Limits...
Induction of apoptosis by directing oncogenic Bcr-Abl into the nucleus.

Huang ZL, Gao M, Li QY, Tao K, Xiao Q, Cao WX, Feng WL - Oncotarget (2013)

Bottom Line: We show that a rapalog nuclear transport system (RNTS) containing six nuclear localization signals directs Bcr-Abl into the nucleus and that nuclear entrapped Bcr-Abl induces apoptosis and inhibits proliferation of CML cells by activating p73 and shutting down cytoplasmic oncogenic signals mediated by Bcr-Abl.Coupling cytoplasmic depletion with nuclear entrapment of Bcr-Abl synergistically enhances the inhibitory effect of nuclear Bcr-Abl on its oncogenicity in mice.These results provide evidence that direction of cytoplasmic Bcr-Abl to the nucleus offers an alternative CML therapy.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Hematology, Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of Education, Chongqing Medical University, Chongqing, People's Republic of China.

ABSTRACT
The chimeric Bcr-Abl oncoprotein, which causes chronic myeloid leukemia, mainly localizes in the cytoplasm, and loses its ability to transform cells after moving into the nucleus. Here we report a new strategy to convert Bcr-Abl to be an apoptotic inducer by altering its subcellular localization. We show that a rapalog nuclear transport system (RNTS) containing six nuclear localization signals directs Bcr-Abl into the nucleus and that nuclear entrapped Bcr-Abl induces apoptosis and inhibits proliferation of CML cells by activating p73 and shutting down cytoplasmic oncogenic signals mediated by Bcr-Abl. Coupling cytoplasmic depletion with nuclear entrapment of Bcr-Abl synergistically enhances the inhibitory effect of nuclear Bcr-Abl on its oncogenicity in mice. These results provide evidence that direction of cytoplasmic Bcr-Abl to the nucleus offers an alternative CML therapy.

Show MeSH

Related in: MedlinePlus

RNTS activates p73 and its downstream target molecules
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3926824&req=5

Figure 4: RNTS activates p73 and its downstream target molecules

Mentions: Nuclear c-Abl kinase can be activated by DNA damage to induce expression of p73 protein, a functional homolog of the tumor suppressor p53, and then p73 induces apoptosis of cells[13]. Therefore, we tested if apoptosis induced by nuclear entrapment of Bcr-Abl caused by RNTS was resulted from p73 activation. We found that the mRNA expression of p73 was upregulated by RNTS treatment (Supplemental Figure 3), and the level of p73 protein was also increased (Figure 4A). Because c-Abl stabilizes p73 by phosphorylation of Tyr99[25], we tested the level of Tyr99 phosphorylation. We found that Tyr99 phosphorylation of p73 was enhanced by RNTS (Figure 4A). Although activation of p73 was associated with increased expression of p21 and PUMA (Supplemental Figure 4, Figure 4B)[26,27], expression of Bax at both mRNA and protein levels was not influenced by p73 activation (Supplemental Figure 4, Figure 4B). It has been shown that p73 does not regulate Bax expression at a transcriptional level[28], and that by interacting with Bax, p73 promotes Bax activation as well as its insertion into the mitochondrial membrane[26]. Thus, in RNTS-treated cells, p73 may regulate Bax function post-transcriptionally. We further tested if the effect elicited by RNTS could be mediated by interacting with p73. p73 was silencing by siRNA, and maximal inhibitory effect was reached at 48 h after transfection (Supplemental Figure 5). Also, the levels of p73 and its phosphorylation were largely reduced by p73 silencing in K562 and K562/G01 cells (Figure 4C). Consistent with the effect on p73, expression of p21 and PUMA were also reduced (Figure 4D). As expected, expression of Bax was not affected (Figure 4D). Apoptosis and growth inhibition induced by RNTS were also reversed by p73 silencing (Figure 4E, F). Taken together, these results provide evidence that RNTS functions by activating p73 and its downstream target molecules.


Induction of apoptosis by directing oncogenic Bcr-Abl into the nucleus.

