Scavenger Receptor A1 Prevents Metastasis of Non-Small Cell Lung Cancer via Suppression of Macrophage Serum Amyloid A1

Detailed role of SR-A1 and SR-E3 in tumor biology, progression, and therapy

The first host defense systems are the innate immune response and the inflammatory response. Among innate immune cells, macrophages, are crucial because they preserve tissue homeostasis and eradicate infections by phagocytosis, or the ingestion of particles. Macrophages exhibit phenotypic variability contingent on their stimulation state and tissue environment and may be detected in several tissues. Meanwhile, critical inflammatory functions are played by macrophage scavenger receptors, in particular, SR-A1 (CD204) and SR-E3 (CD206), in a variety of pathophysiologic events. Such receptors, which are mainly found on the surface of multiple types of macrophages, have different effects on processes, including atherosclerosis, innate and adaptive immunity, liver and lung diseases, and, more recently, cancer. Although macrophage scavenger receptors have been demonstrated to be active across the disease spectrum, conflicting experimental findings and insufficient signaling pathways have hindered our comprehension of the molecular processes underlying its array of roles. Herein, as SR-A1 and SR-E3 functions are often binary, either protecting the host or impairing the pathophysiology of cancers has been reviewed. We will look into their function in malignancies, with an emphasis on their recently discovered function in macrophages and the possible therapeutic benefits of SR-A1 and SR-E3 targeting.

The Biological Role of Macrophage in Lung and Its Implications in Lung Cancer Immunotherapy

The lungs are the largest surface of the body and the most important organ in the respiratory system, which are constantly exposed to the external environment. Tissue Resident Macrophages in lung constitutes the important defense against external pathogens. Macrophages connects the innate and adaptive immune system, and also plays important roles in carcinogenesis and cancer immunotherapy. Lung cancer is the leading cause of cancer-related death worldwide, with an overall five-year survival rate of only 21%. Macrophages that infiltrate or aggregate in lung tumor microenvironment are defined as tumor-associated macrophages (TAMs). TAMs are the main components of immune cells in the lung tumor microenvironment. The differentiation and maturation process of TAMs can be roughly divided into two different types: classical activation pathway produces M1 tumor-associated macrophages, and bypass activation pathway produces M2 tumor-associated macrophages. Studies have found that TAMs are related to tumor invasion, metastasis, and treatment resistance, and show potential as a new target for tumor immunotherapy. Therefore, the biological function of macrophages in lung and the role of TAMs in the occurrence, development, and treatment of lung cancer are discussed in this paper.

Single-cell RNA sequencing reveals epithelial cells driving brain metastasis in lung adenocarcinoma

Brain metastases (BM) of lung adenocarcinoma (LUAD) are the most common intracranial malignancy leading to death. However, the cellular origins and drivers of BM from LUAD have not been clarified. Cellular composition was characterized by single-cell sequencing analysis of primary lung adenocarcinoma (pLUAD), BM and lymph node metastasis (LNM) samples in GSE131907. Our study briefly analyzed the tumor microenvironment (TME), focusing on the role of epithelial cells (ECs) in BM. We have discovered a population of brain metastasis-associated epithelial cells (BMAECs) expressing SPP1, SAA1, and CDKN2A, and it has been observed that this population is mainly composed of aneuploid cells from pLUAD, playing a crucial role in brain metastasis. Our study concluded that both LNM and BM in LUAD originated from pLUAD lesions, but there is currently insufficient evidence to prove a direct association between BM lesions and LNM lesions, which provides inspiration for further investigation of the TME in BM.

