IGFBP-3 inhibits Wnt signaling in metastatic melanoma cells.

In previous works, we have shown that insulin-like growth factor-binding protein-3 (IGFBP-3), a tissue and circulating protein able to bind to IGFs, decreases drastically in the blood serum of patients with diffuse metastatic melanoma. In agreement with the clinical data, recombinant IGFBP-3 was found to inhibit the motility and invasiveness of cultured metastatic melanoma cells and to prevent growth of grafted melanomas in mice. The present work was aimed at identifying the signal transduction pathways underlying the anti-tumoral effects of IGFBP-3. We show that the anti-tumoral effect of IGFBP-3 is due to inhibition of the Wnt pathway and depends upon the presence of CD44, a receptor protein known to modulate Wnt signaling. Once it has entered the cell, IGFBP-3 binds the Wnt signalosome interacting specifically with its component GSK-3ß. As a consequence, the ß-catenin destruction complex dissociates from the LRP6 Wnt receptor and GSK-3ß is activated through dephosphorylation, becoming free to target cytoplasmic ß-catenin which is degraded by the proteasomal pathway. Altogether, the results suggest that IGFBP-3 is a novel and effective inhibitor of Wnt signaling. As IGFBP-3 is a physiological protein which has no detectable toxic effects either on cultured cells or live mice, it might qualify as an interesting new therapeutic agent in melanoma, and potentially many other cancers with a hyperactive Wnt signaling. © 2016 The Authors. Molecular Carcinogenesis Published by Wiley Periodicals, Inc.

Insulin-like-growth-factor-binding-protein-3 (IGFBP-3) contrasts melanoma progression in vitro and in vivo.

Insulin-like-factor-binding-protein 3 (IGFBP-3) is known to modulate the activity of insulin-like growth factors (IGFs) besides having a number of IGF-independent effects on cell growth and survival. IGFBP-3 has been reported to decrease significantly in the blood serum of patients affected by certain cancers. In the present work, we have evaluated the levels of IGFBP-3 in the blood serum and tissues of patients affected by cutaneous melanoma, showing that loss of IGFBP-3 from both is strongly correlated with disease progression and reduced survival. In vitro treatment with IGFBP-3 of human and murine metastatic melanoma cell lines specifically inhibited the cells' migratory and invasive behaviour, inducing up-regulation of melanocytic differentiation markers such as tyrosinase activity and melanin content. A molecular analysis of the cellular pathways transducing the effect of IGFBP-3 implicated the Akt-GSK3ß axis. Moreover, administration of IGFBP-3 in vivo to SCID mice inoculated with human metastatic melanoma cells strongly reduced or completely inhibited tumor growth. In summary, IGFBP-3 appears to exert a specific inhibitory effect on melanoma growth and dissemination, suggesting that it may qualify as a useful therapeutic agent in melanomas and perhaps other cancers, at the least as a valid adjuvant therapy during treatment with conventional anti-tumoral drugs.

Correlation between insulin-like growth factor binding protein-3 serum level and melanoma progression.

BACKGROUND: Insulin-like growth factor (IGF) binding protein (IGFBP)-3 is the main carrier of circulating IGFs and the main modulator of their activity. IGFBP-3 controls cellular availability of IGFs, which cannot exert their pro-proliferative activity while bound to IGFBP-3. Proteolysis of IGFBP-3 is one mechanism to control IGF release. A reduction of serum IGFBP-3 levels and the associated increased availability of IGFs may represent a strategy whereby melanoma increases its metastatic potential. OBJECTIVE: The aim of our study was to evaluate the correlation between the IGFBP-3 serum level and melanoma stage. METHODS: The study included 41 patients, 24 male and 17 female, with median age of 60 years (range 24-80), affected by cutaneous melanoma. Blood samples were taken from each patient and IGFBP-3 serum levels were measured using Western blot analysis with commercial antibodies. Values were normalized using commercial IGFBP-3. RESULTS: The statistical analysis showed that full-size, glycosylated IGFBP-3 concentrations were significantly lower in the sera of patients with stage IV melanoma. Low serum levels of IGFBP-3 correlated with both disease progression and presence of disease at the time of sample collection. In patients who underwent follow-up visits with further collections of blood samples, the concentrations of glycosylated IGFBP-3 decreased only in those who showed progression of disease. LIMITATIONS: Our study shows only preliminary results on a limited number of patients. CONCLUSION: We demonstrate that there is a significant inverse correlation between the serum concentration of full-size, glycosylated IGFBP-3 and disease progression in patients with melanoma.