Among all the stromal cells that present in the tumor microenvironment, cancer-associated fibroblasts (CAFs) are one of the most abundant and critical components of the tumor mesenchyme, which not only provide physical support for tumor cells but also play a key role in promoting and retarding tumorigenesis in a context-dependent manner. CAFs have also been involved in the modulation of many components of the immune system, and recent studies have revealed their roles in immune evasion and poor responses to cancer immunotherapy. In this review, we describe our current understanding of the tumorigenic significance, origin, and heterogeneity of CAFs, as well as the roles of different CAFs subtypes in distinct immune cell types. More importantly, we highlight potential therapeutic strategies that target CAFs to unleash the immune system against the tumor.

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Cancer-associated fibroblasts: an emerging target of anti-cancer immunotherapy.

Cancer-associated fibroblasts (CAFs), a stromal cell population with cell-of-origin, phenotypic and functional heterogeneity, are the most essential components of the tumor microenvironment (TME). Through multiple pathways, activated CAFs can promote tumor growth, angiogenesis, invasion and metastasis, along with extracellular matrix (ECM) remodeling and even chemoresistance. Numerous previous studies have confirmed the critical role of the interaction between CAFs and tumor cells in tumorigenesis and development. However, recently, the mutual effects of CAFs and the tumor immune microenvironment (TIME) have been identified as another key factor in promoting tumor progression. The TIME mainly consists of distinct immune cell populations in tumor islets and is highly associated with the antitumor immunological state in the TME. CAFs interact with tumor-infiltrating immune cells as well as other immune components within the TIME via the secretion of various cytokines, growth factors, chemokines, exosomes and other effector molecules, consequently shaping an immunosuppressive TME that enables cancer cells to evade surveillance of the immune system. In-depth studies of CAFs and immune microenvironment interactions, particularly the complicated mechanisms connecting CAFs with immune cells, might provide novel strategies for subsequent targeted immunotherapies. Herein, we shed light on recent advances regarding the direct and indirect crosstalk between CAFs and infiltrating immune cells and further summarize the possible immunoinhibitory mechanisms induced by CAFs in the TME. In addition, we present current related CAF-targeting immunotherapies and briefly describe some future perspectives on CAF research in the end.

/pdf/crosstalk-between-cancer-associated-fibroblasts-and-immune-1htbn130xw.pdf

Crosstalk between cancer-associated fibroblasts and immune cells in the tumor microenvironment: new findings and future perspectives.

Immunotherapy for melanoma

Unraveling the crosstalk between melanoma and immune cells in the tumor microenvironment

To flourish, cancers greatly depend on their surrounding tumor microenvironment (TME), and cancer-associated fibroblasts (CAFs) in TME are critical for cancer occurrence and progression because of their versatile roles in extracellular matrix remodeling, maintenance of stemness, blood vessel formation, modulation of tumor metabolism, immune response, and promotion of cancer cell proliferation, migration, invasion, and therapeutic resistance. CAFs are highly heterogeneous stromal cells and their crosstalk with cancer cells is mediated by a complex and intricate signaling network consisting of transforming growth factor-beta, phosphoinositide 3-kinase/AKT/mammalian target of rapamycin, mitogen-activated protein kinase, Wnt, Janus kinase/signal transducers and activators of transcription, epidermal growth factor receptor, Hippo, and nuclear factor kappa-light-chain-enhancer of activated B cells, etc., signaling pathways. These signals in CAFs exhibit their own special characteristics during the cancer progression and have the potential to be targeted for anticancer therapy. Therefore, a comprehensive understanding of these signaling cascades in interactions between cancer cells and CAFs is necessary to fully realize the pivotal roles of CAFs in cancers. Herein, in this review, we will summarize the enormous amounts of findings on the signals mediating crosstalk of CAFs with cancer cells and its related targets or trials. Further, we hypothesize three potential targeting strategies, including, namely, epithelial–mesenchymal common targets, sequential target perturbation, and crosstalk-directed signaling targets, paving the way for CAF-directed or host cell-directed antitumor therapy.

/pdf/signaling-pathways-in-cancer-associated-fibroblasts-and-1ck8l3ovk7.pdf

Signaling pathways in cancer-associated fibroblasts and targeted therapy for cancer

