Regulators for the rat clusterin gene: DNA methylation and cis-acting regulatory elements.
Clusterin, also known as sulphated glycoprotein-2 or testosterone-repressed prostate message-2, is a ubiquitous protein found in a variety of tissues and species. In the reproductive tract of the male rat, clusterin is regulated in a complex age-dependent and cell-specific manner. It is expressed at high levels in the epididymis and testis and at very low levels in the prostate under basal conditions. The expression of this gene in the prostate and seminal vesicles is associated with androgen withdrawal, while in the testis clusterin mRNA is repressed by cyclic AMP (cAMP). To understand the mechanisms that control the expression of the clusterin gene better, we isolated and characterized the gene encoding rat clusterin, and analysed its cytosine methylation pattern in various tissues. Several putative regulatory DNA elements were identified, including a consensus AP-1 site in the 5' flanking region. Two AP-1 sites and two transforming growth factor-beta inhibitory elements, one AP-2 site and eight half-sites for glucocorticoid/androgen response elements were found within the first intron, and one cAMP response element was found in the first exon. The cytosine methylation pattern indicated that testicular or epididymal DNA in the rat is hypomethylated in the region between positions -534 and -99 of the clusterin gene, when compared with tissues with lower levels of expression such as prostate as well as liver, lung, kidney and spleen.