Cancer-associated fibroblast-specific expression of the matricellular protein CCN1 coordinates neovascularization and stroma deposition in melanoma metastasis.

Melanoma is the leading cause of skin cancer-related death. As prognosis of melanoma patients remains problematic, identification of new therapeutic targets remains essential. Matricellular proteins are non-structural extracellular matrix proteins. They are secreted into the tumor microenvironment to coordinate behavior among different cell types, yet their contribution to melanoma is under-investigated. Examples of matricellular proteins include those comprising the CCN family. The CCN family member, CCN1, is highly pro-angiogenic. Herein, we show that, in human melanoma patients, although found in several tumor cell types, CCN1 is highly expressed by a subset of cancer-associated fibroblasts in melanoma patients and this expression correlates positively with expression of pro-angiogenic genes and progressive disease/resistance to anti-PD1 checkpoint inhibitors. Consistent with these observations, in a syngeneic C57BL6 mouse model of melanoma, loss of CCN1 expression from Col1A2-Cre-, herein identified as "universal", fibroblasts, impaired metastasis of subcutaneously-injected B16F10 tumor cells to lung, concomitant with disrupted neovascularization and collagen organization. Disruption of the extracellular matrix in the loss of CCN1 was validated using a novel artificial intelligence-based image analysis platform that revealed significantly decreased phenotypic fibrosis and composite morphometric collagen scores. As drug resistance is linked to matrix deposition and neo-angiogenesis, these data suggest that CCN1, due to its multifaceted role, may represent a novel therapeutic target for drug-resistant melanoma. Our data further emphasize the essential role that cancer-associated, (universal) Col1A2-Cre-fibroblasts and extracellular matrix remodeling play in coordinating behavior among different cell types within the tumor microenvironment.