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Determinants of coactivator LXXLL motif specificity in nuclear receptor transcriptional activation
E M McInerney1, D W Rose, S E Flynn
1Howard Hughes Medical Institute, Department and School of Medicine, University of California at San Diego, La Jolla, California 92093-0648 USA.
Abstract:
Ligand-dependent activation of gene transcription by nuclear receptors is dependent on the recruitment of coactivators, including a family of related NCoA/SRC factors, via a region containing three helical domains sharing an LXXLL core consensus sequence, referred to as LXDs. In this manuscript, we report receptor-specific differential utilization of LXXLL-containing motifs of the NCoA-1/SRC-1 coactivator. Whereas a single LXD is sufficient for activation by the estrogen receptor, different combinations of two, appropriately spaced, LXDs are required for actions of the thyroid hormone, retinoic acid, peroxisome proliferator-activated, or progesterone receptors. The specificity of LXD usage in the cell appears to be dictated, at least in part, by specific amino acids carboxy-terminal to the core LXXLL motif that may make differential contacts with helices 1 and 3 (or 3') in receptor ligand-binding domains. Intriguingly, distinct carboxy-terminal amino acids are required for PPARgamma activation in response to different ligands. Related LXXLL-containing motifs in NCoA-1/SRC-1 are also required for a functional interaction with CBP, potentially interacting with a hydrophobic binding pocket. Together, these data suggest that the LXXLL-containing motifs have evolved to serve overlapping roles that are likely to permit both receptor-specific and ligand-specific assembly of a coactivator complex, and that these recognition motifs underlie the recruitment of coactivator complexes required for nuclear receptor function.
Insights
Nuclear receptors utilize specific LXXLL motifs (LXDs) on coactivators like NCoA-1/SRC-1 for gene transcription. Different receptors require distinct LXD combinations, dictated by flanking amino acids, enabling precise coactivator complex assembly.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Nuclear receptors regulate gene transcription through coactivator recruitment.
- Coactivators, such as NCoA-1/SRC-1, possess LXXLL motifs (LXDs) crucial for this interaction.
- The precise usage of these LXDs varies among different nuclear receptors.
Purpose of the Study:
- To investigate the receptor-specific utilization of LXXLL motifs in the NCoA-1/SRC-1 coactivator.
- To understand how specific amino acids influence LXD recognition and coactivator complex assembly.
- To explore the role of LXDs in ligand-specific activation.
Main Methods:
- Analysis of LXXLL motif usage in NCoA-1/SRC-1 across different nuclear receptors.
- Investigating the impact of carboxy-terminal amino acids on LXD function.
- Assessing interactions with coactivator-associated proteins like CBP.
Main Results:
- Estrogen receptor requires a single LXD, while other receptors (thyroid hormone, retinoic acid, PPAR, progesterone) need specific LXD combinations.
- Carboxy-terminal amino acids flanking the LXXLL motif dictate receptor specificity.
- Distinct carboxy-terminal residues are essential for PPARgamma activation by different ligands.
- LXXLL motifs also mediate interaction with CBP.
Conclusions:
- LXXLL motifs in NCoA-1/SRC-1 exhibit differential usage, enabling receptor- and ligand-specific coactivator complex formation.
- These motifs are critical for nuclear receptor-mediated gene transcription.
- The findings provide insights into the molecular mechanisms of coactivator recruitment and specificity.