SUN-LB39 ATAC-Seq Reveals Dynamic Changes in Chromatin Accessibility Following PKA Activation in NCI-H295R Adrenocortical Cells

The adrenal cortex is comprised of distinct concentric zones that produce hormones essential for life - the outermost zona glomerulosa (zG) produces aldosterone, and the innermost zona fasciculata (zF) produces cortisol. Adrenal zonation is maintained by a balance between paracrine (Wnt/β-catenin) and endocrine (ACTH/PKA) signaling. Wnt/β-catenin signaling is maintained in the outer cortex (zG, upper zF) by a gradient of Wnt ligands that diminish centripetally, and PKA signaling is maintained in the inner cortex (zF) by ACTH. Recent studies in vivo suggest that sustained PKA signaling promotes zF proliferation, enabling lineage conversion towards zF by inhibiting Wnt/β-catenin transcriptional programming. While these studies were crucial in elucidating mechanisms supporting adrenal zonation, it remains unclear if PKA-mediated repression of Wnt/β-catenin is carried out at the chromatin level or if it is secondary to ligand-dependent modulation of paracrine signaling as may happen in vivo. To address this question, we utilized the adrenocortical cell line (NCI-H295R), which harbors a mutation in CTNNB1 rendering Wnt/β-catenin signaling constitutively active. We stimulated PKA in NCI-H295R using forskolin, and assessed genome-wide chromatin accessibility by ATAC-seq and transcriptome changes by RNA-seq. Motif analysis of ATAC-seq from baseline NCI-H295R revealed that chromatin accessibility is dominated by transcription factors SF1 (master regulator of the adrenal cortex and steroidogenesis), AP1 (effector of PKA) and LEF1 (effector of Wnt/β-catenin). Following forskolin administration, we observed decreased accessibility in chromatin containing LEF1 binding motifs, and increased accessibility in chromatin bearing AP1 and SF1 motifs, suggesting that PKA activation drives AP1/SF1-dependent transcription and inhibits Wnt/β-catenin-dependent transcription at the chromatin level. Indeed, RNA-seq revealed that forskolin administration decreased the expression of zG and Wnt/β-catenin target genes, while simultaneously increasing expression of AP1/SF1 target genes. Collectively, these data demonstrate that PKA activation leads to profound chromatin remodeling that enables zF identity even in the setting of constitutive Wnt/β-catenin signaling. Ongoing studies are aimed at elucidating how chromatin modifiers and transcriptional machinery coordinate the dynamic regulation of differentiation programs required for adrenocortical homeostasis and zonation.