ETHANOL-INDUCED ALTERATIONS OF THE MICROTUBULE CYTOSKELETON IN HEPATOCYTES

Ethanol has been predicted to alter vesicle-based protein traffic in h epatocytes, in part, via a disruption of the microtubule (MT) cytoskel eton. However, information on the effects of chronic ethanol exposure on MT function in vivo is sparse. Therefore the goal of this study was to test for ethanol-induced changes in rat liver tubulin expression, assembly, and cellular organization, using molecular, biochemical and morphological methods. The results of this study showed that tubulin m RNA and protein levels were not altered by ethanol. Tubulin, isolated from control and ethanol-fed rats, showed similar polymerization chara cteristics as assessed by calculation of the critical concentration fo r assembly and morphological structure. In contrast, the total amount of assembly-competent tubulin was reduced in livers from ethanol-fed r ats compared with control rats when assessed by quantitative immunoblo t analysis using a tubulin antibody. In addition, we observed that MT regrowth and organization in cultured hepatocytes treated with cold an d nocodazole was markedly impaired by chronic ethanol exposure. In sum mary, these results indicate that tubulin levels in liver are not redu ced by ethanol exposure. While there is a substantial amount of tubuli n protein capable of assembling into functional MTs in ethanol-damaged livers, a marked portion of this tubulin is polymerization incompeten t. This may explain why these hepatocytes exhibit a reduced number of MTs with an altered organization.