Interaction of captan with mammalian microtubules

Antimicrotubular effect of calvatic acid and of some related compounds

A structure-activity relationship has been established between calvatic acid and some related synthetic compounds, and their ability to inhibit GTP-induced microtubular protein polymerization in vitro. These compounds were effective in a dose- and a time-dependent manner. The most active drug was the p-chloro substituted compound, which showed its inhibitory activity without any preincubation period, which the others needed. Since if cysteine was present, polymerization was no longer affected, an involvement of titratable -SH groups of tubulin could be suggested. In contrast, taxol-induced polymerization was only slightly inhibited by these compounds, and colchicine-binding activity was not generally impaired.

Normal and Ha-ras-1 oncogene transformed Buffalo rat liver (BRL) cells show differential resistance to cytoskeletal protein inhibitors

In the present study, using immunofluorescence microscopy, we have demonstrated that normal and Ha-ras-1 transformed Buffalo rat liver (BRL) cells which were exposed to cytoskeletal protein inhibitors, showed a differential resistance of their microfilament and microtubule networks. One hour exposure of normal BRL cells to 10(-5) M cytochalasin B provoked a clear and already total breakdown of actin filaments. However, at this concentration of cytochalasin B, the microfilaments of transformed BRLHO6T1-1 cells were not seriously affected; a higher cytochalasin B concentration (> or = 2 x 10(-5) M) was required to induce a significant breakdown of microfilaments in these transformed cells. The two cell lines also demonstrated differential microtubule stability when they were treated with either colchicine or triethyllead. Three hours exposure to 10(-6) M of either antimicrotubule agents was sufficient to disrupt the microtubules of normal BRL cells, without affecting their counterparts in the transformed BRLHO6T1-1 cells. A 10-fold higher drug concentration (10(-5) M) was required to induce microtubular breakdown in the transformed BRL cells. The differential stability of microfilaments and microtubules in normal and transformed BRL cells that was observed could not be attributed to a differential internalization of the agents, as shown by experiments on the uptake of [3H]-cytochalasin B and triethyllead. In addition, the transformed BRLHO6T1-1 cells did not express altered actin and tubulin isoforms, as demonstrated by isoelectric focusing followed by immunoblotting analysis. We conclude that the transformation of BRL cells with the Ha-ras-1 oncogene results in a greater stability of microfilaments and microtubules, leading to a structurally firmer cell shape.(ABSTRACT TRUNCATED AT 250 WORDS)