H19 is a long non-coding RNA precursor of miR-675microRNA. H19 is increasingly described to play key roles in the progression and metastasis of cancers from different tissue origins. We have previously shown that the H19 gene is activated by growth factors and increases breast cancer cell invasion. In this study, we established H19/miR-675 ectopic expression models of MDA-MB-231 breast cancer cells to further investigate the underlying mechanisms of H19 oncogenic action. We showed that overexpression of H19/miR-675 enhanced the aggressive phenotype of breast cancer cells including increased cell proliferation and migration in vitro, and increased tumor growth and metastasis in vivo. Moreover, we identified ubiquitin ligase E3 family (c-Cbl and Cbl-b) as direct targets of miR-675 in breast cancer cells. Using a luciferase assay, we demonstrated that H19, through its microRNA, decreased both c-Cbl and Cbl-b expression in all breast cancer cell lines tested. Thus, by directly binding c-Cbl and Cbl-b mRNA, miR-675 increased the stability and the activation of EGFR and c-Met, leading to sustained activation of Akt and Erk as well as enhanced cell proliferation and migration. Our data describe a novel mechanism of protumoral action of H19 in breast cancer.

Binding of macrophage colony stimulating factor (M‐CSF) to its receptor (Fms) induces dimerization and activation of the tyrosine kinase domain of the receptor, resulting in autophosphorylation of cytoplasmic tyrosine residues used as docking sites for SH2‐containing signaling proteins that relay growth and development signals. To determine whether a distinct signaling pathway is responsible for the Fms differentiation signal versus the growth signal, we sought new molecules involved in Fms signaling by performing a two‐hybrid screen in yeast using the autophosphorylated cytoplasmic domain of the wild‐type Fms receptor as bait. Clones containing SH2 domains of phospholipase C‐γ2 (PLC‐γ2) were frequently isolated and shown to interact with phosphorylated Tyr721 of the Fms receptor, which is also the binding site of the p85 subunit of phosphatidylinositol 3‐kinase (PI3‐kinase). At variance with previous reports, M‐CSF induced rapid and transient tyrosine phosphorylation of PLC‐γ2 in myeloid FDC‐P1 cells and this activation required the activity of the PI3‐kinase pathway. The Fms Y721F mutation strongly decreased this activation. Moreover, the Fms Y807F mutation decreased both binding and phosphorylation of PLC‐γ2 but not that of p85. Since the Fms Y807F mutation abrogates the differentiation signal when expressed in FDC‐P1 cells and since this phenotype could be reproduced by a specific inhibitor of PLC‐γ, we propose that a balance between the activities of PLC‐γ2 and PI3‐kinase in response to M‐CSF is required for cell differentiation.

The M-CSF receptor (M-CSFR) is expressed in monocytes-macrophages and their progenitors, and drives growth and development of this blood cell lineage. The M-CSFR is a member of a small family of growth factor receptors exhibiting related structures but distinct tissue-specific functions. This review discusses the early molecular events in the M-CSF signaling mechanisms, positive signals, negative signals, the possible organization of individual signaling pathways, and the problem of achieving specificity in the signal transduction mechanism.