Oestrogen regulates the expression of cathepsin E-A-like gene through ERΒ in liver of chicken (Gallus gallus).

The cathepsin E-A-like, also known as 'similar to nothepsin', is a new member of the aspartic protease family, which may take part in processing of egg yolk macromolecules, due to it was identified in the chicken egg-yolk. Previously, studies have suggested that the expression of cathepsin E-A-like increased gradually during sexual maturation of pullets, but the exact regulation mechanism is poorly understood. In this study, to gain insight into the function and regulation mechanism of the gene in egg-laying hen, we cloned the cathepsin E-A-like gene and evaluated its evolutionary origin by using both phylogenetic and syntenic methods. The mode of the gene expression regulation was analysed through stimulating juvenile hens with 17β-estradiol and chicken embryo hepatocytes with 17β-estradiol combined with oestrogen receptor antagonists including MPP, ICI 182,780 and tamoxifen. Our results showed that cathepsin E-A-like was an orthologoues gene with nothepsin, which is present in birds but not in mammals. The expression of cathepsin E-A-like significantly increased in a dose-dependent manner after the juvenile hens were treated with 17β-estradiol (P < 0.05). Compared with the 17β-estradiol treatment group, the expression of cathepsin E-A-like was not significantly changed when the hepatocytes were treated with 17β-estradiol combined with MPP (P < 0.05). In contrast, compared with the 17β-estradiol combined with MPP treatment group, the expression of cathepsin E-A-like was significantly downregulated when the hepatocytes were treated with 17β-estradiol combined with tamoxifen or ICI 182,780 (P < 0.05). These results demonstrated that cathepsin E-A-like shared the same evolutionary origin with nothepsin. The expression of cathepsin E-A-like was regulated by oestrogen, and the regulative effect was predominantly mediated through ER-Β in liver of chicken.