Microtubule acetylation and stability may explain alcohol-induced alterations in hepatic protein trafficking.
We have been using polarized hepatic WIF-B cells to examine ethanol-induced liver injury. Previously, we determined microtubules were more highly acetylated and more stable in ethanol-treated WIF-B cells. We proposed that the ethanol-induced alterations in microtubule dynamics may explain the ethanol-induced defects in membrane trafficking that have been previously documented. To test this, we compared the trafficking of selected proteins in control cells and cells treated with ethanol or with the histone deacetylase 6 inhibitor trichostatin A (TSA). We determined that exposure to 50 nM TSA for 30 minutes induced microtubule acetylation ( approximately 3-fold increase) and stability to the same extent as did ethanol. As shown previously in situ, the endocytic trafficking of the asialoglycoprotein receptor (ASGP-R) was impaired in ethanol-treated WIF-B cells. This impairment required ethanol metabolism and was likely mediated by acetaldehyde. TSA also impaired ASGP-R endocytic trafficking, but to a lesser extent. Similarly, both ethanol and TSA impaired transcytosis of the single-spanning apical resident aminopeptidase N (APN). For both ASGP-R and APN and for both treatments, the block in trafficking was internalization from the basolateral membrane. Interestingly, no changes in transcytosis of the glycophosphatidylinositol-anchored protein, 5'-nucleotidase, were observed, suggesting that increased microtubule acetylation and stability differentially regulate internalization. We further determined that albumin secretion was impaired in both ethanol-treated and TSA-treated cells, indicating that increased microtubule acetylation and stability also disrupted this transport step.


CONCLUSIONS
These results indicate that altered microtubule dynamics explain in part alcohol-induced defects in membrane trafficking.
Joseph
Rohan A
RA
Department of Biology, The Catholic University of America, Washington, DC 20064, USA.
Shepard
Blythe D
BD
Kannarkat
George T
GT
Rutledge
Tara M
TM
Tuma
Dean J
DJ
Tuma
Pamela L
PL
D000107:Acetylation; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D000431:Ethanol / Q000633:toxicity*; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000293:injuries / Q000378:metabolism* / Q000473:pathology*; D008113:Liver Neoplasms / Q000378:metabolism; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D011506:Proteins / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D012709:Serum Albumin / Q000378:metabolism
D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D011506:Proteins; D012709:Serum Albumin; D000431:Ethanol; C012589:trichostatin A