Immunolocalization of G(alpha)i-3 in foetal lung fibroblasts.

Guanosine triphosphate (GTP)-binding proteins or G proteins are involved in a wide variety of well-recognized signalling activities between cell surface receptors and effectors. The heterotrimeric G proteins have alpha,beta and gamma subunits organized in a trimeric structure. The aim of this study was to localize G(alpha)i-3, an important heterotrimeric G protein, in foetal lung cells. Using a foetal lung fibroblast cell line (RFL-6), the localization of G(alpha)i-3 was determined by immunofluorescence using a specific antibody to G(alpha)i-3, colocalization with a lectin known to bind the Golgi complex and Western blotting of RFL-6 cellular membrane proteins. This study identified G(alpha)i-3 on the Golgi membranes in rat foetal lung cells. Treatment with cycloheximide, to block protein synthesis, diminished the cytosolic distribution of the protein, but intense Golgi staining remained. G(alpha)i-3, therefore, appears to be part of the Golgi complex and not present transiently during protein synthesis. In the nonpolar foetal lung fibroblasts studied, the intracellular concentration of G(alpha)i-3 suggests a role for this protein in the intracellular trafficking and regulation of proteins needed for normal lung development.