Integrin beta4 signaling promotes tumor angiogenesis.

Mice carrying a targeted deletion of the signaling portion of the integrin beta4 subunit display drastically reduced angiogenesis in response to bFGF in the Matrigel plug assay and to hypoxia in the retinal neovascularization model. Molecular cytology indicates that alpha6beta4 signaling promotes branching of beta4+ medium- and small-size vessels into beta4- microvessels without exerting a direct effect on endothelial cell proliferation or survival. Signaling studies reveal that alpha6beta4 signaling induces endothelial cell migration and invasion by promoting nuclear translocation of P-ERK and NF-kappaB. Upon subcutaneous implantation of various cancer cells, the mutant mice develop smaller and significantly less vascularized tumors than wild-type controls. These results provide genetic evidence that alpha6beta4 signaling promotes the onset of the invasive phase of pathological angiogenesis and hence identify a novel target for antiangiogenic therapy.

Targeted deletion of the integrin beta4 signaling domain suppresses laminin-5-dependent nuclear entry of mitogen-activated protein kinases and NF-kappaB, causing defects in epidermal growth and migration.

The alpha6beta4 integrin-a laminin-5 receptor-mediates assembly of hemidesmosomes and recruitment of Shc and phosphoinositide 3-kinase through the unique cytoplasmic extension of beta4. Mice carrying a targeted deletion of the signaling domain of beta4 develop normally and do not display signs of skin fragility. The epidermis of these mice contains well-structured hemidesmosomes and adheres stably to the basement membrane. However, it is hypoplastic due to reduced proliferation of basal keratinocytes and undergoes wound repair at a reduced rate. Keratinocytes from beta4 mutant mice undergo extensive spreading but fail to proliferate and migrate in response to epidermal growth factor (EGF) on laminin-5. EGF causes significant phosphorylation of extracellular signal-regulated kinase (ERK) and Jun N-terminal protein kinase (JNK) and phosphorylation and degradation of IkappaB in beta4 mutant cells adhering to laminin-5. Unexpectedly, however, ERK, JNK, and NF-kappaB remain in the cytoplasm in beta4 mutant cells on laminin-5, whereas they enter effectively into the nucleus in the same cells on fibronectin or in wild-type cells on both matrix proteins. Inhibitor studies indicate that alpha6beta4 promotes keratinocyte proliferation and migration through its effect on NF-kappaB and P-JNK. These findings provide evidence that beta4 signaling promotes epidermal growth and wound healing through a previously unrecognized effect on nuclear translocation of NF-kappaB and mitogen-activated protein kinases.

Alpha 5 beta 1 integrin activates an NF-kappa B-dependent program of gene expression important for angiogenesis and inflammation.

GeneCalling, a genome-wide method of mRNA profiling, reveals that endothelial cells adhering to fibronectin through the alpha 5 beta 1 integrin, but not to laminin through the alpha 2 beta 1 integrin, undergo a complex program of gene expression. Several of the genes identified are regulated by the NF-kappa B transcription factor, and many are implicated in the regulation of inflammation and angiogenesis. Adhesion of endothelial cells to fibronectin activates NF-kappa B through a signaling pathway requiring Ras, phosphatidylinositol 3-kinase, and Rho family proteins, whereas adhesion to laminin has a limited effect. Retroviral transfer of the superrepressor of NF-kappa B, I kappa B-2A, blocks basic fibroblast growth factor-induced angiogenesis in vivo. These results suggest that engagement of the alpha 5 beta 1 integrin promotes an NF-kappa B-dependent program of gene expression that coordinately regulates angiogenesis and inflammation.