Estrogen stimulates intracellular traffic in the liver of Rana esculenta complex by modifying Rab protein content.

During vitellogenesis in oviparous animals, estrogens induce the synthesis of the yolk precursor vitellogenin, a lipophosphoprotein rich in cholesterol. Estrogens also induce the activity of 3-hydroxy-3- methylglutaryl CoA reductase, that is necessary for the lipidation of vitellogenin. This increased enzyme activity could also be important for the production of isoprenoid groups that post-translationally modify proteins such as the Rab proteins, which are small G proteins involved in intracellular traffic. The effect of estrogens on the production of prenylated proteins and on the levels of Rab proteins in the liver of Rana esculenta complex has been studied. An increase of the Rabs specifically involved in the exocytic pathway was observed and is probably related to the need for export of massive amounts of newly synthesized vitellogenin.