Andrew Cassity

Introduction. Helicobacter pylori-induced gastric cancer accounts for 75% of gastric cancer cases worldwide and disproportionately affects developing countries.¹ It is usually found in late stages when treatment options have low efficacy.² This is a result of limited knowledge about how H. pylori causes gastric cancer. Studies show that alterations in NF-κB function by H. pylori show high levels of carcinogenesis due to its role in stimulation of cell proliferation and apoptosis inhibition.³ This study aimed at determining the role of the NF-κB pathway regarding oncogenesis and if preventative therapeutic targets could be identified. Methods. Immunohistochemistry was used on several H. pylori infected human cell lines to determine the level of genomic instability, i.e. DNA double strand breaks, under various conditions.⁴ Conditions included treatments with an NF-κB inhibitor, as well as inducing upregulation of RNase H1 expression (degrades R-loops).⁴ Replication protein A (RPA) location was immunohistochemically tagged in AQR knockout HeLa cells and also isolated with RNase H1 whose activity against R-loops was measured with an immunoblot.⁵ Human H. pylori associated gastric mucosa was biopsied and stained for NF-κB inducing kinase (NIK).⁶ HeLa and NCI-N87 cells were stained for components of the non-canonical NF-κB pathway after treatment over time with siRNA specific for NIK and lymphotoxin beta receptor (LTβR) on an immunoblot.⁶ Results. Inhibition of the NF-κB pathway and RNase H1 upregulation prevented genomic instability.⁴ This showed that over activation of the NF-κB pathway by H. pylori caused R-loop formation creating a pro-oncogenic environment.⁴ RPA was found to co-localize with RNase H1 and enhance its activity against R-loops.⁵ Canonical activation of NF-κB with TNF-α did not cause damage indicating the non-canonical pathway played a larger role.⁴ This was confirmed through high levels of NIK in H. pylori gastric mucosa.⁶ The non-canonical pathway also showed reduced activation when RPA and LTβR were degraded by siRNA.⁶ Conclusions. R-loops were found to play a key role in H. pylori oncogenesis. This new information regarding H. pylori, can be observed in other oncogenic models, like with G-quadruplexes, myelodysplastic syndromes, and xenoestrogens, verifying its likelihood.^{7, 8, 9} RPA could be used to identify elevated levels of R-loops before the induction of gastric cancer by applying tagged RPA to gut biopsies and could also be used to prophylactically treat gastric cancer by reducing R-loop induced genomic instability in healthy cells. Molecular targeting of NIK or LTβR could prevent the initiation of gastric cancer by H. pylori infection.

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