic vesicles, and a thickening of the cell wall. At the same time, the external invertase activity is partially inhibited and the carboxypeptidase Y activity is enhanced. In order to understand better the meaning of these observed modifications we followed their evolution during return to vanadate-free conditions. Our results show that recovery from vanadium is a complex phenomenon involving important ultrastructural rearrangements, which could be achieved through the activation of an autophagic process.