A heterotrimeric G alpha i subunit, alpha i-3, is localized on Golgi membranes in LLC-PK1 and NRK epithelial cells where it colocalizes with mannosidase II by immunofluorescence. The alpha i-3 was found to be localized on the cytoplasmic face of Golgi cisternae and it was distributed across the whole Golgi stack. The alpha i-3 subunit is found on isolated rat liver Golgi membranes by Western blotting and G alpha i-3 on the Golgi apparatus is ADP ribosylated by pertussis toxin. LLC-PK1 cells were stably transfected with G alpha i-3 on an MT-1, inducible promoter in order to overexpress alpha i-3 on Golgi membranes. The intracellular processing and constitutive secretion of the basement membrane heparan sulfate proteoglycan (HSPG) was measured in LLC-PK1 cells. Overexpression of alpha i-3 on Golgi membranes in transfected cells retarded the secretion of HSPG and accumulated precursors in the medial-trans-Golgi. This effect was reversed by treatment of cells with pertussis toxin which results in ADP-ribosylation and functional uncoupling of G alpha i-3 on Golgi membranes. These results provide evidence for a novel role for the pertussis toxin sensitive G alpha i-3 protein in Golgi trafficking of a constitutively secreted protein in epithelial cells.
A heterotrimeric G protein, G alpha i-3, on Golgi membranes regulates the secretion of a heparan sulfate proteoglycan in LLC-PK1 epithelial cells.
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J L Stow, J B de Almeida, N Narula, E J Holtzman, L Ercolani, D A Ausiello; A heterotrimeric G protein, G alpha i-3, on Golgi membranes regulates the secretion of a heparan sulfate proteoglycan in LLC-PK1 epithelial cells.. J Cell Biol 15 September 1991; 114 (6): 1113–1124. doi: https://doi.org/10.1083/jcb.114.6.1113
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