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Alkaline Phosphatase Isozymes in Human Testicular Germ Cell Tumors, Their Precancerous Stage, and Three Related Cell Lines¹

Institute of Pathology, University of Zürich, University Hospital, CH-8091 Zürich, Switzerland

The four known isozymes of the human alkaline phosphatase (ALP) were detected by isoelectric focusing in extracts of various types of germ cell tumors, three related cell lines, and their precancerous elements (atypical germ cells).

In seminoma, placental alkaline phosphatase (PLAP) and germ cell alkaline phosphatase (PLAP-like) could be separated by isoelectric focusing following isolation by immunoaffinity. The occurrence of both isozymes in seminoma could explain partial heat sensitivity and variation in electrophoretic patterns of the seminoma isozyme frequently observed upon starch gels, in comparison to the normal placental phenotype.

The four ALP isozymes are produced not only in germ cell tumors, but already in precancerous tissues. Quantitative analysis showed that the amount of the four isozymes varies in parallel in the tumors tested. Maximal expression was found in seminoma. The relation between ALP gene overexpression and gene amplification by polyploidy of chromosomes 1 and 2 in these lesions is discussed. On the other hand, the ectopic expression of intestinal alkaline phosphatase and PLAP associated with overexpression of PLAP-like in tumor cells as well as in their precancerous stage indicates gene activation by some unknown mechanisms, probably a regulatory process affecting the three tissue-specific ALP genes simultaneously.

¹ Supported by the Roche Research Foundation, Basel, and the Krebsliga des Kantons Zürich, Switzerland.

² Present address: La Jolla Cancer Research Foundation, 10901 North Torrey Pines Road, La Jolla, CA 92037.

³ To whom requests for reprints should be addressed, at Laboratory of Reproduction and Development, Department of Gynecology and Obstetrics, University Hospital, CH-8091 Zürich, Switzerland.

Received 10/12/88. Accepted 4/26/89.