Autophagy Degrades Transcription Factor FOXM1 Through Heat Shock Protein HSPA8

FOXM1(Forkhead box M1)is a pivotal proliferation-related regulator involved in the regulation of cell inflammation,proliferation,differentiation,drug resistance,metabolism,stem cell renewal,and is highly expressed in progenitor cells,regenerative tissues,and tumor cells.The stability of FOXM1 proteins is closel y controlled.For example,E3 ubiquitin ligase-mediated proteasome degradation pathways regulate FOXM1 protein levels to maintain cell cycle progression.Whether FOXM1 can be degraded by the autophagy-lysosomal pathway is still unclear.Autophagy is a metabolic degradation process mediated by cell membrane transport.HSPA8,a member of the heat shock protein family,is a constitutively expressed chaperone.In the process of autophagy,HSPA8 recognizes and binds to the substrate protein or cargo,and binds to LAMP2,a lysosome membrane-related protein,to enter the lysosome,thus realizing the degradation of the target protein.We found that FOXM1 may interact with HSPA8 protein in the early stage of FOXM1 interaction mass spectrometry,so we speculated that transcription factor FOXM1 may be recognized by HSPA8 and then enter the autophagy-lysosomal pathway for degradation.This paper will focus on the following four aspects:(1)The effect of autophagy on the transcription factor FOXM1 protein level;(2)Transcription factor FOXM1 is degraded by autophagy-lysosome pathway.(3)Transcription factor FOXM1 interacts with heat shock protein HSPA8;(4)Effect of HSPA8 on autophagy degradation of transcription factor FOXM1.Firstly,the autophagy model was establi shed using different autophagy inducers to study the effect of autophagy on the transcription factor FOXM1 protein level.The protein and m RNA levels of FOXM1 were detected by Western blotting and RT-QPCR,respectively.Secondly,the relationship between transcription factor FOXM1 and autophagosome and lysosome organelles was studied at organelle level.FOXM1 degradation through autophagy-lysosome pathway was investigated by living cell imaging,immunofluorescence and organelle isolation.The interaction of transcription factor FOXM1 with heat shock protein HSPA8 was studied in vitro and in vivo.The interaction between FOXM1 and HSPA8 protein was verified by Bi FC,co-IP,Pulldown and other methods.Finally,HSPA8 was overexpressed to explore the effect of HSPA8 on the autophagy degradation of transcription factor FOXM1 protein.The results of this study show that autophagy induced under diverse conditions can degrade the transcription factor FOXM1 protein in a ll kinds of tumor cell lines.The transcription factor FOXM1 can be autophagic degraded through the autophagy-lysosome pathway.Transcription factor FOXM1 interacts with heat shock protein HSPA8,and HSPA8 can promote FOXM1 protein degradation.In this paper,the autophagy degradation of transcription factor FOXM1 and its possible mechanism were preliminically discussed,providing a new direction for expanding the study of FOXM1 protein stability.