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The role of IMP dehydrogenase 2 in Inauhzin-induced ribosomal stress.

Zhang Q, Zhou X, Wu R, Mosley A, Zeng SX, Xing Z, Lu H - Elife (2014)

Bottom Line: Surprisingly, our current study reveals that Inauzhin (INZ), a novel non-genotoxic p53 activator by inhibiting SIRT1, can also inhibit cellular IMPDH2 activity, and reduce the levels of cellular GTP and GTP-binding nucleostemin that is essential for rRNA processing.Consequently, INZ induces RS and the RPL11/RPL5-MDM2 interaction, activating p53.These results support the new notion that INZ suppresses cancer cell growth by dually targeting SIRT1 and IMPDH2.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, New Orleans, United States.

ABSTRACT
The 'ribosomal stress (RS)-p53 pathway' is triggered by any stressor or genetic alteration that disrupts ribosomal biogenesis, and mediated by several ribosomal proteins (RPs), such as RPL11 and RPL5, which inhibit MDM2 and activate p53. Inosine monophosphate (IMP) dehydrogenase 2 (IMPDH2) is a rate-limiting enzyme in de novo guanine nucleotide biosynthesis and crucial for maintaining cellular guanine deoxy- and ribonucleotide pools needed for DNA and RNA synthesis. It is highly expressed in many malignancies. We previously showed that inhibition of IMPDH2 leads to p53 activation by causing RS. Surprisingly, our current study reveals that Inauzhin (INZ), a novel non-genotoxic p53 activator by inhibiting SIRT1, can also inhibit cellular IMPDH2 activity, and reduce the levels of cellular GTP and GTP-binding nucleostemin that is essential for rRNA processing. Consequently, INZ induces RS and the RPL11/RPL5-MDM2 interaction, activating p53. These results support the new notion that INZ suppresses cancer cell growth by dually targeting SIRT1 and IMPDH2.

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Combination effect of co-depletion of IMPDH2 and SIRT1 on INZ induced cell death. HCT116 cells, transfected with scrambled siRNA (SiControl), IMPDH2 siRNA (SiIMPDH2), SIRT1 siRNA (SiSIRT1) or co-transfected with IMPDH2 and SIRT1 siRNA, were treated with different doses of INZ and cell viability were assessed by WST cell growth assays. IC50 values are represented as mean ± standard deviation (n=3).
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fig5: Combination effect of co-depletion of IMPDH2 and SIRT1 on INZ induced cell death. HCT116 cells, transfected with scrambled siRNA (SiControl), IMPDH2 siRNA (SiIMPDH2), SIRT1 siRNA (SiSIRT1) or co-transfected with IMPDH2 and SIRT1 siRNA, were treated with different doses of INZ and cell viability were assessed by WST cell growth assays. IC50 values are represented as mean ± standard deviation (n=3).

Mentions: A) Our previous studies strongly demonstrate that INZ targets the SIRT1-p53 pathway (Zhang et al 2012b). In this current study, we mainly focus on a new target of INZ, which is the ribosomal stress (RS)-p53 pathway by inhibiting IMPDH2 in cancer cells. It is possible that INZ inhibits SIRT1 and IMPDH2 in a similar fashion, since both of the enzymes utilize NAD as a cofactor. To prove that INZ can target both pathways by inhibiting SIRT1 and IMPDH2 to achieve maximum cell growth inhibition, we performed INZ dose response experiments in HCT116 cells with double knockdown of SIRT1 and IMPDH2. As shown in Author response image 1, co-depletion of SIRT1 and IMPDH2 displayed an obvious combination effect on suppression of INZ-induced cytotoxicity, compared to single knockdown of either SIRT1 or IMPDH2, as their IC50 values increased at least 2 fold, from 3.77 to 10.57μM, and 5.20 to 10.57μM, respectively.Author response image 1.


