Abstract
Besides intrinsic changes, malignant cells also release soluble signals that reshape their microenvironment. Among these signals is WNT1-inducible signaling pathway protein 1 (WISP1), a secreted matricellular protein whose expression is elevated in several cancers, including melanoma, and is associated with reduced survival of patients diagnosed with primary melanoma. Here, we found that WISP1 knockout increases cell proliferation and represses wound healing, migration, and invasion of mouse and human melanoma cells in multiple in vitro assays. Metastasis assays revealed that WISP1 knockout represses tumor metastasis of B16F10 and YUMM1.7 melanoma cells in both C57BL/6Ncrl and NOD-scid IL2Rγnull (NSG) mice. WT B16F10 cells having an invasion phenotype in a transwell assay possessed a gene expression signature similar to that observed in the epithelial-mesenchymal transition (EMT), including E-cadherin repression and fibronectin and N-cadherin induction. Upon WISP1 knockout, expression of these EMT signature genes went in the opposite direction in both mouse and human cell lines, and EMT-associated gene expression was restored upon exposure to media containing WISP1 or to recombinant WISP1 protein. In vivo, Wisp1 knockout-associated metastasis repression was reversed by the reintroduction of either WISP1 or snail family transcriptional repressor 1 (SNAI1). Experiments testing EMT gene activation and inhibition with recombinant WISP1 or kinase inhibitors in B16F10 and YUMM1.7 cells suggested that WISP1 activates AKT Ser/Thr kinase and that MEK/ERK signaling pathways shift melanoma cells from proliferation to invasion. Our results indicate that WISP1 present within the tumor microenvironment stimulates melanoma invasion and metastasis by promoting an EMT-like process.
Highlights
Besides intrinsic changes, malignant cells release soluble signals that reshape their microenvironment
Our results indicate that WNT1-inducible signaling pathway protein 1 (WISP1) present within the tumor microenvironment stimulates melanoma invasion and metastasis by promoting an epithelial–mesenchymal transition (EMT)-like process
WISP1 expression is increased in primary melanoma and is associated with reduced overall survival of patients diagnosed with primary melanoma
Summary
To ground our study clinically, we first reviewed public databases for gene expression profiles in human primary melanoma samples. Real-time qPCR confirmed the significant increase in metastasis after WISP1 or SNAI1 were re-expressed in knockout cells (Fig. 6F) In these experiments, the average lung tumor burden was 4.3 Ϯ 0.6 metastatic tumor cells among 104 lung cells for mice receiving -KO1-pBabe cells, and the numbers were increased to 30.0 Ϯ 7.0 and 21.3 Ϯ 3.2 for mice with -KO1-mWisp and -KO1-hSnai cells, respectively The average liver tumor burden was 715 Ϯ 110 metastatic tumor cells for mice with -KO1-pBabe cells and increased to 1944 Ϯ 249 and 1391 Ϯ 186 for mice with -KO1mWisp and -KO1-hSnai cells, respectively (Fig. 6F, right) These in vitro and in vivo results supported our proposed role of SNAI1 as a downstream effector of WISP1 signaling and illustrate the role of this signaling pathway in promoting melanoma cell metastasis. We think that WISP1 promotes melanoma EMT by stimulating AKT and MEK/ERK signaling pathways
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