Immunolocalization of Gαi-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 effecters. 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 metal 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.