Evidence for the role of glycosylation of proteins in the tryptophan-induced stimulation of nucleocytoplasmic translocation of mRNA in rat liver.

Tryptophan induces a rapid stimulation of polyribosomal aggregation and protein synthesis in the livers of rats or mice. This stimulatory effect of tryptophan correlates with increased levels of mRNA in the cytoplasm of the liver and is related to enhanced translocation of nuclear mRNA into the cytoplasm. In the present study the possible role of glycoproteins of the rat liver, particularly those in the nuclear membranes and in the cytosol, in relation to the effect of tryptophan on enhanced nucleocytoplasmic translocation of mRNA was investigated. In the standard treatment regimen, tryptophan (30 mg/100 gm of body weight) was administered by stomach tube 10 minutes before killing. The following results were noted in the liver: Administration of tryptophan increased [14C]glucosamine incorporation into proteins of the subcellular fractions, particularly those of the soluble, nucleus and nuclear membrane. In vivo treatment of rats with tryptophan increased the in vitro [14C]orotate-labeled nuclear RNA release and [3H]tryptophan binding to proteins of the nuclei or cytosols. Treatment of cytosol proteins with alpha-mannosidase or beta-galactosidase, but not with neuraminidase, inhibited these increases. After treatment of cytosol fractions on a concanavalin A agarose column, the effluents showed decreased activity and the eluates showed increased activity in in vitro nuclear RNA release and in tryptophan binding to proteins of the control and, particularly, of the tryptophan-treated animals. Administration of tryptophan increased the polyribosomal aggregation, the in vitro [14C]leucine incorporation into protein, and the in vitro nuclear RNA release by cytosol. However, tunicamycin pretreatment of rats prevented these increases due to tryptophan. The data of this study suggest that glycosylated proteins, one or more, are the active components whereby tryptophan acts upon the liver.