CONTROL OF THE EXPRESSION AND ACTIVITY OF THE G(ALPHA)-INTERACTING PROTEIN (GAIP) IN HUMAN INTESTINAL-CELLS

The G(alpha)-interacting protein (GAIP) is known to interact with the G(alpha i3) protein, It has been suggested that, depending on its expr ession, GAIP can be a regulator of trimeric G(i) protein signaling pat hways, In the present study we show that the GAIP mRNA content decline s during the enterocytic differentiation of two cell lines derived fro m human colon adenocarcinomas: HT-29 and Caco-2. In undifferentiated H T-29 cells, when the GDP/GTP cycle on the trimeric G(i3) protein is in terrupted by either pertussis toxin treatment or by the transfection o f a mutant of the G(alpha i3) protein with no GTPase activity (Q204L), we observed a decrease in the GAIP mRNA content, As these conditions are known to impair the G(i3)-dependent lysosomal-autophagic pathway e xisting in undifferentiated HT-29 cells, we have investigated the role of G;AIP in controling the lysosomal-autophagic pathway, Overexpressi on of GAIP stimulated protein degradation along the macroautophagic pa thway, In contrast, overexpression of GAIP did not modify the low rate of macroautophagy in cells expressing the Q204L mutant of the G(alpha i3) protein, These results show that GAIP regulates a major catabolic pathway and that the expression of GAIP is dependent upon the activit y of the G(alpha i3) protein and the state of enterocytic differentiat ion of cells.