Activating Transcription Factor 3 (ATF3) in the Human Adrenal Cortex: Its Possible Involvement in Aldosterone Biosynthesis

The activating transcription factor 3 (ATF3) is a member of the cAMP-responsive element-binding (CREB) protein family of transcription factors. ATF3 is expressed in H295R human adrenocortical carcinoma cells and considered a rapid-responder gene to angiotensin-II stimulation. However, the functions of ATF3 in human adrenocortical tissues have remained unknown. In this study, we analyzed the localization and possible regulatory mechanisms of ATF3 in human adrenocortical cells and tissues. The expression levels of ATF3 mRNA were analyzed in 66 aldosterone-producing adenomas (APA) and 14 cortisol-producing adenomas (CPA) using real-time RT-PCR. To localize the ATF3 protein, we performed immunohistochemical analysis in 20 non-pathological adrenal glands, 9 adrenal glands with idiopathic hyperaldosteronism (IHA), 20 APA, and 5 CPA using a mouse monoclonal antibody against human ATF3. We showed that ATF3 mRNA levels were higher in APA compared to CPA (P = 0.0053). ATF3 was immunolocalized to the zona glomerulosa of non-pathological adrenal glands and adrenal glands with IHA, and diffusely detected in the tumor cells of APA and CPA. Subsequently, H295R cells were treated for 6 h with each inhibitor of Src kinase (SRC), PKC, JAK2, and calcium-dependent calmodulin kinase-II (CaMKII) in the presence or absence of angiotensin-II. The expression levels of ATF3 mRNA were increased by angiotensin-II (about 3.5-fold induction), but the magnitude of the induction was significantly decreased in the presence of an inhibitor for SRC (PP2) or CaMKII (KN93). These results suggest that ATF3 is a downstream target of SRC and CaMKII signaling, and may be involved in adrenocortical aldosterone synthesis.