Signaling cascade of insulin-induced stimulation of L-dopa uptake in renal proximal tubule cells

• Published in: American Journal of Physiology: Cell Physiology 2008-12, Vol.295 (6), p.C1602-C1609
• Main Authors: Carranza, Andrea, Musolino, Patricia L, Villar, Marcelo, Nowicki, Susana
• Format: Article
• Language: English
• Subjects: Animals; Blotting, Western; Cells; Enzyme Inhibitors; Epithelial Cells - drug effects; Epithelial Cells - metabolism; Hypoglycemic Agents - metabolism; Hypoglycemic Agents - pharmacology; Immunohistochemistry; Immunoprecipitation; Insulin; Insulin - metabolism; Insulin - pharmacology; Kidney Tubules, Proximal - cytology; Kidney Tubules, Proximal - drug effects; Kidney Tubules, Proximal - metabolism; Kinases; Levodopa - metabolism; Male; Membranes; Phosphorylation; Protein Kinases - drug effects; Protein Kinases - metabolism; Rats; Rats, Sprague-Dawley; Signal transduction; Signal Transduction - drug effects; Signal Transduction - physiology
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00090.2008

1 Centro de Investigaciones Endocrinológicas-Consejo Nacional de Investigaciones Científicas y Técnicas (CEDIE-CONICET), Buenos Aires; and 2 Facultad de Ciencias Biomédicas, Universidad Austral, Buenos Aires, Argentina Submitted 15 February 2008 ; accepted in final form 2 October 2008 The inward L -dihydroxyphenylalanine ( L -dopa) transport supplies renal proximal tubule cells (PTCs) with the precursor for dopamine synthesis. We have previously described insulin-induced stimulation of L -dopa uptake into PTCs. In the present paper we examined insulin-related signaling pathways involved in the increase of L -dopa transport into isolated rat PTCs. Insulin (50–500 µU/ml) increased L -dopa uptake by PTCs, reaching the maximal increment (60% over the control) at 200 µU/ml. At this concentration, insulin also increased insulin receptor tyrosine phosphorylation. Both effects were abrogated by the tyrosine kinase inhibitor genistein (5 µM). In line, inhibition of the protein tyrosine phosphatase by pervanadate (0.2–100 µM) caused a concentration-dependent increase in both the uptake of L -dopa (up to 400%) and protein tyrosine phosphorylation. A synergistic effect between pervanadate and insulin on L -dopa uptake was observed only when threshold (0.2 µM), but not maximal (5 µM), concentrations of pervanadate were assayed. Insulin-induced stimulation of L -dopa uptake was also abolished by inhibition of phosphatidylinositol 3-kinase (PI3K; 100 nM wortmannin, and 25 µM LY-294002) and protein kinase C (PKC; 1 µM RO-318220). Insulin-induced activation of PKC- was confirmed in vitro by its translocation from the cytosol to the membrane fraction, and in vivo by immunohistochemistry studies. Insulin caused a wortmannin-sensitive increase in Akt/protein kinase B (Akt/PKB) phosphorylation and a dose-dependent translocation of Akt/PKB to the membrane fraction. Our findings suggest that insulin activates PKC- , and Akt/PKB downstream of PI3K, and that these pathways contribute to the insulin-induced increase of L -dopa uptake into PTCs. amino acid transport; second messengers; dopamine Address for reprint requests and other correspondence: S. Nowicki, Centro de Investigaciones Endocrinológicas (CEDIE-CONICET), Gallo 1360 (C1425EFD), Buenos Aires, Argentina (e-mail: snowicki{at}cedie.org.ar )