Regulation of expression of type ii sodium-phosphate cotransporters
by protein kinase a and protein kinase c.
Lederer, Eleanor D., Sameet S. Sohi, Jeanine M. Mathiesen, and Jon B.
Klein.
Department of Internal Medicine, Veterans Affairs Medical Center
and University of Louisville
APStracts 5:0075F, 1998.
The purpose of the present study was to determine the effect of
protein kinase A and protein kinase C activation on the membrane
expression of NaPi-4, the Type II sodium-phosphate cotransporter in
OK cells. NaPi-4 expression was measured using polyclonal antisera
produced in rabbits against a peptide identical to the
carboxyterminal 12 amino acid sequence of NaPi-4. The antisera
identified an apically localized protein by confocal imaging of
intact OK cells and a broad band of 110-140 kDa by immunoblot
analysis of OK cell membranes. Treatment of OK cells with PTH
decreased the intensity of the 110-140 kDa band which was detectable
by 2 hours, maximal by 4 hours at 62%, and sustained for 24 hours. 8
-bromo-cAMP inhibited NaPi-4 expression for up to 24 hours by over
90%. However, phorbol myristate acetate inhibited NaPi-4 expression
by less than 10%. PTH 3-34, a fragment which stimulates only protein
kinase C, inhibited phosphate transport but also had no effect on
NaPi-4 expression. We conclude that protein kinase A but not protein
kinase C inhibits sodium-phosphate uptake in OK cells by
downregulation of NaPi-4 expression.
Received 6 January 1997; accepted in final form 12 March 1998.
APS Manuscript Number F6-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 24 April 1998