Activation of Multiple Mitogen-activated Protein Kinase Signal Transduction Pathways by the Endothelin B Receptor Requires the Cytoplasmic Tail

Abstract

Endothelin is a 21-amino acid peptide with remarkably diverse biological properties, including potent vasoconstriction, induction of mitogenesis, and a role in the development of blood vessels. In the present study, stimulation of the endothelin B receptor was found to activate three distinct mitogen-activated protein kinase signal transduction pathways, the extracellular regulated kinase (ERK) 2, c-Jun N-terminal kinase 1 (JNK), and p38 kinase. These mitogen-activated protein kinase isozymes are thought to mediate very different biological outcomes, suggesting that the observed pattern of kinases activation may be important for the diverse biological properties of endothelin. The cytoplasmic tail of the endothelin B receptor was found to be required for activation of all three mitogen-activated protein kinases and stimulation of intracellular calcium levels. An endothelin B receptor truncated at the C-terminal tail was not able to stimulate the mitogen-activated protein kinases or increase cytosolic free calcium. Furthermore, ectopic expression of the cytoplasmic tail attenuated signaling through the wild type receptor. The observed ERK activation appeared to be mediated by heterotrimeric G proteins, since ectopic expression of a transducin ␣-subunit inhibited endothelin-stimulated ERK activation. The data suggest that the cytosolic tail of the endothelin B receptor is involved in calcium mobilization and mitogen-activated protein kinase activation via a G protein-dependent mechanism. Endothelin (ET)1 is a 21-amino acid peptide with diverse physiological effects on cellular development, differentiation, vasoconstriction, and mitogenesis. There are three endothelin isoforms, ET-1, ET-2, and ET-3, that have preference for different endothelin receptor subtypes. The endothelin A (ETA) receptor binds ET-1, ET-2, and ET-3 with decreasing affinities, whereas the endothelin B (ETB) receptor binds ET-1, ET-2, and ET-3 with similar affinity; both are members of the G proteincoupled receptor (GPCR) superfamily (1-7).The putative ET receptor topology includes three extracellular domains, three intracellular cytosolic loops, and a cytoplasmic C-terminal tail, separated by seven highly hydrophobic regions thought to span the lipid bilayer. Ligand binding and specificity is conferred by the conformation of the extracellular portions of the receptor, whereas the intracellular domains physically interact with heterotrimeric G proteins to initiate signal transduction events. Receptor-G protein complexes are thought to form the high affinity ligand binding state of the receptor (8). For example, constitutively activated adrenergic and muscarinic receptor mutants have increased affinity for agonist with little effect on antagonist binding, supporting the view that the receptor-G protein complex is the high affinity binding complex (9, 10).Endothelin receptor mutagenesis studies suggest that residues within extracellular loop two are important for ligand binding. The intracellular domains of the receptor, thought to play a role in...

Endothelin-1 and Transforming Growth Factor-β1 Independently Induce Fibroblast Resistance to Apoptosis via AKT Activation

“…In concordance with previous reports, we found that ET-1 activates p38, ERK1/2, and JNK MAPKs (21,41). Early activation of p38 MAPK is required for ET-1 activation of PI3K/AKT, whereas blockade of ERK1/2 or JNK fails to inhibit ET-1 activation of PI3K/AKT.…”

Regulation of Mitogen-Activated Protein Kinase Signaling Networks by G Protein-Coupled Receptors

“…Although the activation of p38 by GPCRs has been documented in primary cells, immortalized cell lines, perfused organs, and even after in vivo manipulations (186)(187)(188)(189)(190)(191)(192)(193)(194)(195)(196), there is very limited knowledge on the mechanism of activation of this particular family of MAPKs. The p38α enzyme is activated by both Gα q and Gβγ (197), and a role for the tyrosine kinase Btk in G q -mediated stimulation has been suggested from observations in lymphocytic cells (198).…”

G.ALPHA.13 Induces PreproET-1 Gene Expression via JNK.

“…In addition, we previously demonstrated that endothelin B receptor (ETBR) activates Gα13 (6). Gα13 regulates Na/H exchanger activity (7,8), extracellular signal regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK) (9 -11), nuclear factor κB (NF-κB) (12) and the activity of the low molecular weight GTPase, Rho (13 -15), and is also capable of neoplastic transformation, induction of apoptosis, and stimulation of actin reprotein kinases (ERK, JNK, and p38) (23,24). Because of its vasoconstrictor and growth-promoting action, numerous studies indicate that ET-1 is involved in the pathogenesis of a broad spectrum of renal and cardiovascular diseases (21,22,(25)(26)(27).…”