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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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P32 is required for Myc-dependent glutamine metabolism(A) Immunoblot detecting expression of p32, Myc, Erk, phospho Erk (p-Erk), Akt, and phospho-Akt (p-Akt) in lysates from Control and p32 knockdown SF188 cells. (B) Myc was knocked down in both SF188 ShRNA Control and ShRNA p32 cells. Cells were then plated in glutamine free media and 24 hrs later cell viability was determined by trypan blue exclusion. Data shown is the mean of three experiments ± SD. (C) Model for p32 role in cancer cell metabolism downstream of Myc. Myc promotes the expression of p32, which helps maintain OXPHOS and glutamine addiction. Loss of p32 results in a dependence on glucose. Loss of both Myc and p32 inhibits cell growth.
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Figure 7: P32 is required for Myc-dependent glutamine metabolism(A) Immunoblot detecting expression of p32, Myc, Erk, phospho Erk (p-Erk), Akt, and phospho-Akt (p-Akt) in lysates from Control and p32 knockdown SF188 cells. (B) Myc was knocked down in both SF188 ShRNA Control and ShRNA p32 cells. Cells were then plated in glutamine free media and 24 hrs later cell viability was determined by trypan blue exclusion. Data shown is the mean of three experiments ± SD. (C) Model for p32 role in cancer cell metabolism downstream of Myc. Myc promotes the expression of p32, which helps maintain OXPHOS and glutamine addiction. Loss of p32 results in a dependence on glucose. Loss of both Myc and p32 inhibits cell growth.

Mentions: SF188 cells are derived from a brain tumor characterized by Myc amplification [49]. These cells exhibit a glutaminolytic phenotype that correlates with Myc-dependent cellular addiction to glutamine metabolism for survival [33]. Myc inhibition in these cells is associated with reduced sensitivity to glutamine withdrawal [33]. We examined if loss of p32 impacts Myc-dependent glutamine metabolism. SF188 cells depleted of p32 exhibited enhanced uptake of glutamine (Fig. S2, supplementary data). Interestingly, p32 knockdown in these Myc-induced glutamine addicted cells displayed reduced sensitivity to glutamine withdrawal (Fig. 6B right panel and 6C). However, resistance to glutamine deprivation in p32 knockdown cells was not due to changes in Myc expression levels, as western blot analysis of SF188 cell lysates revealed equal amounts of Myc protein in control versus p32 knockdown lysates (Fig. 7A). We examined if enhanced glucose metabolism and sensitivity to glucose withdrawal in p32 knockdown cells was a consequence of activated PI3K/Akt [50] or ras/MAPK signaling [51]. Consistent with results reported for lung adenocarcinoma cell lines [52], p32 knockdown glioma cells showed significant decrease in Akt and Erk phosphorylation (Fig. 6A). Thus the increase in glucose uptake and metabolism was not a result of altered oncogenic signaling.


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)

P32 is required for Myc-dependent glutamine metabolism(A) Immunoblot detecting expression of p32, Myc, Erk, phospho Erk (p-Erk), Akt, and phospho-Akt (p-Akt) in lysates from Control and p32 knockdown SF188 cells. (B) Myc was knocked down in both SF188 ShRNA Control and ShRNA p32 cells. Cells were then plated in glutamine free media and 24 hrs later cell viability was determined by trypan blue exclusion. Data shown is the mean of three experiments ± SD. (C) Model for p32 role in cancer cell metabolism downstream of Myc. Myc promotes the expression of p32, which helps maintain OXPHOS and glutamine addiction. Loss of p32 results in a dependence on glucose. Loss of both Myc and p32 inhibits cell growth.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: P32 is required for Myc-dependent glutamine metabolism(A) Immunoblot detecting expression of p32, Myc, Erk, phospho Erk (p-Erk), Akt, and phospho-Akt (p-Akt) in lysates from Control and p32 knockdown SF188 cells. (B) Myc was knocked down in both SF188 ShRNA Control and ShRNA p32 cells. Cells were then plated in glutamine free media and 24 hrs later cell viability was determined by trypan blue exclusion. Data shown is the mean of three experiments ± SD. (C) Model for p32 role in cancer cell metabolism downstream of Myc. Myc promotes the expression of p32, which helps maintain OXPHOS and glutamine addiction. Loss of p32 results in a dependence on glucose. Loss of both Myc and p32 inhibits cell growth.
Mentions: SF188 cells are derived from a brain tumor characterized by Myc amplification [49]. These cells exhibit a glutaminolytic phenotype that correlates with Myc-dependent cellular addiction to glutamine metabolism for survival [33]. Myc inhibition in these cells is associated with reduced sensitivity to glutamine withdrawal [33]. We examined if loss of p32 impacts Myc-dependent glutamine metabolism. SF188 cells depleted of p32 exhibited enhanced uptake of glutamine (Fig. S2, supplementary data). Interestingly, p32 knockdown in these Myc-induced glutamine addicted cells displayed reduced sensitivity to glutamine withdrawal (Fig. 6B right panel and 6C). However, resistance to glutamine deprivation in p32 knockdown cells was not due to changes in Myc expression levels, as western blot analysis of SF188 cell lysates revealed equal amounts of Myc protein in control versus p32 knockdown lysates (Fig. 7A). We examined if enhanced glucose metabolism and sensitivity to glucose withdrawal in p32 knockdown cells was a consequence of activated PI3K/Akt [50] or ras/MAPK signaling [51]. Consistent with results reported for lung adenocarcinoma cell lines [52], p32 knockdown glioma cells showed significant decrease in Akt and Erk phosphorylation (Fig. 6A). Thus the increase in glucose uptake and metabolism was not a result of altered oncogenic signaling.

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