THE VON-HIPPEL-LINDAU TUMOR-SUPPRESSOR PROTEIN IS REQUIRED FOR PROPERASSEMBLY OF AN EXTRACELLULAR FIBRONECTIN MATRIX

Fibronectin coimmunoprecipitated with wild-type von Hippel-Lindau prot ein (pVHL) but not tumor-derived pVHL mutants. Immunofluorescence and biochemical fractionation experiments showed that fibronectin colocali zed with a fraction of pVHL associated with the endoplasmic reticulum, and cold competition experiments suggested that complexes between fib ronectin and pVHL exist in intact cells. Assembly of an extracellular fibronectin matrix by VHL-/- renal carcinoma cells, as determined by i mmunofluorescence and ELISA assays, was grossly defective compared wit h VHL+/+ renal carcinoma cells. Reintroduction of wildtype, but not mu tant, pVHL into VHL-/- renal carcinoma cells partially corrected this defect. Finally, extracellular fibronectin matrix assembly by VHL-/- m ouse embryos and mouse embryo fibroblasts (MEFs), unlike their VHL+/counterparts, was grossly impaired. These data support a direct role o f pVHL in fibronectin matrix assembly.