Cancer-associated fibroblasts exert a pro-angiogenic activity in Merkel cell carcinoma

Abstract

Background and aims: The tumor microenvironment (TME) is a complex niche enveloping a tumor formed by extracellular matrix, blood vessels, immune cells, and fibroblasts constantly interacting with cancer cells. Although TME is increasingly recognized as a major player in cancer initiation and progression in many tumor types, its involvement in Merkel cell carcinoma (MCC) pathogenesis is currently unknown. Here, we provide the first molecular and functional characterization of cancer- associated fibroblasts (CAFs), the major TME component, in MCC patient-derived xenografts. Methods: CAFs were established from eight patients undergoing surgical excision of MCC. To define the functional role of CAFs on MCC progression and metastasis, CAFs were co-injected along with an established MCC cell line, MKL-1, in a spontaneous MCC metastasis mouse model we recently published. Explanted tumors were deeply analyzed by immunohistochemistry and bulk RNA transcriptomic analysis. Furthermore, in vitro functional assays were performed to dissect the mechanisms involved in the proangiogenic role of CAFs. Results: Subcutaneous co-injection of patient-derived CAFs and the MCC cell line MKL-1 into SCID mice significantly promotes tumor growth, metastasis, and angiogenesis. Transcriptome analysis of the explanted tumors further highlighted the role of CAFs in MCC angiogenesis. In addition, in vitro tube formation assay provided evidence that the growth-promoting activity of MCC-derived CAFs is mediated by the APA/AngII-III/AT1R axis, with the expression of aminopeptidase A (APA) in CAFs being the upstream triggering event Conclusion: Altogether, our findings highlight the proangiogenic role of MCC-CAFs and point to APA as a potential marker. Background and aims: The tumor microenvironment (TME) is a complex niche enveloping a tumor formed by extracellular matrix, blood vessels, immune cells, and fibroblasts constantly interacting with cancer cells. Although TME is increasingly recognized as a major player in cancer initiation and progression in many tumor types, its involvement in Merkel cell carcinoma (MCC) pathogenesis is currently unknown. Here, we provide the first molecular and functional characterization of cancer- associated fibroblasts (CAFs), the major TME component, in MCC patient-derived xenografts. Methods: CAFs were established from eight patients undergoing surgical excision of MCC. To define the functional role of CAFs on MCC progression and metastasis, CAFs were co-injected along with an established MCC cell line, MKL-1, in a spontaneous MCC metastasis mouse model we recently published. Explanted tumors were deeply analyzed by immunohistochemistry and bulk RNA transcriptomic analysis. Furthermore, in vitro functional assays were performed to dissect the mechanisms involved in the proangiogenic role of CAFs. Results: Subcutaneous co-injection of patient-derived CAFs and the MCC cell line MKL-1 into SCID mice significantly promotes tumor growth, metastasis, and angiogenesis. Transcriptome analysis of the explanted tumors further highlighted the role of CAFs in MCC angiogenesis. In addition, in vitro tube formation assay provided evidence that the growth-promoting activity of MCC-derived CAFs is mediated by the APA/AngII-III/AT1R axis, with the expression of aminopeptidase A (APA) in CAFs being the upstream triggering event Conclusion: Altogether, our findings highlight the proangiogenic role of MCC-CAFs and point to APA as a potential marker.