ABSTRACT
Oncogenic RAS and RAF signaling has been implicated in contributing to radioresistance in pancreatic and thyroid cancers. In this study, we sought to better clarify molecular mechanisms contributing to this effect. We discovered that miRNA 296-3p (miR-296-3p) is significantly correlated with radiosensitivity in a panel of pancreatic cancer cells, and miR-296-3p is highly expressed in normal cells, but low in cancer cell lines. Elevated expression of miR-296-3p increases radiosensitization while decreasing the expression of the DNA repair enzyme RAD18 in both pancreatic and thyroid cancer cells. RAD18 is overexpressed in both pancreatic and thyroid tumors compared to matched normal controls, and high expression of RAD18 in tumors is associated with poor prognostic features. Modulating the expression of mutant KRAS in pancreatic cancer cells or mutant BRAF in thyroid cancer cells demonstrates a tight regulation of RAD18 expression in both cancer types. Depletion of RAD18 results in DNA damage and radiation-induced cell death. Importantly, RAD18 depletion in combination with radiotherapy results in marked and sustained tumor regression in KRAS mutant pancreatic cancer orthotopic tumors and BRAF mutant thyroid heterotopic tumors. Overall, our findings identify a novel coordinated RAS/RAF-miR-296-3p-RAD18 signaling network in pancreatic and thyroid cancer cells, which leads to enhanced radioresistance.
Subject(s)
DNA-Binding Proteins , Gene Expression Regulation, Neoplastic , MicroRNAs , Pancreatic Neoplasms , Proto-Oncogene Proteins p21(ras) , Radiation Tolerance , Signal Transduction , Thyroid Neoplasms , Humans , MicroRNAs/genetics , MicroRNAs/metabolism , Radiation Tolerance/genetics , Pancreatic Neoplasms/genetics , Pancreatic Neoplasms/radiotherapy , Pancreatic Neoplasms/pathology , Pancreatic Neoplasms/metabolism , Thyroid Neoplasms/genetics , Thyroid Neoplasms/radiotherapy , Thyroid Neoplasms/pathology , Thyroid Neoplasms/metabolism , Cell Line, Tumor , Animals , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Proto-Oncogene Proteins p21(ras)/genetics , Proto-Oncogene Proteins p21(ras)/metabolism , Proto-Oncogene Proteins B-raf/genetics , Mice, Nude , Mutation , DNA Damage , Xenograft Model Antitumor Assays , ras Proteins/genetics , ras Proteins/metabolism , TransfectionABSTRACT
Murine norovirus (MNV), which can be used as a model system to study human noroviruses, can infect macrophages/ monocytes, neutrophils, dendritic, intestinal epithelial, T and B cells, and is highly prevalent in laboratory mice. We previously showed that MNV infection significantly reduces bone marrow B cell populations in a Stat1-dependent manner. We show here that while MNV-infected Stat1-/- mice have significant losses of bone marrow B cells, splenic B cells capable of mounting an antibody response to novel antigens retain the ability to expand. We also investigated whether increased granulopoiesis after MNV infection was causing B cell loss. We found that administration of anti-G-CSF antibody inhibits the pronounced bone marrow granulopoiesis induced by MNV infection of Stat1-/- mice, but this inhibition did not rescue bone marrow B cell losses. Therefore, MNV-infected Stat1-/- mice can still mount a robust humoral immune response despite decreased bone marrow B cells. This suggests that further investigation will be needed to identify other indirect factors or mechanisms that are responsible for the bone marrow B cell losses seen after MNV infection. In addition, this work contributes to our understanding of the potential physiologic effects of Stat1-related disruptions in research mouse colonies that may be endemically infected with MNV.
