Identification of tumour-reactive lymphatic endothelial cells capable of inducing progression of gastric cancer

Machine learning and single-cell sequencing reveal the potential regulatory factors of mitochondrial autophagy in the progression of gastric cancer

BACKGROUND

As an important regulatory mechanism to remove damaged mitochondria and maintain the balance between internal and external cells, mitochondrial autophagy plays a key role in the progression and treatment of cancer Onishi (EMBO J 40(3): e104705, 2021). The purpose of this study is to comprehensively analyze the role of mitochondrial autophagy-related genes in the progression of gastric cancer (GC) by RNA sequencing (RNA-seq) and single-cell RNA sequencing (scRNA-seq).

METHODS

GSE26942, GSE54129,GSE66229,GSE183904 and other data sets were obtained by GEO databases. Using support vector machine recursive feature elimination (SVM-RVF) algorithm and random forest algorithm, the mitochondrial autophagy-related genes related to gastric cancer were obtained, respectively. After that, the model was constructed and the inflammatory factors, immune score and immune cell infiltration were analyzed. Furthermore, according to the scRNA-seq data of 28,836 cells from 13 GC samples, 18 cell clusters and 7 cell types were identified by scRNA-seq analysis. The expression level and signal pathway of related genes were verified by cell communication analysis. Finally, the regulatory network of cells was analyzed by SCENIC.

RESULTS

MAP1LC3B, PGAW5, PINK1, TOMM40 and UBC are identified as key genes through machine learning algorithms. CXCL12-CXCR4, LGALS9-CD44, LGALS9-CD45 and MIF (CD74 + CD44) pathways may play an important role in endothelial cells with high score scores of T cells and monocytes in tumor environment. CEBPB, ETS1, GATA2, MATB, SPl1 and XBP1 were identified as candidate TF with specific regulatory expression in the GC cell cluster.

CONCLUSION

The results of this study will provide implications for the study of the mechanism, diagnosis and treatment of mitochondrial autophagy in GC.

Liver Endothelium Microenvironment Promotes HER3-mediated Cell Growth in Pancreatic Ductal Adenocarcinoma

~90% metastatic pancreatic ductal adenocarcinoma (mPDAC) occurs in the liver, and the 5-year survival rate for patients with mPDAC is only at 3%. The liver has a unique endothelial cell (EC)-rich microenvironment, and preclinical studies showed that ECs promote cancer cell survival pathways by secreting soluble factors in a paracrine fashion in other types of cancer. However, the effects of liver ECs on mPDAC have not been elucidated. In this study, we used primary liver ECs and determined that liver EC-secreted factors containing conditioned medium (CM) increased PDAC cell growth, compared to control CM from PDAC cells. Using an unbiased receptor tyrosine kinase array, we identified human epidermal growth factor receptor 3 (HER3, also known as ErbB3) as a key mediator of liver EC-induced growth in PDAC cells with HER3 expression (HER3 +ve). We found that EC-secreted neuregulins activated the HER3-AKT signaling axis, and that depleting neuregulins from EC CM or blocking HER3 with an antibody, seribantumab, attenuated EC-induced functions in HER3 +ve PDAC cells, but not in cells without HER3 expression. Furthermore, we determined that EC CM increased PDAC xenograft growth in vivo, and that seribantumab blocked EC-induced growth in xenografts with HER3 expression. These findings elucidated a paracrine role of liver ECs in promoting PDAC cell growth, and identified the HER3-AKT axis as a key mediator in EC-induced functions in HER3 +ve PDAC cells. As over 70% mPDAC express HER3, this study highlights the potential of using HER3-targeted therapies for treating patients with HER3 +ve mPDAC.

