title: p16INK4A represses breast stromal fibroblasts migration/invasion and their VEGF-A-dependent promotion of angiogenesis through Akt inhibition.
abstract: Stromal fibroblasts, the most abundant and probably the most active cellular component of breast cancer-associated stroma, become active and promote angiogenesis through paracrine effects. However, it still unclear how these processes are regulated. Here, we have shown that down-regulation of the tumor suppressor p16(INK4A) protein enhances the migration/invasion abilities of breast stromal fibroblasts, which form dendritic network of extensions into matrigel. Furthermore, we present clear evidence that p16(INK4A) represses the expression/secretion of the proangiogenesis protein vascular endothelial growth factor A (VEGF-A). Consequently, p16(INK4A)-deficient breast stromal fibroblasts and mouse embryonic fibroblasts enhanced endothelial cell differentiation into capillary-like structures in a paracrine manner. This effect was suppressed by adding bevacizumab, a specific VEGF-A inhibitor. Additionally, p16(INK4A)-defective mouse embryonic fibroblasts enhanced angiogenesis in breast cancer xenografts in mice. Furthermore, we have shown that p16(INK4A) suppresses the Akt/mammalian target of rapamycin (mTOR) signaling pathway and its downstream effector hypoxia-inducible factor 1-alpha (HIF-1α), which transactivates VEGF-A. Consequently, Akt inactivation suppressed both the p16(INK4A)-dependent autocrine effect on fibroblast migration/invasion and the paracrine effect on angiogenesis, showing the important role of this protein kinase in mediating the various effects related to p16(INK4A) deficiency. These results indicate that p16(INK4A) is an efficient inhibitor of the migration/invasion abilities of breast stromal fibroblasts and also their paracrine proangiogenic effects, through inhibition of Akt. Therefore, pharmacologic restoration of p16(INK4A) level in stromal fibroblasts may be exploited as therapeutic strategy to help eradicate tumor cells and/or prevent their recurrence, through suppressing cell non-autonomous procarcinogenic mediators.
authors: Department of Molecular Oncology, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia.
authors: Mysoon M
authors: MM
authors: Al-Ansari
authors: Siti-Fauziah
authors: SF
authors: Hendrayani
authors: Asma
authors: A
authors: Tulbah
authors: Taher
authors: T
authors: Al-Tweigeri
authors: Afaf I
authors: AI
authors: Shehata
authors: Abdelilah
authors: A
authors: Aboussekhra
mesh_terms: D020533:Angiogenesis Inhibitors / Q000494:pharmacology; D000818:Animals; D061067:Antibodies, Monoclonal, Humanized / Q000494:pharmacology; D019898:Autocrine Communication; D000068258:Bevacizumab; D001943:Breast Neoplasms / Q000098:blood supply* / Q000378:metabolism*; D002454:Cell Differentiation; D002465:Cell Movement; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D051379:Mice; D009389:Neovascularization, Pathologic / Q000378:metabolism*; D016366:Open Reading Frames; D019899:Paracrine Communication; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering; D015398:Signal Transduction; D017154:Stromal Cells / Q000378:metabolism / Q000473:pathology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D014407:Tumor Cells, Cultured; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
chemical_list: D020533:Angiogenesis Inhibitors; D061067:Antibodies, Monoclonal, Humanized; D019941:Cyclin-Dependent Kinase Inhibitor p16; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering; D042461:Vascular Endothelial Growth Factor A; D000068258:Bevacizumab; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases