Role of microtubule structure in the maintenance of m3-muscarinic acetylcholine receptor rnRNA levels.
The regulation of m3-muscarinic acetylcholine receptor (mAChR) mRNA following exposure to microtubule-disrupting agents was studied in cultured cerebellar granule cells. Colchicine (10 muM), an antimicrotubular agent, decreased the levels of m3-mAChR mRNA in a time-dependent fashion. Concentration levels of m3m-AChR mRNA were attenuated by 29, 49, and 85% of original values at 4, 8, and 24 h, respectively, after exposure to 10 muM colchicine in these cells on the eighth day of culture. This colchicine-induced m3-mAChR mRNA down-regulation correlated with a decrease of mAChR sites measured by binding with N-[(3)H]methylscopolamine and loss of carbachol-inducible phosphoinositide turnover. No changes in morphology or levels of total cellular RNA or beta-actin mRNA were detected after 8 h of exposure to 10 muM colchicine. The levels of m3-mAChR mRNA decreased in cells exposed to colchicine in a dose-dependent manner. An inactive derivative of colchicine, beta-lumicolchicine, did not change the steady-state level of m3-mAChR mRNA. The presence of taxol (10 muM), a microtubule stabilizer, reversed colchicine- but not nocodazole-induced m3-mAChR mRNA down-regulation that occurred at 8 h. Taxol was also able to reverse, at least in part, carbachol-induced m3-mAChR mRNA down-regulation after 8 h of exposure. These results indicate that an intact microtubule structure is critical for the maintenance of m3-mAChR mRNA levels.
Fukamauchi
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section on Molecular Neurobiology, Biological Psychiatry Branch, National Institute of Mental Health, Building 10, Room 3N-212, 9000 Rockville Pike, Bethesda, Maryland 20892, USA.
Hough
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Chuang
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