Identification and characterization of alkaline phosphatase isozymes in human colorectal adenocarcinomas.

Using alkaline phosphatase isozyme-specific immunocatalytical assays, the content of isozymes was determined in normal mucosas and adenocarcinomas from human colon or rectum. Tumor levels of both the tissue (liver)-unspecific and the placental-like alkaline phosphatase (PLAP-like) were elevated compared to normal mucosas of the same patients. Such elevations have been reported previously, particularly in seminomas and ovarian tumors. In several tumors, moreover, the intestinal isozyme was expressed in lesser amounts than in the adjacent mucosa. The present results indicate that the activation of two of the phosphatase isozymes, including expression of the typical germ cell line phosphatase (the PLAP-like isozyme), may occur even in nongonadal tumors. This may reflect an induction pattern of phosphatase isozymes, with implications for malignant transformation also in other tumors.