Differential association of tau with subsets of microtubules containing posttranslationally-modified tubulin variants in neuroblastoma cells

Neuronal cells display different subsets of dynamic microtubules. In axons and extending neurites, this intrinsic dynamics is modulated by the microtu bule-associated protein tau. Moreover, posttranslational modifications of t ubulin, namely acetylation, tyrosination or glutamylation are directly invo lved in determining the stability of neuronal microtubules. Studies were ca rried out to analyze the interaction patterns of tau with subsets of microt ubules in N2A neuroblastoma cells, which can differentiate in the presence of dibutyryl cAMP. Double labeling studies showed a differential pattern of tau association with microtubules containing acetylated and tyrosinated tu bulin. Furthermore, studies using depolymerizing drugs revealed a selectivi ty in the association of tau with microtubular polymers and microfilaments, within the organization of the neuronal cytoskeleton. In order to study th e association of specific tau isoforms with microtubules containing modifie d tubulin variants, immunoprecipitation studies were carried out. The coimm unoprecipitation data indicated a selective binding of specific tau isoform s to either modified tubulin variant. To assess the hypothesis on the roles of tau isoforms in the stabilization of microtubules containing modified t ubulins, the association of those variants with tau isoforms was analyzed i n overlay experiments. A preferential binding of acetylated tubulin from un differentiated N2A cell extracts, to at least one slow-migrating tau isofor m was revealed. However, acetylated tubulin from N2A cells containing long neurites displayed a preferential association with two isoforms of tau. On the other hand, tyrosinated tubulin from N2A extracts bound to the entire s et of neuronal tau isoforms. These studies, along with the tau association with microtubules with different stability, indicate that tau segregates in to subsets of microtubules in the axonal processes. The studies also sugges t that these interactions may respond to a functional versatility of these polymers in differentiating neurons.