Characterization of Carbonic Anhydrases in Models of Neuronal Differentiation and in the Nematode Caenorhabditis elegans

CA IX is a member of the carbonic anhydrase family of enzymes. It is a well known marker of hypoxia and it is involved in pH and survival regulation in hypoxic cells. The main aim of my PhD project was to identify molecular interactors of CA IX and, based on the knowledge of its ligands, to contribute to functional characterization of CA IX in neuronal cells. A complex protein network of novel CA IX interactors has been highlighted: several proteins of the nucleo-cytoplasmatic machinery have been found to bind CA IX under hypoxic condition; many of the CA IX protein interactors belong to the family of the ARM and HEAT-repeat containing proteins. Both in normoxic and hypoxic conditions CA IX also interacts with Cullin-associated NEDD8-dissociated protein 1 (CAND1), which is a nuclear HEAT/ARM-containing protein that is involved in gene transcription and assembly of the SCF E3 ubiquitine ligase complexes. Immunofluorescence (IF) analysis demonstrated an accumulation of CA IX in the nuclei of neuroblastoma cell lines and in neurons derived from murine ESCs. Putative NLS/NES sequences were identified in the CA IX protein sequence; IF analysis showed that they were able to affect distribution of the reporter protein GFP inside the cell. Collectively, these data suggest that subcellular localization and functions of CA IX are more complex than previously thought. CA IX may have intracellular functions different from those already known at the plasma membrane. A nuclear function for CA IX is in fact suggested by its localization on transcribed chromatin. Finally, the nematode Caenorhabditis elegans was used as an animal model, in order to characterize the function of two carbonic anhydrases of the worm, namely, cah-5 and cah-6, during hypoxic and anoxic stresses. Although preliminary, the observed phenotypes allow to predict fundamental roles for carbonic anhydrases in vivo.