Estrogen abrogates transcervical tight junctional resistance by acceleration of occludin modulation

The present study explored the effects of estrogen on transcervical tight-junctional resistance (R(TJ)) and the mechanisms involved. Treatment of cultured human cervical epithelial cells with 17beta-estradiol decreased in a time- and dose-related manner the R(TJ). Estrogen had no significant effect on the expression of E-Cadherin, zonula-occluden-1, or Claudin-4. In contrast, 17beta-estradiol modulated expression of the transmembrane tight-junctional protein occludin: at low concentrations (1 and 10 nm) estradiol increased the density of occludin 65-kDa form but at the higher concentration of 100 nm estradiol induced only a mild 2-fold increase in the density of this form. Estradiol also increased the expression of occludin 50-kDa form in a dose-related manner. The R(TJ) and occludin effects of estradiol were reversible and could be blocked by tamoxifen but not progesterone. The present results rule out estrogen modulation of occludin transcription. In contrast, the results suggest that the occludin effects of estrogen involve posttranslational up-regulation of occludin turnover, including synthesis and degradation. The effects of estrogen on occludin expression were compared with those of proteinase-K, plasmin, and matrix-metaloproteinase-2 (all added extracellularly). The three proteinases abrogated irreversibly the R(TJ) and induced expression de novo of occludin low-molecular-weight forms. The latter, however, differed from the effect of estrogen, which generated only a single 50-kDa form. Collectively, the present data suggest that the occludin 50-kDa form is an estrogen-specific-induced occludin isoform and that the mechanism of estrogen-abrogation of transcervical R(TJ) involves occludin modulation.