ABSTRACT: Chromaffin cells synthesize and release catecholamines, epinephrine and norepinephrine, into the systemic circulation to coordinate the stress response and regulate a variety of behavioral, endocrine, metabolic, immune, and cardiovascular functions. The mechanisms responsible for the development and maintenance of chromaffin cell differentiation and how these pathways are disrupted in pheochromocytomas (PCs) remain poorly understood.Here, we identify BRD4 as a critical regulator of chromaffin-cell biology through a PROTAC-based screen in human chromaffin organoids. Integrated analyses of human embryonic adrenal tissues, patient-derived pheochromocytomas, chromaffin organoids, and chromaffin cell-specific BRD4 conditional knockout mice demonstrated that BRD4 is required for maintaining chromaffin-cell identity and epinephrine-producing capacity. BRD4 deficiency disrupted chromaffin-cell differentiation programs, reduced expression of key lineage and functional genes, depleted mature PNMT-positive chromaffin cells, and impaired epinephrine production in vivo. Conversely, BRD4 overexpression enhanced chromaffin-cell gene expression and epinephrine secretion. Mechanistically, we identified SMAD2 as a BRD4-interacting transcriptional cofactor. CUT&Tag and chromatin immunoprecipitation analyses revealed direct BRD4 occupancy at key chromaffin-cell genes, including TH, CHGB, and PHOX2A. Pharmacological inhibition of BRD4 suppressed catecholamine-associated metabolic pathways, disrupted chromaffin-cell transcriptional programs, and inhibited pheochromocytoma growth. Together, our findings establish the BRD4-SMAD2 axis as a central regulator of chromaffin-cell identity and reveal a lineage-dependent mechanism linking catecholamine production to pheochromocytoma progression, highlighting BRD4 as a potential therapeutic target for pheochromocytoma.
