Biomedical subjects

Taijiro Okabe

Publications and source records attributed to Taijiro Okabe.

25 records · Page 2Linked to original sources

PubMed2003

Protein kinase A potentiates adrenal 4 binding protein/steroidogenic factor 1 transactivation by reintegrating the subcellular dynamic interactions of the nuclear receptor with its cofactors, general control nonderepressed-5/transformation/transcription domain-associated protein, and suppressor, dosage-sensitive sex reversal-1: a laser confocal imaging study in living KGN cells.

The mechanism through which protein kinase A (PKA) potentiates the transactivation ability of adrenal 4 binding protein/steroidogenic factor 1 (Ad4BP/SF-1) is currently unclear. In the present study, we investigated the mechanism by applying laser confocal microscopy and fluorescence recovery after photobleaching technique. In KGN cells, forskolin (a PKA stimulator) could reorganize wild-type Ad4BP/SF-1, but not mutant Ad4BP/SF-1 (G35E), from a diffuse distribution pattern to foci formation in the nucleus. The subcellular distributions of GCN5 (general control nonderepressed) and TRRAP (transformation/transcription domain-associated protein), both of which were recently proved to be working in the same complex as the third class of nuclear receptor coactivators, were unexpectedly diffuse inside and outside the nucleus, respectively, when they were separately transfected. However TRRAP was translocated into the nucleus in the presence of GCN5, and together with GCN5 colocalized with Ad4BP/SF-1 in the same foci when PKA was activated. A luciferase assay also indicated that these two cofactors enhanced Ad4BP/SF-1 transactivation.Dosage-sensitive sex reversal (DAX-1) interacts with and thus inhibits Ad4BP/SF-1 transactivation. The coexistence of the two proteins dramatically altered their respective subnuclear distributions. They colocalized extensively, suggestive of binding, and Ad4BP/SF-1 was sharply immobilized when DAX-1 was coexpressed, whereas PKA could maintain mobility, as evidenced by Fluorescence Recovery After Photobleaching showing that Ad4BP/SF-1 mobility recovered after forskolin treatment.Therefore, the PKA signal pathway may modify the interaction between Ad4BP/SF-1 and its activators and repressor (GCN5 and TRRAP are integrated, whereas DAX-1 is disassociated), and thus stimulate the Ad4BP/SF-1 transactivation.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Activation function-1 domain of androgen receptor contributes to the interaction between two distinct subnuclear compartments.

The nucleus contains different sets of functional compartments often called "speckles". The splicing factor compartment (SFC) has been speculated to consist of SFs and transcription factors, which thus make transcription-splicing coupling possible at the periphery of SFC. Androgen receptor (AR), as well as glucocorticoid receptor (GR), is unique since most, if not all, of its activities are mediated via the constitutive activity of the activation function-1 (AF-1) function. Transcriptionally active AR produces 250-400 subnuclear fine speckles11 shared with GR or estrogen receptor (ER), which colocalize with chiefly activation function-2 (AF-2)-interacting p160 family- or CBP-related speckles. We herein report the isolation of ANT-1 (AR N-terminal domain (NTD) transactivating protein-1) enhancing autonomous AF-1 transactivation function of AR or GR, but not of estrogen receptor alpha (ERalpha). The ANT-1 was identical to a binding protein of human splicing factor U5 snRNP (U5 snRNP-associated protein). ANT-1 was compartmentalized into 15-20 coarse SFC speckles which were spatially distinct from but surrounded by the AR compartments. Our results suggest that ANT-1 may play a key role in the molecular interaction between two spatially distinct subnuclear compartments in a receptor-specific fashion, and thereby induce the strong autonomous transactivation functions either of AR- or GR-AF-1.

Binding Sites↗

PubMed2003

Aromatase in bone: roles of Vitamin D3 and androgens.

We have mainly focused on the regulatory mechanism of cytochrome P450 aromatize in bone cells. Our previous study demonstrated a strong positive correlation of serum dehydroepiandrosterone sulfate (DHEA-S) and estrone (E1) with BMD in postmenopausal women but no correlation between serum estradiol (E2) and BMD in the same group. In addition, administration of DHEA to ovariectomized rat significantly increased BMD. These in vivo findings strongly suggested that circulating adrenal androgen may be converted to estrogen in osteoblast and may contribute to BMD maintenance. Actually, in cultured human osteoblast cells, DHEA was found to convert to androstenedione by 3beta-hydroxysteroid dehydrogenase (3beta-HSD) activity and then androstenedione to estrone through the apparent aromatase activity. The aromatase activity in cultured human osteoblast cells was significantly increased by dexamethasone (DEX). Interestingly, DEX and 1alpha,25-dihydroxyvitamin D3 (VD3) synergistically enhanced aromatase activity as well as P450arom mRNA expression. A little stronger induction of aromatase activity by DEX and VD3 was observed in cultured human fibroblasts. The increase of the aromatase activity by DEX and VD3 was accompanied with the increase of luciferase activity of fibroblast cells transfected with Exon 1b-promoter-luciferase construct, but not of osteoblasts transfected with the same construct, suggesting a different regulatory mechanism of aromatase by DEX and 1alpha,25-dihydroxyvitamin D3 (VD3) between these two cells despite the same promotor usage. In human bone cells, intracrine mechanism through aromatase activity, together with a positive regulation of aromatase activity by glucocorticoid and VD3, may contribute to the local production of estrogens, thus leading to protective effect against osteoporosis especially after menopause. The effect of sex steroids (estrogen versus testosterone) in bone remodeling was also briefly reviewed based on several recent findings in this field.

