BIRC6 mediates imatinib resistance independently of Mcl-1

Abstract

Baculoviral IAP repeat containing 6 (BIRC6) is a member of the inhibitors of apoptosis proteins (IAPs), a family of functionally and structurally related proteins that inhibit apoptosis. BIRC6 has been implicated in drug resistance in several different human cancers, however mechanisms regulating BIRC6 have not been extensively explored. Our phosphoproteomic analysis of an imatinib-resistant chronic myelogenous leukemia (CML) cell line (MYL-R) identified increased amounts of a BIRC6 peptide phosphorylated at S480, S482, and S486 compared to imatinib-sensitive CML cells (MYL). Thus we investigated the role of BIRC6 in mediating imatinib resistance and compared it to the well-characterized anti-apoptotic protein, Mcl-1. Both BIRC6 and Mcl-1 were elevated in MYL-R compared to MYL cells. Lentiviral shRNA knockdown of BIRC6 in MYL-R cells increased imatinib-stimulated caspase activation and resulted in a ~20-25-fold increase in imatinib sensitivity, without affecting Mcl-1. Treating MYL-R cells with CDK9 inhibitors decreased BIRC6 mRNA, but not BIRC6 protein levels. By contrast, while CDK9 inhibitors reduced Mcl-1 mRNA and protein, they did not affect imatinib sensitivity. Since the Src family kinase Lyn is highly expressed and active in MYL-R cells, we tested the effects of Lyn inhibition on BIRC6 and Mcl-1. RNAi-mediated knockdown or inhibition of Lyn (dasatinib/ponatinib) reduced BIRC6 protein stability and increased caspase activation. Inhibition of Lyn also increased formation of an N-terminal BIRC6 fragment in parallel with reduced amount of the BIRC6 phosphopeptide, suggesting that Lyn may regulate BIRC6 phosphorylation and stability. In summary, our data show that BIRC6 stability is dependent on Lyn, and that BIRC6 mediates imatinib sensitivity independently of Mcl-1 or CDK9. Hence, BIRC6 may be a novel target for the treatment of drug-resistant CML where Mcl-1 or CDK9 inhibitors have failed.

<p>Long Non-Coding RNA DLEU1 Up-Regulates BIRC6 Expression by Competitively Sponging miR-381-3p to Promote Cisplatin Resistance in Nasopharyngeal Carcinoma</p>

“…[22][23][24][25] Several studies also demonstrated that BIRC6 participated in tumor cell chemoresistance, including imatinib, enzalutamide and cisplatin. [26][27][28] Here, we observed that BIRC6 level was higher in NPC tissues compared with normal controls and strongly correlated with DLEU1 expression. DLEU1 knock-down reduced BIRC6 expression while BIRC6 knock-down reversed DLEU1-modulated DDP resistance in NPC cells.…”

Mitochondrial Protease ClpP is a Target for the Anticancer Compounds ONC201 and Related Analogues

“…Caspase 3/7 activity was analyzed using a fluorescent peptide substrate (7-amido-4-methylcoumarin). 19 The cells were plated at 8 × 10 5 cells per plate (6 cm plate) and treated for 24 h with 3, 30, and 300 nM TR57 and TR31; 300 nM, 3 μM, and 30 μM ONC201, as well as 0.1% DMSO and 10 nM staurosporine (IC25 on SUM159 cells determined by MTS cell viability assay (data not shown)). The samples were harvested by mechanical scraping of the cells into 400 μL of lysis buffer (50 mM HEPES (pH: 7.4), 5 mM CHAPS, and 5 mM DTT), and caspase activity was measured as described earlier.…”

“…The samples were harvested by mechanical scraping of the cells into 400 μL of lysis buffer (50 mM HEPES (pH: 7.4), 5 mM CHAPS, and 5 mM DTT), and caspase activity was measured as described earlier. 19…”

MiR-204 acts as a potential therapeutic target in acute myeloid leukemia by increasing BIRC6-mediated apoptosis

“…Notably, in addition to ubiquitin degradation function, BIRC6 carries a baculovirus IAP repeat (BIR) domain characteristic for the binding sites of Caspase and confers cell apoptosis ( 26 ). Moreover, Caspase in turn mediates BIRC6 degradation, which further decreases chemoresistance in human cancer ( 27 ). These findings suggest that BIRC6 also regulates cell apoptosis by a p53-independent pathway.…”