Female gender-specific inhibition of KCNQ1 channels and chloride secretion by 17beta-estradiol in rat distal colonic crypts

Membrane ERalpha-dependent activation of PKCalpha in endometrial cancer cells by estradiol

The purpose of this study was to investigate the role of the oestrogen receptor subtypes ERalpha and ERbeta in mediating the non-genomic effects of 17-beta-estradiol (E(2)) in two human endometrial cancer cell lines (RL95-2 and HEC-1A) expressing different levels of these receptor subtypes. Western blotting analysis using phosphorylation site-specific antibodies showed that physiological concentrations of E(2) rapidly (<20 min) activated PKCalpha, but not PKCdelta in the RL95-2 cell line. E(2) had no effect on PKCalpha or PKCdelta activity in the HEC-1A cell line and suppressed basal levels of PKA activity in both cell lines. PKCalpha activation coincided with its membrane translocation. ERalpha was detected in the RL95-2 cell line by Western blotting and RT-PCR but not in the HEC-1A cells, which did express ERbeta. A selective ERalpha agonist PPT had the same effect as E(2) on PKCalpha activation in the RL95-2 cells, but the selective ERbeta agonist DPN had no such effect. A 46kDa variant of ERalpha increased in abundance in the cell membrane within 20 min of E(2) treatment suggesting that ERalpha mediated the E(2) non-genomic effects on PKCalpha through the formation of a membrane associated signalling complex.

Hormonal regulation of cardiac KCNE2 gene expression

The KCNE2 gene encodes a single transmembrane domain protein that modulates a variety of K+ channel functions in various tissues. Here we show that cardiac KCNE2 transcript levels are approximately 10-fold upregulated at the end of pregnancy. This upregulation was mimicked by 17-beta estradiol but not by 5alpha-dihydrotestosterone treatments in ovariectomized mice. To investigate the mechanism of KCNE2 transcriptional regulation by estrogen, we experimentally identified KCNE2 transcription start sites, delineated its gene structure and characterized its promoter region. Estrogen treatment stimulated KCNE2 promoter activity in a dose-dependent manner and ICI 182,780 blocked estrogen stimulation. A direct genomic mechanism was demonstrated by (i) the loss of estrogen responsiveness in the presence of a DNA-binding domain mutant estrogen receptor alpha or mutant KCNE2 ERE and (ii) binding of ERalpha to the KCNE2 ERE. These findings show that a genomic mechanism of estrogen action alters KCNE2 expression, which may have important physiological implications.

Direct Binding and Activation of Protein Kinase C Isoforms by Aldosterone and 17β-Estradiol

Protein kinase C (PKC) is a signal transduction protein that has been proposed to mediate rapid responses to steroid hormones. Previously, we have shown aldosterone directly activates PKCα whereas 17β-estradiol activates PKCα and PKCδ; however, neither the binding to PKCs nor the mechanism of action has been established. To determine the domains of PKCα and PKCδ involved in binding of aldosterone and 17β-estradiol, glutathione S-transferase fusion recombinant PKCα and PKCδ mutants were used to perform in vitro binding assays with [3H]aldosterone and [3H]17β-estradiol. 17β-Estradiol bound both PKCα and PKCδ but failed to bind PKC mutants lacking a C2 domain. Similarly, aldosterone bound only PKCα and mutants containing C2 domains. Thus, the C2 domain is critical for binding of these hormones. Binding affinities for aldosterone and 17β-estradiol were between 0.5–1.0 nM. Aldosterone and 17β-estradiol competed for binding to PKCα, suggesting they share the same binding site. Phorbol 12,13-dybutyrate did not compete with hormone binding; furthermore, they have an additive effect on PKC activity. EC50 for activation of PKCα and PKCδ by aldosterone and 17β-estradiol was approximately 0.5 nM. Immunoblot analysis using a phospho-PKC antibody revealed that upon binding, PKCα and PKCδ undergo autophosphorylation with an EC50 in the 0.5–1.0 nm range. 17β-Estradiol activated PKCα and PKCδ in estrogen receptor-positive and -negative breast cancer cells (MCF-7 and HCC-38, respectively), suggesting estrogen receptor expression is not required for 17β-estradiol-induced PKC activation. The present results provide first evidence for direct binding and activation of PKCα and PKCδ by steroid hormones and the molecular mechanisms involved.