MTOR Promotes Tissue Factor Expression and Activity in EGFR-Mutant Cancer.

Ying Cong,Qingrou Li,Ker Yu,Xuesai Zhang,Yaqing Chen

doi:10.3389/fonc.2020.01615

Abstract

Mechanistic target of rapamycin (mTOR) signaling pathway mediates the function of oncogenic receptor tyrosine kinases (RTKs). We aimed to elucidate new role of mTOR in EGFR-mutant (EGFR-mut) non-small cell lung cancer (NSCLC) and glioblastoma (GBM) with a focus on tumor microenvironments. Here, we report a novel regulatory link between mTOR complexes (mTORCs) and tissue factor (TF), an initiator of tumor-derived thrombosis. TF is elevated in EGFR-mut NSCLC/GBM cell lines and tumors from patients with poor prognosis. Application of mTORC1/2 inhibitors (AZD8055, WYE-125132, MTI-31, and rapamycin) or genetic mTORC-depletion all reduced TF expression, which appeared to be differentially mediated depending on cellular context. In U87MG and HCC827 cells, mTORC1 exerted a dominant role via promoting TF mRNA transcription. In EGFR-TKI-resistant H1975 and PC9 cells, it was mTORC2 that played a major role in specific repression of lysosomal-targeted TF protein degradation. Successful inhibition of TF expression was demonstrated in AZD8055- or MTI-31-treated H1975 and U87MG tumors in mice, while a TF-targeted antibody antagonized TF activity without reducing TF protein. Both the mTOR- and TF-targeted therapy induced a multifaceted remodeling of tumor microenvironment reflecting not only a diminished hypercoagulopathy state (fibrin level) but also a reduced stromal fibrosis (collagen distribution), compromised vessel density and/or maturity (CD31 and/or α-SMA) as well as a substantially decreased infiltration of immune-suppressive M2-type tumor-associated macrophages (CD206/F4/80 ratio). Thus, our results have identified TF as a functional biomarker of mTOR. Downregulation of mTOR-TF axis activity likely contributes to the therapeutic mechanism of mTORC1/2- and TF-targeted agents in EGFR-mut advanced NSCLC and GBM.

Highlights

The signaling pathway of the mechanistic target of rapamycin is one of the most important signaling network downstream of the oncogenic receptor tyrosine kinases (RTKs), which participate in tumor growth, metastasis and therapy evasion [1, 2]. Mechanistic target of rapamycin (mTOR) exists as two molecularly distinct protein complexes termed mTORC1 and mTORC2, which differentially and coordinately function in a multitude of biological processes [1, 2]
Given the critical role of mTOR in oncogenic EGFR signaling function, we considered the possibility that mTOR may promote tissue factor (TF) expression in EGFR-mutant cancers
As U87MG/HCC827 and H1975/PC9 differ in relative contribution from mTORC1 versus mTORC2 in promoting TF expression (Figures 2D–F), we considered the possibility that mTORC2 may mediate TF protein stability in the mTORC2-dominant tumor cells like H1975 and PC9

Summary

Introduction

The signaling pathway of the mechanistic target of rapamycin (mTOR) is one of the most important signaling network downstream of the oncogenic receptor tyrosine kinases (RTKs), which participate in tumor growth, metastasis and therapy evasion [1, 2]. mTOR exists as two molecularly distinct protein complexes termed mTORC1 and mTORC2, which differentially and coordinately function in a multitude of biological processes [1, 2]. The signaling pathway of the mechanistic target of rapamycin (mTOR) is one of the most important signaling network downstream of the oncogenic receptor tyrosine kinases (RTKs), which participate in tumor growth, metastasis and therapy evasion [1, 2]. In non-small cell lung cancer (NSCLC) or glioblastoma where EGFR driver mutation (EGFR-mut) and/or gene amplification are prevalent, mTOR-TF Axis in EGFR-mut Cancer mTOR activation contributes to disease progression, metastasis and tyrosine kinase inhibitor (TKI) resistance [3,4,5,6]. The molecular underpinnings and/or functional mediators of mTOR complexes in disease progression, and especially in tumor microenvironment conformation, remains poorly understood. To expand our knowledge in this area, we are interested in searching for new and previously uncharacterized component(s) of the mTOR signaling network in advanced EGFR-mut cancers

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