Point Mutation of the Proteasome β5 Subunit Gene Is an Important Mechanism of Bortezomib Resistance in Bortezomib-Selected Variants of Jurkat T Cell Lymphoblastic Lymphoma/Leukemia Line

Shuqing Lü, Jianmin Yang, Jianmin Wang et al. JPET 326:423?431, 2008

Department of Hematology, Changhai Hospital,
Second Military Medical University,
174 Changhai Road, 200433 Shanghai, China

ABSTRACT
To study the mechanism of acquired resistance to bortezomib,
a new antitumor drug that is the first therapeutic proteasome上海长海医院血液内科吕书晴
inhibitor, we established a series of bortezomib-resistant T lymphoblastic
lymphoma/leukemia cell lines, designated the JurkatBs,
from the parental Jurkat line via repeated drug selection.
There were no significant differences in the growth curves or
colony formation between the JurkatB cells and parental Jurkat
cells. The effects of bortezomib on cytotoxicity, cell cycle arrest,
and induction of apoptosis were decreased in JurkatB cells compared
with parental Jurkat cells. A mutation in the proteasome β5
subunit (PSMB5) gene (G322A), which encodes an amino acid
change from Ala to Thr at polypeptide position 108, was detected
by sequencing full-length cDNA clones and direct polymerase
chain reaction products of the PSMB5 gene. Bortezomib caused
less inhibition of chymotrypsin-like activity in resistant cells. When
the G322A mutant PSMB5 was retrovirally introduced into parental
Jurkat cells, it conferred bortezomib resistance to these cells,
resulting in decreased cytotoxicity, apoptosis, and inhibition of
chymotrypsin-like activity. The predicted structure of A108Tmutated
PSMB5 shows a conformational change that suggests
decreased affinity to bortezomib. In short, the G322A mutation of
the PSMB5 gene is a novel mechanism for bortezomib resistance.