INVOLVEMENT OF THE UBIQUITIN-MEDIATED

CALATAYUD, C.A., PASQUINI, L.A., PASQUINI, J.M., SOTO, E.F.

Innsruck, Austria

Congreso; 20th biennial Meeting of the International Society for Neurochemistry and the European Society for Neurochemistry; 2005

International Society for Neurochemistry and European Society for Neurochemistry

The selective degradation of abnormal or short half-life proteins in eucaryotic cells proceeds through the ubiquitin (Ub) dependent proteolytic system. The signals that tag the proteins for their ubiquitination are not well known. In the present study, our aim was to investigate the relationship between the action of ceramide and the changes in the expression of certain Ub pathway proteins mRNAs and in the activation of the Ub-dependent system in cultured astrocytes. Changes in the expression of components which are known to be substrates of the Ub mediated pathway and that participate in the regulation of cell death process were also studied. Addition of different concentrations of ceramide to cultured astrocytes produced an increase in the expression of the Ub gene and in the gene that codifies for E1, one of the enzymes involved in the ubiquitination process, without any changes on cell viability. Immunocytochemical studies showed an increase in the expression of bcl-2, a decrease in IKB and in its phosphorylated form as well as a translocation of NFK-B to the nucleus. All of these compounds appear to be acting as possible modulators of astrocyte antiapoptotic responses to ceramide. Our results seem to indicate that ceramide, at the concentrations used in this study, does not produce apoptosis in astrocyte primary cultures. However, it induces an activation of the Ub-dependent proteolytic pathway, probably as a consequence of theactivation of phosphatases and kinases, or through the generation of reactive oxygen species (ROS), which act as triggering signals of the Ub-dependent pathway.