The mechanism of angiotensin Ii-induced extracellular signal-regulated kinase-1/2 activation is independent of angiotensin AT(1A) receptor internalisation

The aim of this study was to determine whether internalisation of the angio tensin II (Ang II) ATI, receptor (AT(1A)R) was a prerequisite for Ang II-in duced activation of the extracellular signal-regulated kinases, ERK-1/2. Th e human embryonic kidney (HEK293) cell line stably transfected with either the wild-type rat AT(1A)R or an internalisation-deficient C-terminal trunca ted mutant of the AT1AR (AT(1A)T318R) was used as a model for these studies . Inhibition of AT(1A)R internalisation by treatment with an inhibitor of c lathrin-mediated endocytosis, Concanavalin A (Con A), did not inhibit Ang I I-induced ERK-1/2 activation. Furthermore, cells transfected with the inter nalisation-deficient AT(1A)T318R mutant readily activated ERK-1/2 in respon se to Ang IT. Ang II activated ERK-1/2 via two distinct signalling pathways in HEK-AT(1A)R cells. Approximately half of Ang II-induced ERK-1/2 activat ion was protein kinase C (PKC)-dependent, and the remainder was calcium- an d c-Src-dependent and involved transactivation of the epidermal growth fact or receptor (EGFR). In summary, Ang II-induced activation of ERK-1/2 occurs via two distinct pathways in HEK293 cells, neither of which requires AT(1A )R internalisation. (C) 2001 Elsevier Science Inc. All rights reserved.