Effects of S100A1 and S100B on microtubule stability. An in vitro study using triton-cytoskeletons from astrocyte and myoblast cell lines

S100A1 and S100B are members of a multigenic family of Ca2+-binding protein s of the EF-hand type highly abundant in astrocyte and striated muscle cell s that have been implicated in the Ca2+-dependent regulation of several int racellular activities including the assembly and disassembly of microtubule s and type III intermediate filaments. Ln the present work we tested S100A1 and S100B for their ability to cause microtubule and/or intermediate filam ent disassembly in situ using triton-cytoskeletons obtained from U251 gliom a cells and rat L6 myoblasts. Our results indicate that: (i) both proteins cause a Ca2+-dependent disassembly of cytoplasmic microtubules in a dose-de pendent manner; (ii) the S100A1- and S100B-inhibitory peptide, TRTK-12, blo cks the S100A1 and S100B effects on microtubules; (iii) S100A1 Delta 88-93, an S100A1 mutant lacking the C-terminal extension, does not affect microtu bule stability; and (iv) no obvious S100A1- or S100B-dependent intermediate filament disassembly could be observed under the experimental conditions u sed in the present study, but S100A1- and S100B-dependent microtubule disas sembly results in a tendency of vimentin intermediate filaments to aggregat e into bundles and/or to condense. Together, these results suggest that S10 0A1 and S100B probably cause microtubule disassembly by interacting with th e microtubule wall, and that the two proteins do not affect intermediate fi lament stability via interaction with preformed intermediate filaments, in agreement with previous biochemical investigation. Our present data lend support to the possibility that S100A1 and S100B migh t have a role in the in vivo regulation of the state of assembly of microtu bules in a Ca2+-regulated manner and, potentially, on microtubule-based act ivities in astrocytes and myoblasts. Also, these data suggest that the both S100 proteins use their C-terminal extension for interacting with microtub ules. (C) 2000 IBRO. Published by Elsevier Science Ltd. All rights reserved .