Proceedings of The Physiological Society

University College London (2011) Proc Physiol Soc 24, C08 and PC08

Oral Communications

Activation of the epithelial sodium channel (ENaC) by the cysteine protease cathepsin S

S. Haerteis1, M. Krappitz1, N. W. Bunnett2, C. Korbmacher1

1. Institut f

There is good evidence that proteolytic processing of the epithelial sodium channel (ENaC) by serine proteases (e.g. furin, trypsin, chymotrypsin, plasmin, elastase, prostasin) is critically important for channel activation [1; 2]. An inappropriate ENaC activation by proteases may be involved in sodium retention and the pathogenesis of arterial hypertension in the context of renal disease [3]. However, at present the molecular mechanisms by which proteases activate ENaC are not yet fully understood. In addition to serine proteases other types of proteases, e.g. cathepsin proteases of the group of cysteine proteases, may be able to activate ENaC under physiological and/or pathophysiological conditions. In particular cathepsin proteases are known to play an important role in inflammatory diseases. As far as we know there are no data yet on the effect of cathepsins on ENaC activity. For our investigation cathepsin S (Cat S) was chosen as candidate protease because Cat S is expressed in the kidney and plays a role in renal development. Thus, the aim of this study was to investigate the effects of Cat S on human ENaC. Using the two-electrode voltage-clamp technique we could demonstrate that Cat S activates amiloride-sensitive ENaC whole-cell currents (ΔIami) in αβγ-human ENaC expressing oocytes. Cat S (1 μM) stimulated ENaC-mediated currents by about two-fold compared to a five- to sixfold stimulatory effect of chymotrypsin applied in a concentration (2 μg/ml) known to elicit a near maximal effect on ENaC. Moreover, we examined the effect of morpholinurea-leucine-homophenylalanine-vinylsulfone-phenyl (LHVS), an irreversible and specific Cat S inhibitor [4], on proteolytic ENaC activation. For this purpose, Cat S (1 µM) was pre-incubated with the inhibitor LHVS (2 µM) for ten minutes and then its effect on ENaC currents was tested. The inhibition of Cat S by administration of LHVS abolished the stimulatory effect of Cat S on ΔIami. In contrast, LHVS (2 µM) had no effect on the activation of ENaC by the serine proteases trypsin and chymotrypsin (different concentrations: 0.02; 0.2; 2 µg/ml). In summary, our findings reveal for the first time an activation of ENaC by a cysteine protease of the family of cathepsin proteases (Cat S). Furthermore, by using the selective Cat S inhibitor LHVS we showed that Cat S activity is required for the stimulatory effect on ENaC. Our findings indicate that Cat S may play a (patho-)physiological role in proteolytic ENaC activation.

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