Phosphorylation of MBP increased its interaction with microtubules in oligodendrocytes.

MAURICIO R. GALIANO; MARTA E. HALLAK

washington

Congreso; 38th Annual Meeting Society for Neuroscience; 2008

Society for Neuroscience

The activity of myelin basic protein (MBP) as a microtubule-interacting protein is thought to play a critical role in the synchronization of cytoskeleton changes during oligodendrocyte differentiation. Indeed we have determined that MBP induced microtubule-cold stability in differentiated oligodendrocytes (Galiano et al., 2006). From in vitro studies, it has been demonstrated that the interactions of MBP with microtubules (Mts) might be regulated by Ca2+-calmodulin binding and by post-translational modifications (see Boggs, 2006). Moreover MBP induced inhibition of the enzyme tubulin-tyrosine-carboxypeptidase (TTCP) (Modesti and Barra, 1986). Because TTCP preferentially acts on Mts converting tyrosinated tubulin (Tyr-tub) in detyrosinated tubulin (Glu-tub), we evaluated if the association of MBP to Mts is regulating TTCP activity in oligodendrocytes. The putative inhibitory effect of MBP was analyzed after MBP phosphorylation induced by phorbol ester (TPA). Oligodendrocytes treated 2 h with 300nM TPA showed a higher degree of colocalization of MBP with tubulin than control oligodendrocytes, and these TPA-treated cells revealed an increased relationship of Tyr-tub/Glu-tub than control cells. To ascertain if this was a consequence from the association of MBP to Mts, we analyzed this relationship on fibroblasts transfected with a cDNA of 17 kD MBP or with a variant of MBP lacking the last C-terminal 21 amino acids (17 kD-DC-MBP), a sequence that includes a Ca2+-Calmodulin interacting module and putative phosphorylation serine- sites. After 24 h of transfection, in control or TPA treated cells, we found that fibroblasts transfected with 17 kD MBP cDNA showed a higher Tyr-tub/Glu-tub ratio than the control cells. Whereas cells transfected with 17 kD-DC-MBP did not showed any difference. These findings demonstrated the physiological importance of MBP and its post-translational modifications on cytoskeleton dynamics during oligodendrocyte differentiation. The characterization of cytosolic carboxypeptidases in these cells will help to further elucidate the role of these interactions in myelin formation. Supported in part by SECyT-UNC and CONICET (Argentina).