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Acidosis decreases c-Myc oncogene expression in human lymphoma cells: a role for the proton-sensing G protein-coupled receptor TDAG8.

Li Z, Dong L, Dean E, Yang LV - Int J Mol Sci (2013)

Bottom Line: The pH-sensing receptor TDAG8 (GPR65) is involved in acidosis-induced c-Myc downregulation.Acidic pH alone is insufficient to reduce c-Myc expression, as it does not decrease c-Myc in H1299 lung cancer cells expressing very low levels of pH-sensing G protein-coupled receptors (GPCRs).Collectively, our results identify a novel mechanism of c-Myc regulation by acidosis in the tumor microenvironment and indicate that modulation of TDAG8 and related pH-sensing receptor pathways may be exploited as a new approach to inhibit Myc expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Oncology, Brody School of Medicine, East Carolina University, Greenville, NC 27834, USA. yangl@ecu.edu.

ABSTRACT
Acidosis is a biochemical hallmark of the tumor microenvironment. Here, we report that acute acidosis decreases c-Myc oncogene expression in U937 human lymphoma cells. The level of c-Myc transcripts, but not mRNA or protein stability, contributes to c-Myc protein reduction under acidosis. The pH-sensing receptor TDAG8 (GPR65) is involved in acidosis-induced c-Myc downregulation. TDAG8 is expressed in U937 lymphoma cells, and the overexpression or knockdown of TDAG8 further decreases or partially rescues c-Myc expression, respectively. Acidic pH alone is insufficient to reduce c-Myc expression, as it does not decrease c-Myc in H1299 lung cancer cells expressing very low levels of pH-sensing G protein-coupled receptors (GPCRs). Instead, c-Myc is slightly increased by acidosis in H1299 cells, but this increase is completely inhibited by ectopic overexpression of TDAG8. Interestingly, TDAG8 expression is decreased by more than 50% in human lymphoma samples in comparison to non-tumorous lymph nodes and spleens, suggesting a potential tumor suppressor function of TDAG8 in lymphoma. Collectively, our results identify a novel mechanism of c-Myc regulation by acidosis in the tumor microenvironment and indicate that modulation of TDAG8 and related pH-sensing receptor pathways may be exploited as a new approach to inhibit Myc expression.

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TDAG8 expression is lower in lymphomas than that in normal lymphoid tissues. (A,B) Human lymphoma tissue cDNA arrays (OriGene Technologies) were subject to real-time RT-PCR using TDAG8 specific primer probes. β-actin was used as an internal control for normalization. TDAG8 expression was compared between non-tumorous lymphoid tissues (lymph nodes and spleens) and all tested lymphoma tissues (A) or different subtypes of lymphoma tissues (B). The expression of TDAG8 in lymph nodes and spleens was set as one. Each dot represents an individual sample. Error bars indicate ±SEM. *p < 0.05; ***p < 0.001; ns, not significant (p > 0.05); (C) Analyses of the Oncomine cancer microarray database revealed that TDAG8 expression was reduced by two-fold in follicular lymphoma in comparison to normal lymphocytes (p < 0.001). x-axis: 1, B-lymphocyte; 2, centroblast; 3, memory B-lymphocyte; 4, naive pregerminal center B-lymphocyte; 5, small cleaved follicle center cell; 6, follicular lymphoma. y-axis: log2 median-centered intensity.
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f6-ijms-14-20236: TDAG8 expression is lower in lymphomas than that in normal lymphoid tissues. (A,B) Human lymphoma tissue cDNA arrays (OriGene Technologies) were subject to real-time RT-PCR using TDAG8 specific primer probes. β-actin was used as an internal control for normalization. TDAG8 expression was compared between non-tumorous lymphoid tissues (lymph nodes and spleens) and all tested lymphoma tissues (A) or different subtypes of lymphoma tissues (B). The expression of TDAG8 in lymph nodes and spleens was set as one. Each dot represents an individual sample. Error bars indicate ±SEM. *p < 0.05; ***p < 0.001; ns, not significant (p > 0.05); (C) Analyses of the Oncomine cancer microarray database revealed that TDAG8 expression was reduced by two-fold in follicular lymphoma in comparison to normal lymphocytes (p < 0.001). x-axis: 1, B-lymphocyte; 2, centroblast; 3, memory B-lymphocyte; 4, naive pregerminal center B-lymphocyte; 5, small cleaved follicle center cell; 6, follicular lymphoma. y-axis: log2 median-centered intensity.

