The growth suppressing gas1 product is a GPI-linked protein

Growth arrest specific (gas) 1 gene product is expressed in non-transformed fibroblasts in response to stimuli driving cells into Go phase. Gas1 has been demonstrated to inhibit cell proliferation when over-expressed in proliferating fibroblasts. This activity depends on a function of the p53 protein independent of its transactivating ability. To better define the pathway leading from Gas1, which is located on the plasma membrane, to p53, we have undertaken a detailed characterization of its topology. We demonstrate that the protein undergoes cotranslational modifications in the endoplasmic reticulum, consisting of signal peptide cleavage, N-linked glycosylation and glycosyl-phosphatidylinositol anchor addition. Immunoelectron microscopy shows that, in its mature form, Gas1 is randomly distributed over the outer leaflet of the plasma membrane and that upon antibody-induced clustering it relocalizes to caveolae.