M. Rehli et al., CARBOXYPEPTIDASE-M IS IDENTICAL TO THE MAX.1 ANTIGEN AND ITS EXPRESSION IS ASSOCIATED WITH MONOCYTE TO MACROPHAGE DIFFERENTIATION, The Journal of biological chemistry, 270(26), 1995, pp. 15644-15649
The two monoclonal antibodies MAX.1 and MAX.11 recognize cell surface
antigens that are almost undetectable on monocytes but highly expresse
d on differentiated macrophages. Biochemical characterization revealed
that both antibodies detect the same 58-64-kDa glycoprotein anchored
to the plasma membrane by glycosyl-phosphatidylinositol linkage. We pu
rified the MAX.1/11 antigen by immunoaffinity chromatography using mon
oclonal antibody MAX.11. The NH2-terminal amino acid sequence was dete
rmined and turned out to be identical to the NH2-terminal sequence of
the membrane-bound carboxypeptidase M. By precipitation with antibodie
s MAX.1 and MAX.11, membrane preparations of macrophages and placental
microvilli were almost completely depleted of enzyme activity, indica
ting that the two antibodies indeed recognize carboxypeptidase M. Immu
noreactivity of both antibodies correlates with the reported tissue di
stribution of enzyme activity. Expression of carboxypeptidase M on mRN
A level and enzymatic activity markedly increase during in vitro diffe
rentiation of monocytes, according to the described increase in MAX.1
and MAX.11 antigen expression. Moreover, in vitro differentiated macro
phages show the highest specific activity yet described in any tissue.
In addition, carboxypeptidase M expression could be detected in HL-60
, U937, and THP-1 myeloid cell lines. Vitamin D-3-induced monocytic di
fferentiation resulted in an increased carboxypeptidase M expression i
n all three cell lines. Further studies are needed to elucidate the fu
nctional role of carboxypeptidase M during monocytic differentiation a
nd activation.