Abstract P36: The Intrinsically Disordered Activation Function 1 of Progesterone Receptor is Required for Regulation of Cell Proliferation

Progesterone receptor (PgR) is well known for its role in mammary gland and uterus development upon response to progesterone. PgR is critically involved in cancer development of these organs, and hence its understanding is vital for development therapeutic intervention. PgR belongs to nuclear receptor superfamily, expressed mainly in two isoform PRA and PRB. PgR activity is mediated by Activation Function AF1 and AF2, where AF1 mapped to highly variable and disordered N-terminal domain (NTD) while AF2 to highly structured ligand binding domain (LBD). It is established that AF2 form coregulator binding interface upon ligand binding, but little is known about the disordered AF1. 3 critical AF1 residues K464, K481 and R492 were identified that can be monomethylated, and mutation of these residues to phenylalanine (KKR/FFF) greatly abolish PR activity in reporter gene assay but increased AF1 interactions with coactivator SRC1 and AF2. This greater interaction could cause a slowdown in transcription complex assembly and disassembly, leading to impaired gene regulation. To evaluate the effect of AF1 mutation on PR activity in breast cancer cells, MCF-7 cells were made to express Wt PRB or KKR/FFF mutant using Lentiviral transduction. It was found that KKR/FFF mutation significantly impair progestin induced cell proliferation and spreading. Furthermore, the effect of progestin on cell cycle progression was delayed in KKR/FFF mutant expressing cells as compared to Wt PRB cells, lending support to the notion that KKR/FFF mutant suffered slower transcriptional dynamics. RNA-seq analysis revealed overall impairment in gene regulation by KKR/FFF mutant particularly in cell growth related genes. Moreover, KKR/FFF mutant interaction with gene enhancers was unabated, or even better, consistent with tighter interaction of AF1-KKR/FFF with AF2 and coactivator SRC1. Our data support the tripartite relationship among AF1, AF2 and coregulators, suggest critical role of AF1 in modulating dynamics of PgR transcription complex. Citation Format: Pheck Khee Lau, Qian Yee Woo, Shi Hao Lee, Chew Leng Lim, Amanda Woo Rui En, Valerie C.L Lin. The Intrinsically Disordered Activation Function 1 of Progesterone Receptor is Required for Regulation of Cell Proliferation [abstract]. In: Proceedings of Frontiers in Cancer Science 2024; 2024 Nov 13-15; Singapore. Philadelphia (PA): AACR; Cancer Res 2025;85(15_Suppl):Abstract nr P36.