Cell recognition

Extracellular matrix The surfaces of animal cells are covered with a flexible and sticky layer of complex carbohydrates, proteins, and lipids. This complex coating is cell-specific, serves in cell-cell recognition and communication, creates cell adhesion, and provides a protective outer layer. 

Glycosphingolipids are constituents of the outer leaflet of plasma membranes and are important in cell adhesion and cell recognition. Some are antigens, eg, ABO blood group substances. Certain gangliosides function as receptors for bacterial toxins (eg, for cholera toxin, which subsequently activates adenylyl cyclase). 

SHARON N, LIS H (1989) Lectins as cell recognition molecules. Science. 246 227-34. 

N. Sharon, Bacterial lectins, cell-cell recognition and infectious disease, FEBS Lett., 217 (1987) 145-157. 

Neurexins a protein kinase. A component of active zones that interact with RIM, syntaxin and other proteins. Cell surface proteins with more than 1,000 isoforms generated by alternative splicing from three genes. Neurexins include one of the receptors for aratrotoxin and may function in cell-cell recognition between neurons. 

Butcher, E.C., Leukocyte-endothelial cell recognition Three (or more) steps to specificity and diversity, Cell, 67, 1033, 1991. 

The natural ligand for the amine oxidase activity is not known for certain. While SSAO/VAP-1 will oxidize endogenous molecules such as methylamine and tyramine, the substrates associated with diapedesis are unknown. It has been speculated that leukocyte cell surface lysine residues or amino sugars, such as mannosamine residues (5) known to be associated with cell/cell recognition may be involved [14,15]. 

Although most work to date has focused on the enzyme inhibition aspect, it is possible that the monoclonal VAP-1 antibody discussed above may well be closer to the clinic. The task of designing small molecules to interfere with cell-cell recognition is certainly feasible, but this will not be a trivial effort, more akin to the search for selective selectin antagonists which has proven to be very challenging. As confidence grows in the pharmaceutical industry that SSAO/VAP-1 is a validated target, it is inevitable that considerable resources will be directed to all avenues to block the functional action of this protein. 

The process of cell recognition is a molecular one, the final destruction of the cell membrane, however, is a physical process. The exact mechanism is still unclear. At least three possibilities are discussed a locally high concentration of lysophospholipids... 

Polymeric vesicles could be of better use for such an antitumor therapy on a cellular level, since they have at least one of the properties required, namely an extraordinary membrane stability. For a successful application, however, the simple systems prepared so far must be varied to a great extent, because the stability of a model cell membrane is not the only condition to be fulfilled. Besides stability and possibilities for cell recognition as discussed above the presence of cell membrane destructing substances such as lysophospholipids is necessary. These could e.g. be incorporated into the membrane of stabilized liposomes without destruction of the polymeric vesicles. There have already been reports about thekilling of tumor cells by synthetic alkyl lysophospholipids (72). 

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