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A signature motif in transcriptional co-activators mediates binding to nuclear receptors
D M Heery1, E Kalkhoven, S Hoare
1Molecular Endocrinology Laboratory, Imperial Cancer Research Fund, London, UK.
Abstract:
The binding of lipophilic hormones, retinoids and vitamins to members of the nuclear-receptor superfamily modifies the DNA-binding and transcriptional properties of these receptors, resulting in the activation or repression of target genes. Ligand binding induces conformational changes in nuclear receptors and promotes their association with a diverse group of nuclear proteins, including SRC-1/p160, TIF-2/GRIP-1 and CBP/p300 which function as co-activators of transcription, and RIP-140, TIF-1 and TRIP-1/SUG-1 whose functions are unclear. Here we report that a short sequence motif LXXLL (where L is leucine and X is any amino acid) present in RIP-140, SRC-1 and CBP is necessary and sufficient to mediate the binding of these proteins to liganded nuclear receptors. We show that the ability of SRC-1 to bind the oestrogen receptor and enhance its transcriptional activity is dependent upon the integrity of the LXXLL motifs and on key hydrophobic residues in a conserved helix (helix 12) of the oestrogen receptor that are required for its ligand-induced activation function. We propose that the LXXLL motif is a signature sequence that facilitates the interaction of different proteins with nuclear receptors, and is thus a defining feature of a new family of nuclear proteins.
Insights
A newly identified LXXLL motif is crucial for nuclear receptor interactions. This sequence facilitates the binding of nuclear proteins like SRC-1 to activated nuclear receptors, influencing gene transcription.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Nuclear receptors bind lipophilic molecules, regulating gene expression.
- Ligand binding causes conformational changes, recruiting nuclear proteins.
- Proteins like SRC-1 and RIP-140 interact with nuclear receptors, but their roles are not fully understood.
Purpose of the Study:
- To identify the molecular basis for the interaction between nuclear receptors and associated nuclear proteins.
- To investigate the role of specific sequence motifs in mediating these interactions.
Main Methods:
- Sequence analysis to identify conserved motifs.
- Co-immunoprecipitation assays to study protein-ligand interactions.
- Reporter gene assays to assess transcriptional activity.
Main Results:
- A conserved LXXLL motif was identified in nuclear proteins RIP-140, SRC-1, and CBP.
- This LXXLL motif is necessary and sufficient for binding to liganded nuclear receptors.
- SRC-1's interaction with the oestrogen receptor and transcriptional enhancement depend on LXXLL motifs and helix 12.
Conclusions:
- The LXXLL motif acts as a molecular signature for nuclear receptor interaction.
- This motif facilitates the recruitment of diverse nuclear proteins, including coactivators and other factors.
- A new family of nuclear proteins defined by the LXXLL motif is proposed.