Alterations of signal transduction pathways involved in 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced malignant transformation of human cells in culture

2,3,7,8-tetrachlorodibenzo-p-dioxin potentially attenuates the gene expression of pituitary gonadotropin β-subunits in a fetal age-specific fashion: a comparative study using cultured pituitaries

Our previous studies have demonstrated that maternal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) causes a reduction in gonadotropin biosynthesis in the fetal pituitary, resulting in the attenuated expression of steroidogenic proteins in the fetal gonads and the impairment of sexual behaviors in adulthood. However, the mechanism of the attenuation remains unknown. To address this issue, we investigated whether TCDD affects the pituitary production of gonadotropins, using cultured pituitary. In the absence of gonadotropin-releasing hormone (GnRH), a regulator of gonadotropin biosynthesis, TCDD did not affect the expression of gonadotropin mRNAs both in fetal and postnatal pituitaries. On the other hand, in the presence of GnRH, TCDD interfered with the synthesis of gonadotropin β-subunit mRNAs only in the fetal pituitary. A protein kinase C (PKC) activator (phorbol 12-myristate 13-acetate) and a PKA activator (8-bromoadenosine-3' 5'-cyclic monophosphate) induced the expression of gonadotropin mRNAs in the fetal pituitary. Among the subunits, only the induction of β-subunit was reduced by TCDD treatment. These results suggest that TCDD reduces gonadotropin biosynthesis via damage to GnRH-stimulated PKC and PKA signaling in a β-subunit- and fetal age-specific manner.

Protein kinase C delta is activated in mouse ovarian surface epithelial cancer cells by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Interactions between the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and protein kinase C (PKC) signaling pathways are governed in cell and tissue-specific manners, albeit the physiological significance of which is unclear. This research sought to define the effects of TCDD on the PKC pathway using a mouse ovarian surface epithelial cancer cell line (ID8). Phorbol-12-myristate-13-acetate (PMA) potentiated (1 nM) TCDD-induced 7-ethoxyresorufin-O-deethylase (EROD) activity after 24h of treatment, and pre-treatment with (1 microM) of either a general PKC inhibitor (BisI) or PKCdelta-specific inhibitor (Rotterlin) abolished the potentiation indicating that activation of PKC enhances TCDD signal transduction. Western blot analysis revealed that unstimulated ID8 cells express PKCalpha, beta, epsilon, tau, lambda and RACK1. PKCgamma, eta, theta and DGKtheta were not detected. TCDD (1 nM) increased PKCdelta protein approximately eight-fold after 24h of treatment and this effect was dose-dependent (0.1-100 nM); other PKC isoforms and related signaling proteins tested were unaffected by TCDD treatment. Immunofluorescent microscopy revealed that TCDD (1 nM) promoted the subcellular redistribution of PKCdelta, from the cytoplasm and the nucleus to the perinuclear area after 2h of treatment, however, after 24h of treatment PKCdelta was observed in nuclear structures that resembled nucleoli. TCDD (1 nM) also increased total PKC and PKCdelta-specific kinase activities in biphasic time-responsive manners. Total PKC and PKCdelta-specific activities increased after 1-2h of treatment. Then TCDD increased the total PKC activity again after 12h of treatment, whereas, PKCdelta-specific activity resurged at 24h and remained elevated at 48 h after treatment. The results indicate that TCDD preferentially induces PKCdelta protein expression and phosphotransferase activity, and its membrane translocation, indicating a potential intracellular role for PKCdelta as an effector molecule for TCDD-mediated biological events in this ovarian cancer cell line.