The insulin-stimulated cell surface presentation of low density lipoprotein receptor-related protein in 3T3-L1 adipocytes is sensitive to phosphatidylinositide 3-kinase inhibition.

The regulation of low density lipoprotein receptor-related protein (LRP) activity by insulin was studied using 3T3-L1 adipocytes. The LRP mRNA and protein expression were independent of differentiation state of the cells and of insulin treatment. In differentiated cells, insulin treatment acutely stimulated the cell surface presentation of LRP (approximately 2-fold) as evidenced by methylamine-activated alpha(2)-macroglobulin binding and by biotinylation of cell surface LRP. The increased cell surface presentation was accompanied by a 39% decrease in LRP level in the low density microsomes. The magnitude of insulin-stimulated cell surface presentation of LRP was similar to that of transferrin receptor but was much less than that of GLUT4. Both the increases in LRP and GLUT4 cell surface presentation upon insulin treatment were abolished by inhibition of phosphatidylinositide 3-kinase. The increased cell surface presentation of LRP was associated with proportionally increased endocytic activity, and the internalization rate constant (K(e)) was not decreased by insulin treatment. Thus, insulin treatment most likely stimulates recycling of LRP from an endosomal pool to the plasma membrane, which is regulated in a phosphatidylinositide 3-kinase-dependent manner in 3T3-L1 adipocytes.