The KRAB Zinc Finger Protein RSL1 Regulates Sex- and Tissue-Specific Promoter Methylation and Dynamic Hormone-Responsive Chromatin Configuration

Over 400 Krüppel-associated box zinc finger proteins (KRAB-ZFPs) are encoded in mammalian genomes. While KRAB-ZFPs strongly repress transcriptionin vitro , little is known about their biological function or gene targetsin vivo . Regulator of sex limitation 1 (Rsl1 ), one of the firstKRAB-Zfp genes assigned a physiological role, accentuates sex-biased liver gene expression, most dramatically for mouse sex-limited protein (Slp ), which provides anin vivo reporter of KRAB-ZFP function.Slp is induced in males in the liver and kidney by growth hormone (GH) and androgen, respectively. In the liver but not kidney, theRsl1 genotype correlates with methylation of a CpG dinucleotide in theSlp promoter that is demethylated at puberty. RSL1 binds 2 kb upstream of theSlp promoter, bothin vitro andin vivo , within an enhancer containing response elements for STAT5b. Chromatin immunoprecipitation (ChIP) assays demonstrate that RSL1 recruits KAP1/TRIM28, the corepressor for KRAB actionin vitro , to this enhancer.Slp induction requires rapid cycling of STAT5b in chromatin. Remarkably, RSL1 simultaneously binds adjacent to STAT5b with a reciprocal binding pattern that limits hormonal response. These experiments demonstrate a surprisingly dynamic interplay between a hormonal activator, STAT5b, and a KRAB-ZFP repressor and provide unique insights into KRAB-ZFP epigenetic mechanisms.