[Acetylation of microtubules during endocytosis of epidermal growth factor receptor (c-ErbB1) in interphase HeLa cells].

Acetylation of microtubules (MT) during endocytosis of epidermal growth factor receptor, c-ErbB1, was studied by confocal immunofluorescence microscopy. It was found that stimulation of endocytosis of c-ErbB1 complexed with the epidermal growth factor (EGF), resulted in continuous raising of MT acetylation that reached its maximum at 60-90 min and then went down to the control level. Simultaneously, the receptor-containing endosomes grew in size and were redistributed into juxtranuclear region. Enlarged endosomes formed dense clusters around MTOC in 60-90 min. Another native c-ErbB1 ligand, transforming growth factor-alpha (TGF-alpha) and unlike EGF causing the receptor recycling, also initiated a wave of MT acetylation, but the effect was expressed more poorly. In this case, endosomes did not grow in size and did not form dense clusters near the MTOC. Cell treatment with deacetylase inhibitor trichostatin A (TSA) caused acetylation of the whole cellular MT population. Under these conditions, translocations of EGF-c-ErbB1-containing endosomes had the same pattern as in the cells untreated with the inhibitor, but the size of endosomes didn't increase during their redistribution into juxtranuclear region. Acetylation was especially pronounced in strongly bent MT regions positioned proximally to MTOC and forming there a dense meshwork whereas peripheral MT plus-ends were basically straight and not modified. We assume that MT acetylation is not so much crucial for preferential interaction with dynein or kinesin and, accordingly, for organization of endosome translocations in a certain direction. It is rather the result of stabilization of some MT pool which supports homotypic fusion of endosomes at early stage of their maturation.