The tumour microenvironment is the primary location in which tumour cells and the host immune system interact. Different immune cell subsets are recruited into the tumour microenvironment via interactions between chemokines and chemokine receptors, and these populations have distinct effects on tumour progression and therapeutic outcomes. In this Review, we focus on the main chemokines that are found in the human tumour microenvironment; we elaborate on their patterns of expression, their regulation and their roles in immune cell recruitment and in cancer and stromal cell biology, and we consider how they affect cancer immunity and tumorigenesis. We also discuss the potential of targeting chemokine networks, in combination with other immunotherapies, for the treatment of cancer.

Chemokines in the cancer microenvironment and their relevance in cancer immunotherapy

The TYRO3, AXL (also known as UFO) and MERTK (TAM) family of receptor tyrosine kinases (RTKs) are aberrantly expressed in multiple haematological and epithelial malignancies. Rather than functioning as oncogenic drivers, their induction in tumour cells predominately promotes survival, chemoresistance and motility. The unique mode of maximal activation of this RTK family requires an extracellular lipid–protein complex. For example, the protein ligand, growth arrest-specific protein 6 (GAS6), binds to phosphatidylserine (PtdSer) that is externalized on apoptotic cell membranes, which activates MERTK on macrophages. This triggers engulfment of apoptotic material and subsequent anti-inflammatory macrophage polarization. In tumours, autocrine and paracrine ligands and apoptotic cells are abundant, which provide a survival signal to the tumour cell and favour an anti-inflammatory, immunosuppressive microenvironment. Thus, TAM kinase inhibition could stimulate antitumour immunity, reduce tumour cell survival, enhance chemosensitivity and diminish metastatic potential.

The TAM family: phosphatidylserine-sensing receptor tyrosine kinases gone awry in cancer

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1002/1878-0261.12095

EMT and inflammation: inseparable actors of cancer progression

Antitumor immunity driven by intratumoral dendritic cells contributes to the efficacy of anthracycline-based chemotherapy in cancer. We identified a loss-of-function allele of the gene coding for formyl peptide receptor 1 (FPR1) that was associated with poor metastasis-free and overall survival in breast and colorectal cancer patients receiving adjuvant chemotherapy. The therapeutic effects of anthracyclines were abrogated in tumor-bearing Fpr1(-/-) mice due to impaired antitumor immunity. Fpr1-deficient dendritic cells failed to approach dying cancer cells and, as a result, could not elicit antitumor T cell immunity. Experiments performed in a microfluidic device confirmed that FPR1 and its ligand, annexin-1, promoted stable interactions between dying cancer cells and human or murine leukocytes. Altogether, these results highlight the importance of FPR1 in chemotherapy-induced anticancer immune responses.

https://science.sciencemag.org/content/sci/350/6263/972.full.pdf

Chemotherapy-induced antitumor immunity requires formyl peptide receptor 1

Epithelial-mesenchymal transition (EMT) is a crucial embryonic programme that is executed by various EMT transcription factors (EMT-TFs) and is aberrantly activated in cancer and other diseases. However, the causal role of EMT and EMT-TFs in different disease processes, especially cancer and metastasis, continues to be debated. In this Review, we identify and describe specific, non-redundant functions of the different EMT-TFs and discuss the reasons that may underlie disputes about EMT in cancer.

Non-redundant functions of EMT transcription factors.

There is increasing evidence that mast cells (MCs) and their mediators are involved in the remodeling of the tumor microenvironment and promote tumor growth, angiogenesis and metastasis. We have found that an increased density of MCs in thyroid cancer (TC) correlates with enhanced invasiveness. However, the MC-derived factors responsible for this activity and the mechanisms by which they enhance TC invasiveness remain unidentified. Here, we report that MCs, when activated by TC cells, produce soluble factors that induce epithelial-to-mesenchymal transition (EMT) and stemness features of TC cells. We identified CXCL8/interleukin (IL)-8 as the main mediator contained in activated MC conditioned media (CM) capable of inducing both EMT and stemness of TC cells. Mechanistically, MC CM or exogenous IL-8 stimulated Akt phosphorylation and Slug expression in TC cells. The inhibition of the Akt pathway or depletion of the Slug transcription factor by RNA interference, reverted EMT and stemness responses. TC cells stably transfected with exogenous IL-8 underwent EMT, displayed increased stemness and enhanced tumorigenicity with respect to control cells. The analysis of TC surgical specimens by immunohistochemical analysis demonstrated a positive correlation between MC density (Tryptase(+) cells) and stemness features (OCT4 staining). Taken together, our data identify an MC-dependent IL-8-Akt-Slug pathway that sustains EMT/stemness of TC cells. The blockade of this circuit might be exploited for the therapy of advanced TC.

