Heterogeneous localization of G protein alpha-subunits in rat kidney

Abstract

The Gs alpha and Gi alpha 1-3 subunits of GTP-binding proteins were localized in sections of rat kidney using antibodies against unique synthetic decapeptides from the different G alpha subunits. All of the G alpha subunits were found to have a polarized distribution on renal tubule epithelial cells, and staining was typically found on either basolateral or apical membranes in a given cell type. Gi alpha 1 was localized to the apical pole of both thick ascending limb cells and cells forming the papillary epithelium, Gi alpha 2 labeled the basolateral plasma membrane and the cytoplasm of collecting duct principal cells, and Gi alpha 3 was most abundant in the apical region of proximal tubule cells of the S1 segment, where it was concentrated in sub-brush-border invaginations. It was also found in the perinuclear Golgi complex in these cells. Gs alpha was heavily concentrated on the basolateral plasma membranes of thick ascending limb cells and both principal and intercalated cells of the collecting duct. Less intense subapical staining of G alpha s was also found in proximal tubule cells. The cells of the macula densa had a unique G protein distribution that was distinct from the surrounding cells of the thick ascending limb of Henle. Antibodies specific for the Gi alpha 1 and Gi alpha 3 subunits both stained intracellular vesicles clustered at the basal pole of the cell. A heterogeneous distribution of G alpha subunits was also found by Western blotting on isolated cortical membrane fractions.

Calnuc, an EF-Hand Ca 2+ binding protein, specifically interacts with the C-terminal α5-helix of Gαi3

“…G␣ subunits are localized on the plasma membrane as well as on intracellular membranes such as Golgi membranes (36)(37)(38), as shown here for G␣i3-GFP (see Fig. 3B), where they regulate vesicular trafficking (39,40).…”

Promotion of Gαi3 subunit down-regulation by GIPN, a putative E3 ubiquitin ligase that interacts with RGS-GAIP

“…Interestingly, this is the site where the majority of GPCRs and many G proteins (43,44) are located in these cells, suggesting that GIPN could be part of a GPCR͞G␣͞ RGS-GAIP signaling complex. The presence of two different cross-immunoreactive species in cytosolic (38 kDa) and membrane (Ͼ94 kDa) fractions from mouse kidney raises the question of the relationship between the two forms.…”

Differential distribution of alpha subunits and beta gamma subunits of heterotrimeric G proteins on Golgi membranes of the exocrine pancreas.

“…The partial overlap with Man II suggested that Gets and Geti3 may be associated with Golgi membranes of the pancreatic exocrine cell. Since G~i3 had been previously localized to the Golgi in other cell types (53,60) and information on the localization of Gas is more limited, we focused on Get s and compared its distribution in the Golgi to that of 13-COP, ARF, and caveolin, proteins with unique Golgi localizations. Staining for the coatamer components (28, 51) 13-COP ( Fig.…”