ABSTRACT
BACKGROUND & AIMS: N6-Methyladenosine (m6A) is the most prevalent RNA modification and recognized as an important epitranscriptomic mechanism in colorectal cancer (CRC). We aimed to exploit whether and how tumor-intrinsic m6A modification driven by methyltransferase like 3 (METTL3) can dictate the immune landscape of CRC. METHODS: Mettl3 knockout mice, CD34+ humanized mice, and different syngeneic mice models were used. Immune cell composition and cytokine level were analyzed by flow cytometry and Cytokine 23-Plex immunoassay, respectively. M6A sequencing and RNA sequencing were performed to identify downstream targets and pathways of METTL3. Human CRC specimens (n = 176) were used to evaluate correlation between METTL3 expression and myeloid-derived suppressor cell (MDSC) infiltration. RESULTS: We demonstrated that silencing of METTL3 in CRC cells reduced MDSC accumulation to sustain activation and proliferation of CD4+ and CD8+ T cells, and eventually suppressed CRC in ApcMin/+Mettl3+/- mice, CD34+ humanized mice, and syngeneic mice models. Mechanistically, METTL3 activated the m6A-BHLHE41-CXCL1 axis by analysis of m6A sequencing, RNA sequencing, and cytokine arrays. METTL3 promoted BHLHE41 expression in an m6A-dependent manner, which subsequently induced CXCL1 transcription to enhance MDSC migration in vitro. However, the effect was negligible on BHLHE41 depletion, CXCL1 protein or CXCR2 inhibitor SB265610 administration, inferring that METTL3 promotes MDSC migration via BHLHE41-CXCL1/CXCR2. Consistently, depletion of MDSCs by anti-Gr1 antibody or SB265610 blocked the tumor-promoting effect of METTL3 in vivo. Importantly, targeting METTL3 by METTL3-single guide RNA or specific inhibitor potentiated the effect of anti-programmed cell death protein 1 (anti-PD1) treatment. CONCLUSIONS: Our study identifies METTL3 as a potential therapeutic target for CRC immunotherapy whose inhibition reverses immune suppression through the m6A-BHLHE41-CXCL1 axis. METTL3 inhibition plus anti-PD1 treatment shows promising antitumor efficacy against CRC.
Subject(s)
CD8-Positive T-Lymphocytes , Colorectal Neoplasms , Animals , Basic Helix-Loop-Helix Transcription Factors , CD8-Positive T-Lymphocytes/metabolism , Cell Line, Tumor , Chemokine CXCL1 , Colorectal Neoplasms/pathology , Cytokines/metabolism , Humans , Methyltransferases/genetics , Methyltransferases/metabolism , Mice , Mice, Knockout , Phenylurea Compounds , RNA, Guide, Kinetoplastida , Receptors, Interleukin-8B/genetics , Receptors, Interleukin-8B/metabolism , TriazolesABSTRACT
Patients with spinal muscular atrophy (SMA) are susceptible to the respiratory infections and might be at a heightened risk of poor clinical outcomes upon contracting coronavirus disease 2019 (COVID-19). In the face of the COVID-19 pandemic, the potential associations of SMA with the susceptibility to and prognostication of COVID-19 need to be clarified. We documented an SMA case who contracted COVID-19 but only developed mild-to-moderate clinical and radiological manifestations of pneumonia, which were relieved by a combined antiviral and supportive treatment. We then reviewed a cohort of patients with SMA who had been living in the Hubei province since November 2019, among which the only 1 out of 56 was diagnosed with COVID-19 (1.79%, 1/56). Bioinformatic analysis was carried out to delineate the potential genetic crosstalk between SMN1 (mutation of which leads to SMA) and COVID-19/lung injury-associated pathways. Protein-protein interaction analysis by STRING suggested that loss-of-function of SMN1 might modulate COVID-19 pathogenesis through CFTR, CXCL8, TNF and ACE. Expression quantitative trait loci analysis also revealed a link between SMN1 and ACE2, despite low-confidence protein-protein interactions as suggested by STRING. This bioinformatic analysis could give hint on why SMA might not necessarily lead to poor outcomes in patients with COVID-19.