Augmented ERO1α upon mTORC1 activation induces ferroptosis resistance and tumor progression via upregulation of SLC7A11.

BACKGROUND: The dysregulated mechanistic target of rapamycin complex 1 (mTORC1) signaling plays a critical role in ferroptosis resistance and tumorigenesis. However, the precise underlying mechanisms still need to be fully understood. METHODS: Endoplasmic reticulum oxidoreductase 1 alpha (ERO1α) expression in mTORC1-activated mouse embryonic fibroblasts, cancer cells, and laryngeal squamous cell carcinoma (LSCC) clinical samples was examined by quantitative real-time PCR (qRT-PCR), western blotting, immunofluorescence (IF), and immunohistochemistry. Extensive in vitro and in vivo experiments were carried out to determine the role of ERO1α and its downstream target, member 11 of the solute carrier family 7 (SLC7A11), in mTORC1-mediated cell proliferation, angiogenesis, ferroptosis resistance, and tumor growth. The regulatory mechanism of ERO1α on SLC7A11 was investigated via RNA-sequencing, a cytokine array, an enzyme-linked immunosorbent assay, qRT-PCR, western blotting, IF, a luciferase reporter assay, and a chromatin immunoprecipitation assay. The combined therapeutic effect of ERO1α inhibition and the ferroptosis inducer imidazole ketone erastin (IKE) on mTORC1-activated cells was evaluated using cell line-derived xenografts, LSCC organoids, and LSCC patient-derived xenograft models. RESULTS: ERO1α is a functional downstream target of mTORC1. Elevated ERO1α induced ferroptosis resistance and exerted pro-oncogenic roles in mTORC1-activated cells via upregulation of SLC7A11. Mechanically, ERO1α stimulated the transcription of SLC7A11 by activating the interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (STAT3) pathway. Moreover, ERO1α inhibition combined with treatment using the ferroptosis inducer IKE exhibited synergistic antitumor effects on mTORC1-activated tumors. CONCLUSIONS: The ERO1α/IL-6/STAT3/SLC7A11 pathway is crucial for mTORC1-mediated ferroptosis resistance and tumor growth, and combining ERO1α inhibition with ferroptosis inducers is a novel and effective treatment for mTORC1-related tumors.

Elevated ITGA5 facilitates hyperactivated mTORC1-mediated progression of laryngeal squamous cell carcinoma via upregulation of EFNB2.

Background: Laryngeal squamous cell carcinoma (LSCC) is one of the most common malignant tumors of the head and neck, and it has shown increasing incidence and mortality. The mechanistic target of rapamycin complex 1 (mTORC1) is frequently dysregulated in LSCC, but its underlying mechanisms remain unclear. Methods: Establishment of a novel LSCC cell line using primary LSCC tumor tissues with dysregulated mTORC1 activity and then stable knockdown of Raptor (an mTORC1 specific component) in this cell line. Transcriptomic sequencing, quantitative real-time PCR, western blot analysis, and immunofluorescence assays were used to identify the crucial downstream effector of mTORC1. A series of experiments were conducted to investigate the functions and underlying mechanisms of the mTORC1 target gene in LSCC progression. Clinical LSCC samples were used to evaluate the association of mTORC1 and its downstream targets with clinicopathological features and patient prognosis. Finally, the influence on cisplatin (CDDP) sensitivity upon depletion of the mTORC1 target gene was assessed using a cell culture system, a cell line-derived xenograft (CDX) model, and a patient-derived xenograft (PDX) model. Results: We successfully established a novel LSCC cell line with hyperactivated mTORC1 activity and then identified integrin subunit alpha 5 (ITGA5) as a novel functional downstream effector of mTORC1 in the progression of LSCC. Elevated ITGA5 promotes LSCC progression through augmentation of ephrin-B2 (EFNB2). Clinical data analysis indicated that the activation of the mTORC1-ITGA5-EFNB2 signaling pathway is associated with malignant progression and poor prognosis of LSCC patients. Inhibition of ITGA5 significantly sensitized LSCC cells to CDDP. Conclusions: Our findings highlight a novel molecular mechanism for the tumorigenesis driven by deregulated mTORC1 signaling in LSCC, suggesting that the ITGA5-EFNB2 axis may be a therapeutic target for the treatment of mTORC1-related LSCC.

RUNX1/EGFR pathway contributes to STAT3 activation and tumor growth caused by hyperactivated mTORC1.

Loss of function of tuberous sclerosis complex 1 or 2 (TSC1 or TSC2) leads to the activation of mammalian target of rapamycin complex 1 (mTORC1). Hyperactivated mTORC1 plays a critical role in tumor growth, but the underlying mechanism is still not completely elucidated. Here, by analyzing Tsc1- or Tsc2-null mouse embryonic fibroblasts, rat Tsc2-null ELT3 cells, and human cancer cells, we present evidence for the involvement of epidermal growth factor receptor (EGFR) as a downstream target of mTORC1 in tumor growth. We show that mTORC1 leads to increased EGFR expression through upregulation of runt-related transcriptional factor 1 (RUNX1). Knockdown of EGFR impairs proliferation and tumoral growth of Tsc-deficient cells, while overexpression of EGFR promotes the proliferation of the control cells. Moreover, the mTOR signaling pathway has been shown to be positively correlated with EGFR in human cancers. In addition, we demonstrated that EGFR enhances cell growth through activation of signal transducer and activator of transcription 3 (STAT3). We conclude that activation of the RUNX1/EGFR/STAT3 signaling pathway contributes to tumorigenesis caused by hyperactivated mTORC1 and should be targeted for the treatment of mTORC1-related tumors, particularly TSC.

Poly-L-arginine promotes asthma angiogenesis through induction of FGFBP1 in airway epithelial cells via activation of the mTORC1-STAT3 pathway.

Angiogenesis is a key characteristic of asthma airway remodeling. By releasing cationic granule proteins, such as major basic protein (MBP), activated eosinophils play a prominent role in asthma, but the underlying mechanisms are still not fully understood. In this study, we demonstrated that fibroblast growth factor-binding protein 1 (FGFBP1) was dramatically upregulated in airway epithelial cell lines treated by poly-L-arginine (PLA), a mimic of MBP. Elevated FGFBP1 expression was also detected in asthma clinical samples, as well as in ovalbumin (OVA)-induced chronic asthma mouse models. PLA enhanced FGFBP1 expression through activation of the mechanistic target of rapamycin complex 1-signal transducer and activator of transcription 3 (mTORC1-STAT3) signaling pathway. STAT3 transactivated FGFBP1 by directly binding to the promoter of the FGFBP1 gene. Furthermore, we identified that FGFBP1 secreted by PLA-treated airway epithelial cells served as a proangiogenesis factor. Lastly, we found the mTORC1-STAT3-FGFBP1 signaling pathway was activated in an OVA-induced chronic asthma model with airway remodeling features. Rapamycin treatment alleviated respiratory symptoms and reduced angiogenesis in asthmatic mice. Therefore, activation of the mTORC1-STAT3-FGFBP1 pathway in the airway epithelium contributes to the progress of angiogenesis and should be targeted for the treatment of asthma.