Mentions: To correlate the biochemical function of TDAG8 with tumor biology, we compared the expression of TDAG8 transcripts between lymphomas and lymphoid tissues. Real-time RT-PCR was performed on lymphoma tissue cDNA arrays containing 84 cDNA samples from lymphoma patients and 12 cDNA samples from non-tumorous lymph nodes and spleens (see Table S1 for detailed information). The results demonstrated that TDAG8 mRNA expression was decreased by 56% in lymphoma samples in comparison to lymph nodes and spleens (p < 0.001) (Figure 6A). To further analyze lymphoma subtypes, the TDAG8 mRNA level was decreased by 60%–70% in follicular lymphoma, diffuse large B-cell lymphoma and small lymphocytic lymphoma samples when compared to normal lymphoid tissues (p < 0.05) (Figure 6B). The expression of TDAG8 mRNA was also decreased in other types of lymphomas, such as extranodal marginal zone B-cell lymphoma, Hodgkin’s lymphoma, mantle cell lymphoma, splenic marginal zone B-cell lymphoma, nodal marginal zone B-cell lymphoma and peripheral T-cell lymphoma, but the results were not statistically significant, likely due to the small sample size (Figure 6B). Furthermore, bioinformatic analysis of the Oncomine microarray database revealed that the expression of TDAG8 (GPR65) was significantly lower (2.021 fold decrease, p < 0.001) in follicular lymphoma when compared to normal lymphocytes (Figure 6C), concordant with the real-time RT-PCR results of lymphoma samples (Figure 6A,B).


Acidosis decreases c-Myc oncogene expression in human lymphoma cells: a role for the proton-sensing G protein-coupled receptor TDAG8.

Li Z, Dong L, Dean E, Yang LV - Int J Mol Sci (2013)

TDAG8 expression is lower in lymphomas than that in normal lymphoid tissues. (A,B) Human lymphoma tissue cDNA arrays (OriGene Technologies) were subject to real-time RT-PCR using TDAG8 specific primer probes. β-actin was used as an internal control for normalization. TDAG8 expression was compared between non-tumorous lymphoid tissues (lymph nodes and spleens) and all tested lymphoma tissues (A) or different subtypes of lymphoma tissues (B). The expression of TDAG8 in lymph nodes and spleens was set as one. Each dot represents an individual sample. Error bars indicate ±SEM. *p < 0.05; ***p < 0.001; ns, not significant (p > 0.05); (C) Analyses of the Oncomine cancer microarray database revealed that TDAG8 expression was reduced by two-fold in follicular lymphoma in comparison to normal lymphocytes (p < 0.001). x-axis: 1, B-lymphocyte; 2, centroblast; 3, memory B-lymphocyte; 4, naive pregerminal center B-lymphocyte; 5, small cleaved follicle center cell; 6, follicular lymphoma. y-axis: log2 median-centered intensity.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC3821613&req=5

