Structural determinants for the activation mechanism of the angiotensin II type 1 receptor differ for phosphoinositide hydrolysis and mitogen-activated protein kinase …

J Hines, SJ Fluharty, DK Yee - Biochemical pharmacology, 2003 - Elsevier
J Hines, SJ Fluharty, DK Yee
Biochemical pharmacology, 2003Elsevier
While the mechanism whereby the angiotensin II type 1 receptor (AT1 receptor) activates its
classical effector phospholipase C-β (PLC-β) has largely been elucidated, there is little
consensus on how this receptor activates a more recently identified effector, the p42/44
mitogen-activated protein kinases (p42/44MAPK). Using transfected COS-1 cells, we
investigated the activation of this signaling pathway at the receptor level itself. Previous
mutational studies that relied on phosphoinositide turnover as an index of receptor activation …
While the mechanism whereby the angiotensin II type 1 receptor (AT1 receptor) activates its classical effector phospholipase C-β (PLC-β) has largely been elucidated, there is little consensus on how this receptor activates a more recently identified effector, the p42/44 mitogen-activated protein kinases (p42/44MAPK). Using transfected COS-1 cells, we investigated the activation of this signaling pathway at the receptor level itself. Previous mutational studies that relied on phosphoinositide turnover as an index of receptor activation have indicated that key residues in the second and seventh transmembrane domains participate in AT1 receptor activation mechanisms. Thus, we introduced a variety of mutations—AT1[D74N], AT1[Y292F], AT1[N295S], and AT1[AT2 TM7], which is composed of a chimeric substitution of the AT1 seventh transmembrane domain with its AT2 counterpart. These mutations that strongly diminished the receptor’s ability to activate PLC-β had little to no effect on its ability to activate p42/44MAPK, which not only suggests that p42/44MAPK does not exclusively lie downstream of the G-protein Gq/PLC-β pathway but also indicates that more than one activation state may exist for the AT1 receptor. The failure of a protein kinase C inhibitor to block AT1 receptor activation of p42/44MAPK further corroborated evidence that the receptor’s activation of p42/44MAPK is largely independent of the Gq/PLC-β/PKC pathway. Taken together, the experimental evidence strongly suggests that the mechanism whereby the AT1 receptor activates p42/44MAPK is fundamentally different from that for PLC-β, even at the level of the receptor itself.
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