Ethanol Destabilizes Liver Galβl, 4GlcNAc α2,6-Sialyltransferase, mRNA by Depleting a 3′-Untranslated Region-Specific Binding Protein

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Abstract
Asialoconjugates are viable biomarkers for alcohol abuse. We previously showed that chronic ethanol feeding down-regulated liver Galβl, 4GlcNAc α2,6-sialyltransferase (ST6Gal l) mRNA by destabilizing it. Since RNA-binding proteins are known to stabilize many eukaryotic mRNAs by interacting with the 3′-untranslated region (UTR), we have delineated the possible mechanism by which ethanol destabilizes ST6Gal l mRNA. Using 32P-labeled RNA probes generated from a 2.7-kb 3′-UTR of ST6Gal l mRNA, we identified a liver cytosolic 41-kDa specific binding protein that interacts with its 3′-UTR domain and protects it from degradation in normal rat liver but disappears after chronic ethanol treatment. Mapping of the binding region revealed that four RNA probes of 80-base pair (bp) length spanning the 304 bp of the 3′-UTR of ST6Gal l mRNA showed equal binding intensity. The corresponding cDNA sequences for the four 80-bp RNA probes share the 13-bp consensus sequence. Mutagenesis analysis identified that four nucleotides, AG and TC, among the consensus sequences were critical for the RNA-protein interaction. Therefore, 5′-CAGCCTCCTCCCT-3′ serves as a cis-element critically involved in this interaction. The RNA-protein complex formation progressively decreased with increasing dietary ethanol, resulting in its virtual disappearance with 36% of the dietary calories as ethanol. Concomitantly, the same ethanol diet decreased sialic acid index of plasma apolipoprotein J by 45% (p < 0.05). Thus, depletion of a binding protein that specifically interacts with its 3′-UTR region of ST6Gal l mRNA may account for its destabilization and consequent appearance of asialoconjugates as alcohol biomarkers.

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