L-cells were cotransfected with plasmids coding for mouse E-cadherin (uvomorulin) and the neophosphotransferase gene, and stable transfectants expressing E-cadherin at the cell surface were selected and cloned. Control transfection was done with the neophosphotransferase gene alone. The invasive migration of transfected and untransfected L-cells into three-dimensional collagen gels was then analyzed. L-cells not expressing E-cadherin migrated efficiently into the gels, whereas invasion of the E-cadherin-expressing L-cells was restricted in a cell density dependent manner. At sparse density, when the cells exhibited little cell-cell contacts, no difference was observed between the level of invasion of the cadherin-expressing cells and the control cells. However, with increasing cell density, decreasing amounts of the cadherin-expressing cells but increasing amounts of the control cells migrated into the gels. At confluent density hardly any cadherin-expressing cells were able to migrate into the gels. The inhibition of the invasion of the cadherin-expressing cells could be reverted if confluent cells were cultured in the presence of monoclonal antibodies against E-cadherin. Since the expression of E-cadherin did not influence the invasive mobility of single cells, these results indicate that E-cadherin-mediated cell-cell contacts inhibited invasive cellular migration. Time-lapse videoscopy and studies of cell migration from a monolayer into a cell-free area demonstrated that the restricted invasion could be explained by contact inhibition of cell movement of the cadherin-expressing cells.

We recently identified a 105,000-dalton plasma membrane glycoprotein, denoted cell-CAM 105 (CAM, cell adhesion molecule), that is involved in intercellular adhesion of reaggregating rat hepatocytes (Ocklind, C., and B. Obrink, 1982, J. Biol. Chem., 257:6788-6795). In this communication we used a monospecific rabbit antiserum against cell-CAM 105 to localize the antigen by indirect immunofluorescence on isolated rat cells and on frozen rat tissue sections. This antiserum stained the surface of freshly isolated hepatocytes. In liver sections, however, the fluorescence seemed to be located exclusively along the bile canaliculi. In addition, cell-CAM 105 showed a very specific tissue distribution. Thus a specific fluorescence was seen only in the epithelia of the stomach, the small intestine, the large intestine, the glandular epithelium of the parotid gland, and the tubules of the kidney. No specific fluorescence was found in variety of other tissues, including cartilage, interstitial connective tissue, smooth muscle, skeletal muscle, heart muscle, eye, brain, skin, the epithelia of oesophagus, bladder, uterin mucosa, thyroid follicles, prostate gland, or collecting ducts of the kidney. In the simple epithelia of the intestine and the kidney tubules the fluorescence was confined to the apical, luminal portion. Thus, both in these epithelia and in liver, cell-CAM 105 was confined to the apical, luminal portion. Thus, both in these epithelia and in liver, cell-CAM 105 was located where the typical junctional complexes between cells are found. These findings taken together with the fact that cell-CAM 105 is involved in intercellular adhesion between hepatocytes suggest with the fac that cell-CAM 105 is involved in intercellular adhesion between hepatocytes suggest that cell-CAM 105 is a member of the junctional complexes of hepatocytes and some simple epithelia.

As a model of ligand-dependent protein secretion the biosynthesis, intracellular transport, and release of the retinol-binding protein (RBP) were studied in primary cultures of rat hepatocytes pulse-labeled with [35S]methionine. After various periods of chase RBP was isolated by immunoprecipitation and identified by SDS PAGE. Both normal and vitamin A-deficient hepatocytes synthesized RBP. The normal cells secreted the pulse-labeled RBP within 2 h. RBP synthesized by deficient cells was not secreted, and intracellular degradation of the protein appeared to be slow. Deficient cells could be induced to secrete RBP on the addition of retinol to the culture medium. This occurred also after protein synthesis had been blocked by cycloheximide. Since retinol induces the secretion of RBP, accumulated in the endoplasmic reticulum (ER), it seems reasonable to conclude that the transport of RBP from the ER to the Golgi complex is regulated by retinol.