Cyclin D1 Binding to the Androgen Receptor (AR) NH2-Terminal Domain Inhibits Activation Function 2 Association and Reveals Dual Roles for AR Corepression

Abstract

The androgen receptor (AR) is a member of the nuclear receptor superfamily, the activity of which is critical for the development and progression of prostate cancer. We and others have previously demonstrated that cyclin D1 is a potent corepressor of the AR. Although cyclin D1 is suspected to recruit histone deacetylases to the AR complex, previous studies have demonstrated that this activity alone is insufficient for cyclin D1 function. Here, we uncover a novel, secondary means of cyclin D1-mediated repression, through modulation of AR amino-carboxy terminal interactions. We show that cyclin D1 predominantly binds the N-terminal domain of the AR, dependent on the AR 23FxxLF27 motif. Through this motif, cyclin D1 abrogates the ability of the AR N-terminal domain to interact with the C terminus. Secondary amino-terminal domain sites capable of fostering interaction with the C terminus were refractory to cyclin D1 action, indicating that the ability of cyclin D1 to modulate AR amino-carboxy terminal interactions is specific to 23FxxLF27. Deletion of the N-terminal cyclin D1 binding site severely compromised AR activity (due to loss of FxxLF) but unmasked a repressor action through interaction with the AR C terminus. In summary, these data reveal novel, unexpected mechanisms of cyclin D1 activity and demonstrate that this function of cyclin D1 is critical for AR modulation.

Cyclin D1: polymorphism, aberrant splicing and cancer risk

“…Specifically, cyclin D1 has been shown to regulate a number of sequence-specific transcription factors, including C/EBPb (Lamb et al, 2003), STAT3 (Bienvenu et al, 2001), DMP1 (Inoue and Sherr, 1998), and BETA2/NeuroD (Ratineau et al, 2002). The largest class of transcription factors regulated by cyclin D1 belong to the nuclear receptor superfamily, and include the estrogen receptor (Zwijsen et al, 1998;Lamb et al, 2000), androgen receptor (Knudsen et al, 1999;Reutens et al, 2001;Petre et al, 2002;Burd et al, 2005), thyroid hormone receptor (Pibiri et al, 2001), and peroxisome proliferator activated receptor-g (Qin et al, 2003). In many cases cyclin D1 was shown to directly associate with the transcription factors, independent of CDK4 association, and modify transcription factor action through cell-cycle independent mechanisms.…”

Cyclin D3 action in androgen receptor regulation and prostate cancer

“…Given the capacity of cyclin D3 to bind AR, functional studies were performed. To determine if cyclin D3 alters the requisitive intramolecular interactions of AR that occur after ligand binding (N-Cterminal interaction) (He et al, 2000;Li et al, 2007), a well-characterized mammalian two-hybrid assay was utilized (Lim et al, 2000;Burd et al, 2005) where luciferase activity from the Gal4 promoter provided a readout of AR N-C-terminal interaction. Introduction of cyclin D3 resulted in approximately a 75% reduction in N-C-terminal interaction (Figure 3c).…”

“…These mechanisms include abrogation of AR N-Cterminal interaction and require HDAC function. Both modes are required for repressor function, and are CDK4-independent (Knudsen et al, 1999;Reutens et al, 2001;Petre et al, 2002;Petre-Draviam et al, 2003;Burd et al, 2005). As shown, cyclin D3 invokes similar mechanisms to repress ligand-dependent AR activity (Figure 1), likely attributed to a conserved central repressor domain within cyclin D3.…”

“…In specific cell types, cyclin D1 is found in association with the estrogen receptor a, thyroid hormone receptor, peroxisome proliferatoractivated receptor-g and the androgen receptor (AR) (Neuman et al, 1997;Zwijsen et al, 1998;Knudsen et al, 1999;Reutens et al, 2001;Lin et al, 2002;Petre et al, 2002;Petre-Draviam et al, 2003;Wang et al, 2003;Burd et al, 2005). With estrogen receptor, cyclin D1 can potentiate receptor activity independently of ligand and CDK4-kinase activity (Neuman et al, 1997), through formation of a ternary complex with estrogen receptor a and P/CAF, thereby altering chromatin structure to facilitate gene transcription (McMahon et al, 1999).…”

“…In prostatic cells, cyclin D1 associates with and inhibits AR function, independent of CDK4 activating function and the LxxLL motif (Knudsen et al, 1999;Petre et al, 2002;Burd et al, 2005). Mechanisms are attributed to a discrete repressor domain, which binds to the AR N-terminus and prevents ligand-dependent conformational changes in AR .…”