CHAC2 Induces Apoptosis And Autophagy Through Unfolded Protein Response In Gastric And Colorectal Cancer Cells

In China,digestive cancers are the major causes of death.And the mortality of gastric and colorectal cancers remain in top five among malignant neoplasms.It is believed that tumorigenesis is a multistep process involving numerous genetic and epigenetic factors that are accumulated abnormally and interplay with each other.In these intricate phases,there are many oncogenes activated and tumor suppressor genes(TSGs)inactivated.Hence,we should figure out the functions of newfound tumor suppressor genes,exploring the relationship between these genes and the malignant properties of gastrointestinal neoplasms,which may help us understand the molecular mechanisms of tumorigeneses and achieve early diagnosis,as well as perform individualized treatment.Purpose:CHAC2 is a member of cation transport regulator-like protein(CHAC)family and we found that CHAC2 is frequently downregulated in gastric and colorectal cancers.Thus we worked on it and wanted to reveal its functions in the pathogenesis of both gastric and colorectal cancers.Methods:CHAC2 expression was determined by quantitative RT-PCR,immunohistochemistry and western blot in human normal tissues,gastric and colorectal cancer tissues,as well as the tumor cells.We established the model of CHAC2 overexpression with gastric and colorectal cancer cells by plasmid transfection.And then,the effects of CHAC2 were examined including the alteration of growth,migration,cell cycle,concentration of Ca+、ROS and GSH in vitro.Western Blot was performed to confirm the regulation mechanism of CHAC2,especially apoptosis and autophagy.Xenograft tumors were developed in BALB/c nude mice using CHAC2 transfected tumor cells to observe the change of growth and migration abilities in vivo.Results:CHAC2 protein can be hardly detected in most cell lines except for SW48.Immunohistochemistry(IHC)and western blot reveal that CHAC2 protein is highly expressed mainly in the cytoplasm of normal tissues.In contrast,CHAC2 is silenced or just downregulated in gastric and colorectal cancer tissues.And CHAC2 expression is significantly correlated with histopathological grading,lymph node metastasis and 3-year survival rate.The 3-year survival rate of patients with low CHAC2 expression is significantly lower than those with high CHAC2 expression both in gastric(P<0.001)and colorectal cancer(P= 0.001)cases.CHAC2 overexpression inhibited tumor cell proliferation and migration both in vitro and in vivo.Furthermore,flow cytometry and western blot tell that CHAC2 leads to glutathione depletion,increased intracellular Ca2+concentration and ROS,as well as enhanced apoptosis and autophagy,implying its role in unfolded protein response(UPR).Conclusions:CHAC2 acts as a functional tumor suppressor in gastric and colorectal cancers.It is downregulated or silenced in gastric and colorectal neoplasms,displaying the potential to become a prognostic marker.CHAC2 can suppress the growth and migration of gastric and colorectal cancer cells both in vitro and in vivo and induce mitochondrial apoptosis and autophagy simultaneously through unfolded protein response(UPR).