Inhibition of type I and III IP(3)Rs by TGF-beta is associated with impaired calcium release in mesangial cells.
Inositol 1,4,5-trisphosphate receptors (IP(3)Rs) mediate cytosolic free calcium concentration ([Ca(2+)](c)) signals in response to a variety of agonists that stimulate mesangial cell contraction and proliferation. In the present study, we demonstrate that mesangial cells express both type I and III IP(3)Rs and that these receptors occupy different cellular locations. Chronic treatment with transforming growth factor-beta1 (TGF-beta1; 10 ng/ml, 24 h) leads to downregulation of both type I and III IP(3)Rs as measured by immunoblot and confocal analysis. TGF-beta1 treatment does not affect IP(3) levels, and downregulation of type I IP(3)R is not due to enhanced degradation of the protein, as the half-life of type I IP(3)R is unchanged in the presence or absence of TGF-beta1. Functional effects of TGF-beta1-induced downregulation of the IP(3)Rs were evaluated by measuring [Ca(2+)](c) changes in response to epidermal growth factor (EGF) in intact cells and sensitivity of [Ca(2+)](c) release to IP(3) in permeabilized cells. TGF-beta1 pretreatment led to a significant decrease of [Ca(2+)](c) release induced by EGF in intact cells and by submaximal IP(3) (400 nm) in permeabilized cells. Total IP(3)-sensitive [Ca(2+)](c) stores were not changed, as assessed by stimulation with maximal doses of IP(3) (10.5 microm) and thapsigargin-mediated calcium release in permeabilized cells. We conclude that prolonged exposure to TGF-beta1 leads to downregulation of both type I and III IP(3)Rs in mesangial cells and this is associated with impaired sensitivity to IP(3).
Sharma
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Department of Medicine, Cell Biology, and Pathology, Thomas Jefferson University, Philadelphia, PA 19107, USA. Kumar.Sharma@mail.tju.edu
Mc Gowan
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Wang
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Madesh
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Kaspar
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Szalai
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Thomas
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Hajnóczky
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D000818:Animals; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects* / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002460:Cell Line; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005920:Glomerular Mesangium / Q000187:drug effects* / Q000378:metabolism*; D006207:Half-Life; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051379:Mice; D008954:Models, Biological; D020033:Protein Isoforms / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000145:classification / Q000187:drug effects* / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D016212:Transforming Growth Factor beta; D004815:Epidermal Growth Factor; D015544:Inositol 1,4,5-Trisphosphate