Phorbol esters down-regulate expression of the sodium-calcium exchanger in
renal epithelial cells.
Smith, Lucinda, Hartmut Porzig, Hyeon-Woo Lee, and Jeffrey Bingham Smith.
Department of Pharmacology, Schools of Medicine and Dentistry, University
of Alabama at Birmingham, Birmingham, AL 35294 and the Department of
Pharmacology, University of Bern, CH-3010 Bern Switzerland
APStracts 2:0075C, 1995.
The Na+-Ca2+ exchanger (NCX) contributes to Ca2+ reabsorption by connecting
tubules of the nephron. A line of renal epithelial cells from monkey kidney
(LLC-MK2) was used to investigate the regulation of NCX expression. Following
the activation of protein kinase C (PKC) by phorbol myristate acetate (PMA)
NCX activity decreased exponentially by 75% in 48 h (half- time 19 h). PMA
decreased NCX mRNA by 85% in 24 h. The decrease in NCX transcript preceded
the down-regulation of NCX activity. NCX protein was quantified with a
monoclonal antibody to cardiac NCX. PMA decreased the binding of
[3H]labeled antibody to cell sonicates by 40% in 24 h. Immunoblots show
that PMA produced a marked and extended increase in membrane-associated
PKC[alpha], although PMA depleted total PKC[alpha] by 65% in 24 h. In vivo
[32P] labeling of MARCKS, a specific PKC substrate, confirmed that PMA
produced a rapid and extended activation of PKC. 4[alpha]PMA, a stereoisomer
of PMA which neither binds nor activates PKC, had no effect on NCX activity or
transcript. These findings indicate that activation of PKC with phorbol esters
down-regulates NCX mRNA, protein, and activity in renal epithelial cells.
Received 28 November 1994; accepted in final form 18 January 1995.
APS Manuscript Number C690-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 February 1995.