HIGH-MOLECULAR-WEIGHT TAU-DISTRIBUTION AND MICROTUBULE STABILITY IN NEUROBLASTOMA N115-CELLS

The localization of high molecular weight (HMW) tau proteins in neurob lastoma N115 cells and of their transcripts was compared to that of no n-tyrosinated and tyrosinated tubulin before and after treatment with depolymerizing drugs. Microtubules stained by tau antibodies were pres ent both in a limited region of the cell center and in the cell proces ses, whereas tau transcripts were detected only in the cell body. The microtubules localized in the cell center and labeled by tau antibodie s resisted colcemid treatment, whereas those in the neurites were comp letely depolymerized by the drug. Microtubules containing stable and u nstable microtubule tracts were identified in the neurites after colce mid treatment. These composite microtubules were not labeled by tau an tibodies. It is concluded that stable and unstable polymers - localize d in the cell center and in the neurites, respectively - contain HMW t au proteins, whereas composite microtubules displayed in the cell proc esses do not. Microtubule stability in this cell line does not therefo re seem to be related to the association of tau proteins to the polyme rs but, rather, to posttranslational modifications of the tubulin subu nits.