Isolation of cell-to-cell adherens junctions from rat liver

A new isolation procedure for cell-to-cell adherens junctions has been developed using rat liver. From the bile canaliculi-enriched fraction obtained by homogenization of the liver and sucrose gradient centrifugation, the fraction rich in adherens junction was recovered by detergent treatment followed by sucrose gradient centrifugation. Light and electron microscopy revealed that this final fraction was mainly composed of the belt-like adherens junctions with their associated short actin filaments. Biochemical and immunological analyses have shown that vinculin is highly enriched in this fraction. Considering that vinculin is known to be localized in the cell-to-cell adherens junctions, we can conclude that we have succeeded in isolating the cell- to-cell adherens junctions. Furthermore, the constituents of the undercoat (dense layer underlying the membrane) of adherens junctions were selectively extracted from the fraction rich in junctions. Upon SDS electrophoresis of this extract, 10 polypeptides including vinculin, alpha-actinin, and actin were dominant. The results obtained are discussed with special reference to the molecular organization of the undercoats of cell-to-cell adherens junctions.