Investigation Of The Role Of GADD45A In Acquired Radioresistance In Cervical Cancer And Underlying Mechanisms

Background and objective: Cervical cancer is one of most common forms of cancer,with 470,000 new cases and 233,000 mortalities per year worldwide.The five-year survival rate is about 68% in the United States.The occurrence rate is high,at about 70% in developing countries,while,the rate has been markedly reduced in developed country with the application of HPV screening programs.Radiotherapy plays an important role in cervical cancer treatment.The improved disease-free and overall survival rates were demonstrated in the past decades.However,radioresistance is a fundamental barrier for radiotherapy of cervical cancer.Radioresistance may present at the beginning of therapy(intrinsic radioresistance),or emerge over time during radiotherapy treatment(acquired radioresistance).Fractionated radiation(FR)is often used to facilitate the recovery of the normal tissues in radiotherapy,while,it is the primary cause of acquired radioresistance of cancer cells which leads to treatment failure.Thus overcoming the acquired radioresisitance could improve the outcome of the cervical cancer radiotherapy.Nuclear proteins,such as CREB and STAT,are a type of proteinsresponsible for transmission of molecular signals from exterior of nuclear to its interior,that are involved in regulating essential signaling pathways in cellular processes of cancer initiation,progression,metastasis as well as acquired resistance.Dysregulation of nuclear proteins leads to facilitation of the process of cell transformation,tumor progression.However,the roles of nuclear proteins in acquired radioresistance are rarely understood.In this study,we identified dysregulated nuclear proteins by comparison of the mRNA expression level between induced radioresisitant cervical cancer cells and their parental control cells and revealed that GADD45 A serves as a tumor suppressor which regulates radiosensitivity in cervical cancer cells through PI3K/AKT signaling pathway.Methods: Acquired radioresistant cervical cancer cell lines were established by continuous segmentation irradiation,and differentially expressed nuclear proteins were obtained by qRT-PCR array between acquired radioresistant cell lines and parental radiosensitive cell lines.The cell viability was detected by CCK-8 method,and the cell clone formation ability was detected by colony formation assay.The apoptosis state was detected by AnexinV/7AAD double staining method.The cell invasion ability was detected by Transwell.ChIP(Chromatin Immunoprecipitation)was used to study the binding of GADD45 A and FGFR4 promoters.The luciferase reporter gene technology was used to study the regulation of GADD45 A on FGFR4 promoter.Results: we showed that aberrant downregulation of GADD45 A induces radioresistance in cervical cancer through PI3K/AKT signaling pathway.The expression of GADD45 A is downregulated in induced radioresistant cervical cancer cells as well as in cancer tissues obtained from non-radiosensitive group of cervical cancer patients.Knockdown of GADD45 A in radiosensitive parentalcells induced radioresistance.Oppositely,overexpression of GADD45 A in induced radioresistant cells restored the radiosensitivity.Mechanistic analysis showed that downregulation of GADD45 A upregulates FGFR4,activates PI3K/AKT signaling pathway,thereby inducing radioresistance in cervical cancer cells.Conclusion: Taken together,these results demonstrated that downregulation of GADD45 A induces Radioresistance in cervical cancer through PI3K/AKT signaling pathway.