MiR-155-mediated loss of C/EBPß shifts the TGF-ß response from growth inhibition to epithelial-mesenchymal transition, invasion and metastasis in breast cancer.

During breast cancer progression, transforming growth factor-beta (TGF-ß) switches from acting as a growth inhibitor to become a major promoter of epithelial-mesenchymal transition (EMT), invasion and metastasis. However, the mechanisms involved in this switch are not clear. We found that loss of CCAAT-enhancer binding protein beta (C/EBPß), a differentiation factor for the mammary epithelium, was associated with signs of EMT in triple-negative human breast cancer, and in invasive areas of mammary tumors in MMTV-PyMT mice. Using an established model of TGF-ß-induced EMT in mouse mammary gland epithelial cells, we discovered that C/EBPß was repressed during EMT by miR-155, an oncomiR in breast cancer. Depletion of C/EBPß potentiated the TGF-ß response towards EMT, and contributed to evasion of the growth inhibitory response to TGF-ß. Furthermore, loss of C/EBPß enhanced invasion and metastatic dissemination of the mouse mammary tumor cells to the lungs after subcutaneous injection into mice. The mechanism by which loss of C/EBPß promoted the TGF-ß response towards EMT, invasion and metastasis, was traced to a previously uncharacterized role of C/EBPß as a transcriptional activator of genes encoding the epithelial junction proteins E-cadherin and coxsackie virus and adenovirus receptor. The results identify miR-155-mediated loss of C/EBPß as a mechanism, which promotes breast cancer progression by shifting the TGF-ß response from growth inhibition to EMT, invasion and metastasis.

Fibroblast-dependent regulation of the stem cell properties of cancer cells.

There is emerging evidence that cancer stem cells (CSCs), like normal tissue stem cells, are regulated by a niche formed of mesenchymal cells. In this review we summarize the current knowledge of the role of cancer associated fibroblasts (CAFs) in a tentative CSC niche. We also discuss findings from our own studies showing that CAF derived factors have a strong stimulatory effect on the stem cell properties of breast cancer cells. Based on recent literature we conclude that CAFs are strong modulators of the stem cell properties of cancer cells. This effect is likely to be particularly relevant under circumstances of early stages of tumor cell dissemination and metastasis.

Therapeutic efficacy of a DNA vaccine targeting the endothelial tip cell antigen delta-like ligand 4 in mammary carcinoma.

The Notch ligand delta-like ligand 4 (DLL4) is an essential component expressed by endothelial tip cells during angiogenic sprouting. We have described a conceptually novel therapeutic strategy for targeting tumor angiogenesis and endothelial tip cells based on DNA vaccination against DLL4. Immunization with DLL4-encoding plasmid DNA by in vivo electroporation severely retarded the growth of orthotopically implanted mammary carcinomas in mice by induction of a nonproductive angiogenic response. Mechanistically, vaccination brought about a break in tolerance against the self-antigen, DLL4, as evidenced by the production of inhibitory and inherently therapeutic antibodies against mouse DLL4. Importantly, no evidence for a delayed wound healing response, or for toxicity associated with pharmacological blockade of DLL4 signaling, was noted in mice immunized with the DLL4 vaccine. We have thus developed a well-tolerated DNA vaccination strategy targeting the endothelial tip cells and the antigen DLL4 with proven therapeutic efficacy in mouse models of mammary carcinoma; a disease that has been reported to dramatically induce the expression of DLL4. Conceivably, induction of immunity toward principal mediators of pathological angiogenesis could provide protection against recurrent malignant disease in the adjuvant setting.