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BIM-mediated AKT phosphorylation is a key modulator of arsenic trioxide-induced apoptosis in cisplatin-sensitive and -resistant ovarian cancer cells.

Yuan Z, Wang F, Zhao Z, Zhao X, Qiu J, Nie C, Wei Y - PLoS ONE (2011)

Bottom Line: However, surprisingly, gene silencing of AKT or FOXO3A had little effect on BIM expression and phosphorylation.Moreover, the activation of caspase-3 by ATO treatment improved AKT dephosphorylation, not only by cleaving the regulatory A subunit of protein phosphatase 2A (PP2A), but also by increasing its activation.Furthermore, our data indicated that the c-Jun N-terminal kinases (JNK) pathway is involved in the regulation of BIM expression.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China.

ABSTRACT

Background: Chemo-resistance to cisplatin-centered cancer therapy is a major obstacle to the effective treatment of human ovarian cancer. Previous reports indicated that arsenic trioxide (ATO) induces cell apoptosis in both drug-sensitive and -resistant ovarian cancer cells.

Principal findings: In this study, we determined the molecular mechanism of ATO-induced apoptosis in ovarian cancer cells. Our data demonstrated that ATO induced cell apoptosis by decreasing levels of phosphorylated AKT (p-AKT) and activating caspase-3 and caspase-9. Importantly, BIM played a critical role in ATO-induced apoptosis. The inhibition of BIM expression prevented AKT dephosphorylation and inhibited caspase-3 activation during cell apoptosis. However, surprisingly, gene silencing of AKT or FOXO3A had little effect on BIM expression and phosphorylation. Moreover, the activation of caspase-3 by ATO treatment improved AKT dephosphorylation, not only by cleaving the regulatory A subunit of protein phosphatase 2A (PP2A), but also by increasing its activation. Furthermore, our data indicated that the c-Jun N-terminal kinases (JNK) pathway is involved in the regulation of BIM expression.

Conclusions: We demonstrated the roles of BIM in ATO-induced apoptosis and the molecular mechanisms of BIM expression regulated by ATO during ovarian cancer cell apoptosis. Our findings suggest that BIM plays an important role in regulating p-AKT by activating caspase-3 and that BIM mediates the level of AKT phosphorylation to determine the threshold for overcoming cisplatin resistance in ovarian cancer cells.

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A diagram of signaling pathway for ATO-mediated BIM activation and apoptosis in ovarian caner cells.ATO induced JNK pathway activation, and then activated JNK regulated BIM activation. BIM expression upregulated caspase-3 activation and subsequent apoptosis at the first stage. Activated caspase-3 triggered PP2A-linked AKT dephosphorylation, and then AKT dephosphorylation further enhanced caspase-3 cleavage and apoptosis at the second stage.
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pone-0020586-g007: A diagram of signaling pathway for ATO-mediated BIM activation and apoptosis in ovarian caner cells.ATO induced JNK pathway activation, and then activated JNK regulated BIM activation. BIM expression upregulated caspase-3 activation and subsequent apoptosis at the first stage. Activated caspase-3 triggered PP2A-linked AKT dephosphorylation, and then AKT dephosphorylation further enhanced caspase-3 cleavage and apoptosis at the second stage.

Mentions: In this study, we attempted to determine how BIM controls the phosphorylation of AKT during ATO-induced ovarian cancer cell apoptosis and which factors mediate BIM expression during cell apoptosis. We first examined the mechanism of p-AKT, as regulated by BIM. We observed that BIM shRNA could prevent caspase-3 cleavage, suggesting that BIM expression is an upstream event in caspase-3 activation. PP2A-linked, caspase-dependent pathways were required for downregulation of AKT kinase [34], [39], [40]. In this study, we also observed that AKT phosphorylation was regulated by caspase-3-mediated PP2A activation. Our results further confirm that BIM-mediated AKT phosphorylation requires two stages. In the first stage, BIM expression is regulated during ATO-induced apoptosis, and activated BIM triggers caspase-3 cleavage and subsequent events. In the second stage, caspase-3 activation mediates AKT dephosphorylation, further enhancing caspase-3 activation and ATO-induced apoptosis through a positive-feedback regulation (Figure 7). Subsequently, we detected which factors regulate BIM activation. A previous study suggested that ATO induces the JNK pathway activation in apoptosis [41]. In fact, activated JNK could modulate BIM expression and phosphorylation [42], [43]. Accordingly, we propose that JNK may participate in regulating BIM expression and phosphorylation during ATO-induced ovarian cancer cell apoptosis. Our data support the hypothesis that JNK activation triggers BIM expression and phosphorylation in ATO-induced apoptosis. Moreover, JNK activation was observed to be an early response to ATO treatment and was required for subsequent apoptotic events in cells. These result were consistent with a recent report from García-Pardo's group [51]. Their study indicated that ATO induces JNK activation, resulting in inhibition of the PI-3K/AKT signaling pathway in B-CLL cells and upregulation of PTEN. However, our results did not demonstrate PTEN upregulation during ATO-induced apoptosis. This discrepancy regarding the process of PTEN induction requires further research.


