CDK7 inhibition suppresses Castration-Resistant Prostate Cancer through MED1 inactivation

We performed RNA-seq and ChIP-seq in three prostate cell lines (VCaP, LNCaP and DU145) to ascertain the role of the mediator complex MED1 in AR signaling. Upon androgen stimulation, MED1 undergoes phosphorylation by CDK7 and physically engages with AR at super-enhancer sites, which is essential for AR-mediated transcription. The CDK7 specific inhibitor THZ1 blunts AR-dependent neoplastic growth by preventing the co-recruitment of AR/MED1 in a genome-wide fashion, and reverts the enzalutamide resistance characterized by hyper-phosphorylated MED1. The effect of THZ1 phenocopies that for MED1 and CDK7 knockdown. Overall design: Genome wide gene expression levels in three prostate cancer cell lines (VCaP, LNCaP and DU145) were determined using RNA-seq. The RNA-seq experiments were performed under three treatment conditions: (i) Treatment for 6 hrs with VEH/DHT/DHT+THZ1 (VCaP and LNCaP), (ii) treatment for 24hrs with DMSO/THZ1 (VCaP, LNCaP and DU145), and (iii) knockdown of MED1 and CDK7 in VCaP and LNCaP cell lines. We also determined using ChIP-seq the genome-wide binding levels of AR, MED1, and H3K27ac, in VCaP and LNCaP cells for treatment condition (i). Genome wide binding levels of AR and MED1 in VCaP prostate cancer cell lines were determined using ChIP-seq. The ChIP-seq experiments were performed under three treatment conditions, namely VEH, DHT stimulation for 6hrs with or without treatment with 200 nM THZ1.