Assembly of laminin polymers is dependent on beta1-integrins.
Recent reports suggest that laminin deposition is controlled by the cell via specific receptors, one of which is dystroglycan. In this study, the involvement of beta1-integrins in this process was investigated by comparing beta1-integrin-deficient cells of different phenotypes with their normal counterparts. Normal embryonic stem (ES) cells and embryoid bodies (EBs) derived from them were found to deposit cell-associated laminin into fibrillar networks, and in the EBs a basement membrane was assembled under the primitive endoderm. beta1-deficient ES cells and their EBs formed only small amounts of dot-like laminin deposits. Skeletal myotubes formed after prolonged differentiation in EBs were found to be surrounded by laminin, nidogen, and perlecan by immunofluorescent staining irrespective of the presence of beta1-integrins on the myotubes. However, at the electron microscope level only very thin sheet-like structures were detected close to the beta1-deficient myotubes, while the wt myotubes formed thick basement membranes. An epithelial cell line, GE11, derived from the beta1-integrin-deficient ES cells was also unable to assemble laminin on the cell surface, while transfection of the cells with the integrin beta1 subunit resulted in formation of a dense laminin network. Taken together, these results suggest that dystroglycan and beta1-integrins can both contribute to the recruitment of laminin to cell surfaces and that integrins are required at a subsequent step in the formation of basement membranes.
Department of Medical Biochemistry and Microbiology, The Biomedical Center, Uppsala, S-751 25, Sweden.
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Lohikangas
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Gullberg
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Johansson
D000818:Animals; D002460:Cell Line; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism* / Q000502:physiology; D007797:Laminin / Q000378:metabolism*; D011108:Polymers
D019012:Integrin beta1; D007797:Laminin; D011108:Polymers