The Protein Kinase C Inhibitor Go6976 [12-(2-Cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole] Potentiates Agonist-Induced Mitogen-Activated Protein Kinase Activation through Tyrosine Phosphorylation of the Epidermal Growth Factor Receptor

Abstract

Protein kinase C (PKC) isoforms are important transducers of signals from G protein-coupled receptors (GPCRs) to diverse cellular targets, including extracellular signal-regulated kinases 1 and 2 (ERK1/2). Clone 9 rat hepatocytes (C9 cells) express receptors for angiotensin II (Ang II) type 1, lysophosphatidic acid (LPA), and epidermal growth factor (EGF), and their stimulation causes transient ERK1/2 phosphorylation through transactivation of the epidermal growth factor receptor (EGF-R). Inhibition of PKC by Go6983 [2-[1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl)maleimide], or PKC depletion by prolonged phorbol 12-myristate 13-acetate (PMA) treatment, attenuated ERK1/2 activation by Ang II and PMA, but not by LPA and EGF. In contrast, another PKC inhibitor, Go6976 [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole], enhanced basal and agonist-stimulated phosphorylation of ERK1/2, which was not caused by alteration in receptor binding and internalization, stimulation of inositol phosphate production, or activation of Pyk2 and Src tyrosine kinases. However, Go6976 enhanced agonist-induced tyrosine phosphorylation of the EGF receptor, possibly through inhibition of protein tyrosine phosphatase (PTP), because the PTP inhibitor sodium orthovanadate mimicked the effects of Go6976. Selective blockade of EGF-R kinase by AG1478 [4-(3-chloroanilino)6,7-dimethoxyquinazoline] abolished the ERK1/2 activation induced by Go6976. Similar experiments were conducted in human embryonic kidney 293 cells, which express receptors for LPA and EGF but exhibit no significant cross-communication between them. Although Go6976 caused a significant increase in EGF-induced tyrosine phosphorylation of the EGF-R and subsequent ERK1/2 activation, it had no such effects on LPA-induced responses. In Chinese hamster ovary cells, which express receptors for LPA but not for EGF, Go6976 also had no significant effect on LPA-induced ERK1/2 activation. These data indicate that Go6976 potentiates agonist-induced ERK1/2 activation through stimulation of tyrosine phosphorylation of the EGF-R.G protein-coupled receptor (GPCR) signaling is a primary mechanism by which cells transduce changes from the external environment to their interior. GPCRs mediate responses to numerous ligands by binding and activating intracellular heterotrimeric G proteins. Stimulation of the pertussis toxininsensitive G proteins, G q/11 , triggers the hydrolysis of membrane inositol phospholipids by phospholipase-C␤ to form two important second messengers, inositol 1,4,5-triphosphate and diacylglycerol. The binding of inositol 1,4,5-Article, publication date, and citation information can be found at

Cigarette smoke extract induces COX-2 expression via a PKCα/c-Src/EGFR, PDGFR/PI3K/Akt/NF-κB pathway and p300 in tracheal smooth muscle cells

“…Our results were also consistent with the reports showing that activation of EGFR and PDGFR lead to COX-2 expression in various cell types (17,56,57). Gö6976 has been shown to enhance agonist-induced tyrosine phosphorylation of the EGFR, possibly through inhibition of PTP, since a PTP inhibitor, sodium orthovanadate, mimicked the effects of Gö6976 (49). Moreover, in HTSMCs, we found that pretreatment with sodium orthovanadate, but not Gö6976, markedly enhanced CSE-regulated EGFR or PDGFR phosphorylation.…”

“…There was no change in the level of COX-1 in these cells. Gö6976 has been shown to enhance agonist-induced tyrosine phosphorylation of the EGFreceptor, possibly through inhibition of protein tyrosine phosphatase (PTP), since a PTP inhibitor, sodium orthovanadate, mimicked the effects of Gö6976 (49). We found that pretreatment with 10 M sodium orthovanadate markedly enhanced CSE-regulated COX-2 expression (Fig.…”

Mechanisms of angiotensin II-induced ERK1/2 activation in fetal cardiomyocytes

“…These findings demonstrate that both PLC and PKC can have negative regulatory roles in Ang II-induced ERK1/2 phosphorylation in fetal cardiomyocytes, in contrast to previous reports in newborn and adult cardiomyocytes (7,13,16). These observations are consistent with a previous report on the ability of Gö6976 w12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo (2,3-a)pyrrolo(3,4-c) carbazolex, another PKC inhibitor, to potentiate agonist-induced ERK1/2 phosphorylation (20). These findings reflect the ability of conventional PLCs and PKCs to mediate feedback inhibition of G-protein-coupled receptor-induced ERK1/2 activation.…”

Interleukin-8 stimulates cell proliferation in non-small cell lung cancer through epidermal growth factor receptor transactivation

“…They were found to activate growth factor signalling cascades via additional mechanisms involving receptor tyrosine kinases phosphorylation, which is illustrated by various studies that have shown a cross-talk between GPCRs and EGFR. This was found to involve metalloprotease-mediated release of membrane-bound EGFR ligands that subsequently activate the EGFR, in a process called transactivation [18][19][20]. This transactivation of the EGFR via GPCR results in cellular activity such as proliferation and migration.…”