PADI2 Promotes The Progression Of Endometrial Cancer Through The ERK/IGF2BP1/SOX2 Axis

To date,the morbidity and mortality of endometrial cancer(EC)are getting higher.The occurrence of EC has a significant impact on women's reproductive health.Molecular targeted therapy has been given attention in the clinic.Therefore,it is particularly important to find specific molecular targets in tumor cells and use them as new targets for tumor detection or treatment.First of all,we found in the tumor database that the transcription level of PADI2 in EC is elevated,suggesting that PADI2 may be involved in the occurrence and development of EC.After knockdown of PADI2 in EC cells,the degree of malignancy of EC cells was reduced;transcriptome analysis found that the oncogene IGF2BP1 was the main response factor by PADI2.Similar to the effect of PADI2,knocking down IGF2BP1 can also reduce the invasion,3D spheroidization,and tumor formation abilities of EC cells,indicating that PADI2 may affect the malignant degree of EC cells through the oncogene IGF2BP1.Further study of the mechanism found that knocking down PADI2 can reduce the activation of ERK,thereby reducing the expression of IGF2BP1.However,knocking down PADI2 does not affect the phosphorylation of MEK1,an upstream kinase of ERK,suggesting that PADI2 may specifically regulate the kinase activity of MEK1 and thus affect the activation of ERK by MEK1.To test this hypothesis,we first proved that PADI2 can interact with MEK1 and catalyze the citrullination of MEK1.Mass spectrometry analysis and intracellular functional experiments found that PADI2 mainly catalyzes the citrullination of the two arginine residues R113 and R189 in the kinase region of MEK1,thereby promoting the kinase activity of MEK1.In EC cells,compared with overexpression of wild-type MEK1,overexpression of MEK1 R113 E and MEK1R189 E mutants can reduce the activation of ERK.Meanwhile,the proliferation,invasion,3D spheroidization and tumor formation ability of EC cells both are reduced.After knocking down PADI2 in EC cells,the citrullination modification of MEK1 R189 was significantly reduced.Importantly,we found in clinical samples of EC tissues that the citrullination of MEK1 R189 was significantly higher than that of adjacent tissues.In order to further explore how the PADI2/MEK1/ERK/IGF2BP1 axis affects the progression of EC cell malignancy,we explored stem factors related to tumor malignancy.The results showed that SOX2 is the main downstream effector of the PADI2/MEK1/ERK/IGF2BP1 axis in EC cells.Mechanismically,IGF2BP1 binds to three independent m6 A sites on the 3'UTR of SOX2 and regulates the stability of SOX2 m RNA,thereby promoting the expression of SOX2.Therefore,the abnormal regulation of IGF2BP1 by the PADI2/MEK1/ERK signal axis,resulting in abnormal accumulation of SOX2 expression may be the key reason for maintaining the malignant state of EC cells.This study found that knocking down PADI2 in EC cells,using PADI2 inhibitors to inhibit the citrullination modification of MEK1 by PADI2,or mutating MEK1R113/R189(to prevent citrullination at this site)can inhibit the malignant progress of EC cells,indicating that the citrullination of MEK1 catalyzed by PADI2 is expected to become a potential drug target for EC.In view of the fact that drug combinations targeting different targets in the same pathway can expand the efficacy of drugs,our findings provide a theoretical basis for the combined use of PADI2 inhibitors and MEK1 inhibitors in the treatment of EC.