No abstract

Pharmacological studies support the idea that nitric oxide (NO) serves as a retrograde messenger during long-term potentiation (LTP) in area CA1 of the hippocampus. Mice with a defective form of the gene for neuronal NO synthase (nNOS), however, exhibit normal LTP. The myristoyl protein endothelial NOS (eNOS) is present in the dendrites of CA1 neurons. Recombinant adenovirus vectors containing either a truncated eNOS (a putative dominant negative) or an eNOS fused to a transmembrane protein were used to demonstrate that membrane-targeted eNOS is required for LTP. The membrane localization of eNOS may optimally position the enzyme both to respond to Ca2+ influx and to release NO into the extracellular space during LTP induction.

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Preincubation of Vero cells with 1 microM phorbol 12-myristate 13-acetate (PMA) decreased the specific binding of diphtheria toxin by about 50%, whereas the toxic effect, endocytic uptake and membrane translocation were completely blocked. Toxin bound to PMA-treated cells was released upon incubation with heparinase. The effect of PMA was abrogated in the presence of EDTA or N-(DL-[2-(hydroxyaminocarbonyl)methyl]-4-methyl-pentanoyl)-L-3-(2' - naphthyl)-alanyl-L-alanine 2-aminoethyl-amide (TAPI), a specific inhibitor of matrix metalloproteases. The results indicate that PMA induces proteolytic cleavage of the diphtheria-toxin receptor [heparin-binding EGF-like growth factor (HB-EGF)-precursor] outside the membrane anchor, and that about 50% of the growth-factor ecto-domain remains associated with the cells, due to binding to surface proteoglycans containing heparan sulphates. Although the cleaved cell-associated HB-EGF binds diphtheria toxin, it does not serve as a functional receptor, since neither toxin internalization nor translocation occurs. Thus the intact HB-EGF precursor is of crucial importance for its function as the diphtheria-toxin receptor.

No abstract