For the investigation of the possibility of its being a marker
enzyme for
tumor cells, the activity of
dipeptidyl peptidase (DPP) IV (EC 3.4.14.5), a membrane-bound
enzyme, in cultured human
carcinoma cells was examined. The homogenates of three
carcinoma cell lines (HeLa, KB, and K-44) contained lower glycylprolyl methylcoumarinamide (
Gly-Pro-MCA)
hydrolase activities at pH 8.7 (assumed to be DPP IV) and higher activities of
alkaline phosphatase and
gamma-glutamyl transpeptidase, which are also membrane-bound
enzymes, than those of normal human fibroblasts (HF). Examination of
carcinoma cells for the subcellular localization and pH optimum of
Gly-Pro-MCA hydrolase activity revealed that the activity of a lysosomal
enzyme that hydrolyzes
Gly-Pro-MCA at pH 6.4 was markedly increased in
carcinoma cells, but not in normal cells. The separation and characterization of
Gly-Pro-MCA hydrolases by gel filtration, affinity chromatography, and substrate specificity demonstrated that HF have three peaks indicating DPP IV, DPP II, and an unknown
enzyme, whereas the three
carcinoma cell lines gave a prominent peak indicating DPP II and a trace of DPP IV. The DPP II activity was 6- to 24-fold higher in
carcinoma cell lines than in HF, and it also was 2.85- to 4.13-fold higher than the DPP IV activity in
carcinoma cell lines but was 10-fold lower in HF. These clear enzymatic differences between
carcinoma cells and normal HF may be useful as a marker of
malignancy.