Differential cytokine sensitivities of mammary-specific and universal STAT5 enhancers depends on Stat5 autoregulation

Cytokines utilize the transcription factor STAT5 to control cell-specific and universal genes. In general, the magnitude of cell-restricted gene activation greatly exceeds that of universal genes, with a mechanistic explanation yet to be supplied. Genome-wide studies have identified putative STAT5-based mammary-specific enhancers and universal STAT5-controlled regulatory elements, an opportunity to investigate mechanisms underlying their differential response to cytokines. We have now interrogated the integrity and function of both categories of regulatory elements using biological and genetic approaches. During lactation, STAT5 occupies mammary-specific and universal cytokine-responsive elements. Following lactation, prolactin levels decline and STAT5-dependent enhancers at mammary-specific genes are decommissioned with 24 hours while universal regulatory complexes remain intact. These differential sensitivities are linked to STAT5 concentrations and the mammary-specific Stat5 autoregulatory enhancer. In its absence, mammary-specific enhancers, but not universal elements, fail to be fully established. Upon termination of lactation, STAT5 binding to a subset of mammary enhancers is substituted by STAT3. No STAT3 binding was observed at the most sensitive STAT5 enhancers, suggesting that upon hormone withdrawal their chromatin becomes inaccessible. This study, for the first time, provides molecular insight into the differential sensitivities of mammary-specific and universal cytokine-sensing enhancers. Overall design: ChIP-seq for STAT5A, GR, H3K27ac, STAT3 in wild type mammary tissues at lactation day one (L1), involution 12 hours (I12) and involution 24 hours (I24). ChIP-seq for STAT5A and H3K27ac of mice heterozygous for Stat5 (Stat5+/-), homozygous for the Stat5 enhancer mutation (Stat5?E/?E) and mice carrying one Stat5-null allele and one mutant allele (Stat5?E/-) at L1. ChIP-seq for STAT5A and H3K27ac of mice homozygous for the Stat5 enhancer mutation (Stat5?E/?E) at I12 and I24.