CCN Proteins in Metastatic Melanoma

Melanoma cells recruit host tissue to become a part of the activated tumour stroma. This stromal microenvironment is similar to that seen in fibrotic tissue. CCN1 and CCN2 are tightly spatiotemporally regulated matricellular proteins involved in development and wound healing, and are abberantly expressed in fibrosis. Additionally they have been seen to be abnormally highly expressed in several cancers, including melanoma. Recent evidence has shown that deletion of CCN2 in the fibroblasts renders mice resistant to several models of fibrosis. Given this, I tested the hypothesis that deletion of CCN1 and CCN2 from fibroblasts could similarly impede the formation of the activated stromal microenvironment in melanoma. I used B16F(10) murine melanoma cells and syngeneic C57 BL6 mice with a tamoxifen-dependent conditional deletion of CCN1 or CCN2 in their fibroblasts. First I determined that loss of CCN2 in the fibroblasts prevents the metastasis of melanoma to the lungs of the mice, while loss of CCN2 in the tumour alone does not. Second I determined that loss of CCN2 from the fibroblasts prevented the expression of myofibroblast marker α SMA and reduced the expression of pluripotency marker SOX2. This loss of CCN2 was accompanied by a reduced tumour vascularisation, and a reduction in tumour cell vasculogenic mimicry. Finally I determined that loss of CCN1 in the fibroblasts results in highly disorganized collagen in the skin, which results in reduced metastasis of the melanoma cells. These observations were supported by in vitro experiments showing that deletion of CCN1 or CCN2 from melanoma cells reduce their ability to invade through a collagen basement membrane, and that deletion of CCN2 impedes the ability of melanoma cells to form tubule networks in nutrient-deficient environments. The results presented here suggest that CCN1 and CCN2 in the stromal microenvironment mediate the metastasis of melanoma through different mechanisms, with CCN2 being required for the activated stromal microenvironment and tumour vascularisation, and CCN1 being required for formation of a stiff and organized collagen network that facilitates tumour cell invasion, and thus they might both present novel targets for therapies to improve patient outcome.

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