Macrophage scavenger receptors: Tumor support and tumor inhibition

Tumor-associated macrophages (TAMs) are a heterogeneous population of myeloid cells that constitute up to 50% of the cell mass of human tumors. TAMs interact with the components of the tumor microenvironment (TME) by using scavenger receptors (SRs), a large superfamily of multifunctional receptors that recognize, internalize and transport to the endosomal/lysosomal pathway apoptotic cells, cytokines, matrix molecules, lipid modified lipoproteins and other unwanted-self ligands. In our review, we summarized state-of-the art for the role of macrophage scavenger receptors in tumor development and their significance as cancer biomarkers. In this review we focused on functional activity of TAM-expressing SRs in animal models and in patients, and summarized the data for different human cancer types about the prognostic significance of TAM-expressed SRs. We discussed the role of SRs in the regulation of cancer cell biology, cell-cell and cell-matrix interaction in TME, immune status in TME, angiogenesis, and intratumoral metabolism. Targeting of tumor-promoting SRs can be a promising therapeutic approach in anti-cancer therapy. In our review we provide evidence for both tumor supporting and tumor inhibiting functions of scavenger receptors expressed on TAMs. We focused on the key differences in the prognostic and functional roles of SRs that are specific for cancer types. We highlighted perspectives for inhibition of tumor-promoting SRs in anti-cancer therapy.

TGR5 deficiency activates antitumor immunity in non-small cell lung cancer via restraining M2 macrophage polarization

The bile acid-responsive G-protein-coupled receptor TGR5 is expressed in monocytes and macrophages, and plays a critical role in regulating inflammatory response. Our previous work has shown its role in promoting the progression of non-small cell lung cancer (NSCLC), yet the mechanism remains unclear. Here, using Tgr5-knockout mice, we show that TGR5 is required for M2 polarization of tumor-associated macrophages (TAMs) and suppresses antitumor immunity in NSCLC via involving TAMs-mediated CD8⁺ T cell suppression. Mechanistically, we demonstrate that TGR5 promotes TAMs into protumorigenic M2-like phenotypes via activating cAMP-STAT3/STAT6 signaling. Induction of cAMP production restores M2-like phenotypes in TGR5-deficient macrophages. In NSCLC tissues from human patients, the expression of TGR5 is associated with the infiltration of TAMs. The co-expression of TGR5 and high TAMs infiltration are associated with the prognosis and overall survival of NSCLC patients. Together, this study provides molecular mechanisms for the protumor function of TGR5 in NSCLC, highlighting its potential as a target for TAMs-centric immunotherapy in NSCLC.

SAA induces suppressive neutrophils via the TLR2-mediated signaling pathway to promote progression of breast cancer

Immune inflammation plays a key role in breast cancer development, progression, and therapeutic efficacy. Neutrophils are crucial for the regulation of the suppressive tumor microenvironment and are associated with poor clinical survival. However, the mechanisms underlying the activation of suppressive neutrophils in breast cancer are poorly understood. Here, we report that breast cancer cells secrete abundant serum amyloid A 1 (SAA1), which is associated with the accumulation of suppressive neutrophils. High expression of SAA1 in breast cancer induces neutrophil immunosuppressive cytokine production through the activation of toll like receptor 2 (TLR2)-mediated signaling pathways. These include the TLR2/myeloid differentiation primary response 88 (MYD88)-mediated phosphatidylinositol 3-kinase (PI3K)/nuclear factor κB (NF-κB) signaling pathway and p38 mitogen-activated protein kinase (MAPK)-associated apoptosis resistance pathway, which eventually promote the progression of breast cancer. Our study demonstrates a mechanistic link between breast cancer cell secretion of SAA1 and suppressive neutrophils that potentiate tumor progression. These findings provide potential therapeutic targets for breast cancer.