Huang ZL, Gao M, Li QY, Tao K, Xiao Q, Cao WX, Feng WL - Oncotarget (2013)

RNTS activates p73 and its downstream target molecules
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3926824&req=5

Figure 4: RNTS activates p73 and its downstream target molecules
Mentions: Nuclear c-Abl kinase can be activated by DNA damage to induce expression of p73 protein, a functional homolog of the tumor suppressor p53, and then p73 induces apoptosis of cells[13]. Therefore, we tested if apoptosis induced by nuclear entrapment of Bcr-Abl caused by RNTS was resulted from p73 activation. We found that the mRNA expression of p73 was upregulated by RNTS treatment (Supplemental Figure 3), and the level of p73 protein was also increased (Figure 4A). Because c-Abl stabilizes p73 by phosphorylation of Tyr99[25], we tested the level of Tyr99 phosphorylation. We found that Tyr99 phosphorylation of p73 was enhanced by RNTS (Figure 4A). Although activation of p73 was associated with increased expression of p21 and PUMA (Supplemental Figure 4, Figure 4B)[26,27], expression of Bax at both mRNA and protein levels was not influenced by p73 activation (Supplemental Figure 4, Figure 4B). It has been shown that p73 does not regulate Bax expression at a transcriptional level[28], and that by interacting with Bax, p73 promotes Bax activation as well as its insertion into the mitochondrial membrane[26]. Thus, in RNTS-treated cells, p73 may regulate Bax function post-transcriptionally. We further tested if the effect elicited by RNTS could be mediated by interacting with p73. p73 was silencing by siRNA, and maximal inhibitory effect was reached at 48 h after transfection (Supplemental Figure 5). Also, the levels of p73 and its phosphorylation were largely reduced by p73 silencing in K562 and K562/G01 cells (Figure 4C). Consistent with the effect on p73, expression of p21 and PUMA were also reduced (Figure 4D). As expected, expression of Bax was not affected (Figure 4D). Apoptosis and growth inhibition induced by RNTS were also reversed by p73 silencing (Figure 4E, F). Taken together, these results provide evidence that RNTS functions by activating p73 and its downstream target molecules.

Bottom Line: We show that a rapalog nuclear transport system (RNTS) containing six nuclear localization signals directs Bcr-Abl into the nucleus and that nuclear entrapped Bcr-Abl induces apoptosis and inhibits proliferation of CML cells by activating p73 and shutting down cytoplasmic oncogenic signals mediated by Bcr-Abl.Coupling cytoplasmic depletion with nuclear entrapment of Bcr-Abl synergistically enhances the inhibitory effect of nuclear Bcr-Abl on its oncogenicity in mice.These results provide evidence that direction of cytoplasmic Bcr-Abl to the nucleus offers an alternative CML therapy.

View Article: PubMed Central - PubMed

Affiliation: Department of Clinical Hematology, Key Laboratory of Laboratory Medical Diagnostics Designated by the Ministry of Education, Chongqing Medical University, Chongqing, People's Republic of China.

ABSTRACT
The chimeric Bcr-Abl oncoprotein, which causes chronic myeloid leukemia, mainly localizes in the cytoplasm, and loses its ability to transform cells after moving into the nucleus. Here we report a new strategy to convert Bcr-Abl to be an apoptotic inducer by altering its subcellular localization. We show that a rapalog nuclear transport system (RNTS) containing six nuclear localization signals directs Bcr-Abl into the nucleus and that nuclear entrapped Bcr-Abl induces apoptosis and inhibits proliferation of CML cells by activating p73 and shutting down cytoplasmic oncogenic signals mediated by Bcr-Abl. Coupling cytoplasmic depletion with nuclear entrapment of Bcr-Abl synergistically enhances the inhibitory effect of nuclear Bcr-Abl on its oncogenicity in mice. These results provide evidence that direction of cytoplasmic Bcr-Abl to the nucleus offers an alternative CML therapy.

Show MeSH
Related in: MedlinePlus