Placental growth factor (PlGF) enhances breast cancer cell motility by mobilising ERK1/2 phosphorylation and cytoskeletal rearrangement

BACKGROUND: During metastasis, cancer cells migrate away from the primary tumour and invade the circulatory system and distal tissues. The stimulatory effect of growth factors has been implicated in the migration process. Placental growth factor (PlGF), expressed by 30–50% of primary breast cancers, stimulates measurable breast cancer cell motility in vitro within 3 h. This implies that PlGF activates intracellular signalling kinases and cytoskeletal remodelling necessary for cellular migration. The PlGF-mediated motility is prevented by an Flt-1-antagonising peptide, BP-1, and anti-PlGF antibody. The purpose of this study was to determine the intracellular effects of PlGF and the inhibiting peptide, BP-1. METHODS: Anti-PlGF receptor (anti-Flt-1) antibody and inhibitors of intracellular kinases were used for analysis of PlGF-delivered intracellular signals that result in motility. The effects of PlGF and BP-1 on kinase activation, intermediate filament (IF) protein stability, and the actin cytoskeleton were determined by immunohistochemistry, cellular migration assays, and immunoblots. RESULTS: Placental growth factor stimulated phosphorylation of extracellular-regulated kinase (ERK)1/2 (pERK) in breast cancer cell lines that also increased motility. In the presence of PlGF, BP-1 decreased cellular motility, reversed ERK1/2 phosphorylation, and decreased nuclear and peripheral pERK1/2. ERK1/2 kinases are associated with rearrangements of the actin and IF components of the cellular cytoskeleton. The PlGF caused rearrangements of the actin cytoskeleton, which were blocked by BP-1. The PlGF also stabilised cytokeratin 19 and vimentin expression in MDA-MB-231 human breast cancer cells in the absence of de novo transcription and translation. CONCLUSIONS: The PlGF activates ERK1/2 kinases, which are associated with cellular motility, in breast cancer cells. Several of these activating events are blocked by BP-1, which may explain its anti-tumour activity.