Abstract
SF-1 is a key transcription factor for all steroidogenic genes. It up-regulates the expression of the steroidogenic Cyp11a1 gene in the adrenal in a pathway stimulated by cAMP through HIPK3-mediated JNK/c-Jun phosphorylation. In the present study, we have investigated the factors mediating cAMP-dependent HIPK3 action to potentiate the activity of SF-1 for Cyp11a1 transcription in mouse adrenocortical Y1 cells. We found Daxx, a HIPK kinase substrate in the apoptosis pathway, was phosphorylated by HIPK3 at Ser-669 in response to cAMP stimulation. Daxx participated in SF-1-dependent Cyp11a1 expression as shown by experiments involving both overexpression and down-regulation via a dominant negative Daxx mutant. The S669A mutant of Daxx, which could not be phosphorylated by HIPK3, lost the ability to potentiate SF-1 activity for Cyp11a1 expression. The enhancement of SF-1 activity by Daxx required JNK and c-Jun phosphorylation. Thus, Daxx functioned as a signal transducer linking cAMP-stimulated HIPK3 activity with JNK/c-Jun phosphorylation and SF-1-dependent Cyp11a1 transcription for steroid synthesis.
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