Structural features discriminate androgen receptor N/C terminal and coactivator interactions

Area of Science:

• Molecular Biology
• Structural Biology
• Endocrinology

Background:

• Androgen receptor (AR) transcriptional activity relies on interactions between its amino- and carboxyl-termini, particularly involving the ligand binding domain (LBD).
• Previous studies elucidated structural aspects of the interaction between the AR NH2-terminal FXXLF motif and activation function 2 (AF2) within the LBD.

Purpose of the Study:

• To investigate the role of AR LBD helix 12 residues outside the AF2 binding cleft in mediating interactions with FXXLF and LXXLL motifs.
• To understand the functional consequences of mutations in helix 12 on AR transcriptional activity and androgen binding.

Main Methods:

• Site-directed mutagenesis of AR LBD helix 12 (e.g., Q902A).
• Assays to measure FXXLF and LXXLL motif binding to the AR LBD.
• Androgen binding and dissociation rate measurements.
• Assessment of AR transcriptional activity.

Main Results:

• Mutagenesis of glutamine 902 (Q902A) disrupted FXXLF motif binding but enhanced LXXLL motif binding.
• The Q902A mutation slowed androgen dissociation, suggesting functional compensation.
• Germline (Q902R) and somatic (Q902K) mutations at position 902 increased androgen dissociation and decreased transcriptional activity.
• Mutations at Tyr-739 and Lys-905 affected transcriptional activity and androgen dissociation, with rescue by the H874Y mutation.
• The N-terminal sequence adjacent to the FXXLF motif influences AR NH2- and carboxyl-terminal interactions.

Conclusions:

• AR LBD helix 12 residues outside the AF2 cleft are critical modulators of AR transcriptional activity.
• These residues provide conformational flexibility, enabling accommodation of both FXXLF and LXXLL motifs.
• Mutations in helix 12 can alter androgen sensitivity and are implicated in conditions like partial androgen insensitivity and prostate cancer.