Sex steroid receptors in skeletal differentiation and epithelial neoplasia: is tissue-specific intervention possible?

Sex steroids, through their receptors, have potent effects on the signal pathways involved in osteogenic or myogenic differentiation. However, a considerable segment of those signal pathways has a prominent role in epithelial neoplastic transformation. The capability to intervene locally has focused on specific ligands for the receptors. Nevertheless, many signals are mapped to interactions of steroid receptor motifs with heterologous regulatory proteins. Some of those proteins interact with the glucocorticoid receptor and other factors essential to cell fate. Interactions of steroid receptor domain motifs with heterologous proteins affect specific target pathways; consequently, manipulation of specified protein modules complexed with steroid receptors may be a next major step for enhancing molecular targeted therapeutics. In the future, intervention at specific sections of receptor primary sequence may prove therapeutically more efficient in targeting pathways of choice than ligand selectivity can be.

Organic cation transporter 3: Keeping the brake on extracellular serotonin in serotonin-transporter-deficient mice.

Mood disorders cause much suffering and are the single greatest cause of lost productivity worldwide. Although multiple medications, along with behavioral therapies, have proven effective for some individuals, millions of people lack an effective therapeutic option. A common serotonin (5-HT) transporter (5-HTT/SERT, SLC6A4) polymorphism is believed to confer lower 5-HTT expression in vivo and elevates risk for multiple mood disorders including anxiety, alcoholism, and major depression. Importantly, this variant is also associated with reduced responsiveness to selective 5-HT reuptake inhibitor antidepressants. We hypothesized that a reduced antidepressant response in individuals with a constitutive reduction in 5-HTT expression could arise because of the compensatory expression of other genes that inactivate 5-HT in the brain. A functionally upregulated alternate transporter for 5-HT may prevent extracellular 5-HT from rising to levels sufficiently high enough to trigger the adaptive neurochemical events necessary for therapeutic benefit. Here we demonstrate that expression of the organic cation transporter type 3 (OCT3, SLC22A3), which also transports 5-HT, is upregulated in the brains of mice with constitutively reduced 5-HTT expression. Moreover, the OCT blocker decynium-22 diminishes 5-HT clearance and exerts antidepressant-like effects in these mice but not in WT animals. OCT3 may be an important transporter mediating serotonergic signaling when 5-HTT expression or function is compromised.

Interleukin-10 regulated gene expression in cells of hypothalamic-pituitary-adrenal axis origin.

AIM: The hypothalamic-pituitary-adrenal (HPA) axis is a mediator for interactions between the immune and neuroendocrine systems. Pro-inflammatory cytokines such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) have been shown to activate the HPA axis. Recently, interleukin-10, an important anti-inflammatory cytokine in the immune system, has been shown to be expressed in the central nervous system and neuroendocrine system. Little is known, however, about IL-10's functions in the HPA axis. METHODS: The Affymetrix DNA microarray (mouse genome U74Av2 Probe Array) was conducted to determine the gene expression profile regulated by IL-10 in cells of HPA axis origin. RESULTS: In this study, we analyzed gene expression regulated by IL-10 in cells derived from the HPA axis. The results showed that quorums of genes are modulated by IL-10 in these neuroendocrine cells. CONCLUSIONS: These findings will provide a valuable repository to aid in understanding IL-10's functions in the HPA axis at the molecular level.

Serotonin regulation of serotonin uptake in RN46A cells.

AIM: The role of the serotonin transporter (SERT) is to remove serotonin (5-HT) from the synaptic space. In vitro studies have shown that 5-HT uptake via SERT is influenced by the availability of its substrate, 5-HT. We used RN46A cells, a line that expresses SERT, to investigate 5-HT regulation of 5-HT uptake and the intracellular signaling pathways involved. RN46A cells also express mRNAs for 5-HT receptors (5-HT(1A), 5-HT(1B), 5-HT(2A), and 5-HT(2C)) and as cAMP and intracellular Ca(2+) are modulated by different 5-HT receptors, we studied both pathways. METHODS: 5-HT uptake was determined as imipramine-inhibitable uptake of [(3)H]5-HT, intracellular cAMP was measured by RIA and intracellular Ca(2+) changes were determined using the ratiometric method of intracellular Ca(2+) imaging. RESULTS: For uptake experiments, cells were kept for 30 min either with or without 1 microM 5-HT in the medium before measuring uptake. Removal of 5-HT for 30 min significantly decreased [(3)H]5-HT uptake. The absence of 5-HT for 15 min failed to induce any changes in intracellular cAMP levels. Removal of 5-HT from the medium did not change intracellular Ca(2+) levels either; however, adding 1 microM 5-HT after 5 min in 5-HT-free conditions rapidly increased intracellular Ca(2+) levels in 50% of the cells. The remaining cells showed no changes in the intracellular Ca(2+) levels. CONCLUSIONS: We have shown that in RN46A cells, that endogenously express SERT and mRNAs for several 5-HT receptors, changes in 5-HT levels influence 5-HT uptake rate as well as induce changes in intracellular Ca(2+) levels. This suggests that 5-HT may utilize intracellular Ca(2+) to regulate 5-HT uptake.

