ABSTRACT
Cutaneous repair after injury requires activation of resident dermal fibroblasts and their transition to myofibroblasts. The key stimuli for myofibroblast formation are activation of transforming growth factor-ß (TGF-ß) receptors and mechanotransduction mediated by integrins and associated proteins. We investigated the role of integrin-linked kinase (ILK) in TGF-ß1 induction of dermal fibroblast transition to myofibroblasts. ILK-deficient fibroblasts treated with TGF-ß1 exhibited attenuation of Smad 2 and 3 phosphorylation, accompanied by impaired transcriptional activation of Smad targets, such as α-smooth muscle actin. These alterations were not limited to Smad-associated TGF-ß1 responses, as stimulation of noncanonical mitogen-activated protein kinase pathways by this growth factor was also diminished in the absence of ILK. ILK-deficient fibroblasts exhibited abnormalities in the actin cytoskeleton, and did not form supermature focal adhesions or contractile F-actin stress fibers, indicating a severe impairment in their capacity to differentiate into myofibroblasts. These defects extended to the inability of cells to contract extracellular matrices when embedded in collagen lattices. We conclude that ILK is necessary to transduce signals implicated in the transition of dermal fibroblasts to myofibroblasts originating from matrix substrates and TGF-ß1.
Subject(s)
Cell Differentiation/physiology , Dermis/cytology , Dermis/metabolism , Myofibroblasts/cytology , Myofibroblasts/metabolism , Protein Serine-Threonine Kinases/metabolism , Transforming Growth Factor beta1/metabolism , Actins/metabolism , Animals , Cell Movement/physiology , Cell Proliferation , Cells, Cultured , Collagen/metabolism , Gene Expression Regulation/physiology , Mice , Models, Animal , Protein Serine-Threonine Kinases/deficiency , Signal Transduction/physiology , Smad2 Protein/metabolism , Smad3 Protein/metabolism , Transforming Growth Factor beta1/geneticsABSTRACT
Transforming growth factor (TGF)-beta1 is associated with tumor progression and resistance to chemotherapy in established cancers, as well as host immune suppression. Here, we show that the serum glycoprotein alpha2-HS-glycoprotein (AHSG) blocks TGF-beta1 binding to cell surface receptors, suppresses TGF-beta signal transduction, and inhibits TGF-beta-induced epithelial-mesenchymal transition, suggesting that AHSG may play a role in tumor progression. In 66 consecutive sporadic human colorectal cancer specimens, we observed a 3-fold depletion of ASHG in tumor compared with normal tissue, whereas levels of other abundant plasma proteins, albumin and transferrin, were equivalent. Using the Multiple intestinal neoplasia/+ (Min/+) mouse model of intestinal tumorigenesis, we found twice as many intestinal polyps overall, twice as many large polyps (>3 mm diameter), and more progression to invasive adenocarcinoma in Min/+ Ahsg-/- mice than in littermates expressing Ahsg. Phosphorylated Smad2 was more abundant in the intestinal mucosa and tumors of Min/+ mice lacking Ahsg, demonstrating increased TGF-beta signaling in vivo. Furthermore, TGF-beta-mediated suppression of immune cell function was exaggerated in Ahsg-/- animals, as shown by inhibition of macrophage activation and reduction in 12-O-tetradecanoylphorbol 13-acetate-induced cutaneous inflammation. Reconstitution of Ahsg-/- mice with bovine Ahsg suppressed endogenous TGF-beta-dependent signaling to wild-type levels, suggesting that therapeutic enhancement of AHSG levels may benefit patients whose tumors are driven by TGF-beta.
