Induction of apoptosis by proteasome inhibitors in B-CLL cells is associated with downregulation of CD23 and inactivation of Notch2.
Recently, proteasome inhibitors (PI) have attracted interest as novel anticancer agents in B-cell chronic lymphocytic leukemia (B-CLL). A prominent feature of B-CLL cells is the high expression of CD23, which is closely related to cell survival and is regulated by Notch2. Since several components of the Notch signaling cascade are tightly regulated by proteasomal degradation, we studied the effect of PI on Notch2 activity and CD23 expression. Exposure of B-CLL cells to PI led to induction of apoptosis, a time- and dose-dependent downregulation of CD23 expression and a decline in DNA binding of transcriptionally active Notch2. In contrast, the transcription factor NF-AT and its putative target gene CD5, which is highly expressed in B-CLL cells, were unaffected. When the late phase of PI-induced apoptosis was arrested by inhibition of caspase 3, the reduction of Notch2 activity was still observed, indicating that reduction of active Notch2 took place already during an earlier phase of apoptosis. Enforced expression of constitutively active Notch2 decreased PI-mediated apoptosis in a human B-cell line. These data indicate that downregulation of CD23 and loss of Notch2 activity are early steps in PI-induced apoptosis of B-CLL lymphocytes and may be part of the full apoptotic response.
Duechler
M
M
Ludwig Boltzmann Institute for Cytokine Research, Medical University Vienna, Vienna, Austria.
Shehata
M
M
Schwarzmeier
J D
JD
Hoelbl
A
A
Hilgarth
M
M
Hubmann
R
R
D015703:Antigens, CD / Q000235:genetics; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D045744:Cell Line, Tumor; D017931:DNA Primers; D015972:Gene Expression Regulation, Neoplastic / Q000276:immunology*; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000473:pathology*; D011480:Protease Inhibitors / Q000494:pharmacology*; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D051883:Receptor, Notch2; D011956:Receptors, Cell Surface / Q000037:antagonists & inhibitors*; D017455:Receptors, IgE / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D015703:Antigens, CD; D000970:Antineoplastic Agents; D001897:Boronic Acids; D017931:DNA Primers; C497764:NOTCH2 protein, human; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D012333:RNA, Messenger; D051883:Receptor, Notch2; D011956:Receptors, Cell Surface; D017455:Receptors, IgE; D000069286:Bortezomib