Protein zero, a nervous system adhesion molecule, triggers epithelial reversion in host carcinoma cells.

Protein zero (P(o)) is the immunoglobulin gene superfamily glycoprotein that mediates the self-adhesion of the Schwann cell plasma membrane that yields compact myelin. HeLa is a poorly differentiated carcinoma cell line that has lost characteristic morphological features of the cervical epithelium from which it originated. Normally, HeLa cells are not self-adherent. However, when P(o) is artificially expressed in this line, cells rapidly aggregate, and P(o) concentrates specifically at cell-cell contact sites. Rows of desmosomes are generated at these interfaces, the plasma membrane localization of cingulin and ZO-1, proteins that have been shown to be associated with tight junctions, is substantially increased, and cytokeratins coalesce into a cohesive intracellular network. Immunofluorescence patterns for the adherens junction proteins N-cadherin, alpha-catenin, and vinculin, and the desmosomal polypeptides desmoplakin, desmocollin, and desmoglein, are also markedly enhanced at the cell surface. Our data demonstrate that obligatory cell-cell adhesion, which in this case is initially brought about by the homophilic association of P(o) molecules across the intercellular cleft, triggers pronounced augmentation of the normally sluggish or sub-basal cell adhesion program in HeLa cells, culminating in suppression of the transformed state and reversion of the monolayer to an epithelioid phenotype. Furthermore, this response is apparently accompanied by an increase in mRNA and protein levels for desmoplakin and N-cadherin which are normally associated with epithelial junctions. Our conclusions are supported by analyses of ten proteins we examined immunochemically (P(o), cingulin, ZO-1, desmoplakin, desmoglein, desmocollin, N-cadherin, alpha-catenin, vinculin, and cytokeratin-18), and by quantitative polymerase chain reactions to measure relative amounts of desmoplakin and N-cadherin mRNAs. P(o) has no known signaling properties; the dramatic phenotypic changes we observed are highly likely to have developed in direct response to P(o)-induced cell adhesion. More generally, the ability of this "foreign" membrane adhesion protein to stimulate desmosome and adherens junction formation by augmenting well-studied cadherin-based adhesion mechanisms raises the possibility that perhaps any bona fide cell adhesion molecule, when functionally expressed, can engage common intracellular pathways and trigger reversion of a carcinoma to an epithelial-like phenotype.

Magnesium dietary intake modulates blood lipid levels and atherogenesis.

In this study, we have examined the effects of variation in dietary Mg on the atherogenic process. Oral supplementation of rabbits fed a high cholesterol diet (1% or 2%) with the Mg salt magnesium aspartate hydrochloride (Magnesiocard) (i) lowers the level of serum cholesterol and triglycerides in normal (25-35%) as well as atherosclerotic (20-40%) animals and (ii) attenuates the atherosclerotic process markedly. In addition, we found that dietary deficiency of Mg augments atherogenesis markedly and stimulates (or activates) macrophages of the reticuloendothelial system. Evidence is presented to indicate that the hypercholesterolemic state may cause the loss of Mg from soft tissues to the serum, thereby masking an underlying Mg deficiency.

Protein zero of peripheral nerve myelin: biosynthesis, membrane insertion, and evidence for homotypic interaction.

Protein zero (P0), an integral membrane glycoprotein synthesized by Schwann cells, is the major glycoprotein of peripheral nerve myelin. The predicted disposition of P0 with respect to the membrane bilayer postulates the existence of extracellular and intracellular domains, that mediate compaction of the myelin lamellae. We used in vitro translations programmed with sciatic nerve mRNA and cells transfected with a P0 cDNA construct to study the biosynthesis and topology of P0 in the bilayer. The behavior of P0 at the cell surface, when expressed under physiological conditions, was also examined. We have verified the topological predictions of an earlier model, derived from analysis of a P0 cDNA, and provide evidence that the extracellular domain of P0 mediates homotypically cell-cell interactions in the transfectants.

Physiologic properties of myelin proteins revealed by their expression in nonglial cells.

The transfection paradigm described herein can be used to investigate the functional properties of individual nervous system proteins in ways that have not been explored before. In particular, observations on the "structural" proteins of myelin are being made that have already yielded certain unique insights into the physiologic properties of these polypeptides. The ease with which site-directed mutagenesis procedures can be applied to these systems should eventually enable us to define with great precision the "functional domains" within each myelin protein.