The Role Of IGFBP5 In Melanoma Tumor Growth And Metastasis

Malignant melanoma (MM), which arises from melanocytes, is the most aggressive form of skin cancers, with poor prognosis and high mortality. Only about 16% patients with stage IV metastatic melanoma can survive for 5 years and the median survival is 6-10 months. The incidence of melanoma has increased 15 times during the last 40 years. Thorough researches are needed to explore the mechanisms underlying occurrence and progress of melanoma, in order to find more therapeutic strategies and novel targeted therapeutic molecules in the quest for clinically meaningful progresses in the melanoma field. Through using RNA-seq technique, we previously constructed a differentially expressed gene database from melanocytes, primary melanoma cells, and cells from lymph node metastasis and IGFBP5 (Insulin-like Growth Factor Binding Protein 5) gene was screened as one of the most differentially expressed genes, and the biological function of IGFBP5 in melanoma remains largely elusive. Our preliminary data showed the abnormal expression of IGFBP5 in melanoma cells and melanoma samples. Currently, we focus on the molecular mechanism that IGFBP5 regulates melanoma tumorigenesis and metastasis with in vitro and in vivo functional assays.In this study, we establish the stable cell line of A375 and A2058 with IGFBP5 overexpression and deficiency respectively, and different functional assays including cell proliferation assay (CCK-assays), colony formation assay, cell cycle and cell apoptosis assay, transwell assay, xenograft models, tumor metastasis in vivo experiments, and RNA-seq assay are performed to uncover the role of IGFBP5 in melanoma cells. We characterize IGFBP5 as a suppressor of tumor growth and metastasis of human melanoma in vitro and in vivo, revealing that overexpression of IGFBP5 dramatically inhibits the proliferation, migration, and invasion of human melanoma cells in vitro and suppressed tumor growth and pulmonary metastasis in human melanoma-grafted mice. In addition, the overexpression of IGFBP5 leads to the inhibitory effects on epithelial-mesenchymal transition (EMT) phenotypes and changes of the stem cell properties of tumor cells via reduction in the expression of the stem cell markers NANOG, SOX2, OCT4, KLF4 and CD133. Mechanistically, we speculate that IGFBP5 exerts its inhibitory activity by down-regulating the IGF1R, ERK1/2, and p38-MAPK pathways that lead to a decreased expression of HIFla. The targeted genes downstream of HIF1a, VEGF and MMP9, are both decreased in IGFBP5-overexpressed cells. Furthermore, we analyzed the mRNA transcriptome database of A375 cells with IGFBP5 overexpressed and deficiency, and find that the IGF1 signaling pathway and p38-MAPK signaling pathway are affected and a quantity of cancer-related signaling pathways are also involved in the dysregulation of IGFBP5.In summary, our current findings indicate that IGFBP5 acts as a tumor suppressor in melanoma through modulation of the ERK1/2 and p38-MAPK pathways, as well as the progression of EMT, which might inhibit the migratory and invasive ability of melanoma cells by reducing the expression of HIF1a, VEGF and MMP9, three potential target genes downstream of the MAPK-ERK signaling pathway, suggesting IGFBP5 might be a novel target for the therapeutics of human melanoma.