Nocodazole and taxol affect subcellular compartments but not secretory activity of GH3B6 prolactin cells.

The effects of two drugs known to affect microtubules (nocodazole, a depolymerizing agent, and taxol, a polymerizing and stabilizing agent) have been tested in GH3B6 prolactin (PRL) cells, a rat pituitary cell line. Under basal condition, GH3B6 cells displayed a dense and entangled microtubule (MT) network, and a tight perinuclear cage of cytokeratin fibers with branching bundles in the cytoplasm. Nocodazole induced a disappearance of MT in the cytoplasm accompanied by the formation of tubulin blebs at the cell periphery, and a slackening of the perinuclear cage of cytokeratin. Taxol induced the formation of straight MT bundles in the cytoplasm, and a tightening of the cytokeratin cage. In parallel, nocodazole induced a fragmentation of the Golgi apparatus which appeared, after staining with antibodies against PRL or against mannosidase II, a Golgi membrane antigen, as small subunits dispersed in the cytoplasm. Taxol induced a perturbation of the Golgi apparatus which, however, remained located near the nucleus. Surprisingly, despite their obvious effects on the subcellular organization, the two MT drugs did not perturb the basal and thyroliberin (TRH)-stimulated PRL release. Moreover, they do not seem to affect the intracellular transport and release of neosynthesized PRL as appreciated by "pulse-chase" experiments. These observations demonstrate that, although MT assume an important role in the spatial compartmentalization of GH3B6 cells, they are not directly involved in the different steps of the intracellular PRL transport from its synthesis site to its release site, as well as in the associated membrane traffic.