Down-regulation of inositol 1,4,5-trisphosphate receptor in cells stably expressing the constitutively active angiotensin II N111G-AT(1) receptor.
The diverse cellular changes brought about by the expression of a constitutively active receptor are poorly understood. QBI-human embryonic kidney 293A cells stably expressing the constitutively active N111G-AT(1) receptor (N111G cells) showed elevated levels of inositol phosphates and frequent spontaneous intracellular Ca(2+) oscillations. Interestingly, Ca(2+) transients triggered with maximal doses of angiotensin II were much weaker in N111G cells than in wild-type cells. These blunted responses were observed independently of the presence or absence of extracellular Ca(2+) and were also obtained when endogenous muscarinic and purinergic receptors were activated, revealing a heterologous desensitization process. The desensitized component of the Ca(2+) signaling cascade was neither the G protein G(q) nor phospholipase C. The intracellular Ca(2+) store of N111G cells and their mechanism of Ca(2+) entry also appeared to be intact. The most striking adaptive response of N111G cells was a down-regulation of their inositol 1,4,5-trisphosphate receptor (IP(3)R) as revealed by reduced IP(3)-induced Ca(2+) release, lowered [(3)H]IP(3) binding capacity, diminished IP(3)R immunoreactivity, and accelerated IP(3)R degradation involving the lysosomal pathway. Treatment with the inverse agonist EXP3174 reversed the desensitized phenotype of N111G cells. Down-regulation of IP(3)R represents a reversible adaptive response to protect cells against the adverse effects of constitutively active Ca(2+)-mobilizing receptors.
Department of Pharmacology, Faculty of Medicine, Université de Sherbrooke, 3001, 12th Avenue North, Sherbrooke, Quebec, Canada J1H 5N4.
Mannix
M
Auger-Messier
Guillaume
G
Arguin
Benoit
B
Chaloux
Richard
R
Leduc
Emanuel
E
Escher
Gaetan
G
Guillemette
D000804:Angiotensin II / Q000494:pharmacology / Q000502:physiology*; D000959:Antihypertensive Agents / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics* / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D015536:Down-Regulation; D004622:Embryo, Mammalian / Q000166:cytology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000502:physiology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007668:Kidney / Q000166:cytology / Q000196:embryology; D019808:Losartan; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D044140:Receptor, Angiotensin, Type 1 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics* / Q000378:metabolism; D013777:Tetrazoles / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology
D000959:Antihypertensive Agents; D015220:Calcium Channels; C506926:ITPR1 protein, human; D007093:Imidazoles; D053496:Inositol 1,4,5-Trisphosphate Receptors; D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; D018160:Receptors, Cytoplasmic and Nuclear; D013777:Tetrazoles; D000804:Angiotensin II; D019284:Thapsigargin; D015544:Inositol 1,4,5-Trisphosphate; C066026:losartan carboxylic acid; D019808:Losartan; D002118:Calcium