MicroRNA (miR)-355 Suppressed Small Cell Lung Cancer Cell Metastasis via Regulating P38 Mitogen-Activated Protein Kinases (MAPKs) Signaling

MicroRNA (miR)-355 was reported to mediate p38 mitogen-activated protein kinases (MAPKs) signaling, which exerted an effect on cell invasion and metastasis. But whether miR-355 could inhibit small cell lung cancer cell line H446 cell metastasis by regulating p38 MAPKs signaling needs further study. H446 cells were cultured to establish miR-355 overexpression group and blank group. The expression of MT1-MMP, the activity and migration of H446 cells were evaluated. Further, the ability of invasion, the level of p-p38 MAPKs and the activity degree of MT1-MMP were observed in H446 cells. MT1-MMP was mainly expressed on the cell membrane. miR-355 overexpression significantly decreased cellular viability and reduced MT1-MMP and p-p38 MAPKs levels relative to the blank group without influencing p38 MAPKs level. In addition, miR-355 overexpression suppressed cell migration and invasive ability in H446 cells. Finally, miR-355 overexpression reduced pro-MMP and MMP-2 activity in H446 cells. miR-355 overexpression suppressed H446 cell metastasis through regulating P38 MAPKs signaling.

Recognition of lipoproteins by scavenger receptor class A members

Scavenger receptor class A (SR-A) proteins are type II transmembrane glycoproteins that form homotrimers on the cell surface. This family has five known members (SCARA1 to 5, or SR-A1 to A5) that recognize a variety of ligands and are involved in multiple biological pathways. Previous reports have shown that some SR-A family members can bind modified low-density lipoproteins (LDLs); however, the mechanisms of the interactions between the SR-A members and these lipoproteins are not fully understood. Here, we systematically characterize the recognition of SR-A receptors with lipoproteins and report that SCARA1 (SR-A1, CD204), MARCO (SCARA2), and SCARA5 recognize acetylated or oxidized LDL and very-low-density lipoprotein in a Ca2+-dependent manner through their C-terminal scavenger receptor cysteine-rich (SRCR) domains. These interactions occur specifically between the SRCR domains and the modified apolipoprotein B component of the lipoproteins, suggesting that they might share a similar mechanism for lipoprotein recognition. Meanwhile, SCARA4, a SR-A member with a carbohydrate recognition domain instead of the SRCR domain at the C terminus, shows low affinity for modified LDL and very-low-density lipoprotein but binds in a Ca2+-independent manner. SCARA3, which does not have a globular domain at the C terminus, was found to have no detectable binding with these lipoproteins. Taken together, these results provide mechanistic insights into the interactions between SR-A family members and lipoproteins that may help us understand the roles of SR-A receptors in lipid transport and related diseases such as atherosclerosis.

A critical role for MSR1 in vesicular stomatitis virus infection of the central nervous system

Macrophage scavenger receptor 1 (MSR1) plays an important role in host defense to bacterial infections, M2 macrophage polarization, and lipid homeostasis. However, its physiological function in viral pathogenesis remains poorly defined. Herein, we report that MSR1 facilitates vesicular stomatitis virus (VSV) infection in the central nervous system. Msr1-deficient (Msr1^−/−) mice presented reduced morbidity, mortality, and viral loads in the spinal cord following lethal VSV infection, along with normal viremia and innate immune responses, compared to Msr1^+/− littermates and wild-type mice. Msr1 expression was most significantly upregulated in the spinal cord, the predominant target of VSV. Mechanistically, through its extracellular domains, MSR1 interacted with VSV surface glycoprotein and facilitated its cellular entry in a low-density lipoprotein receptor-dependent manner. In conclusion, our results demonstrate that MSR1 serves as a cofactor for VSV cellular entry and facilitates its infection preferentially in the spinal cord.

•

MSR1 contributes to VSV pathogenesis in mice

•

MSR1 is highly upregulated and facilitates VSV infection in the central nervous system

•

MSR1 facilitates cellular entry of VSV in an LDLR family-dependent manner

•

MSR1 interacts with VSV glycoprotein G via its extracellular domains

Mechanisms of Progression and Heterogeneity in Multiple Nodules of Lung Adenocarcinoma

