The Mechanism And Function Of Upregulation Of EGFR Induced By The Inactivation Of TSC1/TSC2 Complex

Tuberous sclerosis complex?TSC?is an autosomal dominant disorder characterized by the formation of benign tumors in multiple organs,which is main caused by inactivating mutations in either of two tumor suppressor genes:TSC1 or TSC2.TSC1/TSC2complex acts an important inhibitor of mammalian target of rapamycin?mTOR?.TSC1or TSC2 gene mutations or activation of the upstream PI3K-AKT signaling pathway can cause TSC1/TSC2 complex inactivated and Rheb-GTP accumulated,which leads to the activation of mTORC1,promotes cell growth and proliferation,and leads to tumorigenesis.However,the specific mechanism by which mTORC1 activation promotes the occurrence of TSC tumors remains unclear.This is a scientific problem that needs to be solved urgently.In the previous work,we performed RNA-seq analysis on Tsc2-deficient mouse embryonic fibroblasts?MEFs?and control cells(denoted as Tsc2^-/-and Tsc2^+/+MEFs).Compared with control cells,the expression of epidermal growth factor receptor?EGFR?was significantly up-regulated in TSC2-deficient cells.Like Tsc2^-/-MEFs,we detected the expression of EGFR in TSC1-deficient mouse embryonic fibroblasts by Western Blot and Real-time quantitative PCR?qRT-PCR?,which was significantly higher than the control Tsc1^+/+MEFs.The results of RNA-seq were confirmed.Therefore,we performed data analysis on the NCBI-GEO database and found that the abundance of EGFR mRNA in tumor tissues of patients with TSC was significantly higher than that of normal tissues,indicating that the loss of TSC1/TSC2complex promotes high expression of EGFR.In this study,we explored in depth the mechanism and function of up-regulation of EGFR induced by inactivation of the TSC1/TSC2 complex.mTOR showed abnormal activation in Tsc1^-/-and Tsc2^-/-MEFs,and the expression of EGFR was decreased after specific inhibition of mTORC1 activity,indicating that high expression of EGFR is dependent on mTORC1.Subsequently,Tsc2^-/-MEFs knockdown of EGFR and Tsc1^+/+MEFs overexpressing EGFR were successfully constructed,and biological function studies were performed.Treatment of Tsc1^-/-and Tsc2^-/-MEFs with the EGFR inhibitor gefitinib confirmed that EGFR expression levels regulate STAT3 activity,whereas STAT3 mediates EGFR's function in promoting cell proliferation and tumor growth.In summary,our study further elucidated the molecular mechanism and function of TSC1/TSC2 negative regulation of EGFR.It was found that TSC1/TSC2 negatively regulates EGFR dependent mTORC1,and confirmed that EGFR promotes cell proliferation and tumorigenesis,and mTOR activation promotes high expression of EGFR to up-regulate STAT3 activity.Furthermore,we propose that the mTOR/EGFR/STAT3 signaling pathway plays an important role in tumor development and provides new targets for mTOR-activated tumor therapy.