Bortezomib blocks the catabolic process of autophagy via a cathepsin-dependent mechanism, affects endoplasmic reticulum stress, and induces caspase-dependent cell death in antiestrogen–sensitive and resistant ER+ breast cancer cells

Abstract

In recent studies, we and others showed that autophagy is critical to estrogen receptor positive (ER+) breast cancer cell survival and the development of antiestrogen resistance. Consequently, new approaches are warranted for targeting autophagy in breast cancer cells undergoing antiestrogen therapy. Because crosstalk has been demonstrated between the autophagy- and proteasome-mediated pathways of protein degradation, this study investigated how the proteasome inhibitor bortezomib affects autophagy and cell survival in antiestrogen-treated ER+ breast cancer cells. Bortezomib, at clinically achievable doses, induced a robust death response in ER+, antiestrogen-sensitive and antiestrogen-resistant breast cancer cells undergoing hormonal therapy. Cleavage of PARP and lamin A was detectable as a read-out of cell death, following bortezomib-induced mitochondrial dysfunction. Prior to induction of cell death, bortezomib-treated cells showed high levels of light chain 3 (LC3) and p62, two protein markers for autophagy. The accumulation of these proteins was due to bortezomib-mediated blockade of long-lived protein turnover during macroautophagy. This novel action of bortezomib was linked to its blockade of cathepsin-L activity, which is required for autolysosomal-mediated protein turnover in ER+ breast cancer cells. Further, bortezomib-treated breast cancer cells showed induction of the unfolded protein response, with upregulation of CH OP and GRP78. Bortezomib also induced high levels of the pro-apoptotic protein BNIP3. Knockdown of CH OP and/or BNIP3 expression via RNAi targeting significantly attenuated the death-promoting effects of bortezomib. Thus, bortezomib inhibits prosurvival autophagy, in addition to its known function in blocking the proteasome, and is cytotoxic to hormonally treated ER+ breast cancer cells. These findings indicate that combining a proteasome inhibitor like bortezomib with antiestrogen therapy may have therapeutic advantage in the management of early-stage breast cancer.

Roles of Estrogen Receptor and p21Waf1 in Bortezomib-Induced Growth Inhibition in Human Breast Cancer Cells

“…2D). We also found a 50% decreased of ERa expression at 24 hours as previously showed by Powers and colleagues and Periyasamy-Thandavan and colleagues (33,34). To evidence the ERa role in p21 regulation, we knocked down ERa with specific siRNA.…”

p62/Sequestosome-1 Up-regulation Promotes ABT-263-induced Caspase-8 Aggregation/Activation on the Autophagosome

“…In addition to chloroquine, recent data indicate that bortezomib can also inhibit autophagy via a cathepsin-dependent mechanism that results in p62 up-regulation (12). Our data indicate that p62 up-regulation is critical to its ability to aggregate caspase-8 on the autophagosome (LC3II) in ABT-263-treated cells.…”

“…Because p62 is degraded by autophagy, its level can be increased by autophagy inhibition. Specifically, autophagy blockade by chloroquine and/or by cathepsin-dependent inhibition using bortezomib (12) were shown to upregulate p62 expression (Fig. 1C) and to enhance ABT-263-induced caspase cleavage (Fig.…”

“…p62 serves as an ubiquitin-binding protein that chaperones protein aggregates to the lysosome or the proteasome (7) for degradation by autophagy (8 -10). In addition to genetic means, autophagy can be disabled by the lysosomal inhibitor chloroquine (11) or by bortezomib, which blocks autophagy via a cathepsin-dependent mechanism resulting in up-regulation of p62 (12). p62 is rich in protein-interacting sequences and contains domains that include a protein-protein interaction module (PB1) that facilitates its oligomerization, a ubiquitin-associated (UBA) 3 domain, and an LC3 interaction region that are essential for p62 function (8,13,14).…”

Proteasome Subunit Beta Type 1 P11A Polymorphism Is a New Prognostic Marker in Multiple Myeloma

“…Bortezomib is thought to drive cells to programmed cell death by inhibiting the proteasomal degradation of unfolded proteins thereby overwhelming the degradation capacity of the cell and triggering the unfolded protein response. 26,27 This may help explain why bortezomib has an apparent potentiating effect when given as co-therapy with 17-AAG, a heat shock protein 90 inhibitor in patients with relapsed or refractory MM. 12 As regards to another component of the proteasome complex, namely PSMA5 it has been reported that low plasma levels are associated with longer PFS in mantle cell lymphoma treated with bortezomib.…”