Alcohol-induced defects in hepatic transcytosis may be explained by impaired dynein function

Aug 24, 2014Molecular and cellular biochemistry

Alcohol-related liver cell transport problems may be caused by weaker motor protein function

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Abstract

Ethanol-treated hepatic cells display impaired canalicular delivery of all tested proteins.

Microtubules are hyperacetylated and more stable in ethanol-treated liver cells.
Defects in protein trafficking, including nuclear translocation of transcription factors, may be linked to these microtubule modifications.
Transcytosis of newly synthesized canalicular proteins is impaired in ethanol-treated hepatic cells.
Stalled transcytosing proteins colocalize with dynein/dynactin, indicating disrupted motor function.
Enhanced dynein binding to microtubules in ethanol-treated cells could lead to decreased motor activity and vesicle stalling.
Modulating cellular acetylation with deacetylase agonists may offer a new therapeutic approach for alcoholic liver disease.

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Alcoholic liver disease has been clinically well described, but the molecular mechanisms leading to hepatotoxicity have not been fully elucidated. Previously, we determined that microtubules are hyperacetylated and more stable in ethanol-treated WIF-B cells, VL-17A cells, liver slices, and in livers from ethanol-fed rats. From our recent studies, we believe that these modifications can explain alcohol-induced defects in microtubule motor-dependent protein trafficking including nuclear translocation of a subset of transcription factors. Since cytoplasmic dynein/dynactin is known to mediate both microtubule-dependent translocation and basolateral to apical/canalicular transcytosis, we predicted that transcytosis is impaired in ethanol-treated hepatic cells. We monitored transcytosis of three classes of newly synthesized canalicular proteins in polarized, hepatic WIF-B cells, an emerging model system for the study of liver disease. As predicted, canalicular delivery of all proteins tested was impaired in ethanol-treated cells. Unlike in control cells, transcytosing proteins were observed in discrete sub-canalicular puncta en route to the canalicular surface that aligned along acetylated microtubules. We further determined that the stalled transcytosing proteins colocalized with dynein/dynactin in treated cells. No changes in vesicle association were observed for either dynein or dynactin in ethanol-treated cells, but significantly enhanced dynein binding to microtubules was observed. From these results, we propose that enhanced dynein binding to microtubules in ethanol-treated cells leads to decreased motor processivity resulting in vesicle stalling and in impaired canalicular delivery. Our studies also importantly indicate that modulating cellular acetylation levels with clinically tolerated deacetylase agonists may be a novel therapeutic strategy for treating alcoholic liver disease.

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Alcohol-induced defects in hepatic transcytosis may be explained by impaired dynein function

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