1. Upregulation of the Na-Coupled Phosphate Cotransporters NaPi-IIa and NaPi-IIb by B-RAF.
- Author
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Pakladok, Tatsiana, Hosseinzadeh, Zohreh, Lebedeva, Aleksandra, Alesutan, Ioana, and Lang, Florian
- Subjects
PROTEIN kinases ,SERINE/THREONINE kinases ,CELLULAR signal transduction ,SOMATOMEDIN C ,RENAL tubular transport ,XENOPUS eggs ,CELL membranes ,CHEMILUMINESCENCE - Abstract
B-RAF, a serine/threonine protein kinase, contributes to signaling of insulin-like growth factor IGF1. Effects of IGF1 include stimulation of proximal renal tubular phosphate transport, accomplished in large part by Na-coupled phosphate cotransporter NaPi-IIa. The related Na-coupled phosphate cotransporter NaPi-IIb accomplishes phosphate transport in intestine and tumor cells. The present study explored whether B-RAF influences protein abundance and/or activity of type II Na-coupled phosphate cotransporters NaPi-IIa and NaPi-IIb. cRNA encoding wild-type NaPi-IIa and wild-type NaPi-IIb was injected into Xenopus oocytes with or without additional injection of cRNA encoding wild-type B-RAF, and electrogenic phosphate transport determined by dual-electrode voltage clamp. NaPi-IIa protein abundance in Xenopus oocyte cell membrane was visualized by confocal microscopy and quantified by chemiluminescence. Moreover, in HEK293 cells, the effect of B-RAF inhibitor PLX-4720 on NaPi-IIa cell surface protein abundance was quantified utilizing biotinylation of cell surface proteins and western blotting. In NaPi-IIa-expressing Xenopus oocytes, but not in oocytes injected with water, addition of phosphate to extracellular bath generated a current ( I), which was significantly increased following coexpression of B-RAF. According to kinetic analysis, coexpression of B-RAF enhanced the maximal I. Coexpression of B-RAF further enhanced NaPi-IIa protein abundance in the Xenopus oocyte cell membrane. Treatment of HEK293 cells for 24 h with PLX-4720 significantly decreased NaPi-IIa cell membrane protein abundance. Coexpression of B-RAF, further significantly increased I in NaPi-IIb-expressing Xenopus oocytes. Again, B-RAF coexpression enhanced the maximal I. In conclusion, B-RAF is a powerful stimulator of the renal and intestinal type II Na-coupled phosphate cotransporters NaPi-IIa and NaPi-IIb, respectively. [ABSTRACT FROM AUTHOR]
- Published
- 2014
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