3-Hydroxy-3-methylglutaryl coenzyme A reductase is sterol-dependently cleaved by cathepsin L-type cysteine protease in the isolated endoplasmic reticulum
T. Moriyama et al., 3-Hydroxy-3-methylglutaryl coenzyme A reductase is sterol-dependently cleaved by cathepsin L-type cysteine protease in the isolated endoplasmic reticulum, ARCH BIOCH, 386(2), 2001, pp. 205-212
We have recently shown that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA)
reductase, an endoplasmic reticulum (ER) membrane protein, is degraded in
ER membranes prepared from sterol pretreated cells and that such degradatio
n is catalyzed by a cysteine protease within the reductase membrane domain.
The use of various protease inhibitors suggested that degradation of HMG-C
oA reductase in vitro is catalyzed by a cathepsin L-type cysteine protease,
Purified ER contains E-64-sensitive cathepsin L activity whose inhibitor s
ensitivity was well matched to that of HMG-CoA reductase degradation in vit
ro. CLIK-148 (cathepsin L inhibitor) inhibited degradation of HMG-CoA reduc
tase in vitro. Purified cathepsin L also efficiently cleaved HMG-CoA reduct
ase in isolated ER preparations. To determine whether a cathepsin L-type cy
steine protease is involved in sterol-regulated degradation of HMG-CoA redu
ctase in vivo we examined the effect of E-64d, a membrane-permeable cystein
e protease inhibitor, in living cells, While lactacystin, a proteasome-spec
ific inhibitor, inhibited sterol-dependent degradation of HMG-CoA reductase
, E-64d failed to do so. In contrast, degradation of HMG-CoA reductase in s
onicated cells was inhibited by E-64d, CLIK-148, and leupeptin but not by l
actacystin, Our results indicate that HMG-CoA reductase is degraded by the
proteasome under normal conditions in living cells and that it is cleaved b
y cathepsin L leaked from lysosomes during preparation of the ER, thus clar
ifying the apparently paradoxical in vivo and in vitro results. Cathepsin L
-dependent proteolysis was observed to occur preferentially in sterol-pretr
eated cells, suggesting that sterol treatment results in conformational cha
nges in HMG-CoA reductase that make it more susceptible to such cleavage. (
C) 2001 Academic Press.