DRUGS THAT INFLUENCE TUBULIN POLYMERIZATION MODULATE THYROTROPIN-RELEASING-HORMONE RECEPTOR NUMBER IN ATT-20 CELLS

In order to examine the role of cytoskeleton in modulating the cell su rface receptors, AtT-20 cells (stably expressing thyrotropin-releasing hormone receptors) were incubated with drugs that are known to modify the tubulin-microtubule system. The binding of [H-3]methyl thyrotropi n-releasing hormone ([H-3]mTRH) to intact cells increased as a functio n of time, and was linear from 1.25x10(6) to 6.25x10(6) cells/ml. Cell s incubated with colchicine, vinblastine, and taxol for 16 hr were har vested and the cell concentration was determined using a haemocytomete r. Because the drugs inhibited the cell proliferation at 100 nM, it wa s decided to examine the effect of 100 nM of each of the three drugs o n the ability of [H-3]mTRH to bind cell surface receptors. Cells were incubated with the drugs for 16 hr at 37 degrees. After the incubation , cells (5x10(6) cells/ml) from each group were assayed for [H-3]mTRH binding. Colchicine, vinblastine, and taxol stimulated [H-3]mTRH bindi ng by up to 27, 27, and 21%, respectively, without altering the K-a of the ligand to the receptor. These results suggest that perturbation o f cytosolic microtubules leads to a reorganization of the spatial loca tion of hormone receptors.