Co-existing proteins interfere with the action of nordihydroguaiaretic acid on retrograde Golgi-to-ER protein trafficking in NRK cells and alpha-glucosidase reaction in vitro

Nordihydroguaiaretic acid, of a new family of microtubule-stabilizing agents, shows effects differentiated from paclitaxel

Nordihydroguaiaretic acid (NDGA) protected microtubules in NRK cells from depolymerization caused by structurally and functionally diverse drugs such as nocodazole, colchicine, vinblastine, and ilimaquinone. Hitherto reported drugs, although structurally unrelated to paclitaxel, stabilize microtubules in a way similar to that of paclitaxel and compete for paclitaxel binding to tubulin. However, NDGA had activity toward microtubules different from the effects of paclitaxel. In NRK cells, paclitaxel caused microtubule bundle formation in the presence and absence of microtubule-depolymerizing drugs. However, microtubule bundle did not form, and microtubules radiated from the microtubule-organizing center, in cells treated with NDGA. Acceleration of tubulin polymerization in vitro by paclitaxel was strong but that by NDGA was weak. Microtubules polymerized in vitro in the presence of paclitaxel, but not those polymerized in the presence of NDGA, resisted the effects of cold. NDGA seemed to bind to tubulin, but did not compete for [3H]paclitaxel binding to tubulin. These observations indicate that NDGA belongs to a novel family of microtubule-stabilizing drugs.

Possible implication of Golgi-nucleating function for the centrosome

The Golgi apparatus breaks down at mitosis, resulting in the dispersal of Golgi-resident proteins. In NRK cells, however, subsets of both TGN38 and golgin-97, but not ManII and GM130, remained associated with the centrosome throughout the cell cycle. This centrosome association of TGN38 and golgin-97 was not disrupted by treatment with brefeldin A, additional inducers of retrograde trafficking and inhibitors of either kinases or protein phosphatases. Anchoring of the Golgi apparatus within the juxtanuclear region depends on microtubules; the association of TGN38 and golgin-97 subsets with the centrosome, however, was insensitive to nocodazole treatment. Drugs such as PDMP, which block Golgi dispersal both by nocodazole, despite microtubule depolymerization, and by inducers of retrograde trafficking, strengthened the microtubule-nucleating activity of the centrosome. These observations cumulatively suggest the centrosome is implicated in nucleation of the Golgi apparatus through interactions with Golgi-resident proteins, such as TGN38 and golgin-97.