Protein isoaspartyl methyltransferase protects from Bax-induced apoptosis.

Protein L-isoaspartyl methyltransferase (Pimt) is a highly conserved enzyme utilising S-adenosylmethionine (AdoMet) to methylate aspartate residues of proteins damaged by age-related isomerisation and deamidation. We have been particularly interested in this enzyme since addition of the compound CGP3466 to primary rat astroglia cell cultures resulted in an upregulation of Pimt at the mRNA level, as shown here by semi-quantitative RT-PCR. CGP3466 is a compound related to the anti-Parkinson's drug R-(-)-deprenyl, which has been shown to protect from neural apoptosis induced by trophic factor withdrawal [Tatton et al., 1994. J. Neurochem. 63, 1572]. The pro-apoptotic gene Bax is required in the cascade of events following withdrawal [Deckwerth et al., 1996. Neuron 17, 401]. We therefore investigated whether Pimt overexpression was able to affect Bax-induced apoptosis in primary mouse cortical neurons. Our results show that Pimt is indeed able to protect from Bax-induced apoptosis. Furthermore, this activity is not restricted to brain-specific cell types, since the same effect is also demonstrated in COS1 cells. In addition, mutational analysis suggests that the protective effect is dependent on the adenosine methionine-binding motif, which is well conserved in protein methyltransferases, and that a mutation destroying this motif crucially affects cytoskeletal structures of the cell.