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 colchicine or to 1 mu M colcemid, a tubulin-binding anti-mitotic alkaloid, levels 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 level of alpha B crystallin returned to near the control level within two subsequent days of culture in the normal medium, Northern blot analysis showed that the accumulation of alpha B crystallin was preceded by an increase in the level of the mRNA for alpha B crystallin, Nuclear run-off transcription assays showed that colchicine induced new synthesis of mRNA for alpha B crystallin, Immunofluorescence staining revealed that alpha B crystallin accumulated in the peripheral areas of cells, as did the depolymerized tubulin, after several hours of treatment with colcemid, and then it gradually became more conspicuous in the cytoplasm, Vinblastine and nocodazole, which also promote the disassembly 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-mitotic agent, did not stimulate the synthesis of alpha B crystallin, but rather, it suppressed the induction of synthesis of alpha B crystallin by the microtubule-disrupting drugs. Induction of alpha B crystallin by colchicine or by other drugs that promote the disassembly of microtubules was sensitive to staurosporine, an inhibitor of protein kinases, and the induction was completely suppressed in the presence of 10 nM staurosporine. These results suggest that the expression of alpha B crystallin is stimulated, via phosphorylation reactions that are sensitive to staurosporine, when the depolymerization of microtubules is enhanced.