Androgens↗

PubMed2003

Activin signaling through type IB activin receptor stimulates aromatase activity in the ovarian granulosa cell-like human granulosa (KGN) cells.

In addition to a stimulatory effect on FSH production by the pituitary gland, activin is thought to have a paracrine or autocrine role in follicular development in the ovary, where it is produced. Recently, we established a human ovarian granulosa tumor cell line, KGN, which possesses in vivo characteristics of granulosa cells, namely the expression of functional FSH receptors and cytochrome P-450 aromatase. Here, we have demonstrated the activin signaling pathway and its role in KGN cells. A series of transient transfection experiments revealed that activin type IB receptor (ActRIB) is an essential component of the activin signaling pathway in KGN cells. Smad2 was found to act downstream of ActRIB as an intracellular signal transmitter. Smad7, but not Smad6, was an inhibitory Smad in the pathway. Finally, we show that FSH receptor expression and cytochrome P-450 (P-450) aromatase activity was up-regulated by activin stimulation through ActRIB in KGN cells. These results show that we have clarified the signaling mechanisms and the roles of activin in the human granulosa cell line, KGN. Activin signaling mediated by ActRIB-Smad2 system in the ovary may thus be essential for the regulation of follicular differentiation.

Activin Receptors, Type I↗

PubMed2003

[Trials of regeneration and gene therapies in endocrine organs, especially in adrenal glands].

Recent progress in trials of regeneration and gene therapy in endocrine organs, especially in adrenal glands has been reviewed. Gene therapies using adenovirus have been most frequently tested in vivo and in vitro, aiming at improvement of steroidogenesis and suppression of adrenal tumor growth. Although the effects were temporal, promising results have been obtained. Interestingly, adrenocortical tissue was shown to be formed by transplantation of adrenocortical cells and to replace the adrenal functions of adrenalectomized animals. Engineered ES cells stably expressing Ad4BP/SF-1 were shown to be directed toward steroidogenic lineage, suggesting a future possibility of regeneration of adrenal cells.

Adenoviridae↗

PubMed2002

Activation function-1 domain of androgen receptor contributes to the interaction between subnuclear splicing factor compartment and nuclear receptor compartment. Identification of the p102 U5 small nuclear ribonucleoprotein particle-binding protein as a coactivator for the receptor.

In the androgen receptor (AR), most of its transactivation activity is mediated via the activation function-1 (AF-1). By employing yeast two-hybrid assay, we isolated a cDNA sequence encoding a protein binding to AR-AF-1. This protein, named ANT-1 (AR N-terminal domain transactivating protein-1), enhanced the ligand-independent autonomous AF-1 transactivation function of AR or glucocorticoid receptor but did not enhance that of estrogen receptor alpha. In contrast, the ANT-1 did not enhance any ligand-dependent AF-2 activities. Furthermore, the ligand-independent interaction between AR-AF-1 and ANT-1 was confirmed in vivo and in vitro. The ANT-1 sequence was identical to that of a protein that binds to U5 small nuclear ribonucleoprotein particle, a human homologue of yeast splicing factor Prp6p, involved in spliceosome. ANT-1 was compartmentalized into 20-40 coarse splicing factor compartment speckles against the background of the diffuse reticular distribution. AR colocalized with ANT-1 only in the diffusely distributed area, whereas the ANT-1 speckles were spatially distinct from but surrounded by the AR compartments. The active gene transcription has been shown to couple simultaneously with pre-mRNA processing at the periphery of the splicing factor compartment. The molecular interaction between two spatially distinct subnuclear compartments mediated by ANT-1 may therefore recruit AR into the transcription-splicing-coupling machinery.

Animals↗

PubMed2002

Mechanism of action of anti-aging DHEA-S and the replacement of DHEA-S.

The plasma ACTH and cortisol levels do not change during aging. On the other hand, the plasma dehydroepiandrosterone sulfate (DHEA-S) changes remarkably during aging. Before puberty, the plasma DHEA-S level both in males and females is very low, however, it rapidly increases at puberty, and thereafter significantly decreases both linearly and age-dependently. Cytochrome P450c17 has two enzyme activities, 17-alpha-hydroxylase and 17,20-lyase. Cortisol is synthesized by 17-alpha-hydroxylase, and DHEA is synthesized by 17,20-lyase. The mechanism of dissociation of cortisol and DHEA synthesis in aging depends on another regulator of 17,20-lyase of cytochrome P450c17 such as cytochrome P450 reductase. We demonstrated significant decrease in cytochrome P450 reductase activity in bovine aged adrenal glands. We clarified the beneficial effects of DHEA as an anti-aging steroid based on both in vitro and in vivo experiments, such as the stimulatory effect of immune system, anti-diabetes mellitus, anti-atherosclerosis, anti-dementia (neurosteroid), anti-obesity and anti-osteoporosis. It is very important to identify the mechanism of action of DHEA. We clarified the conversion of DHEA to estrone by cytochrome P450 aromatase in primary cultured human osteoblasts. We indentified high affinity of DHEA binding with K(d)=6.6 nM in antigen and DHEA stimulated human T lymphocytes. We searched for the target genes that are specifically induced in activated T lymphocytes in the presence of DHEA by subtractive hybridization screening for differentially expressed transcripts. The double blind, randomized human replacement therapies utilizing DHEA are also reviewed.

Aging↗