Oxidative stress increases A1 adenosine receptor expression by activating nuclear factor kappa B

Cisplatin up-regulates adenosine A(1) receptors in rat testes

Reactive oxygen species contribute to male infertility by reducing sperm function. Our laboratory has recently demonstrated that reactive oxygen species stimulate the expression of adenosine A(1) receptor which confers cytoprotection in a variety of tissues. Since the adenosine A(1) receptor is highly expressed in the testis, the goal of this study was to determine whether this testicular adenosine A(1) receptor could also be regulated in vivo by reactive oxygen species. Cisplatin, a chemotherapeutic agent shown to alter testicular function, was used to generate reactive oxygen species in vivo. Testes obtained from Sprague-Dawley rats treated with cisplatin (8 mg kg(-1)) demonstrate increased lipid peroxidation and induction of heat shock protein by day 3. In addition, radioligand binding and Western blotting studies indicate an increase in testicular adenosine A(1) receptor in these rats. Scatchard analysis of [3H]8-cyclopentyl-1,3-dipropylxanthine (DPCPX) binding data indicates a significant increase in adenosine A(1) receptor number (B(max)) from 309+/-77 to 540+/-69 fmol mg(-1) protein in the cisplatin-treated group. The respective equilibrium dissociation constants (K(d)s) were 3.2+/-1.5 and 3.0+/-0.7 nM for the control and cisplatin-treated groups, respectively. Northern blotting analysis of rat testicular poly (A)(+) RNA indicates two adenosine A(1) receptor transcripts migrating at 3.4 and 5.6 kb, whose combined levels were increased by 49.3+/-9.3% following cisplatin treatment. These results indicate that cisplatin enhances adenosine A(1) receptor expression in the rat testis, possibly through promotion of oxidative stress.

Dexamethasone stimulates human A1 adenosine receptor (A1AR) gene expression through multiple regulatory sites in promoter B

The expression of the human A1 adenosine receptor gene is controlled by two promoters, promoters A and B, and they are located 600 base pairs apart. The characteristics of the two promoters differ by the activity of expression, tissue specificity, and the potential regulatory elements around them. Promoter A is more active but its expression is observed only in selected tissues, whereas promoter B is constitutively expressed but at much reduced levels. In Chinese hamster ovary (CHO) cells transiently transfected with plasmids containing either promoter linked to a reporter gene, dexamethasone (dex) can stimulate (or enhance) the expression of promoter B much more effectively than that of promoter A. Mutation and deletion studies on plasmids containing promoter B have shown that the stimulation is mediated through multiple regulatory sites, including a serum response element, AP1, and TATA box. However, a single-glucocorticoid response element monomer-binding site between promoters A and B does not have significant contribution to dex-regulated expression. The interactions between glucocorticoid receptor (GR) and some regulatory sites are probably occurring via this protein (GR) interacting with other DNA-binding proteins because there is no GR DNA-binding sequence in the sites studied. The stimulation can be eliminated by mifepristone, an antagonist of GR, indicating the involvement of GR in gene regulation. In addition, dex treatment also stimulated the expression of A1 adenosine receptors in CHO cells transfected with the plasmids containing contiguous genomic sequences of promoter B or promoters A and B linked to the receptor-coding sequence. When promoter A is active and both promoter A and B are present in a construct, dex treatment induced a much smaller percentage of stimulation.