Mast cells induce epithelial-to-mesenchymal transition and stem cell features in human thyroid cancer cells through an IL-8–Akt–Slug pathway

Thyroid cancer is the most common endocrine cancer, but its key oncogenic drivers remain undefined. In this study we identified the TYRO3 and AXL receptor tyrosine kinases as transcriptional targets of the chemokine CXCL12/SDF-1 in CXCR4-expressing thyroid cancer cells. Both receptors were constitutively expressed in thyroid cancer cell lines but not normal thyroid cells. AXL displayed high levels of tyrosine phosphorylation in most cancer cell lines due to constitutive expression of its ligand GAS6. In human thyroid carcinoma specimens, but not in normal thyroid tissues, AXL and GAS6 were often coexpressed. In cell lines expressing both receptors and ligand, blocking each receptor or ligand dramatically affected cell viability and decreased resistance to apoptotic stimuli. Stimulation of GAS6-negative cancer cells with GAS6 increased their proliferation and survival. Similarly, siRNA-mediated silencing of AXL inhibited cancer cell viability, invasiveness, and growth of tumor xenografts in nude mice. Our findings suggest that a TYRO3/AXL-GAS6 autocrine circuit sustains the malignant features of thyroid cancer cells and that targeting the circuit could offer a novel therapeutic approach in this cancer.

https://cancerres.aacrjournals.org/content/canres/71/5/1792.full.pdf

Activation of TYRO3/AXL tyrosine kinase receptors in thyroid cancer.

N-formyl peptide receptors (FPR1, FPR2 and FPR3) are involved in innate immunity, inflammation and cancer. FPR expression, initially described in immune cells, was later observed in non-hematopoietic cell populations and tissues. Several studies suggested a role for FPRs in the progression of various tumor histotypes, including gastric cancer (GC), for which a positive association with a specific FPR1 polymorphism has recently been described. We previously showed that FPRs are expressed on gastric epithelium and are required for wound repair and restitution of barrier integrity. Here we assess the role of FPRs in GC. We characterized the functions of FPRs in GC epithelial cells (MKN28, AGS and MKN45) cultured in vitro by assessing migration, proliferation, resistance to apoptosis and activation of the epithelial-to-mesenchymal transition. Activation of each FPR induced the epithelial-to-mesenchymal transition, proliferation, resistance to apoptosis and migration of GC cells in culture. Blocking compounds or RNA interference of each FPR reverted these effects. We also defined the in vivo tumorigenic potential of GC epithelial cells silenced for FPRs by xenograft experiments in immunocompromised mice. Interestingly, FPR1 silencing in GC cells (shFPR1) significantly enhanced xenograft growth with respect to shCTR, shFPR2 and shFPR3 xenografts, because of augmented vessel density and cell proliferation. Accordingly, HIF-1α and VEGF mRNA levels were higher in shFPR1 xenografts than in controls. Moreover, the in vitro production of proangiogenic factors in response to FPR2/3 agonists (WKYMVm, LL-37, uPA, uPAR84-95, AnxA1) or to other proinflammatory mediators (IL-1α) was higher in shFPR1 GC cells than in shCTR, shFPR2 and shFPR3 cells, suggesting that FPR1 functions as an inhibitor of CG angiogenesis. Thus, we propose that FPR1 stimulation may represent a novel therapeutic approach to counteract tumor angiogenesis.

The formyl peptide receptor 1 exerts a tumor suppressor function in human gastric cancer by inhibiting angiogenesis

It is commonly accepted that cancer is linked to inflammation. The possible mechanisms by which inflammation can contribute to carcinogenesis include induction of genomic instability, alterations in epigenetic events and subsequent inappropriate gene expression, enhanced proliferation of initiated cells, resistance to apoptosis, aggressive tumor neovascularization, invasion through tumor-associated basement membrane and metastasis. Inflammation also affects immune surveillance and responses to therapy. In this review, we overview the current understanding of different aspects of thyroid cancer and inflammation. Several studies have strongly suggested an increased risk of PTC in patients with Hashimoto's thyroiditis (HT), the most common autoimmune disease in thyroid cancer. Furthermore, an intense immune infiltrate is often associated with papillary thyroid carcinoma (PTC), and might play a critical role in the regulation of carcinogenesis and in carcinoma progression. The characterization of the most relevant inflammatory pathways of cancer-related inflammation (CRI) is instrumental for the identification of new target molecules that could lead to improved diagnosis and treatment.

Inflammation in thyroid oncogenesis.

https://www.internationaljournalofcardiology.com/article/S0167-5273(12)01660-9/pdf

Carla Visciano

Papers

Mast cells induce epithelial-to-mesenchymal transition and stem cell features in human thyroid cancer cells through an IL-8–Akt–Slug pathway

Activation of TYRO3/AXL tyrosine kinase receptors in thyroid cancer.

The formyl peptide receptor 1 exerts a tumor suppressor function in human gastric cancer by inhibiting angiogenesis

Inflammation in thyroid oncogenesis.

Serum soluble ST2 and interleukin-33 levels in patients with pulmonary arterial hypertension.