Lung cancer remains the leading cause of cancer-related death worldwide. Lung adenocarcinoma (LUAD) is thought to be caused by precursor lesions of atypical adenoma-like hyperplasia and may have extensive in situ growth before infiltration. To explore the relevant factors in heterogeneity and evolution of lung adenocarcinoma subtypes, the authors perform single-cell RNA sequencing (scRNA-seq) on tumor and normal tissue from five multiple nodules' LUAD patients and conduct a thorough gene expression profiling of cancer cells and cells in their microenvironment at single-cell level. This study gives a deep understanding of heterogeneity and evolution in early glandular neoplasia of the lung. This dataset leads to discovery of the changes in the immune microenvironment during the development of LUAD, and the development process from adenocarcinoma in situ (AIS) to invasive adenocarcinoma (IAC). This work sheds light on the direction of early tumor development and whether they are homologous.

Arecoline induces epithelial-mesenchymal transformation and promotes metastasis of oral cancer by SAA1 expression

Arecoline, the main alkaloid of areca nut, is well known for its role in inducing submucosal fibrosis and oral squamous cell carcinoma (OSCC), however the mechanism remains unclear. The aim of this study was to establish an arecoline‐induced epithelial‐mesenchymal transformation (EMT) model of OSCC cells and to investigate the underlying mechanisms. CAL33 and UM2 cells were induced with arecoline to establish an EMT cell model and perform RNA‐sequence screening. Luminex multiplex cytokine assays, western blot, and RT‐qPCR were used to investigate the EMT mechanism. Arecoline at a concentration of 160 μg/ml was used to induce EMT in OSCC cells, which was confirmed using morphological analysis, transwell assays, and EMT marker detection. RNA‐sequence screening and Luminex multiplex cytokine assays showed that many inflammatory cytokines (such as serum amyloid A1 [SAA1], interleukin [IL]‐6, IL‐36G, chemokine [CCL]2, and CCL20) were significantly altered during arecoline‐induced EMT. Of these cytokines, SAA1 was the most highly upregulated. SAA1 overexpression induced EMT and promoted the migration and invasion of CAL33 cells, while SAA1 knockdown attenuated arecoline‐induced EMT. Moreover, arecoline enhanced cervical lymph node metastasis in an orthotopic xenograft model of the tongue established using BALB/c nude mice. Our findings revealed that arecoline induced EMT and enhanced the metastatic capability of OSCC by the regulation of inflammatory cytokine secretion, especially that of SAA1. Our study provides a basis for understanding the mechanism of OSCC metastasis and suggests possible therapeutic targets to prevent the occurrence and development of OSCC associated with areca nut chewing.

Krüppel like factor 6 splice variant 1 (KLF6-SV1) overexpression recruits macrophages to participate in lung cancer metastasis by up-regulating TWIST1

The aim of this study was to investigate the mechanism by which KLF6-SV1 promoted lung cancer metastasis through tumor-associated macrophages (TAMs). Plasmid transfection was used to construct cells that upregulated or silenced gene. Tumor-bearing mouse model was established using A549 cells. SP staining was performed to detect the CD163 and CD68. Six-well plates and Transwell chamber were used for co-culture of lung cancer A549 cells and macrophages. CCK-8 and Transwell assay were applied to detected the cell viability and migration respectively. Protein and mRNA were tested by Western blot and quantitative real-time polymerase chain reaction (qRT-PCR).KLF6-SV1 overexpression promoted the expression levels of TWIST1 and CCL2, and also induce macrophage polarization to M2 and epithelial-mesenchymal transition (EMT). In vitro experiments showed that KLF6-SV1 might regulate the migration of lung cancer cells by regulating the expression of TWIST1 and CCL-2. M2 macrophages did not affect the expression of KLF6-SV1, TWIST1 and CCL-2. The co-culture system could up-regulate the EMT of A549 cells.Overexpression of KLF6-SV1 promoted the expression of TWIST1 and CCL2, and up-regulation of TWIST1 expression might promote the infiltration of M2 macrophages, which promoted the involvement of EMT in the metastasis of lung cancer cells.