Subcellular localization of the G(alpha 13) protein and G alpha interacting protein, two proteins involved in the control of macroautophagy in human colon cancer HT-29 cells
A. Petiot et al., Subcellular localization of the G(alpha 13) protein and G alpha interacting protein, two proteins involved in the control of macroautophagy in human colon cancer HT-29 cells, BIOCHEM J, 337, 1999, pp. 289-295
Autophagic sequestration is controlled by the G(alpha i3) protein in human
colon cancer HT-29 cells. Immunofluorescence and subcellular fractionation
studies showed that the G(alpha i3) protein is preferentially associated wi
th Golgi membranes but co-localization was also observed with the endoplasm
ic reticulum (ER) membrane. The G(alpha i2) protein, which is not involved
in the control of autophagic sequestration, is associated with the plasma m
embrane. Transfection of chimaeric G(alpha i) proteins (G(alpha i3/2), G(al
pha i2/3)) containing the N- and C-terminal parts of the relevant G(alpha i
) demonstrated that the C-terminal part of the G(alpha i3) protein, by gove
rning its membrane localization [de Almeida, Holtzman, Peters, Ercolani, Au
siello and Stow (1994) J. Cell Sci. 107, 507-515], is important in the cont
rol of macroautophagic sequestration. G alpha interacting protein (GAIP),wh
ich stimulates the GTPase activity of the G(alpha i3) protein and favours m
acroautophagic sequestration in HT-29 cells,was shown, by immunofluorescenc
e studies using confocal microscopy, to be confined to the cytoplasm. The c
ytoplasmic distribution of GAIP only partially. overlaps with that of the G
(alpha i3) protein. However, the presence of the two proteins on Golgi and
ER membranes was confirmed by subcellular fractionation. These results poin
t to the importance of the cytoplasmic localization of the G(alpha i3) prot
ein and GAIP in controlling autophagic sequestration in HT-29 cells.