The role of IMP dehydrogenase 2 in Inauhzin-induced ribosomal stress.

Zhang Q, Zhou X, Wu R, Mosley A, Zeng SX, Xing Z, Lu H - Elife (2014)

Combination effect of co-depletion of IMPDH2 and SIRT1 on INZ induced cell death. HCT116 cells, transfected with scrambled siRNA (SiControl), IMPDH2 siRNA (SiIMPDH2), SIRT1 siRNA (SiSIRT1) or co-transfected with IMPDH2 and SIRT1 siRNA, were treated with different doses of INZ and cell viability were assessed by WST cell growth assays. IC50 values are represented as mean ± standard deviation (n=3).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4209374&req=5

fig5: Combination effect of co-depletion of IMPDH2 and SIRT1 on INZ induced cell death. HCT116 cells, transfected with scrambled siRNA (SiControl), IMPDH2 siRNA (SiIMPDH2), SIRT1 siRNA (SiSIRT1) or co-transfected with IMPDH2 and SIRT1 siRNA, were treated with different doses of INZ and cell viability were assessed by WST cell growth assays. IC50 values are represented as mean ± standard deviation (n=3).
Mentions: A) Our previous studies strongly demonstrate that INZ targets the SIRT1-p53 pathway (Zhang et al 2012b). In this current study, we mainly focus on a new target of INZ, which is the ribosomal stress (RS)-p53 pathway by inhibiting IMPDH2 in cancer cells. It is possible that INZ inhibits SIRT1 and IMPDH2 in a similar fashion, since both of the enzymes utilize NAD as a cofactor. To prove that INZ can target both pathways by inhibiting SIRT1 and IMPDH2 to achieve maximum cell growth inhibition, we performed INZ dose response experiments in HCT116 cells with double knockdown of SIRT1 and IMPDH2. As shown in Author response image 1, co-depletion of SIRT1 and IMPDH2 displayed an obvious combination effect on suppression of INZ-induced cytotoxicity, compared to single knockdown of either SIRT1 or IMPDH2, as their IC50 values increased at least 2 fold, from 3.77 to 10.57μM, and 5.20 to 10.57μM, respectively.Author response image 1.

Bottom Line: Surprisingly, our current study reveals that Inauzhin (INZ), a novel non-genotoxic p53 activator by inhibiting SIRT1, can also inhibit cellular IMPDH2 activity, and reduce the levels of cellular GTP and GTP-binding nucleostemin that is essential for rRNA processing.Consequently, INZ induces RS and the RPL11/RPL5-MDM2 interaction, activating p53.These results support the new notion that INZ suppresses cancer cell growth by dually targeting SIRT1 and IMPDH2.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Tulane University School of Medicine, New Orleans, United States.

ABSTRACT
The 'ribosomal stress (RS)-p53 pathway' is triggered by any stressor or genetic alteration that disrupts ribosomal biogenesis, and mediated by several ribosomal proteins (RPs), such as RPL11 and RPL5, which inhibit MDM2 and activate p53. Inosine monophosphate (IMP) dehydrogenase 2 (IMPDH2) is a rate-limiting enzyme in de novo guanine nucleotide biosynthesis and crucial for maintaining cellular guanine deoxy- and ribonucleotide pools needed for DNA and RNA synthesis. It is highly expressed in many malignancies. We previously showed that inhibition of IMPDH2 leads to p53 activation by causing RS. Surprisingly, our current study reveals that Inauzhin (INZ), a novel non-genotoxic p53 activator by inhibiting SIRT1, can also inhibit cellular IMPDH2 activity, and reduce the levels of cellular GTP and GTP-binding nucleostemin that is essential for rRNA processing. Consequently, INZ induces RS and the RPL11/RPL5-MDM2 interaction, activating p53. These results support the new notion that INZ suppresses cancer cell growth by dually targeting SIRT1 and IMPDH2.

Show MeSH
Related in: MedlinePlus