DIPHTHERIA-TOXIN ENDOCYTOSIS AND MEMBRANE TRANSLOCATION ARE DEPENDENTON THE INTACT MEMBRANE-ANCHORED RECEPTOR (HB-EGF PRECURSOR) - STUDIESON THE CELL-ASSOCIATED RECEPTOR CLEAVED BY A METALLOPROTEASE IN PHORBOL-ESTER-TREATED CELLS
M. Lanzrein et al., DIPHTHERIA-TOXIN ENDOCYTOSIS AND MEMBRANE TRANSLOCATION ARE DEPENDENTON THE INTACT MEMBRANE-ANCHORED RECEPTOR (HB-EGF PRECURSOR) - STUDIESON THE CELL-ASSOCIATED RECEPTOR CLEAVED BY A METALLOPROTEASE IN PHORBOL-ESTER-TREATED CELLS, Biochemical journal, 310, 1995, pp. 285-289
Preincubation of Vero cells with 1 mu M phorbol 12-myristate 13-acetat
e (PMA) decreased the specific binding of diphtheria toxin by about 50
%, whereas the toxic effect, endocytic uptake and membrane translocati
on were completely blocked. Toxin bound to PMA-treated cells was relea
sed upon incubation with heparinase. The effect of PMA was abrogated i
n the presence of EDTA or N-{DL-[2-(hydroxyaminocarbonyl)methyl]-4- pe
ntanoyl}-L-3-(2'-naphthyl)-alanyl-L-alanine 2-aminoethylamide (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 t
he membrane anchor, and that about 50% of the growth-factor ecto-domai
n remains associated with the cells, due to binding to surface proteog
lycans containing heparan sulphates. Although the cleaved cell-associa
ted HB-EGF binds diphtheria toxin, it does not serve as a functional r
eceptor, since neither toxin internalization nor translocation occurs.
Thus the intact HB-EGF precursor is of crucial importance for its fun
ction as the diphtheria-toxin receptor.