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Mitochondrial p32 is upregulated in Myc expressing brain cancers and mediates glutamine addiction.

Fogal V, Babic I, Chao Y, Pastorino S, Mukthavaram R, Jiang P, Cho YJ, Pingle SC, Crawford JR, Piccioni DE, Kesari S - Oncotarget (2015)

Bottom Line: Loss of p32 in glutamine addicted glioma cells induced resistance to glutamine deprivation and imparted sensitivity to glucose withdrawal.Finally, we provide evidence that p32 expression contributes to Myc-induced glutamine addiction of cancer cells.Our findings suggest that Myc promotes the expression of p32, which is required to maintain sufficient respiratory capacity to sustain glutamine metabolism in Myc transformed cells.

View Article: PubMed Central - PubMed

Affiliation: Translational Neuro-Oncology Laboratories, Moores Cancer Center, University of California San Diego, La Jolla, CA.

ABSTRACT
Metabolic reprogramming is a key feature of tumorigenesis that is controlled by oncogenes. Enhanced utilization of glucose and glutamine are the best-established hallmarks of tumor metabolism. The oncogene c-Myc is one of the major players responsible for this metabolic alteration. However, the molecular mechanisms involved in Myc-induced metabolic reprogramming are not well defined. Here we identify p32, a mitochondrial protein known to play a role in the expression of mitochondrial respiratory chain complexes, as a critical player in Myc-induced glutamine addiction. We show that p32 is a direct transcriptional target of Myc and that high level of Myc in malignant brain cancers correlates with high expression of p32. Attenuation of p32 expression reduced growth rate of glioma cells expressing Myc and impaired tumor formation in vivo. Loss of p32 in glutamine addicted glioma cells induced resistance to glutamine deprivation and imparted sensitivity to glucose withdrawal. Finally, we provide evidence that p32 expression contributes to Myc-induced glutamine addiction of cancer cells. Our findings suggest that Myc promotes the expression of p32, which is required to maintain sufficient respiratory capacity to sustain glutamine metabolism in Myc transformed cells.

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Myc promotes p32 expressionLeft panel: qPCR analysis of target genes from total RNA isolated from MRC5 MycER cells treated with 250 nM OHT or vehicle (EtOH) for 24 hrs. Ubiquitin (Ubb) is included as a negative control while cyclin D2 (CycD2) and glutaminase (GLS1) are positive controls. The bars shown are normalized to an internal β-actin control and represent the mean ± SD of at least three independent experiments. Fold of each gene induction over control treatment is indicated. Middle panel: immunofluorescence staining of Myc and p32 24 hrs post-OHT treatment. The immunoblot on the right shows upregulation of p32 protein upon Myc induction. Tubulin was used as loading control.
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Figure 3: Myc promotes p32 expressionLeft panel: qPCR analysis of target genes from total RNA isolated from MRC5 MycER cells treated with 250 nM OHT or vehicle (EtOH) for 24 hrs. Ubiquitin (Ubb) is included as a negative control while cyclin D2 (CycD2) and glutaminase (GLS1) are positive controls. The bars shown are normalized to an internal β-actin control and represent the mean ± SD of at least three independent experiments. Fold of each gene induction over control treatment is indicated. Middle panel: immunofluorescence staining of Myc and p32 24 hrs post-OHT treatment. The immunoblot on the right shows upregulation of p32 protein upon Myc induction. Tubulin was used as loading control.

Mentions: Genome-wide analysis using microarrays and serial analysis of gene expression (SAGE) [43, 46], and, more recently, a combination of expression profiling and ChIP-chip analysis [44] identified p32 (C1QBP) as one of the Myc target genes. Collectively these studies, together with our correlation data (Fig. 2), suggest that Myc directly affects p32 expression. To study the effect of Myc activation on p32 transcription and protein level, we used immortalized MRC5 cells stably expressing Myc fused to the oestrogen receptor ligand-binding domain (MycER). A 24-h treatment with 4-hydroxy tamoxifen (OHT) lead to a significant upregulation of p32 that was comparable to those observed for the established Myc targets, Cyclin D2 and glutaminase 1 (Fig. 3, left panel). Accordingly, p32 protein levels were also increased upon Myc induction, as indicated by immunofluorescence staining and immunoblot (Fig. 3). Considering that the MycER system is to some extent “leaky” (see some basal nuclear localization in Myc staining of Fig. 3 middle panel) it is possible that the true fold increase of p32 expression following Myc activation is higher than that reported by the system.


