Transcriptional Effects of Estrogen on Neuronal Neurotensin Gene Expression Involve cAMP/Protein Kinase A-Dependent Signaling Mechanisms

Abstract

Steroid hormones exert dramatic effects on neuronal expression of genes that encode neuropeptides. Expression of the neurotensin/neuromedin (NT/N) gene in preoptic area neurons is dramatically enhanced by estrogen in vivo, even though its promoter lacks palindromic estrogen response elements. We report here that estrogen promotes transcription of this gene by interactions with the cAMP cascade in a neuronal cell line, SK-N-SH, and in a mouse model. In neuroblastoma cells, estrogen increases cAMP and the phosphorylation of the cAMP response element-binding protein in a time frame that precedes induction of NT/N gene transcription. Interference with the cAMP/protein kinase A signal transduction cascade blocks the ability of estrogen to elicit increases in transcription of this gene. Furthermore, in studies performed in vivo using mice deficient in protein kinase A, estrogen fails to induce increases in NT/N mRNA but retains its ability to promote estrogen response element-dependent progesterone receptor gene transcription. These data represent the first report of a nonclassical effect of estrogen on the expression of an endogenous estrogen-regulated neuropeptide gene through cAMPmediated mechanisms both in a neuroblastoma cell line and in hypothalamic neurons. More importantly, this "cross-talk" may represent a more generalized mechanism by which steroid hormones act through other signal transduction cascades to regulate the expression of other genes in the brain.

Genetic Analysis of the Hypothalamic Neurotensin System

“…The hypothalamus is a sexually dimorphic organ, and all of the included analyses were performed in males, thus the influence of gender on these QTL cannot be ascertained until the experiment is repeated in females. This is particularly critical for the NT system, as this system is known to be responsive to estrogen and to change predictably across the estrous cycle (Watters and Dorsa, 1998;Kinkead et al, 2000).…”

Pyruvate protects mitochondria from oxidative stress in human neuroblastoma SK-N-SH cells

“…SK-N-SH cells respond to numerous insults including β-amyloid, mitochondrial permeability transition, and serum deprivation, indicating that this cell line could be very useful in the assessment of neurotoxicity and neuroprotection [4]. SK-N-SH cells have been used by this and other laboratories [5,20,21,46,[48][49][50][51]56] as an in vitro model for studying potential neuroprotection mechanisms. Multiple mechanisms have been suggested to contribute to the cytoprotective effect of pyruvate.…”

Membrane-initiated estrogen signaling in hypothalamic neurons

“…For example, E2 binding to its known receptors or a novel membrane ER can upregulate cAMP in hypothalamic neurons by increasing adenylyl cyclase activity (Lagrange et al, 1997). Cyclic-AMP activates PKA, which in turn phosphorylates cAMP-responsive element binding protein (CREB) and elicits new gene transcription (Zhou et al, 1996, Watters and Dorsa, 1998, Abraham et al, 2004. Therefore, genes with CRE binding sites can be activated within a relatively short time course in neurons independent of estrogen receptors interacting with EREs.…”

“…Therefore, genes with CRE binding sites can be activated within a relatively short time course in neurons independent of estrogen receptors interacting with EREs. These actions of estrogen via pCREB result in activation of genes encoding neurotransmitters such as dopamine, enkephalin, dynorphin and neurotensin, which are all critical for hypothalamic function (Gu et al, 1996, Watters andDorsa, 1998). Moreover, in hypothalamic (mouse) GnRH neurons the rapid phosphorylation of CREB following E2 treatment is observed in ERα but not in ERβ knockout mice indicating a role for ERβ in the acute activation by pCREB in GnRH neurons (Abraham et al, 2003).…”