Inhibitory effects of aminoglycosides on renal protein phosphorylation by protein kinase C

Aminoglycosides such as neomycin are commonly prescribed antibiotics; however, there is associated serious damage to the kidney. We examined the effect of aminoglycoside antibiotics on renal protein phosphorylation and found that neomycin selectively inhibited Ca++-activated, phospholipid-dependent phosphorylation of 88-kDa protein in cell lysates of the rabbit kidney. Fifty percent inhibition of phosphorylation of this protein occurred with 5 X 10(-5) to 1 X 10(-4) M neomycin. In living PtK2 cells, neomycin dose-dependently inhibited 12-O-tetradecanoyl-phorbol-13-acetate-induced phosphorylation of 88 K Da protein. This drug also inhibited phosphorylation of exogenous protein catalyzed by protein kinase C, isolated from rabbit kidney in vitro. In contrast, neomycin had little or no inhibitory effect on cyclic GMP-dependent protein kinase, cyclic AMP-dependent protein kinase, casein kinase I, casein kinase II and Ca++-calmodulin-dependent myosin light chain kinase. Whereas activity of protein kinase C was inhibited 65% by neomycin (0.1 mM) at pH 5 to 7, inhibition decreases to 33% at pH 8 and to zero at pH 9. The potencies of a series of aminoglycoside antibiotics to inhibit the kinase agreed well with number of ionizable amino groups of compounds (gamma = 0.99) and this also approximates their known nephrotoxic potential; amikacin less than or equal to kanamycin less than gentamycin less than or equal to tobramycin less than neomycin. As aminoglycoside antibiotics present in the kidney after administration of toxicological doses (10(-2) M) will inhibit the effects of protein kinase C, the aminoglycoside antibiotics-induced nephrotoxicity is discussed in relation to inhibition of intracellular protein kinase C.