Regulation of adrenal glucocorticoid synthesis by interleukin-10: a preponderance of IL-10 receptor in the adrenal zona fasciculata.

Several lines of evidence indicate that cytokines can affect adrenal function. To date most of these cytokines have been shown to be pro-inflammatory, such as interleukin (IL)-1, tumor necrosis factor (TNFalpha), and IL-6. However, we have previously shown that IL-10-/- (IL-10 knockout) mice have higher serum corticosterone levels than IL-10+/+ (wild type) mice following acute immune and physiologic stress, implying that IL-10, an anti-inflammatory cytokine, regulates glucocorticoid synthesis in a negative manner. Here, we show that IL-10 knockout mice produce more corticosterone under basal conditions as well (shown by ELISA). We further support this contention by showing that in Y-1 adrenocortical cells IL-10 inhibits steroid production (StAR) (measured by the production of the corticosterone precursor, progesterone), the expression of steroidogenic acute regulatory protein (semi-quantitative RT-PCR), as well as the activity of the proximal steroidogenic enzymes P450scc and/or 3beta-hydroxysteroid dehydrogenase (3beta-HSD) (measured by progesterone production in 22(R)-hydroxycholesterol-treated cells). Interestingly, all of the above-mentioned effects of IL-10 occur through its inhibition of ACTH effects, but not by IL-10 alone. Furthermore, immunocytochemistry data shows that the region of the adrenal gland responsible for the vast majority of corticosterone synthesis, the zona fasciculata, predominantly expresses the IL-10 receptor 1 (IL-10R1), with little expression in the zona glomerulosa and reticularis. These data demonstrate that IL-10 could play an important role in the regulation of glucocorticoid biosynthesis and in maintenance of homeostasis and immunity during periods of stress.

Intracellular signaling involved in estrogen regulation of serotonin reuptake.

17beta-estradiol (E2) regulates neuronal activity via genomic and rapid, non-genomic mechanisms. The rat serotonergic neuronal cell line (RN46A) was used to investigate the rapid effects of E2 on serotonin (5-HT) reuptake and on potential intracellular signaling pathways. RN46A cells express the serotonin transporter (SERT) and estrogen receptor (ER)beta, but not ERalpha. Fifteen minute E2 treatment (10(-9)M) decreased 5-HT uptake. Intracellular cAMP levels were not increased by 15 min E2 treatment; however, E2 caused an increase in intracellular Ca2+ levels, with a maximum response within the first minute. The response was E2 specific, since other steroids (17alpha-estradiol, testosterone, and progesterone) had no effect. The ER antagonist ICI 182,780 blocked the rapid E2 effects on intracellular Ca2+ levels as did the selective ER modulator tamoxifen. In summary, changes in intracellular Ca2+ levels caused by E2 and mediated through ERbeta may be responsible for observed rapid effects of E2 on SERT activity.

Selective estrogen receptor modulator effects in the rat brain.

The effects in the brain of selective estrogen receptor modulators (SERMs) such as tamoxifen and raloxifene have not yet been fully elucidated. Based upon the hypothesis that serotonin (5-HT)-steroid hormone interactions are important in mood regulation, we have compared six SERMs (tamoxifen, raloxifene, levormeloxifene, NNC 45-0781, NNC 45-0320, NNC 45-1506) with 17beta-estradiol (E(2)) in terms of their ability to regulate mRNA levels of estrogen receptor (ER)alpha, ER beta, 5-HT(1A) receptor, and 5-HT reuptake transporter (SERT) in the midbrain, amygdala, and hypothalamus of ovariectomized (OVX) rats. Female rats (n = 6/group, 8 groups total) were OVX and allowed to recover for 2 weeks. During the third post-OVX week, rats were injected subcutaneously with E(2) (0.1 mg/kg) or one of the SERMs (5 mg/kg) once per day for 7 days. Twenty-four hours after the last injection, tissue was collected for the determination of mRNA levels by ribonuclease protection assay (RPA). E(2) treatment significantly decreased mRNA levels for ER alpha, ER beta, and SERT in midbrain and ER alpha in hypothalamus. Tamoxifen increased ER beta mRNA levels in hypothalamus, while raloxifene increased ER beta mRNA levels in amygdala. NNC 45-0320 decreased ER alpha mRNA in hypothalamus and decreased ER beta mRNA in amygdala. These results suggest that while SERMs are not full estrogen receptor agonists in the brain, the agonist/antagonist profiles for individual SERMs may differ among brain areas. This raises the possibility of developing new SERMs for selective functions in specific brain areas.