Tumor-cell resistance to death receptor–induced apoptosis through mutational inactivation of the proapoptotic Bcl-2 homolog Bax

Abstract

The importance of Bax for induction of tumor apoptosis through death receptors remains unclear. Here we show that Bax can be essential for death receptor--mediated apoptosis in cancer cells. Bax-deficient human colon carcinoma cells were resistant to death-receptor ligands, whereas Bax-expressing sister clones were sensitive. Bax was dispensable for apical death-receptor signaling events including caspase-8 activation, but crucial for mitochondrial changes and downstream caspase activation. Treatment of colon tumor cells deficient in DNA mismatch repair with the death-receptor ligand apo2 ligand (Apo2L)/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selected in vitro or in vivo for refractory subclones with Bax frameshift mutations including deletions at a novel site. Chemotherapeutic agents upregulated expression of the Apo2L/TRAIL receptor DR5 and the Bax homolog Bak in Baxminus sign/minus sign cells, and restored Apo2L/TRAIL sensitivity in vitro and in vivo. Thus, Bax mutation in mismatch repair--deficient tumors can cause resistance to death receptor--targeted therapy, but pre-exposure to chemotherapy rescues tumor sensitivity.

HGS-ETR1, a fully human TRAIL-receptor 1 monoclonal antibody, induces cell death in multiple tumour types in vitro and in vivo

“…The reason for this spectrum of response to TRAIL-R activation is due to the complex downstream regulation of the cell death pathway. Intracellular levels of pro-and antiapoptotic factors such as cFLIP (Kim et al, 2000;Sayers et al, 2003), XIAP Chawla-Sarkar et al, 2002), BCL-2 family members (Burns and El-Deiry, 2001;LeBlanc et al, 2002), and DISC formation and caspase 8 activity (Trauzold et al, 2003) have been reported to regulate cell sensitivity to TRAIL-induced programmed cell death in both tumour and normal cells. Although TRAIL decoy receptors have been implicated in the regulation of TRAIL signalling, the presence of decoy receptors (DcR1, DcR2) are not a factor in resistance to HGS-ETR1 activity, as HGS-ETR1 does not bind to either of these receptors (Figure 1).…”

“…Interestingly, this regression occurred immediately after injection of HGS-ETR1, suggesting that the antitumour action of the mAb to induce apoptosis and reduce tumour volume is rapid. Various mechanisms have been proposed for the enhanced cell death observed by combination of chemotherapy with TRAIL, including upregulation of TRAIL-R1 and TRAIL-R2 (Bouralexis et al, 2001(Bouralexis et al, , 2003Nimmanapalli et al, 2001;Singh et al, 2003), increased levels of the proapoptotic protein, Bak (LeBlanc et al, 2002) and suppression of prosurvival pathways (Asakuma et al, 2003). We have initiated experiments to investigate the mechanisms responsible for the enhancement of antitumour activity by HGS-ETR1 in combination with chemotherapeutic agents.…”

“…While TRAIL alone induces apoptosis in sensitive cancer cell lines, TRAIL activity can be enhanced upon coexposure with various chemotherapeutic agents Keane et al, 1999;Yamanaka et al, 2000;Bouralexis et al, 2001;Evdokiou et al, 2002;Shimoyama et al, 2002). Tumour cells that are resistant to TRAIL can be sensitised by combination treatment with various chemotherapeutic drugs (LeBlanc et al, 2002). In vivo, the antitumour efficacy of TRAIL in combination with chemotherapeutic agents, such as 5-fluorouracil and irinotecan, was greater than the activity of either agent alone Revised 27 January 2005;accepted 2 February 2005Nagane et al, 2000Naka et al, 2002;Ray and Almasan, 2003;Singh et al, 2003).…”

Downregulation of Bid is associated with PKCɛ-mediated TRAIL resistance

“…Resistance to TRAIL-mediated apoptosis by tumor cells, however, limits its therapeutic use. 2,3 An understanding of the mechanism(s) of TRAIL resistance is essential to improve its application in cancer therapy.…”

“…3,[12][13][14][15] The presence of antiapoptotic proteins, such as Akt or Bcl-2 family members can also contribute to TRAIL resistance by affecting either the extrinsic or the intrinsic cell death pathway. 2,10,[15][16][17][18] Protein kinase C (PKC), a family of phospholipid-dependent serine/threonine kinases, is emerging as a critical regulator of cellular responses to TRAIL. 12,14,[18][19][20][21][22][23][24] The PKC family consists of 11 isoforms that are classified as conventional (a, b1, b2 and g), novel (d, e, Z and y) or atypical (z and i/l).…”