Nuclear Structures Regulate Liver-Specific Expression of the Tryptophan Oxygenase Gene

The gene for tryptophan oxygenase (TO) is expressed in a tissue- and development-specific manner and is regulated by glucocorticoid hormone in rat liver. Transcription of the gene is induced 10-fold by glucocorticoids. The TO promoter has two glucocorticoid-responsive elements (GRE), located 450 bp and 1.2 kb Upstream from the cap site, and two TATA boxes. Combination of nuclear fractionation and quantitative PCR analysis showed that a putative matrix attachment region, which resides 8.5 kb upstream of the promoter, bound to nuclear matrix in the hormone-treated adult hepatocytes. However, this DNA region was partly released from the nuclear matrix by removing the hormone. These results indicated that binding of MAR to nuclear matrix was also important for regulation of the TO gene expression.