Cancer-associated fibroblasts (CAFs) play a key role in orchestrating the tumor malignant biological properties within tumor microenvironment and evidences demonstrate that CAFs are a critical regulator of tumoral immunosuppression of the T cell response. However, the functions and regulation of CAFs in the expression of programmed death-ligand 1 (PD-L1) in melanoma and colorectal carcinoma (CRC) are not completely understood. Herein, by scrutinizing the expression of α-SMA and PD-L1 in melanoma and CRC tissues, we found that CAFs was positive correlated with PD-L1 expression. Further analyses showed that CAFs promoted PD-L1 expression in mice tumor cells. By detecting a majority of cytokines expression in normal mice fibroblasts and CAFs, we determined that CXCL5 was abnormal high expression in CAFs and the immunohistochemistry and in situ hybridization confirmed that were CAFs which were expressing CXCL5. In addition, CXCL5 promoted PD-L1 expression in B16, CT26, A375 and HCT116. The silencing of CXCR2, the receptor of CXCL5, inhibited the PD-L1 expression induced by CAFs in turn. Functionally, CXCL5 derived by CAFs promoted PD-L1 expression in mice tumor cells through activating PI3K/AKT signaling. LY294002, the inhibitor of PI3K, confirmed that CXCL5 forested an immunosuppression microenvironment by promoting PD-L1 expression via PI3K/AKT signaling. Meanwhile, the B16/CT26 xenograft tumor models were used and both CXCR2 and p-AKT were found to be positively correlated with PD-L1 in the xenograft tumor tissues. The immunosuppressive action of CAFs on tumor cells is probably reflective of them being a potential therapeutic biomarker for melanoma and CRC.

Cancer-associated fibroblasts promote PD-L1 expression in mice cancer cells via secreting CXCL5

Programmed cell death ligand 1 (PD-L1) is a key suppressor of the cytotoxic immune response. In colorectal carcinoma (CRC), PD-L1 expression results in immune escape and poor prognosis. Extensive researches suggested that metformin had a potential efficacy of enhancing anti-tumor immune response in different types of cancer. However, the detail mechanisms underlying the efficacy in CRC are unclear. Here, we showed that metformin decreases PD-L1 and YAP1 expression in vitro and in vivo. After silencing or inhibiting YAP1 expression by Verteporfin (VP), the inhibitor of YAP1, the expression of PD-L1 were decreased in protein level in CRC cells. Furthermore, metformin directly phosphorylated YAP1 and restricted YAP1 to entry in the nucleus, so that PD-L1 was reduced via western blot and immunofluorescence assays in SW480 and HCT116 cells. Finally, subcutaneous xenotransplanted tumor models of HCT116 cells were established in BALB/c nude mice. Compared with the control group, PD-L1 and YAP1 expressions in tumor tissues, detected by immunohistochemistry, were reduced in the group of metformin treatment. These findings illuminate a new regulatory mechanism, metformin activates Hippo signaling pathway to regulate PD-L1 expression and suggests that metformin has the possibility to increase the efficacy of immunotherapy in human CRC.

Metformin attenuates PD-L1 expression through activating Hippo signaling pathway in colorectal cancer cells.

Fibroblasts become cancer-associated fibroblasts (CAFs) in the tumor microenvironment after activation by transforming growth factor-β (TGF-β) and are critically involved in cancer progression. However, it is unknown whether the TGF superfamily member Nodal, which is expressed in various tumors but not expressed in normal adult tissue, influences the fibroblast to CAF conversion. Here, we report that Nodal has a positive correlation with α-smooth muscle actin (α-SMA) in clinical melanoma and colorectal cancer (CRC) tissues. We show the Nodal converts normal fibroblasts to CAFs, together with Snail and TGF-β signaling pathway activation in fibroblasts. Activated CAFs promote cancer growth in vitro and tumor-bearing mouse models in vivo. These results demonstrate that intercellular crosstalk between cancer cells and fibroblasts is mediated by Nodal, which controls tumor growth, providing potential targets for the prevention and treatment of tumors.

https://www.mdpi.com/2073-4409/8/6/538/pdf

Nodal Facilitates Differentiation of Fibroblasts to Cancer-Associated Fibroblasts that Support Tumor Growth in Melanoma and Colorectal Cancer

Significance The functions of N1-methyladenosine (m1A) in cancer development were largely unknown. We revealed m1A can positively regulate the glycolysis of cancer cells via regulation of ATP5D. Specifically, m1A regulates translation of ATP5D via YTHDF1/eRF3, and m1A negatively regulated message RNA (mRNA) stability of E2F1, which initiates ATP5D transcription. Targeted specific demethylation of ATP5D m1A by dm1ACRISPR system can significantly increase the expression of ATP5D and glycolysis of cancer cells. Our study reveals a crosstalk of mRNA m1A modification and cell metabolism, which broadens the multilayer regulation of metabolism and expands our understanding of such interplays that are essential for therapeutic application.

Jiawang Zhou

Papers

Cancer-associated fibroblasts promote PD-L1 expression in mice cancer cells via secreting CXCL5

Metformin attenuates PD-L1 expression through activating Hippo signaling pathway in colorectal cancer cells.

Nodal Facilitates Differentiation of Fibroblasts to Cancer-Associated Fibroblasts that Support Tumor Growth in Melanoma and Colorectal Cancer

RNA m1A methylation regulates glycolysis of cancer cells through modulating ATP5D

8-Acetonyldihydronitidine inhibits the proliferation of human colorectal cancer cells via activation of p53