f6-ijms-14-20236: TDAG8 expression is lower in lymphomas than that in normal lymphoid tissues. (A,B) Human lymphoma tissue cDNA arrays (OriGene Technologies) were subject to real-time RT-PCR using TDAG8 specific primer probes. β-actin was used as an internal control for normalization. TDAG8 expression was compared between non-tumorous lymphoid tissues (lymph nodes and spleens) and all tested lymphoma tissues (A) or different subtypes of lymphoma tissues (B). The expression of TDAG8 in lymph nodes and spleens was set as one. Each dot represents an individual sample. Error bars indicate ±SEM. *p < 0.05; ***p < 0.001; ns, not significant (p > 0.05); (C) Analyses of the Oncomine cancer microarray database revealed that TDAG8 expression was reduced by two-fold in follicular lymphoma in comparison to normal lymphocytes (p < 0.001). x-axis: 1, B-lymphocyte; 2, centroblast; 3, memory B-lymphocyte; 4, naive pregerminal center B-lymphocyte; 5, small cleaved follicle center cell; 6, follicular lymphoma. y-axis: log2 median-centered intensity.
Mentions: To correlate the biochemical function of TDAG8 with tumor biology, we compared the expression of TDAG8 transcripts between lymphomas and lymphoid tissues. Real-time RT-PCR was performed on lymphoma tissue cDNA arrays containing 84 cDNA samples from lymphoma patients and 12 cDNA samples from non-tumorous lymph nodes and spleens (see Table S1 for detailed information). The results demonstrated that TDAG8 mRNA expression was decreased by 56% in lymphoma samples in comparison to lymph nodes and spleens (p < 0.001) (Figure 6A). To further analyze lymphoma subtypes, the TDAG8 mRNA level was decreased by 60%–70% in follicular lymphoma, diffuse large B-cell lymphoma and small lymphocytic lymphoma samples when compared to normal lymphoid tissues (p < 0.05) (Figure 6B). The expression of TDAG8 mRNA was also decreased in other types of lymphomas, such as extranodal marginal zone B-cell lymphoma, Hodgkin’s lymphoma, mantle cell lymphoma, splenic marginal zone B-cell lymphoma, nodal marginal zone B-cell lymphoma and peripheral T-cell lymphoma, but the results were not statistically significant, likely due to the small sample size (Figure 6B). Furthermore, bioinformatic analysis of the Oncomine microarray database revealed that the expression of TDAG8 (GPR65) was significantly lower (2.021 fold decrease, p < 0.001) in follicular lymphoma when compared to normal lymphocytes (Figure 6C), concordant with the real-time RT-PCR results of lymphoma samples (Figure 6A,B).

Bottom Line: The pH-sensing receptor TDAG8 (GPR65) is involved in acidosis-induced c-Myc downregulation.Acidic pH alone is insufficient to reduce c-Myc expression, as it does not decrease c-Myc in H1299 lung cancer cells expressing very low levels of pH-sensing G protein-coupled receptors (GPCRs).Collectively, our results identify a novel mechanism of c-Myc regulation by acidosis in the tumor microenvironment and indicate that modulation of TDAG8 and related pH-sensing receptor pathways may be exploited as a new approach to inhibit Myc expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Oncology, Brody School of Medicine, East Carolina University, Greenville, NC 27834, USA. yangl@ecu.edu.

ABSTRACT
Acidosis is a biochemical hallmark of the tumor microenvironment. Here, we report that acute acidosis decreases c-Myc oncogene expression in U937 human lymphoma cells. The level of c-Myc transcripts, but not mRNA or protein stability, contributes to c-Myc protein reduction under acidosis. The pH-sensing receptor TDAG8 (GPR65) is involved in acidosis-induced c-Myc downregulation. TDAG8 is expressed in U937 lymphoma cells, and the overexpression or knockdown of TDAG8 further decreases or partially rescues c-Myc expression, respectively. Acidic pH alone is insufficient to reduce c-Myc expression, as it does not decrease c-Myc in H1299 lung cancer cells expressing very low levels of pH-sensing G protein-coupled receptors (GPCRs). Instead, c-Myc is slightly increased by acidosis in H1299 cells, but this increase is completely inhibited by ectopic overexpression of TDAG8. Interestingly, TDAG8 expression is decreased by more than 50% in human lymphoma samples in comparison to non-tumorous lymph nodes and spleens, suggesting a potential tumor suppressor function of TDAG8 in lymphoma. Collectively, our results identify a novel mechanism of c-Myc regulation by acidosis in the tumor microenvironment and indicate that modulation of TDAG8 and related pH-sensing receptor pathways may be exploited as a new approach to inhibit Myc expression.

Show MeSH
Related in: MedlinePlus