Molecular mechanism for the potentiation of the transcriptional activity of human liver receptor homolog 1 by steroid receptor coactivator-1.
The liver receptor homolog 1 ( LRH-1) belongs to the Fushi tarazu factor 1 nuclear receptor subfamily, and its biological functions are just being unveiled. The molecular mechanism for the transcriptional regulation by LRH-1 is not clear yet. In this report, we use mutagenesis and reporter gene assays to carry out a detailed analysis on the hinge region and the proximal ligand binding domain (LBD) of human (h) LRH-1 that possess important regulatory functions. Our results indicate that helix 1 of the LBD is essential for the activity of hLRH-1 and that the steroid receptor coactivator (SRC)-1 interacts directly with the LBD of hLRH-1 and significantly potentiates the transcriptional activity of hLRH-1. Cotransfection assays demonstrate that overexpressed SRC-1 potentiates hLRH-1 mediated activation of the cholesterol 7-alpha-hydroxylase promoter and increases the transcription of the endogenous cholesterol 7-alpha-hydroxylase in Huh7 cells. The interaction between SRC-1 and hLRH-1 assumes a unique pattern that involves primarily a region containing the glutamine-rich domain of SRC-1, and helix 1 and activation function-2 of hLRH-1 LBD. Mutagenesis and molecular modeling studies indicate that, similar to mouse LRH-1, the coactivator-binding cleft of hLRH-1 LBD is not optimized. An interaction between helix 1 of hLRH-1 LBD and a region containing the glutamine-rich domain of SRC-1 can provide an additional stabilizing force and enhances the recruitment of SRC-1. Similar interaction is observed between hLRH-1 and SRC-2/ transcriptional intermediary factor 2 or SRC-3/acetyltransferase. Moreover, transcriptional intermediary factor 2 and acetyltransferase also potentiate the transcriptional activity of hLRH-1, suggesting a functional redundancy among SRC family members. These findings collectively demonstrate an important functional role of helix 1 in cofactor recruitment and reveal a novel molecular mechanism of transcriptional regulation and cofactor recruitment mediated by hLRH-1.[1]References
- Molecular mechanism for the potentiation of the transcriptional activity of human liver receptor homolog 1 by steroid receptor coactivator-1. Xu, P.L., Liu, Y.Q., Shan, S.F., Kong, Y.Y., Zhou, Q., Li, M., Ding, J.P., Xie, Y.H., Wang, Y. Mol. Endocrinol. (2004) [Pubmed]
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