Reorganization of actin cytoskeleton by RhoA is necessary for GLUT4 translocation in 3T3L1 adipocytes.

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p120-catenin is a member of Armadillo-domain proteins found at cell-cell junctions, and interacts with the highly conserved juxtamembrane domain of classical cadherins. There are three kinds of cadherin expressed in 3T3L1 pre-adipocytes, but their expressions are reduced significantly after differentiation to adipocytes. Therefore, main part of p120-catenin goes to cytosole fraction. This unbound form of p120-catenin acts as a Rho-GDI in cytosole, then actin stress fiber disappears in adipocytes since RhoA plays critical role to maintaining actin stress fiber. The other hand, cortical actin, other F-actin structure, is increased in adipocytes. After insulin stimulation, GLUT4 translocation from intracellular GLUT4 storage compartments to plasma membrane occurred simultaneously with up regulation of interaction between cadherin and p120-catenin. Over expression of N-cadherin in adipocytes to suppress Rho-GDI activity of p120-catenin induced GLUT4 translocation to plasma membrane without insulin stimulation. Moreover, a constitutively active RhoA mutant induced GLUT4 translocation and thickened the cortical actin. These results indicated that p120-catenin is a key molecule for regulation of actin structures and GLUT4 translocation, and the functions are controlled through RhoA activity. Taken together, it is possible that one mechanism of GLUT4 translocation by insulin is through p120-catenin, but it is necessary to examine the relationship with other signal cascades of insulin, PKB and ERK pathways, to confirm the importance of the function of p120-catenin.