Comparative levels of CALLA/neutral endopeptidase on normal granulocytes,
leukemic cells, and transfected COS-1 cells
R Tran-Paterson, G Boileau, V Giguere and M Letarte
Division of Immunology, Hospital for Sick Children, Toronto, Canada.
We discovered that the common acute lymphoblastic leukemia antigen, CALLA
(CD10), was identical to human neutral endopeptidase 3.4.24.11 (NEP), a
Zn-binding glycoprotein with an extracellular active site capable of
hydrolyzing several biologically active peptides. In this study we compare
the expression of CALLA/NEP in terms of antigenic density and enzymatic
activity at the cell surface and of messenger RNA (mRNA) levels on
granulocytes, leukemic cells, and CALLA-transfected COS-1 cells. Mature
granulocytes, the only readily available source of normal human CALLA,
express relatively low but constant levels of antigen, NEP activity (3.5
pmol/min/10(6) cells), and mRNA. The two major CALLA-mRNA species of 6.5 kb
and 3.8 kb, observed to date in a variety of cells and tissues, were also
found in four independent granulocyte preparations. With leukemia cell
lines, a correlation was established between the density of CALLA antigen
and the level of enzymatic activity (3.4 to 21.0 pmol/min/10(6) cells).
This paper constitutes the first report of NEP activity on blast cells
derived from patients with non-T acute lymphoblastic leukemia (ALL); the
levels of activity were variable (1.5 to 35.9 pmol/min/10(6) cells for six
cases) but correlated with the level of CALLA assessed by flow cytometry.
Heterogeneous levels of expression of the CALLA-mRNA species were also
observed in non-T ALL cases that correlated with the level of CALLA
expression at the surface of these cells. Very high levels of NEP activity
were achieved by transfecting COS-1 cells with pSV-CALLA; 20% of the
transfected cells were CALLA+ and expressed 550 pmol/min/10(6) cells.
Extracts prepared from COS-1 cells transfected with pSV-CALLA (carrying
human NEP cDNA) and pSVENK19 (carrying rabbit NEP-cDNA), respectively, gave
Michaelis constant (Km) values of 50 mumol/L and similar inhibition curves
with thiorphan. Thus the recombinant proteins encoded by these two genes
have similar enzymatic properties, confirming the high degree of their
structural relatedness. The expression of high levels of CALLA/NEP on COS-1
cells should allow the use of this system to test the effects of specific
mutations on activity and might lead to the understanding of the role of
CALLA in the onset and/or progression of leukemia.
Volume 76,
Issue 4,
pp. 775-782,
08/15/1990
Copyright © 1990 by The American Society of Hematology
