Dynamics of activity of intracellular cysteine-dependent proteases and some peptidases in embryogenesis of Atlantic salmon Salmo salar L.
A PCR-based cDNA subtraction hybridization was performed to identify the genes stimulated by estrogen in the pituitary. A novel tissue-specific calpain (nCL-2'), previously shown to be expressed mainly in the stomach, was markedly induced in the pituitary after estrogen treatment. The 5'-flanking region of the calpain nCL-2' gene was analyzed to assess the molecular mechanism of estrogen regulation. Sequence analysis of the nCL-2' promoter (1.9 kb) revealed a perfectly palindromic putative estrogen-response element (ERE), GGTCATGCTGACC. In transient transfection studies, the nCL-2' promoter was highly responsive to estrogen in the presence of estrogen receptor (ER). Transcriptional activation by estrogen was prevented by an ERE mutation as well as by mutations in the ER DNA-binding domain. An ER antagonist, ICI 182780, blocked estrogen inducibility of the nCL-2' promoter. We conclude that the nCL-2' form of calpain is expressed in the pituitary and upregulated by estrogen at the transcription level.