LACTACYSTIN AND CLASTO-LACTACYSTIN BETA-LACTONE MODIFY MULTIPLE PROTEASOME BETA-SUBUNITS AND INHIBIT INTRACELLULAR PROTEIN-DEGRADATION AND MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I ANTIGEN PRESENTATION
A. Craiu et al., LACTACYSTIN AND CLASTO-LACTACYSTIN BETA-LACTONE MODIFY MULTIPLE PROTEASOME BETA-SUBUNITS AND INHIBIT INTRACELLULAR PROTEIN-DEGRADATION AND MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I ANTIGEN PRESENTATION, The Journal of biological chemistry, 272(20), 1997, pp. 13437-13445
The antibiotic lactacystin was reported to covalently modify beta-subu
nit X of the mammalian 20 S proteasome and inhibit several of its pept
idase activities, However, we demonstrate that [H-3]lactacystin treatm
ent modifies all the proteasome's catalytic beta-subunits. Lactacystin
and its more potent derivative beta-lactone irreversibly inhibit prot
ein breakdown and the chymotryptic, tryptic, and peptidylglutamyl acti
vities of purified 20 S and 26 S particles, although at different rate
s, Exposure to these agents for 1 to 2 h reduced the degradation of sh
ort- and long-lived proteins in four different mammalian cell lines, U
nlike peptide aldehyde inhibitors, lactacystin and the beta-lactone do
not inhibit lysosomal degradation of an endocytosed protein, These ag
ents block class I antigen presentation of a model protein, ovalbumin
(synthesized endogenously or loaded exogenously), but do not affect pr
esentation of the peptide epitope SIINFEKL, which does not require pro
teolysis for presentation. Generation of most peptides required for fo
rmation of stable class I heterodimers is also inhibited, Because thes
e agents inhibited protein breakdown and antigen presentation similarl
y in interferon-gamma-treated cells (where proteasomes contain LMP2 an
d LMP7 subunits in place of X and Y), all beta-subunits must be affect
ed similarly, These findings confirm our prior conclusions that protea
somes catalyze the bulk of protein breakdown in mammalian cells and ge
nerate the majority of class I-bound epitopes for immune recognition.