Participation of PI3K and atypical PKC in Na+-K+-pump stimulation by IGF-I in VSMC.
The activity of the Na+-K+-pump is intricately linked to the maintenance of vascular tone. Here we demonstrate that insulin-like growth factor I (IGF-I) increases Na+-K+-pump activity in the vascular smooth muscle cell (VSMC) clone A7r5 in a time- and dose-dependent manner. This stimulatory effect of IGF-I was prevented by the tyrosine kinase inhibitor genistein (5 microM) and by the specific phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin (100 nM) and LY-294002 (25 microM). IGF-I activated a wortmannin-sensitive PI3K and its purported effector, the atypical protein kinase C (PKC)-zeta. Stimulation of PKC-zeta was prevented by the generic PKC inhibitor GF109203x (bisindolylmaleimide, 10 microM). Downregulation of diacylglycerol-sensitive (conventional and novel) PKCs by 24-h pretreatment with 1 microM phorbol 12-myristate 13-acetate had no effect on IGF-I-stimulated Na+-K+-pump activity. Similarly, inhibition of only conventional and novel PKCs with GF109203x (1 microM) had no effect on IGF-I-stimulated Na+-K+-pump activity. In contrast, a concentration of GF109203x (10 microM) that also inhibits the atypical PKCs abolished Na+-K+-pump stimulation by IGF-I. Neither the Na+-K+-2Cl- cotransporter inhibitor bumetanide (100 microM) nor the Na+/H+ exchanger inhibitor HOE-694 (5 microM) affected the Na+-K+-pump stimulation by IGF-I, suggesting that a rise in intracellular Na+ concentration is not necessary for increased Na+-K+-pump activity. These results suggest that IGF-I directly stimulates the Na+-K+ pump via a signaling pathway involving PI3K and atypical PKC (zeta).
Li
D
D
Programme in Cell Biology, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.
Sweeney
G
G
Wang
Q
Q
Klip
A
A
D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000502:physiology*
D004791:Enzyme Inhibitors; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D011505:Protein-Tyrosine Kinases; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase