The Role of O-GlcNAcylation on G6PD in the Pentose Phosphate Pathway on Tumor Growth of Lung Cancers.

Bosco Giap

Introduction: Lung cancer is the leading causes of cancer deaths amongst both men and women. General prognosis of lung cancer is poor because it is typically not found until it is at an advanced stage. Researchers have gone to the extent of understanding cancer cell metabolism, DNA replication and repair mechanisms in order to target these cancers at an earlier stage. In a study conducted by Rao et al., one specific protein, Glucose-6-phosphate-dehydrogenase (G6PD) was hypothesized to have increased activity via protein modification process known as O-GlcNAcylation, resulting in increased production of nucleotide precursors necessary for DNA replication and repair. This paper seeks to highlight and analyze the study’s hypothesis; through modifications of G6PD and the pentose phosphate pathway by O-GlcNAcylation, there is a change in metabolism displayed in lung cancer cells. Methods: Five individual experiments were conducted to analyze the relationship between the O-GlcNAcylated modified protein, G6PD, and the changes in cancer cell activity and growth. The first experiment determined whether G6PD is O-GlcNAcylated in the cancer cells by enzymatically labelling all O-GlcNac-modified proteins with an azido-N-acetylgalactosamine sugar and overexpressing the O-GlcNAc transferase (OGT) gene. The second experiment sought to determine the biological effects of O-GlcNAcylation on G6PD  via measuring enzyme activity. The third experiment took a larger scale approach to see if O-GlcNAcylated G6PD would promote the pentose phosphate pathway by comparing DNA synthesis between WT or S84V G6PD lung cancer cells. The fourth experiment determined whether G6PD glycosylation would lead to tumor formation in vivo. The fifth experiment demonstrated G6PD upregulation in lung cancer cells compared to normal cells.  Results: The first experiment showed O-GlcNAcylated G6PD was enhanced 4.5 fold by overexpressing OGT, demonstrating that G6PD is O-GlcNAcylated. The second experiment showed enhanced G6PD activity two to fourfold. The third experiment showed that WT G6PD lung cancer cells that were O-GlcNAcylated showed significant increase in DNA synthesis when compared to the S84V mutant replaced cells. The fourth experiment showed a significant difference in tumor growth between WT G6PD mice compared to S84V mice. The fifth experiment showed a higher level of OGT expression correlated with increased G6PD glycosylation. Conclusions: Studies have shown that there is a correlation between glucose-6-phosphate dehydrogenase and cancer cell proliferation, and by limiting G6PD, cancer cell growth and proliferation can be significantly reduced. Understanding the relationship of this modification may lead to possible therapeutic options for treating cancers in the future.

 

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