Two transfected endothelial cell lines expressing high levels of membrane bound or soluble aminopeptidase N.

Abstract

The CD13 molecule, found to be identical with aminopeptidase N (APN/EC 3.4.11.2)1 has been considered as a specific marker for the myeloid lineage within the hematopoietic system, however the occurrence of APN on lymphoid cells was recently described e.g. on tumor-infiltrating lymphocytes2, on T cells in the synovial fluid from patients with rheumatoid arthritis3 and some kinds of leukemia or lymphoma4,5,6. Our group very recently obtained evidence that the coculture of lymphocytic cells with various adherent APN positive cells such as fibroblast-like synoviocytes, HUVEC, kidney tubular epithelial cells or some tumor cell lines can induce the APN molecule on lymphocytes7. In need of a coculture system to further investigate the influence of the CD13/APN molecule we focused our interest on transfecting a APN negative adherent cell line with an expression vector for APN. To this end we used the spontaneously transformed immortal endothelial cell line ECV304 (ATCC CRL-1998) established from the vein of an apparently normal human umbilical cord8. Some reports describe the existence of a solubilized form of aminopeptidase N in serum, originating from liver and increased in hepatobiliary disease9, 10, 11. Therefore it seemed to us of further interest, wether the soluble form of this molecule is also able to induce the lymphocytic expression and if direct cell contact is necessary for induction. For that reason we additionally transformed the ECV304 cell line with an expression vector for the secretory form of aminopeptidase N.