TGF-beta1 binding protein-like modules of fibrillin-1 and -2 mediate integrin-dependent cell adhesion.

Human fibrillin, a major component of the extracellular matrix, exists as two highly homologous forms (fibrillin-1 and -2). Several modules of fibrillin are homologous to TGF-beta1 binding protein. Two of these modules, D25 (the 25th module of fibrillin-1 and -2 D segment) and D12 (the 12th module of fibrillin-2 D segment) contain the cell adhesion motif arginyl-glycyl-aspartyl (RGD). The ability of RGD to mediate adhesion to D25-1 and D12-2 was investigated using bacterially expressed fusion proteins. Human skin fibroblasts and murine L-cells were used in microassays of cell attachment and cell spreading on fibrillin fusion-protein substrata. Dose-dependent experiments and competitive inhibition by soluble RGD-containing peptides demonstrated that D25-1 and D12-2 mediate RGD-dependent cell adhesion. These results provide evidence for a cell adhesion function of fibrillin-2. Inhibition with anti-integrin antibodies showed that alpha(v) and beta3 integrins mediate adhesion to D25-1, while alpha3, alpha(v) and beta1 are involved in adhesion to D12-2. Binding of different receptors may elicit distinct cell signalling supporting the hypothesis that fibrillin-1 and fibrillin-2 have distinct roles.

A novel de novo mutation in exon 14 of the fibrillin-1 gene associated with delayed secretion of fibrillin in a patient with a mild Marfan phenotype.

The Marfan syndrome, an autosomal dominant heritable disorder of connective tissue, is caused by mutations in the gene for fibrillin-1, FBN1. A novel FBN1 mutation was identified using temperature-gradient gel electrophoresis of a reverse-transcribed polymerase chain reaction product spanning exons 14 to 16. The mutation, G1760A, is predicted to result in the amino acid substitution C587Y and thus to disrupt one of the disulfide bonds of the calcium-binding epidermal growth factor-like module encoded by exon 14. C587Y was found to be a de novo mutation in a relatively mildly affected 15-year-old girl whose clinical phenotype was characterized mainly by ectopia lentis and thoracic scoliosis. Metabolic labeling of cultured dermal fibroblasts from the affected patient demonstrated delayed secretion of fibrillin with normal synthesis and no decrease in incorporation into the extracellular matrix compartment. Fibrillin immunostaining of confluent dermal fibroblast cultures revealed no visible difference between the patient's cells and control cells. Characterization of many different FBN1 mutations from different regions of the gene may provide a better understanding of clinical and biochemical genotype-phenotype relationships.