Effect of crosstalk among conspirators in tumor microenvironment on niche metastasis of gastric cancer

In Traditional Chinese medicine, the metaphoric views of the human body are based on observations of nature guided by the theory of "Yin-Yang". The direct meanings of yin and yang are the bright and dark sides of an object, which often represent a wider range of opposite properties. When we shifted our view to gastric cancer (GC), we found that there are more distinctive Yin and Yang features in the mechanism of GC development and metastasis, which is observed in many mechanisms such as GC metastasis, immune escape, and stem cell homing. When illustrating this process from the yin-yang perspective, categorizing different cells in the tumor microenvironment enables new and different perspectives to be put forward on the mechanism and treatment of GC metastasis.

Targeting the tumor stroma for cancer therapy

Tumors are comprised of both cancer cells and surrounding stromal components. As an essential part of the tumor microenvironment, the tumor stroma is highly dynamic, heterogeneous and commonly tumor-type specific, and it mainly includes noncellular compositions such as the extracellular matrix and the unique cancer-associated vascular system as well as a wide variety of cellular components including activated cancer-associated fibroblasts, mesenchymal stromal cells, pericytes. All these elements operate with each other in a coordinated fashion and collectively promote cancer initiation, progression, metastasis and therapeutic resistance. Over the past few decades, numerous studies have been conducted to study the interaction and crosstalk between stromal components and neoplastic cells. Meanwhile, we have also witnessed an exponential increase in the investigation and recognition of the critical roles of tumor stroma in solid tumors. A series of clinical trials targeting the tumor stroma have been launched continually. In this review, we introduce and discuss current advances in the understanding of various stromal elements and their roles in cancers. We also elaborate on potential novel approaches for tumor-stroma-based therapeutic targeting, with the aim to promote the leap from bench to bedside.

Diffuse gastric cancer: Emerging mechanisms of tumor initiation and progression

Gastric cancer is globally the fourth leading cause of cancer-related deaths. Patients with diffuse-type gastric cancer (DGC) particularly have a poor prognosis that only marginally improved over the last decades, as conventional chemotherapies are frequently ineffective and specific therapies are unavailable. Early-stage DGC is characterized by intramucosal lesions of discohesive cells, which can be present for many years before the emergence of advanced DGC consisting of highly proliferative and invasive cells. The mechanisms underlying the key steps of DGC development and transition to aggressive tumors are starting to emerge. Novel mouse- and organoid models for DGC, together with multi-omic analyses of DGC tumors, revealed contributions of both tumor cell-intrinsic alterations and gradual changes in the tumor microenvironment to DGC progression. In this review, we will discuss how these recent findings are leading towards an understanding of the cellular and molecular mechanisms responsible for DGC initiation and malignancy, which may provide opportunities for targeted therapies.

Tumor microenvironment in gastric cancers

The tumor microenvironment favors the growth and expansion of cancer cells. Many cell types are involved in the tumor microenvironment such as inflammatory cells, fibroblasts, nerves, and vascular endothelial cells. These stromal cells contribute to tumor growth by releasing various molecules to either directly activate the growth signaling in cancer cells or remodel surrounding areas. This review introduces recent advances in findings on the interactions within the tumor microenvironment such as in cancer-associated fibroblasts (CAFs), immune cells, and endothelial cells, in particular those established in mouse gastric cancer models. In mice, myofibroblasts in the gastric stroma secrete R-spondin and support normal gastric stem cells. Most CAFs promote tumor growth in a paracrine manner, but CAF population appears to be heterogeneous in terms of their function and origin, and include both tumor-promoting and tumor-restraining populations. Among immune cell populations, tumor-associated macrophages, including M1 and M2 macrophages, and myeloid-derived suppressor cells (MDSCs), are reported to directly or indirectly promote gastric tumorigenesis by secreting soluble factors or modulating immune responses. Endothelial cells or blood vessels not only fuel tumors with nutrients, but also interact with cancer stem cells and immune cells by secreting chemokines or cytokines, and act as a cancer niche. Understanding these interactions within the tumor microenvironment would contribute to unraveling new therapeutic targets.

