SUPPRESSING ROLE OF TRANSFORMING GROWTH-FACTOR-BETA-1 ON CATHEPSIN ACTIVITY IN CULTURED KIDNEY TUBULE CELLS

Elevated expression and activity of transforming growth factor-beta 1 (TGF-beta 1) have been indicated in various renal diseases, implicatin g the potential involvement of this growth factor in the accumulation of extracellular matrix. To assess its potential role on protein turno ver in tubule cells, we investigated in LLC-PK1 cells the effects of T GF-beta 1 on the activities of lysosomal cysteine proteinases cathepsi ns 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 to either the basolateral or 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 enh anced suppression of the enzyme activities (B -37.8%, L + B -31.4%). T his suppression of cathepsin activities was accompanied by a reduction of cellular protein degradation rate by 20.0% after 24 h and 51.7% af ter 48 h. Furthermore, TGF-beta 1 stimulated cellular protein synthesi s by 50.0% after 48 h. The combined effects on protein turnover result ed in cellular hypertrophy: increases of both protein content and cell size after 48 h. Concerning the underlying mechanism, TGF-beta 1 did not induce a rise in intracellular Ca2+ concentration nor did Ca2+ cha nnel blocker verapamil (10(-6) M) ameliorate the TGF-beta 1-induced in hibition of cathepsin activities. However TGF-beta 1 raised the pH in lysosomes, which obviously impaired the acidic cysteine proteinases. I n conclusion, the TGF-beta 1-induced cellular hypertrophy is caused by both enhanced protein synthesis and reduced protein breakdown. Suppre ssion of cathepsin B and L + B activities mediated probably by an alka linization in lysosomes in involved in the decreased protein degradati on.