Activation of Canonical BMP4-SMAD7 Signaling Suppresses Breast Cancer Metastasis

Abstract

Metastasis is the major cause of death in cancer patients; with no therapeutic cure, treatments remain largely palliative. As such, new targets and therapeutic strategies are urgently required. Here we show that bone morphogenetic protein-4 (BMP4) blocks metastasis in animal models of breast cancer and predicts improved survival in patients. In preclinical models of spontaneous metastasis, BMP4 acted as an autocrine mediator to modulate a range of known metastasis-regulating genes, including SMAD7, via activation of canonical BMP-SMAD signaling. Restored BMP4 expression, or therapeutically administered BMP4 protein, blocked metastasis and increased survival by sensitising cancer cells to anoikis, thereby reducing the number of circulating tumour cells. Gene silencing of BMP4, or its downstream mediator SMAD7, reversed this phenotype. Administration of recombinant BMP4 markedly reduced spontaneous metastasis to lung and bone. Elevated levels of BMP4 and SMAD7 were prognostic for improved recurrence-free survival and overall survival in breast cancer patients, indicating the importance of canonical BMP4 signaling in the suppression of metastasis and highlighting new avenues for therapy against metastatic disease.