Integrated profiling identifies SLC5A6 and MFAP2 as novel diagnostic and prognostic biomarkers in gastric cancer patients

Gastric cancer (GC) is one of the leading causes of malignancy‑associated mortality worldwide. However, the underlying molecular mechanisms of GC are unclear and the prognosis of GC is poor. Therefore, it is important and urgent to explore the underlying mechanisms and screen for novel diagnostic and prognostic biomarkers, as well as therapeutic targets. In the current study, scale‑free gene co‑expression networks were constructed using weighted gene co‑expression network analysis, the potential associations between gene sets and clinical features were investigated, and the hub genes were identified. The gene expression profiles of GSE38749 were downloaded from the Gene Expression Omnibus database. RNA‑seq and clinical data for GC from The Cancer Genome Atlas were utilized for verification. Furthermore, the expression of candidate biomarkers in gastric tissues was investigated. Survival analysis was performed using Kaplan‑Meier and log‑rank test. The predictive role of candidate biomarkers in GC was evaluated using a receiver operator characteristic (ROC) curve. Gene Ontology, gene set enrichment analysis and gene set variation analysis methods were used to interpret the function of candidate biomarkers in GC. A total of 29 modules were identified via the average linkage hierarchical clustering. A significant module consisting of 48 genes associated with clinical traits was found; three genes with high connectivity in the clinical significant module were identified as hub genes. Among them, SLC5A6 and microfibril‑associated protein 2 (MFAP2) were negatively associated with the overall survival, and their expression was elevated in GC compared with non‑tumor tissues. Additionally, ROC curves indicated that SLC5A6 and MFAP2 showed a good diagnostic power in discriminating cancerous from normal tissues. SLC5A6 and MFAP2 were identified as novel diagnostic and prognostic biomarkers in GC patients; both of these genes were first reported here in connection with GC and deserved further research.

Endothelial cells in colorectal cancer

The dependence of tumor growth on neovascularization has become an important aspect of cancer biology. Tumor angiogenesis is one of the key mechanisms of tumorigenesis, growth and metastasis. The key events involved in this process are endothelial cell proliferation, migration, and vascular formation. Recent studies have revealed the importance of tumor-associated endothelial cells (TECs) in the development and progression of colorectal cancer (CRC), including epithelial proliferation, stem cell maintenance, angiogenesis, and immune remodeling. Decades of research have identified that the molecular basis of tumor angiogenesis includes vascular endothelial growth factors (VEGFs) and their receptor family, which are the main targets of antiangiogenesis therapy. VEGFs and their receptors play key roles in the pathology of angiogenesis, and their overexpression indicates poor prognosis in CRC. This article reviews the characteristics of the tumor vasculature and the role of TECs in different stages of CRC and immune remodeling. We also discuss the biological effects of VEGFs and their receptor family as angiogenesis regulators and emphasize the clinical implications of TECs in clinical treatment.

Endothelial Cells Promote Colorectal Cancer Cell Survival by Activating the HER3-AKT Pathway in a Paracrine Fashion

The regulation of colorectal cancer cell survival pathways remains to be elucidated. Previously, it was demonstrated that endothelial cells (EC) from the liver (liver parenchymal ECs or LPEC), the most common site of colorectal cancer metastases, secrete soluble factors in the conditioned medium (CM) that, in turn, increase the cancer stem cell phenotype in colorectal cancer cells. However, the paracrine effects of LPECs on other colorectal cancer cellular functions have not been investigated. Here, results showed that CM from LPECs increased cell growth and chemoresistance by activating AKT in colorectal cancer cells in vitro. Using an unbiased receptor tyrosine kinase array, it was determined that human epidermal growth factor receptor 3 (ERBB3/HER3) was activated by CM from LPECs, and it mediated AKT activation, cell growth, and chemoresistance in colorectal cancer cells. Inhibition of HER3, either by an inhibitor AZD8931 or an antibody MM-121, blocked LPEC-induced HER3-AKT activation and cell survival in colorectal cancer cells. In addition, CM from LPECs increased in vivo tumor growth in a xenograft mouse model. Furthermore, inhibiting HER3 with AZD8931 significantly blocked tumor growth induced by EC CM. These results demonstrated a paracrine role of liver ECs in promoting cell growth and chemoresistance via activating HER3-AKT in colorectal cancer cells. IMPLICATIONS: This study suggested a potential of treating patients with metastatic colorectal cancer with HER3 antibodies/inhibitors that are currently being assessed in clinical trials for various cancer types.