BIM-mediated AKT phosphorylation is a key modulator of arsenic trioxide-induced apoptosis in cisplatin-sensitive and -resistant ovarian cancer cells.

Yuan Z, Wang F, Zhao Z, Zhao X, Qiu J, Nie C, Wei Y - PLoS ONE (2011)

A diagram of signaling pathway for ATO-mediated BIM activation and apoptosis in ovarian caner cells.ATO induced JNK pathway activation, and then activated JNK regulated BIM activation. BIM expression upregulated caspase-3 activation and subsequent apoptosis at the first stage. Activated caspase-3 triggered PP2A-linked AKT dephosphorylation, and then AKT dephosphorylation further enhanced caspase-3 cleavage and apoptosis at the second stage.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3105099&req=5

pone-0020586-g007: A diagram of signaling pathway for ATO-mediated BIM activation and apoptosis in ovarian caner cells.ATO induced JNK pathway activation, and then activated JNK regulated BIM activation. BIM expression upregulated caspase-3 activation and subsequent apoptosis at the first stage. Activated caspase-3 triggered PP2A-linked AKT dephosphorylation, and then AKT dephosphorylation further enhanced caspase-3 cleavage and apoptosis at the second stage.
Mentions: In this study, we attempted to determine how BIM controls the phosphorylation of AKT during ATO-induced ovarian cancer cell apoptosis and which factors mediate BIM expression during cell apoptosis. We first examined the mechanism of p-AKT, as regulated by BIM. We observed that BIM shRNA could prevent caspase-3 cleavage, suggesting that BIM expression is an upstream event in caspase-3 activation. PP2A-linked, caspase-dependent pathways were required for downregulation of AKT kinase [34], [39], [40]. In this study, we also observed that AKT phosphorylation was regulated by caspase-3-mediated PP2A activation. Our results further confirm that BIM-mediated AKT phosphorylation requires two stages. In the first stage, BIM expression is regulated during ATO-induced apoptosis, and activated BIM triggers caspase-3 cleavage and subsequent events. In the second stage, caspase-3 activation mediates AKT dephosphorylation, further enhancing caspase-3 activation and ATO-induced apoptosis through a positive-feedback regulation (Figure 7). Subsequently, we detected which factors regulate BIM activation. A previous study suggested that ATO induces the JNK pathway activation in apoptosis [41]. In fact, activated JNK could modulate BIM expression and phosphorylation [42], [43]. Accordingly, we propose that JNK may participate in regulating BIM expression and phosphorylation during ATO-induced ovarian cancer cell apoptosis. Our data support the hypothesis that JNK activation triggers BIM expression and phosphorylation in ATO-induced apoptosis. Moreover, JNK activation was observed to be an early response to ATO treatment and was required for subsequent apoptotic events in cells. These result were consistent with a recent report from García-Pardo's group [51]. Their study indicated that ATO induces JNK activation, resulting in inhibition of the PI-3K/AKT signaling pathway in B-CLL cells and upregulation of PTEN. However, our results did not demonstrate PTEN upregulation during ATO-induced apoptosis. This discrepancy regarding the process of PTEN induction requires further research.

Bottom Line: However, surprisingly, gene silencing of AKT or FOXO3A had little effect on BIM expression and phosphorylation.Moreover, the activation of caspase-3 by ATO treatment improved AKT dephosphorylation, not only by cleaving the regulatory A subunit of protein phosphatase 2A (PP2A), but also by increasing its activation.Furthermore, our data indicated that the c-Jun N-terminal kinases (JNK) pathway is involved in the regulation of BIM expression.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu, China.

ABSTRACT

Background: Chemo-resistance to cisplatin-centered cancer therapy is a major obstacle to the effective treatment of human ovarian cancer. Previous reports indicated that arsenic trioxide (ATO) induces cell apoptosis in both drug-sensitive and -resistant ovarian cancer cells.

Principal findings: In this study, we determined the molecular mechanism of ATO-induced apoptosis in ovarian cancer cells. Our data demonstrated that ATO induced cell apoptosis by decreasing levels of phosphorylated AKT (p-AKT) and activating caspase-3 and caspase-9. Importantly, BIM played a critical role in ATO-induced apoptosis. The inhibition of BIM expression prevented AKT dephosphorylation and inhibited caspase-3 activation during cell apoptosis. However, surprisingly, gene silencing of AKT or FOXO3A had little effect on BIM expression and phosphorylation. Moreover, the activation of caspase-3 by ATO treatment improved AKT dephosphorylation, not only by cleaving the regulatory A subunit of protein phosphatase 2A (PP2A), but also by increasing its activation. Furthermore, our data indicated that the c-Jun N-terminal kinases (JNK) pathway is involved in the regulation of BIM expression.

Conclusions: We demonstrated the roles of BIM in ATO-induced apoptosis and the molecular mechanisms of BIM expression regulated by ATO during ovarian cancer cell apoptosis. Our findings suggest that BIM plays an important role in regulating p-AKT by activating caspase-3 and that BIM mediates the level of AKT phosphorylation to determine the threshold for overcoming cisplatin resistance in ovarian cancer cells.

Show MeSH
Related in: MedlinePlus