Abstract 2876: The androgen receptor utilizes protein kinase docking sites to constitutively activate Elk1

Abstract

The ETS domain transcription factor Elk1 tethers the androgen receptor (AR) to chromatin, enabling sustained activation of a set of genes critical for growth in established prostate cancer cell lines. This process does not entail the transient hyper-activation of immediate early genes typical of activation of Elk1 through phosphorylation by ERK1/2. We compared the structural requirements for the association of AR and Elk1 with that for activation of Elk1 by phosphorylation using mammalian one- and two-hybrid assays. The critical polypeptide segments were mapped by systematic deletion mutagenesis. The amino-terminal A/B domain of AR, which lacks the ligand-binding domain (LBD), was adequate for association with Elk1 and to activate Elk1-AR target genes in LNCaP prostate cancer cells. The AR A/B domain also supported hormone-independent growth of LNCaP cells reflecting the ability of overexpressed natural splice variants of AR, which also lack LBD, to support prostate tumor growth. The association of AR with Elk1 was optimal in the absence of ERK1/2 and serum response factor (SRF), which are the known binding partners of Elk1. We identified two sites on Elk1 that are critical for its association with the AR A/B domain as well as the whole AR molecule. One of those sites spans amino acid residues 307 to 330, overlapping the D box, which is one of two ERK docking sites. The other site on Elk1 mapped to amino acid residues 372 to 397, overlapping the FXFP motif, which comprises the downstream ERK docking site. The results suggest that AR utilizes ERK docking sites to associate with Elk1 and is exclusive of the interaction of Elk1 with ERK1/2 or SRF. A nuclear receptor could thus function as a transcription factor co-activator by binding at protein kinase docking sites. Citation Format: Rayna Rosati, Mugdha Patki, Selvakumar Dakshnamurthy, Venkatesh Chari, Thomas McFall, Manohar Ratnam. The androgen receptor utilizes protein kinase docking sites to constitutively activate Elk1. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2876.