SYNTHESIS AND ACCUMULATION OF ALPHA-B-CRYSTALLIN IN C6 GLIOMA-CELLS IS INDUCED BY AGENTS THAT PROMOTE THE DISASSEMBLY OF MICROTUBULES

When C6 cells in culture were exposed at 37 degrees C to 1 mu M colchi cine or to 1 mu M colcemid, a tubulin-binding anti-mitotic alkaloid, l evels of alpha B crystallin in cells began to increase after about 10 h, reaching a maximum of more than 1 mu g/mg protein after 24 h, The l evel of alpha B crystallin returned to near the control level within t wo subsequent days of culture in the normal medium, Northern blot anal ysis showed that the accumulation of alpha B crystallin was preceded b y an increase in the level of the mRNA for alpha B crystallin, Nuclear run-off transcription assays showed that colchicine induced new synth esis of mRNA for alpha B crystallin, Immunofluorescence staining revea led that alpha B crystallin accumulated in the peripheral areas of cel ls, as did the depolymerized tubulin, after several hours of treatment with colcemid, and then it gradually became more conspicuous in the c ytoplasm, Vinblastine and nocodazole, which also promote the disassemb ly of microtubules by binding to tubulins, also induced the synthesis of alpha B crystallin. Furthermore, induction of alpha B crystallin by these drugs was observed in quiescent cells that had been cultured in serum-free medium. However, taxol, a microtubule-stabilizing anti-mit otic agent, did not stimulate the synthesis of alpha B crystallin, but rather, it suppressed the induction of synthesis of alpha B crystalli n by the microtubule-disrupting drugs. Induction of alpha B crystallin by colchicine or by other drugs that promote the disassembly of micro tubules was sensitive to staurosporine, an inhibitor of protein kinase s, and the induction was completely suppressed in the presence of 10 n M staurosporine. These results suggest that the expression of alpha B crystallin is stimulated, via phosphorylation reactions that are sensi tive to staurosporine, when the depolymerization of microtubules is en hanced.