AR and ER interaction with a p21-activated kinase (PAK6)

Area of Science:

• Molecular Biology
• Cell Signaling
• Endocrinology

Background:

• p21-activated kinases (PAKs) are serine/threonine kinases involved in various cellular processes.
• Steroid hormone receptors, such as the androgen receptor (AR) and estrogen receptor alpha (ERα), regulate gene expression.
• Cdc42 and Rac are small GTPases that regulate the actin cytoskeleton and signaling pathways.

Purpose of the Study:

• To identify and characterize novel proteins that interact with the androgen receptor (AR).
• To investigate the functional consequences of AR interaction with p21-activated kinase 6 (PAK6).
• To explore the potential role of PAK6 in steroid hormone receptor signaling and tamoxifen effects.

Main Methods:

• Cloning and characterization of human PAK6.
• Co-immunoprecipitation and mammalian one-hybrid assays to study protein interactions.
• In vitro binding assays to map interaction domains.
• Transient transfection assays with reporter genes to assess transcriptional activity.
• Western blotting and RT-PCR to determine PAK6 expression levels.

Main Results:

• Human PAK6 was identified as an AR interacting protein with a conserved kinase domain.
• PAK6 bound to GTP-Cdc42 and weakly to GTP-Rac, but its kinase activity was not stimulated by these GTPases.
• PAK6 interacted with both AR and ERα, with binding to ERα enhanced by 4-hydroxytamoxifen.
• PAK6 inhibited AR and ERα transcriptional activities in reporter gene assays.
• PAK6 expression was highest in brain and testis, with lower levels in prostate and breast tissues.

Conclusions:

• PAK6 interacts with AR and ERα, suggesting a mechanism for cross-talk between steroid hormone receptors and Cdc42-mediated signaling.
• PAK6 inhibits the transcriptional activity of AR and ERα.
• PAK6 may play a role in the effects of tamoxifen in breast cancer and other tissues.