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Bax/Bak activation in the absence of Bid, Bim, Puma, and p53.

ABSTRACT: How BH3-only proteins activate Bax/Bak, the two gateway proteins of the mitochondria-dependent apoptotic pathway, remains incompletely understood. Although all pro-apoptotic BH3-only proteins are known to bind/neutralize the anti-apoptotic Bcl-2 proteins, the three most potent ones, Bid (tBid), Bim, and Puma, possess an additional activity of directly activating Bax/Bak in vitro. This latter activity has been proposed to be responsible for triggering Bax/Bak activation following apoptotic stimulation. To test this hypothesis, we generated Bid(-/)(-)Bim(-/)(-)Puma(-/)(-) (TKO), TKO/Bax(-/)(-)/Bak(-/)(-) (PentaKO), and PentaKO/Mcl-1(-/-) (HexaKO) HCT116 cells through gene editing. Surprisingly, although the TKO cells were resistant to several apoptotic stimuli, robust apoptosis was induced upon the simultaneous inactivation of Bcl-xL and Mcl-1, two anti-apoptotic Bcl-2 proteins known to suppress Bax/Bak activation and activity. Importantly, such apoptotic activity was completely abolished in the PentaKO cells. In addition, ABT-737, a BH3 mimetic that inhibits Bcl-xL/Bcl-w/Bcl-2, induced Bax activation in HexaKO cells reconstituted with endogenous level of GFP-Bax. Further, by generating TKO/p53(-/-) (QKO) cells, we demonstrated that p53, a tumor suppressor postulated to directly activate Bax, is not required for Bid/Bim/Puma-independent Bax/Bak activation. Together, these results strongly suggest that the direct activation activities of Bid (tBid), Bim, Puma, and p53 are not essential for activating Bax/Bak once the anti-apoptotic Bcl-2 proteins are neutralized.

SUBMITTER: Zhang J

PROVIDER: S-EPMC5143395 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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Bax/Bak activation in the absence of Bid, Bim, Puma, and p53.

Zhang J J Huang K K O'Neill K L KL Pang X X Luo X X

Cell death & disease 20160616

How BH3-only proteins activate Bax/Bak, the two gateway proteins of the mitochondria-dependent apoptotic pathway, remains incompletely understood. Although all pro-apoptotic BH3-only proteins are known to bind/neutralize the anti-apoptotic Bcl-2 proteins, the three most potent ones, Bid (tBid), Bim, and Puma, possess an additional activity of directly activating Bax/Bak in vitro. This latter activity has been proposed to be responsible for triggering Bax/Bak activation following apoptotic stimul ...[more]

PMID: 27310874

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Project description:Despite recent therapeutic advances that have doubled the median survival time of patients with multiple myeloma, intratumor genetic heterogeneity contributes to disease progression and emergence of drug resistance. miRNAs are noncoding small RNAs that play important roles in the regulation of gene expression and have been implicated in cancer progression and drug resistance. We investigated the role of the miR-221-222 family in dexamethasone-induced drug resistance in multiple myeloma using the isogenic cell lines MM1R and MM1S, which represent models of resistance and sensitivity, respectively. Analysis of array comparative genome hybridization data revealed gain of chromosome X regions at band p11.3, wherein the miR-221-222 resides, in resistant MM1R cells but not in sensitive MM1S cells. DNA copy number gains in MM1R cells were associated with increased miR-221-222 expression and downregulation of p53-upregulated modulator of apoptosis (PUMA) as a likely proapoptotic target. We confirmed PUMA mRNA as a direct target of miR-221-222 in MM1S and MM1R cells by both gain-of-function and loss-of-function studies. In addition, miR-221-222 treatment rendered MM1S cells resistant to dexamethasone, whereas anti-miR-221-222 partially restored the dexamethasone sensitivity of MM1R cells. These studies have uncovered a role for miR-221-222 in multiple myeloma drug resistance and suggest a potential therapeutic role for inhibitors of miR-221-222 binding to PUMA mRNA as a means of overcoming dexamethasone resistance in patients. The clinical utility of this approach is predicated on the ability of antisense miR-221-222 to increase survival while reducing tumor burden and is strongly supported by the metastatic propensity of MM1R cells in preclinical mouse xenograft models of multiple myeloma. Moreover, our observation of increased levels of miR-221-222 with decreased PUMA expression in multiple myeloma cells from patients at relapse versus untreated controls suggests an even broader role for miR-221-222 in drug resistance and provides a rationale for the targeting of miR-221-222 as a means of improving patient outcomes.

Dataset Information

Bax/Bak activation in the absence of Bid, Bim, Puma, and p53.

Publications

Bax/Bak activation in the absence of Bid, Bim, Puma, and p53.

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