12-O-TETRADECANOYL-PHORBOL-13-ACETATE-INDUCED RAT EMBRYO MALFORMATIONS IN-VITRO ARE ASSOCIATED WITH AN INCREASED RELATIVE ABUNDANCE OF EMBRYONIC E-CADHERIN MESSENGER-RNA

Epithelial-cadherin (E-cadherin) is a member of a family of Ca2+-depen dent cell adhesion molecules which are localized in zonulae adherens a nd play an important role during development. E-cadherin is abundant i n rat embryos and their yolk sacs during organogenesis. The phorbol es ter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), has been reported to disrupt the morphology and functional development of the rat embryoni c visceral yolk sac. The present study investigated the possibility th at the effect of TPA on yolk soc development may be due to the altered expression of E-cadherin. Rat embryos, with their yolk sacs intact, w ere cultured on day 10 of gestation for 1 hr. At this time the vehicle , dimethyl sulfoxide (DMSO), pr TPA (at different concentrations) was added to the culture medium; the cultures were continued for up to 24 hr. Embryos and yolk sacs were collected separately at the end of each culture period. The relative abundances of E-cadherin mRNA and protei n were analyzed with Northern and Western blot analyses. Despite the T PA-induced abnormalities in yolk sac development, the relative abundan ce of E-cadherin mRNA or protein in the yolk sac was not altered by TP A exposure. However, in embryos exposed to dysmorphogenic concentratio ns of TPA; the relative abundance of E-cadherin mRNA was significantly increased after 24 hr in culture, compared to either controls or embr yos exposed to non-dysmorphogenic concentrations of TPA. The magnitude of the increase in embryonic E-cadherin mRNA appeared to correlate wi th the severity of the embryo malformations. interestingly, despite th is increase in embryonic E-cadherin mRNA abundance, no increase in E-c adherin protein concentrations was found in the embryo. The timing of the increased relative abundance of E-cadherin mRNA in TPA-exposed mal formed embryos would suggest an indirect relationship with the embryo malformations observed. Activation of protein kinase C is likely to be involved in both the embryotoxic effects of TPA and the induction of increased concentrations of E-cadherin mRNA in the embryo since 4 alph a-phorbol-12,13-didecanoate (4 alpha-PDD), a phorbol ester analog whic h does not activate protein kinase C, had no effect. This study demons trates that TPA-induced embryo malformations are associated with an in creased abundance of E-cadherin mRNA in the embryo, but not in the yol k sac, and that these actions of TPA depend on the activation; of prot ein kinase C. (C) 1994 Wiiey-Liss, Inc.