Proteasome inhibition activates the mitochondrial pathway of apoptosis in human CD4⁺ T cells

Abstract

We have previously shown that inhibition of the proteolytic activity of the proteasome induces apoptosis and suppresses essential functions of activated human CD4(+) T cells, and we report now the detailed mechanisms of apoptosis following proteasome inhibition in these cells. Here we show that proteasome inhibition by bortezomib activates the mitochondrial pathway of apoptosis in activated CD4(+) T cells by disrupting the equilibrium of pro-apoptotic and anti-apoptotic proteins at the outer mitochondrial membrane (OMM) and by inducing the generation of reactive oxygen species (ROS). Proteasome inhibition leads to accumulation of pro-apoptotic proteins PUMA, Noxa, Bim and p53 at the OMM. This event provokes mitochondrial translocation of activated Bax and Bak homodimers, which induce loss of mitochondrial membrane potential (DeltaPsim). Breakdown of DeltaPsim is followed by rapid release of pro-apoptotic Smac/DIABLO and HtrA2 from mitochondria, whereas release of cytochrome c and AIF is delayed. Cytoplasmic Smac/DIABLO and HtrA2 antagonize IAP-mediated inhibition of partially activated caspases, leading to premature activation of caspase-3 followed by activation of caspase-9. Our data show that proteasome inhibition triggers the mitochondrial pathway of apoptosis by activating mutually independent apoptotic pathways. These results provide novel insights into the mechanisms of apoptosis induced by proteasome inhibition in activated T cells and underscore the future use of proteasome inhibitors for immunosuppression.

Diethyldithiocarbamate complex with copper: the mechanism of action in cancer cells

“…This result was reported for several cell lines and multiple of proteasome inhibitors, including bortezomib [87][88][89][90][91][92], MG132 [93][94][95], lactacystin [95][96][97], aLLN [95], MG262 [95], carbobenzoxyLeu-Leu-Leu-aldehyde [97] and N-benzyloxycarbonyl-IleGlu (O-t-butyl)-Ala-leucinal [98]. ROS generation by proteasome inhibitors induces c-Jun N-terminal kinase (JNK) [92] and activator protein-1 (AP-1) activation [95], loss of mitochondrial membrane potential ( m) [87, 91-94, 97, 98], cytochrome-c release [87, 90-92, 97, 98], caspase-3 activation [87][88][89][90][91][92][93]97] and subsequent apoptosis. Similar events (e.g., JNK and AP-1 activation, decreased m and caspase-3 activation) were observed in cells treated with mixtures of EtDTC-Cu(II) [23] or PyDTC-Cu(II) [24].…”

Immediate early response gene X-1, a potential prognostic biomarker in cancers

“…We can, thus, expect therapeutic effects of bortezomib in the setting of IEX-1 overexpression in CTCL patients. Moreover, it has been recently shown that bortezomib activates the mitochondrial pathway of apoptosis in activated CD4 + T cells by altering the equilibrium of proapoptotic and antiapoptotic proteins at the outer mitochondrial membrane and by inducing ROS production [65]. Possible involvement of IEX-1 in bortezomib-induced therapeutics merits further investigation.…”

Immunomodulatory effects of anti-angiogenic drugs

“…51,52 It was further described that exposure to bortezomib led to an increased incidence of varicella-zoster infections and interferes with the priming of naive T cells. 52 Additionally, proteasome inhibition triggered the mitochondrial pathway of apoptosis by activating mutually independent apoptotic pathways 53 and suppressed essential immune functions of human CD4 þ T cells. 54 Immunomodulation by anti-angiogenic drugs A Heine et al Naturally occurring Tregs were resistant to pro-apoptotic effects of bortezomib.…”