Regulation of Androgen-Responsive Transcription by the Chromatin Remodeling Enzyme CHD8.

Abstract

Eukaryotic DNA is packaged into a highly condensed chromatin state, which inherently serves as a barrier to critical cellular processes such as DNA replication, repair and transcription. The modulation of chromatin structure to allow access to the underlying DNA is vital for the appropriate regulation of these processes. One class of enzymes responsible for modulation of chromatin structure is the ATP-dependent chromatin remodeling enzymes. These enzymes use the energy from hydrolysis of ATP to mobilize, disrupt and modulate nucleosomes. These enzymes are divided into different families based on their domain architecture, the largest of which is the CHD (Chromodomain Helicase DNA-binding) family. This family is comprised of nine enzymes, which are divided into three subfamilies, CHD1-2, CHD3-5, and CHD6-9. The research described here is directed towards CHD8, a member of the CHD6-9 subfamily. Previous studies have established a functional association between the CHD6-9 subfamily and nuclear receptor-mediated transcriptional regulation. One such nuclear receptor, the androgen receptor (AR), mediates the effect of androgens through its transcriptional function during both normal prostate development and in the emergence and progression of prostate cancer. Here we identify CHD8 as a novel coregulator of androgen-responsive transcription. We show that CHD8 directly associates with AR and that CHD8 and AR simultaneously localize to the enhancers of androgen-responsive genes following androgen treatment. In the LNCaP prostate cancer cell line, reduction of CHD8 levels by siRNA treatment severely diminishes androgen-dependent activation of these genes. We demonstrate that the recruitment of AR to target promoters in response to androgens requires CHD8. CHD8 also facilitates the androgen-stimulated proliferation of LNCaP cells, emphasizing the physiological importance of CHD8 in prostate cancer. Mechanistic studies revealed that CHD8 can remodel nucleosomes without histone tails and prefers substrates that are methylated at H3K4. The association of CHD8 with H3K4 methylation was supported by our findings that CHD8 interacts with the MLL1-WAR histone methyltransferase complex. The interactions of CHD8 with this complex and their effect on its remodeling activity were further characterized. These studies collectively implicate a role , as well as a potential mechanism, for CHD8 function in the regulation of androgen-responsive gene expression.