The receptor tyrosine kinase EPHB6 regulates catecholamine exocytosis in adrenal gland chromaffin cells

Abstract

The erythropoietin-producing human hepatocellular receptor EPH receptor B6 (EPHB6) is a receptor tyrosine kinase that has been shown previously to control catecholamine synthesis in the adrenal gland chromaffin cells (AGCCs) in a testosterone-dependent fashion. EPHB6 also has a role in regulating blood pressure, but several facets of this regulation remain unclear. Using amperometry recordings, we now found that catecholamine secretion by AGCCs is compromised in the absence of EPHB6. AGCCs from male knockout (KO) mice displayed reduced cortical F-actin disassembly, accompanied by decreased catecholamine secretion through exocytosis. This phenotype was not observed in AGCCs from female KO mice, suggesting that testosterone, but not estrogen, contributes to this phenotype. Of note, reverse signaling from EPHB6 to ephrin B1 (EFNB1) and a 7-amino acid-long segment in the EFNB1 intracellular tail were essential for the regulation of catecholamine secretion. Further downstream, the Ras homolog family member A (RHOA) and FYN proto-oncogene Src family tyrosine kinase (FYN)–proto-oncogene c-ABL–microtubule-associated monooxygenase calponin and LIM domain containing 1 (MICAL-1) pathways mediated the signaling from EFNB1 to the defective F-actin disassembly. We discuss the implications of EPHB6's effect on catecholamine exocytosis and secretion for blood pressure regulation.

MICAL-mediated oxidation of actin and its effects on cytoskeletal and cellular dynamics

“…For example, vascular endothial-derived growth factor (VEGF), platelet-derived Frontiers in Cell and Developmental Biology frontiersin.org growth factor (PDGF), epidermal growth factor (EGF), and fibroblast growth factor (FGF) and their receptors have been linked to increasing the MICAL's F-actin disassembly effects (Hou et al, 2015;Deng et al, 2016;Evans et al, 2017;Yoon et al, 2017;Barravecchia et al, 2019;McGarry et al, 2022). Further results reveal that they enhance the MICAL's F-actin disassembly effects by working with Abl/Arg non-receptor tyrosine kinases, which phosphorylate specific tyrosine (Y) residues within the Redox domain of the MICALs (Y500 in Mical and Y445, Y463 in MICAL-2) [Figure 1A (Yoon et al, 2017;Yoon and Terman, 2018a;Shi et al, 2020;Zhang et al, 2022)]. Furthermore, at least in the case of Mical, this Abl phosphorylation increases its NADPH consumption activity in the presence of F-actin and potentiates its F-actin disassembly/ repulsive activity [Figure 3B (Yoon et al, 2017)].…”

“…MICALs have also been associated with nerve growth factor (NGF) signaling, such that it induces MICAL-2's F-actin disassembly activity in the nucleus to promote gene transcription through the serum response factor (SRF)/MRTF-A (Lundquist et al, 2014). MICALs have also been linked to regulating the effects of other extracellular ligands/receptors, including those of TGFβ/TGFR and Ephrins/Eph, on cell migration and F-actin disassembly (Liu et al, 2019;Shi et al, 2020;Jiang et al, 2021;Pu et al, 2021). MICALs' localization and action in specific subcellular regions is important for their F-actin/cellular effects.…”

Recent developments concerning the investigation of exocytosis with amperometry

“…CFA also contributes to important findings related to the interconnected role between pannexin-1 channels and some purinergic and nicotinic acetylcholine receptors to trigger exocytosis [10]. In the same way, the effects of some signaling pathways from a receptor tyrosine kinaselike EPHB6 on catecholamines secretion are undoubtedly proven with CFA at chromaffin cells with important consequences on the relationship between effect on catecholamine secretion and blood pressure regulation [11]. The issues concerning SNAREs (Soluble NSF Attachment proteins Receptors) during the docking of vesicles with the cell membrane are still addressed with CFA (and complementary measurements, including fluorescence microscopy or electrophysiology).…”

Co-clustering of EphB6 and ephrinB1 in trans suppresses cancer cell invasion

“…In germinal centres, ephrinB1 was found to be abundantly expressed in resident B cells, which selectively repulsed EphB6expressing follicular helper T cells 22 . In addition, in a chromaffin cell line model, EphB6 was shown to activate ephrinB1-dependent, but not ephrinB2-dependent, signaling cascades in trans 23 . Pathologically, an inverse correlation between EphB6 and ephrinB1 protein expression has been reported in metastatic tumors 24 14, 16, 17, 18 , implying that the interaction of EphB6 and ephrinB1 could potentially control tumorigenesis.…”