Association of S100B with intermediate filaments and microtubules in glialcells

Previous in vitro studies have shown that the Ca2+-regulated S100B protein modulates the assembly-disassembly of microtubules (MTs) and type III inter mediate filaments (IFs). In the present report, by double immunofluorescenc e cytochemistry S100B was localized to both GFAP/vimentin Ifs and MTs as we ll as to centrosomes in U251 glial cells. In cells treated with the MT-depo lymerizing agent, colchicine, S100B remained associated with the rearranged GFAP Ifs throughout the cell and, at the cell periphery, vimentin Ifs. In cells treated with the MT stabilizing agent, taxol, S100B followed partly t he rearrangement of MTs and partly the rearrangement of IFs. Under the latt er condition, bundles of MTs with their associated S100B appeared surrounde d and/or flanked by rearranged Ifs with their associated S100B. Colocalizat ion of S100B with closely arranged Ifs and MTs was best evident in cells ma nipulated with taxol and in triton-cytoskeletons. In these cases, MTs and t heir associated S100B appeared surrounded and/or flanked by and/or intermin gled with Ifs and their associated S100B. Also, a preferential association of S100B with GFAP vs, vimentin Ifs could be observed near the nucleus wher e colocalization of S100B with MTs was also maximal. Condensation of Ifs an d alteration of the MT network caused by treatment of cells with the phosph atase inhibitor, okadaic acid, resulted in a concomitant condensation/alter ation of the S100B immunoreactivity. The present results lend support to th e possibility that S100B may be an important factor implicated in the regul ation of the dynamics of MTs and Ifs. (C) 1998 Elsevier Science B.V. All ri ghts reserved.