Suppressing role of transforming growth factor [beta]1 on cathepsin
activity in cultured tubule cells.
Ling, H, S Vamvakas, G Busch, J Daemrich, L Schramm, F Lang, A
Heidland.
Division of Nephrology, Institute of Toxicology, Institute of
Pathology, University of Wuerzberg, Institute of Physiology,
University of Tuebingen, Germany
APStracts 2:0101F, 1995.
Elevated expression and activity of TGF-[beta]1 have been indicated in
various renal diseases, implicating the potential involvement of this
growth factor in the accumulation of extracellular matrix in the
diseased glomeruli. To assess its potential role on protein turnover
in tubule cells, we investigated in LLC-PK1 cells the effects of TGF
-[beta]1 on the activities of lysosomal cysteine proteinases cathepsin
B, H and L+B, which play a major role in the degradation of both
cellular protein and extracellular matrix. The results show that 1 -
10 ng/ml TGF-[beta]1 exerted inhibitory effects on cathepsin B and
L+B activities, when applied either to the basolateral or to the
apical membrane of these cells (basolateral side: B: -23.2%, L+B:
-19.9%; apical side: B: -28.2%, L+B: -22.6%). Application of TGF
-[beta]1 to both sides enhanced suppression of the enzyme activities
(B: -37.8%, L+B: -37.4%). This suppression of cathepsin activities
was accompanied by a reduction of cellular protein degradation rate
by 20.0% after 24 hours and by 51.7% after 48 hours. Furthermore,
TGF-[beta]1 stimulated cellular protein synthesis by 50.0% after 48
hours. The combined effects on protein turnover resulted in cellular
hypertrophy: increases of both protein content and cell size after 48
hours. Concerning the underlying mechanism, neither TGF-[beta]1
induced a rise in intracellular [Ca2+], nor the calcium channel
blocker verapamil (10-6 M) ameliorated the TGF-[beta]1-induced
inhibition of cathepsin activities. However, TGF-[beta]1 raised the
pH in lysosomes, which obviously impaired the acidic cysteine
proteinases. Conclusion: the TGF-[beta]1-induced cellular hypertrophy
is caused by both enhanced protein synthesis and reduced protein
breakdown. Suppression of cathepsin B and L+B activities mediated
probably by an alkalinization in lysosomes is involved in the
decreased protein degradation.
Received 24 January 1995; accepted in final form 6 June 1995.
APS Manuscript Number F22-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.