AJP - Renal Physiology, Vol 260, Issue 2 235-F242, Copyright © 1991 by American Physiological Society
PKC and Pi deprivation modulate differently the ubiquitous Na-dependent Pi uptake in MDCK cells
B. Escoubet, M. C. Garestier, G. Cherqui and C. Amiel
Department of Physiology, Faculte de Medecine X. Bichat, Institut National de la Sante et de la Recherche Medicale Unite 251, Paris, France.
The role of protein kinase C (PKC) in the modulation of the ubiquitous
sodium-dependent phosphate transport and in adaptation of that transport to
phosphate deprivation was investigated in MDCK cells. Phorbol myristate
acetate (PMA) had a biphasic effect on sodium-dependent phosphate uptake
characterized by early inhibition (-25% at 1 h) followed by late
stimulation (2.3-fold at 15 h). Late stimulation was related to a decreased
apparent affinity (Km) with unchanged maximal velocity (Vmax). The 15-h
stimulation of phosphate uptake was also induced by an initial 1-h PMA
treatment followed by a 14-h washout of PMA or by R59 022. The stimulation
was inhibited by PKC downregulation. PMA stimulation was dependent on
protein synthesis but not on transcription, as shown by the respective
effects of cycloheximide, 3'-deoxyadenosine, and actinomycin D. In
phosphate-deprived cells PMA had also a biphasic effect. A potentiation of
PMA stimulation of phosphate uptake with phosphate deprivation was
observed. Adaptation to phosphate deprivation was not prevented by PKC
downregulation. Cytosolic and membranous PKC activities were not changed by
15-h phosphate deprivation. We conclude that 1) PKC modulates
sodium-dependent phosphate uptake in MDCK cells, and 2) phosphate
deprivation and PKC modulation of sodium-dependent phosphate uptake involve
different cellular pathways; that is, phosphate deprivation acts through
gene regulation, and PKC acts through translation regulation.
