Protein restriction specifically decreases the abundance of serum albumin and transthyretin nuclear transcripts in rat liver

The expression of the genes for serum albumin and several other plasma proteins is decreased in animals consuming inadequate amounts of dietary protein. To define the specificity of this phenomenon, we examined the effect of dietary protein restriction on the abundance of the mRNA for nine genes in rat liver. The results of this and previous studies indicate that genes in liver can be divided into two classes based on their response to protein restriction. Group I genes (albumin, transthyretin, carbamyl phosphate synthetase-I, class I alcohol dehydrogenase, insulin-like growth factor-I) exhibit decreased expression in response to protein restriction. In contrast, the expression of group II genes (hypoxanthine-guanine phosphoribosyl transferase, ubiquitin, H-ferritin, insulin-like growth factor binding proteins-1, -2 and -4) is either unchanged or increased in response to protein restriction. To investigate the molecular mechanism(s) leading to the decreased level of albumin and transthyretin mRNA in protein-restricted animals, the effect of protein restriction on the abundance of albumin and transthyretin nuclear transcripts was examined. The results demonstrated that protein restriction specifically decreased the abundance of albumin and transthyretin nuclear transcripts, indicating that the reduction in mRNA levels is caused at least partly by a decrease in gene transcription.