AJP - Renal Physiology, Vol 261, Issue 6 945-F950, Copyright © 1991 by American Physiological Society
cAMP stimulates protein kinase C activity in cultured renal LLC-PK1 cells
R. J. Anderson and R. Breckon
Department of Medicine, Denver Veterans Affairs Medical Center, Colorado.
Exposure of intact LLC-PK1 cells to the phorbol ester 4-phorbol
12-myristate 13-acetate (PMA) increases basal, arginine
vasopressin-stimulated, and forskolin-stimulated adenylate cyclase activity
in LLC-PK1 membranes. This observation suggests that protein kinase C can
increase adenosine 3',5'-cyclic monophosphate (cAMP) in LLC-PK1 cells. To
determine whether cAMP regulates protein kinase C activity in LLC-PK1
cells, intact cells were exposed to either forskolin or to soluble cAMP
analogues. Acute (5 and 30 min) exposure to either forskolin or cAMP
analogues increases protein kinase C activity as observed by two different
methods for measuring protein kinase C. Acute exposure to PMA translocates
protein kinase C from a soluble to a particulate cell fraction, whereas
acute exposure to cAMP increases both soluble and particulate forms of
protein kinase C. Longer exposure (18 h) to PMA results in a loss of
protein kinase C activity, whereas 18-h exposure to cAMP results in a
further increase in protein kinase C activity. The effect of cAMP but not
of PMA to stimulate protein kinase C activity can be attenuated by the
pro-R diastereoisomer of adenosine 3',5'-cyclic phosphorothioate,
suggesting a protein kinase A-mediated effect. These results suggest the
presence of a monodirectional mode of signal transduction system
interaction in LLC-PK1 cells in which protein kinase C and protein kinase A
can potentiate each other.