CXCL1 from tumor-associated lymphatic endothelial cells drives gastric cancer cell into lymphatic system via activating integrin β1/FAK/AKT signaling

Crosstalk between lymphatic endothelial cells (LECs) and tumor cells in the tumor microenvironment plays a crucial role in tumor metastasis. Our previous study indicated chemokine (C-X-C motif) ligand 1 (CXCL1) from LECs stimulates the metastasis of gastric cancer. However, the mechanism is still unclear. Here, we successfully isolated tumor-associated LECs (T-LECs) and normal LECs (N-LECs) from clinical samples by magnetic-activated cell sorting system (MACS) and proved that CXCL1 expression was elevated in T-LECs compared with N-LECs in situ and vitro. Besides, we demonstrated that CXCL1 secreted by T-LECs promoted the migration, invasion, and adhesion of gastric cancer cells by upregulating integrin β1, MMP2, and MMP9. Furthermore, CXCL1 induced MMP2/9 expression by activating integrin β1-FAK-AKT signaling. In the animal model, CXCL1 overexpressed in LECs increased the lymph node metastasis of gastric cancer. In conclusion, CXCL1 expression in T-LECs was upregulated, and CXCL1 secreted by T-LECs promoted the lymph node metastasis of gastric cancer through integrin β1/FAK/AKT signaling, leading to MMP2 and MMP9 expression. Therefore, CXCL1 produced in T-LECs represents a potentially promising target for treating gastric cancer.

Tumor-associated macrophages induce capillary morphogenesis of lymphatic endothelial cells derived from human gastric cancer

Tumor lymphangiogenesis is a major prognostic indicator of gastric cancer. Tumor‐induced inflammation has been shown to attract tumor‐associated macrophages that affect lymphangiogenesis. However, detailed mechanisms of macrophage‐induced lymphangiogenesis have not been elucidated. Here, we evaluated the interaction between tumor‐associated macrophages and lymphatic endothelial cells (LECs) derived from lymph nodes (LNs) of human gastric cancer. Lymphatic endothelial cells were directly or indirectly cocultured with macrophages from healthy human blood, with or without the supernatant of the gastric cancer cell line, OCUM‐12. We analyzed the effect of cancer pretreated macrophages and of macrophages from metastatic LNs of gastric cancer on LECs. We observed morphological changes of LECs in coculture and assessed the gene expression of possible lymphangiogenic molecules of macrophages and LECs after contact coculture, and of cancer pretreated macrophages, by quantitative RT‐PCR. Specimens of metastatic LN of gastric cancer were immunofluorescently stained. We found that tubulogenesis of LECs was observed only in the contact coculture model. OCUM‐12 cells promoted macrophage‐induced tubulogenesis of LECs. Relative gene expression of MMP and adhesion molecules was significantly upregulated in both capillary‐forming LECs and cocultured macrophages. Cancer pretreated macrophages upregulated lymphangiogenic factors including inflammatory cytokines, MMPs, adhesion molecules, and vascular endothelial growth factor‐C. Blocking of intercellular adhesion molecule‐1 and macrophage activation suppressed tubulogenesis of LECs. Immunohistochemistry showed macrophages localized around lymphatic vessels. Our results suggested that interaction between LECs and macrophages may be an important initial step of tumor lymphangiogenesis developing LN metastasis. Understanding of its mechanisms could be useful for future therapeutics of gastric cancer.