SYNTHESIS AND ASSEMBLY OF FIBRILLIN BY FIBROBLASTS AND SMOOTH-MUSCLE CELLS

The expression and assembly of the microfibrillar glycoprotein fibrill in has been investigated in cultures of nuchal ligament fibroblasts, s kin fibroblasts and vascular smooth muscle cells. The level of fibrill in expression varied with the cell type and growth conditions. Higher levels of synthesis were recorded in quiescent post-confluent cells th an in actively dividing subconfluent cultures. Nuchal ligament fibrobl asts consistently synthesized the highest levels of fibrillin. Growth of cells in the presence of ascorbate resulted in an increased proport ion of newly synthesized fibrillin retained within cell layers. Fibril lin was immunoprecipitated from medium and cell layer extracts in the form of monomers and high-M(r) disulphide-bonded aggregates. Rotary sh adowing electron microscopy of cell layer extracts and collagen gels p rovided direct evidence for the assembly of extensive intact microfibr ils by smooth muscle cells and fibroblast cultures. Gel filtration chr omatography of medium and cell layer extracts, in combination with imm unoprecipitation of column fractions, provided a means of analysing th e size distribution and assembly of newly synthesized fibrillin. This cell culture approach provides an opportunity to evaluate normal and a berrant synthesis and assembly of fibrillin in a wide range of cell ty pes.