PELI1 Controls Esophageal Squamous Cell Carcinoma Radiosensitivity Through Modulation Of Noncanonical NF-?B Signaling

Background: Esophageal squamous cell carcinoma(ESCC)has a high morbidity,high mortality and poor prognosis in China.Radiotherapy is a conventional and powerful approach in clinic to fight against ESCC.However,the formation of radiotherapy resistance is the main cause of tumor tolerance against ionizing radiation(IR),leading to poor prognosis.In addition,the molecular mechanism that regulates radiosensitivity is still unclear.We try to study the key factors affecting the radiosensitivity of ESCC.Methods: We collected the 331 tumor tissues from ESCC patients to study the clinical relevance of PELI1 in human esophageal squamous cancer.We also evaluated the guiding role of PELI1 in predicting the efficacy and prognosis for patients who underwent surgical resection of stage III ESCC with postoperative adjuvant radiotherapy.To study the function of PELI1 in regulating radiosensitivity in vivo,Peli1-deficient mice were induced ESCC model by using 4-nitroquinoline 1-oxide(4-NQO),and then examined the radiotherapy-induced tumor apoptosis through microPET/CT.A subcutaneous xenograft model of immunodeficient mice was generated to further verify the effect of PELI1 expression on radiosensitivity.At the cellular level in vitro,ESCC TE-1 and ECA-109 cell lines were applied to investigate the molecular mechanism controlling the radiosensitivity by knocking down of PELI1?Bclxl?NIK,or overexpression of PELI1.Results: We found that the expression of PELI1 in human ESCC was significantly lower than that of matched adjacent tissues,and the expression level of PELI1 showed a significant positive correlation with the prognosis.More interestingly,we observed that high expression of E3 ubiquitin ligase PELI1 was correlated with improved prognosis in human ESCC stage III patients that received postoperative adjuvant radiotherapy.Moreover,we found PELI1 mediated radiotherapy-induced tumor cell apoptosis through an in vivo animal model and in vitro cell cultures.Radiotherapy-induced tumor cell apoptosis was dramatically suppressed in Peli1-deficient mice,indicating inhibited sensitivity of radiotherapy in vivo.Here we found that during radiotherapy,IR activated the noncanonical NF-?B signaling pathway,which inhibited the radiotherapy-induced apoptotic signaling pathway and ultimately resisted the apoptosis of esophageal squamous carcinoma cells.Mechanistically,PELI1 mediated the Lys48-linked polyubiquitination and degradation of NIK,the master kinase of the noncanonical NF-?B pathway,thereby inhibiting radiotherapy-induced activation of the noncanonical NF-?B signaling pathway during radiotherapy.As a consequence,PELI1 inhibited the noncanonical NF-?B-induced expression of the anti-apoptotic gene Bclxl,leading to an enhancement of the radiotherapy-induced apoptotic signaling pathway and ultimately promoting radiotherapy-induced apoptosis in tumor cells.Therefore,Bclxl or NIK knockdown abolished the apoptosis-resistant effect in PELI1-knockdown tumor cells after radiotherapy.Conclusions: These findings established PELI1 as a critical tumor intrinsic regulator in controlling the sensitivity of radiotherapy through modulating of radiotherapyinduced noncanonical NF-?B and highlighted a previously unknown function of noncanonical NF-?B during radiotherapy.