Insulin stimulates the release of a subset of GPI-anchored proteins in a G-protein independent manner

Abstract

The glycosyl-phosphatidylinositol anchored protein, membrane dipeptidase (EC 3.4.13.19) is released from the surface of 3T3-L1 adipocytes in response to insulin treatment through the action of a phospholipase C. The present study investigates the role of guanine-nucleotide binding proteins (G-proteins) in this process. Treatment of permeabilized 3T3-L1 adipocytes with GTP gamma S did not cause release of membrane dipeptidase into the medium, while GDP beta S did not inhibit the insulin-stimulated release of membrane dipeptidase. Other activators of G-proteins, including the tetradecapeptide mastoparan, pertussis toxin and AlF, also caused no significant release of membrane dipeptidase from the surface of the 3T3-L1 adipocytes. From these observations it is concluded that G-proteins are not involved in the insulin stimulated release of membrane dipeptidase. Although X-Pro aminopept idase (EC 3.4.11.9) is GPI-anchored in 3T3-L1 adipocytes as shown by digestion with bacterial phosphatidylinositol specific phospholipase C, it was not released upon insulin treatment of the cells, indicating that only a subset of the GPI-anchored proteins are susceptible to insulin-stimulated release.

• Gpi Anchors Phospholipase C G Proteins Adipocytes Pertussis Toxin