Regulation of the nuclear orphan receptor Nur77 in bone by parathyroid hormone

Osteoblasts function under the control of several hormones and growth factors. Among them, parathyroid hormone (PTH) and steroid hormones have significant effects on bone metabolism. We show that PTH induced the expression of Nur77, a member of the NGFI-B subfamily of nuclear orphan receptors in bone. PTH rapidly and transiently induced Nur77 mRNA in primary mouse osteoblasts that peaked at 1 h and at 10 nM of hormone. Cycloheximide did not affect the induction of Nur77 mRNA, suggesting that protein synthesis is not required for the PTH effect. PTH also induced Nur77 mRNA in calvariae cultures. Finally Nur77 protein expression was induced in nuclear protein extracts of cells treated with PTH. NGFI-B nuclear receptors have been implicated in retinoic acid, vitamin D, and thyroid hormone signaling. We propose that induction of NGFI-B nuclear orphan receptors represents a potential cross-talk mechanism between PTH and steroid hormone signaling to regulate bone metabolism.     

Role of proto-oncogenes in the regulation of proenkephalin mRNA expression induced by repeated nicotine injections in rat adrenal medulla

We have studied the effect of repeated systemic administrations of nicotine (3 mg/kg) at 30 min intervals on proenkephalin (proENK) mRNA level in rat adrenal gland. Northern blot analysis has shown that proENK mRNA expression was enhanced by repeated nicotine administrations. Additionally, repeated administrations of nicotine transiently induced the c-fos and c-jun mRNA levels after the first-third nicotine administration, and the c-fos and c-jun mRNA levels were returned to the basal level after the seventh administration of nicotine. c-Fos, c-Jun and Fra-2 protein levels were persistently increased until the seventh administration. The repeated nicotine administrations also elevated phospho-CREB without altering total CREB level in all tested groups. Immunohistochemical analysis showed that the increase of c-Fos and c-Jun proteins by repeated nicotine administrations is mostly medulla specific, while Fra-2 immuno reactivity was shown both in medulla and cortex. The repeated nicotine administrations enhanced the AP-1 and ENKCRE-2 DNA binding activities. Furthermore, the cross-competition studies revealed that the AP-1 proteins, rather than CREB, actively bind to ENKCRE-2 DNA domain. These results suggest that proENK mRNA expression induced by repeated nicotine administrations may be mediated by AP-1 proteins, such as c-Fos, c-Jun and Fra-2 rather than CREB via interacting to the ENKCRE-2 DNA binding domain in rat adrenal medulla.     

A novel pineal-specific product of the oligopeptide transporter PepT1 gene: circadian expression mediated by cAMP activation of an intronic promoter

The oligopeptide transporter 1, PepT1, is a member of the Slc15 family of 12 membrane-spanning domain transporters; PepT1 has proton/peptide cotransport activity and is selectively expressed in intestinal epithelial cells, where it is responsible for the nutritional absorption of di- and tri-peptides. Here, a novel PepT1 gene product has been identified in the rat pineal gland, termed pgPepT1. It encodes a 150-amino acid protein encompassing the C-terminal 3 membrane-spanning domains of intestinal PepT1 protein, with 3 additional N-terminal residues. Expression of pgPepT1 appears to be restricted to the pineal gland and follows a marked circadian pattern with >100-fold higher levels of mRNA occurring at night; this is accompanied by an accumulation of membrane-associated pgPepT1 protein ( approximately 16 kDa). The daily rhythm in pgPepT1 mRNA is regulated by the well described neural pathway that controls pineal melatonin production. This includes the retina, the circadian clock in the suprachiasmatic nucleus, central structures, and projections from the superior cervical ganglia; activation of this pathway results in the release of norepinephrine. Here it was found that pgPepT1 expression is mediated by a norepinephrine-->cyclic AMP mechanism that activates an alternative promoter located in intron 20 of the gene. pgPepT1 protein was found to have transporter-modulator activity; it could contribute to circadian changes in pineal function through this mechanism.     

Differential daily rhythms of melatonin in the pineal gland and gut of goldfish Carassius auratus in response to light

The objectives of this study were to test the effects of light on melatonin rhythms in the pineal gland and gut of goldfish Carassius auratus and to investigate whether melatonin function differed in these two tissues, which are photosensitive and non-photosensitive respectively. Rhythms were evaluated by measuring arylalkylamine N-acetyltransferase (AANAT2) and melatonin receptor 1 (MT-R1) mRNA expression and melatonin concentration in the pineal gland, gut (in vivo), and cell cultures of the two tissues (in vitro). Compared to control, pineal gland melatonin secretion was higher at night, whereas the 24-h dark and ophthalmectomy groups maintained higher AANAT2 and MT-R1 mRNA expression during the day. Melatonin levels and AANAT2 and MT-R1 mRNA expression in the gut were also the highest at night, but the 24-h light, dark, and ophthalmectomy groups did not significantly differ from control. Furthermore, we measured AANAT2 and MT-R1 mRNA expression in high temperature water (30 °C) to investigate differences in the antioxidant capacity of pineal gland vs. gut melatonin. Melatonin and H₂O₂ levels, as well as AANAT2 and MT-R1 mRNA expression, were all higher in the two tissues under thermal stress, compared with their levels at 22 °C. Taken together, our results suggest that light has no effect on melatonin patterns in the gut, which appears to exhibit its own circadian rhythm, but both gut and pineal gland melatonin exhibit similar antioxidant function.     

大鼠松果体Clock基因和芳烷脘N-乙酰基转移酶基因的昼夜节律性表达及光照影响

探讨12h光照、12h黑暗交替(12h-light：12h-dark cycle,LD)及持续黑暗(constant darkness,DD)光制下松果体Clock基因和芳烷脘N-乙酰基转移酶基因(arylalkylamine N-acetyltransferase gene,NAT)是否存在昼夜节律性表达及其光反应变化。Sprague-Dawley大鼠在LD和DD光制下分别被饲养4周(n=36)和8周(n=36)后,在一昼夜内每隔4h采集一组松果体组织(n=6),提取总RNA,用竞争性定量RT-PCR测定不同昼夜时点样品中Clock及NAT基因的mRNA相对表达量,通过余弦法和ClockLab软件获取节律参数,并经振幅检验是否存在昼夜节律。结果如下：(1)在DD或LD光制下,松果体Clock和NAT基因mRNA的表达均呈现夜高昼低的节律性振荡(P＜0．05)。(2)与DD光制下比较,LD光制下松果体Clock和NAT基因的表达振幅及峰值相的mRNA水平均降低(P＜0．05)。(3)在DD或LD光制下,Clock和NAT基因之间显示相似的节律性表达(P＞0．05)。结果表明,Clock和NAT基因在松果体中存在同步的内源性昼夜节律表达,光照作用可使其表达下调。