Mitochondrial p32 is upregulated in Myc expressing brain cancers and mediates glutamine addiction.

Fogal V, Babic I, Chao Y, Pastorino S, Mukthavaram R, Jiang P, Cho YJ, Pingle SC, Crawford JR, Piccioni DE, Kesari S - Oncotarget (2015)

Myc promotes p32 expressionLeft panel: qPCR analysis of target genes from total RNA isolated from MRC5 MycER cells treated with 250 nM OHT or vehicle (EtOH) for 24 hrs. Ubiquitin (Ubb) is included as a negative control while cyclin D2 (CycD2) and glutaminase (GLS1) are positive controls. The bars shown are normalized to an internal β-actin control and represent the mean ± SD of at least three independent experiments. Fold of each gene induction over control treatment is indicated. Middle panel: immunofluorescence staining of Myc and p32 24 hrs post-OHT treatment. The immunoblot on the right shows upregulation of p32 protein upon Myc induction. Tubulin was used as loading control.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4359224&req=5

Figure 3: Myc promotes p32 expressionLeft panel: qPCR analysis of target genes from total RNA isolated from MRC5 MycER cells treated with 250 nM OHT or vehicle (EtOH) for 24 hrs. Ubiquitin (Ubb) is included as a negative control while cyclin D2 (CycD2) and glutaminase (GLS1) are positive controls. The bars shown are normalized to an internal β-actin control and represent the mean ± SD of at least three independent experiments. Fold of each gene induction over control treatment is indicated. Middle panel: immunofluorescence staining of Myc and p32 24 hrs post-OHT treatment. The immunoblot on the right shows upregulation of p32 protein upon Myc induction. Tubulin was used as loading control.
Mentions: Genome-wide analysis using microarrays and serial analysis of gene expression (SAGE) [43, 46], and, more recently, a combination of expression profiling and ChIP-chip analysis [44] identified p32 (C1QBP) as one of the Myc target genes. Collectively these studies, together with our correlation data (Fig. 2), suggest that Myc directly affects p32 expression. To study the effect of Myc activation on p32 transcription and protein level, we used immortalized MRC5 cells stably expressing Myc fused to the oestrogen receptor ligand-binding domain (MycER). A 24-h treatment with 4-hydroxy tamoxifen (OHT) lead to a significant upregulation of p32 that was comparable to those observed for the established Myc targets, Cyclin D2 and glutaminase 1 (Fig. 3, left panel). Accordingly, p32 protein levels were also increased upon Myc induction, as indicated by immunofluorescence staining and immunoblot (Fig. 3). Considering that the MycER system is to some extent “leaky” (see some basal nuclear localization in Myc staining of Fig. 3 middle panel) it is possible that the true fold increase of p32 expression following Myc activation is higher than that reported by the system.

Bottom Line: Loss of p32 in glutamine addicted glioma cells induced resistance to glutamine deprivation and imparted sensitivity to glucose withdrawal.Finally, we provide evidence that p32 expression contributes to Myc-induced glutamine addiction of cancer cells.Our findings suggest that Myc promotes the expression of p32, which is required to maintain sufficient respiratory capacity to sustain glutamine metabolism in Myc transformed cells.

View Article: PubMed Central - PubMed

Affiliation: Translational Neuro-Oncology Laboratories, Moores Cancer Center, University of California San Diego, La Jolla, CA.

ABSTRACT
Metabolic reprogramming is a key feature of tumorigenesis that is controlled by oncogenes. Enhanced utilization of glucose and glutamine are the best-established hallmarks of tumor metabolism. The oncogene c-Myc is one of the major players responsible for this metabolic alteration. However, the molecular mechanisms involved in Myc-induced metabolic reprogramming are not well defined. Here we identify p32, a mitochondrial protein known to play a role in the expression of mitochondrial respiratory chain complexes, as a critical player in Myc-induced glutamine addiction. We show that p32 is a direct transcriptional target of Myc and that high level of Myc in malignant brain cancers correlates with high expression of p32. Attenuation of p32 expression reduced growth rate of glioma cells expressing Myc and impaired tumor formation in vivo. Loss of p32 in glutamine addicted glioma cells induced resistance to glutamine deprivation and imparted sensitivity to glucose withdrawal. Finally, we provide evidence that p32 expression contributes to Myc-induced glutamine addiction of cancer cells. Our findings suggest that Myc promotes the expression of p32, which is required to maintain sufficient respiratory capacity to sustain glutamine metabolism in Myc transformed cells.

Show MeSH
Related in: MedlinePlus