Immunolocalization of Gαi-3 in foetal lung fibroblasts

The normal development of the lung is dependent on signal transduction and communication within and between cells. A major family of proteins known as guanine nucleotide regulatory proteins (G proteins) is used in translating extracellular signals into intracellular events [1–3]. In particular, the high molecular weight G proteins, which are heterotrimers composed of α, β and γ subunits, have been traditionally associated with transduction at the cell surface, rather than with intracellular activities, such as constitutive protein secretion [4]. These subunits have been conserved in eukaryotes throughout evolution. Functionally, G proteins can be classified as Gs, activated by cholera toxin, or Gi, inhibited by pertussis toxin. The family of guanosine triphosphate (GTP)-binding proteins has been expanded to include proteins involved in secretion [5]. Low molecular weight G proteins, such as rab6p, have been associated with the Golgi complex and identified in the regulation of vesicular trafficking and constitutive protein secretion [6]. Heterotrimeric Gαi-3 has also been found on the Golgi of polarized mature renal epithelial cells [7]. The topographic segregation of the Gαi-3 subunit in foetal lung fibroblasts may suggest a functional intracellular role for the α subunit during lung development. Pertussis toxin-sensitive Gαi-3 could play an important role in the foetal lung by regulating Golgi trafficking and vesicular protein transport. The present study was conducted to determine the association of Gαi-3 with Golgi complex membranes in rat foetal lung fibroblasts (RFL6). Materials and methods