Role Of ER Stress Protein (PDI) In Radiation-induced Mitochondria-dependent Apoptosis In Tumor Cells

Improving the sensitivity of cancer cells to radiotherapy is an important research area in radiation biology.Mitochondrial-dependent apoptosis signal is the key pathway in radiation-induced cell death,and tumor cells could develop radiation resistance through apoptosis signal disorder.Therefore,improving the tumor sensitivity to radiation is a prominent problem in clinical tumor radiotherapy.Recent literatures have reported that endoplasmic reticulum(ER)stress signals are involved in radiation-induced apoptosis signaling,however,the detailed mechanism has not been clarified.PDI family proteins(PDIs)are responsible for the regulation of protein homeostasis in the endoplasmic reticulum lumen by the activity isomerase and molecular chaperone.The expression disorder of PDIs will seriously affect the cells' responding to apoptosis.In this study,using bioinformatics tools,the protein PDI(also known as PDI or P4HB)was found to be the most cancer-related protein in PDI family among the screened 8 proteins from PDIs that were closely related to cancer.Secondly,we explored the mechanism of radiation-induced apoptosis and the role of PDI expression in radiation-induced apoptosis.The main research results are as follows:1.The key PDI family proteins that related to cancer:Firstly,we did the transcriptome analyses of PDIs.Using the ONCOMIN database,we found that most of the PDIs expression levels were up-regulated in kidney cancer.Secondly,Kaplan-Meier curve was used to analyze the prognosis of RCC patients,and 8 proteins was screened out which were related to kidney cancer prognostic.Then IHC was used to analysis the translational levels of PDIs.By constructing the interaction network,we found that the 8 proteins and their adjacent proteins were mainly enriched in the endoplasmic reticulum stress-related pathways,suggesting that the 8 key PDIs might activate the apoptosis pathway by regulating endoplasmic reticulum stress.Finally,ROC curve analysis was used and found eight PDIs that can significantly distinguish normal tissues from cancer.Combined with the survival analysis and immunohistochemical results,we found that PDI could be used as a potential cancer biomarker,which can promote the development of cancer.2.The mechanism of PDI in radiation-induced apoptosis:Using bioinformatics tools,we found that the expression level of PDI was increased in various cancers.Furthermore,radiation can induce the increase of PDI expression in ER,and PDI could inhibit the apoptosis induced by radiation.Using a series of gene knockout cell lines,we found that the apoptosis induced by radiation was mitochondrial-dependent pathway but not the extrinsic pathway.Moreover,radiation induced the release of PDI,which transfered to mitochondria,and ultimately reduced the occurrence of radiation-induced apoptosis.The main reason is that PDI inhibited Bak multimerization and mitochondrial membrane permeability,then the release of cytochrome c and apoptosis signal was inhibited.These results proved that PDI is the key protein in the PDI protein family regulating apoptosis induced by radiation.We clarified the mechanism of PDI inhibiting radiation induced apoptosis and the relationship between ER stress and radiation-induced mitochondrial apoptosis signals,which provided basic data for targeting endoplasmic reticulum and mitochondria in tumor radiotherapy.