Changes in keratin expression during the estrogen-mediated differentiation of rat vaginal epithelium

While vaginal cornification occurs naturally during the estrous cycle of the adult rat, it can also be artificially induced by administering exogenous hormone to ovariectomized animals. When the maturation of rat vaginal epithelium was controlled with a timed course of estradiol (E2) injections, total cell extracts from that tissue revealed that six major keratins exhibited stage-specific increases during a 48-h period of stratification and cornification. One-dimensional polyacrylamide gel electrophoresis and electrophoretic immunoblotting showed that the expression pattern involved an earlier rise of the smaller (50,000, 51,000, and 53,000 mol wt) keratins and a later rise of the larger (57,000, 58,000, and 60,000 mol wt) keratins. Polypeptide levels were quantitated by gel densitometry, and an immunodot assay was developed to specifically measure keratin expression as a function of estrogen agonist activity. By way of comparison, four other estrogenic compounds were also evaluated after their administration under a 48-h double injection protocol. Under these circumstances, diethylstilbestrol provided a more potent stimulus than E2, while estriol, enclomiphene and zuclomiphene each produced a pattern of keratin expression and intensity levels that resembled that 24-h stage of E2 treatment. Although the same keratins were expressed by these different compounds, their synthesis was selective, since they often increased 10- to 20-fold while total protein levels only doubled. Keratin levels were correlated with the various degrees of epithelial growth and differentiation observed in parallel histological studies. These results indicate that the expression of vaginal keratins provide a useful model system for the study of estrogen action.