title: Transforming growth factor-beta regulates collagen gel contraction by increasing alpha 2 beta 1 integrin expression in osteogenic cells.
abstract: The contraction of floating collagen gels is suggested to mimic the reorganization of collagenous matrix during development and tissue healing. Here, we have studied two osteogenic cell lines, namely MG-63 and HOS, and a chemically transformed subclone of HOS cells, HOS-MNNG. Transforming growth factor-beta (TGF-beta), a putative regulator of bone fracture healing, increased collagen gel contraction by MG-63 and HOS-MNNG, but not by HOS cells. Our data show that TGF-beta-induced fibronectin synthesis is not sufficient for the process. Instead, anti-beta 1 integrin antibodies could prevent the contraction. There are three different integrin heterodimers that are known to mediate the cell-collagen interaction, namely alpha 1 beta 1, alpha 2 beta 1, and alpha 3 beta 1. In MG-63 cells TGF-beta increased the expression of alpha 2 beta 1 integrin and decreased the expression of alpha 3 beta 1 integrin, whereas alpha 1 beta 1 integrin is not expressed. HOS cells had no alpha 2 beta 1 integrin, neither did TGF-beta induce its expression. However, HOS-MNNG cells expressed more alpha 2 beta 1 integrin when treated with TGF-beta. Thus, we suggest that the mechanism of the enhanced collagen gel contraction by TGF-beta is the increased expression of alpha 2 beta 1 integrin heterodimer. To further test this hypothesis, we expressed a full-length alpha 2 integrin cDNA in HOS cells and in MG-63 cells. We obtained HOS cell clones that expressed alpha 2 beta 1 heterodimer, and the ability of these cells to contract collagen gels was greatly enhanced. Furthermore, the contraction by MG-63 cells transfected with alpha 2 integrin cDNA was enhanced, and the contraction by cells transfected with antisense oriented alpha 2 integrin cDNA was decreased. Thus, both in MG-63 and HOS cells the increased alpha 2 integrin expression alone was sufficient for the enhanced contraction of collagen gels. Furthermore, the amount of alpha 2 integrin is critical for the process, and its decrease leads to diminished ability to contract gels.
authors.affiliation: Department of Medical Biochemistry, University of Turku, Finland.
authors.forename: T
authors.initials: T
authors.lastname: Riikonen
authors.forename: L
authors.initials: L
authors.lastname: Koivisto
authors.forename: P
authors.initials: P
authors.lastname: Vihinen
authors.forename: J
authors.initials: J
authors.lastname: Heino
mesh_terms: D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D003094:Collagen / Q000378:metabolism*; D016373:DNA, Antisense; D005353:Fibronectins / Q000502:physiology; D006801:Humans; D019012:Integrin beta1; D016023:Integrins / Q000235:genetics / Q000378:metabolism*; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D010012:Osteogenesis; D012516:Osteosarcoma; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000502:physiology*; D014407:Tumor Cells, Cultured
chemical_list: D015703:Antigens, CD; D016373:DNA, Antisense; D005353:Fibronectins; D019012:Integrin beta1; D016023:Integrins; D016212:Transforming Growth Factor beta; D008769:Methylnitronitrosoguanidine; D003094:Collagen