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Specific Localization of Tissue-Type Transglutaminase in Adrenocorticotropin-Producing Cells of the Human Pituitary Gland as Demonstrated by Immunohistochemistry^*

Departments of Clinical Science and Laboratory Medicine (A.K., Y. Y., T.M., R.K.), Pediatrics (A.K., H.M.), and Pathology (H.O.), Kyoto University Faculty of Medicine Kyoto 606, Japan

Address all correspondence and requests for reprints to: Dr. R. Kannagi, Department of Clinical Science, and Laboratory Medicine, Kyoto University Hospital, Shogoin Kawaharacho, Sakyo-ku, Kyoto 606, Japan.

The distribution of transglutaminases, the Ca²⁺-dependent protein cross-linking enzymes, in the human pituitary gland was investigated by immunohistological methods using specific antibodies. Tissue-type transglutaminase was specifically localized in ACTH-producing cells, and the cells producing GH, PRL, TSH, FSH, and LH contained no appreciable amount of the enzyme. No detectable plasma-type transglutaminase (coagulation factor XIII) was found in pituitary tissue. In a previous study we demonstrated that ACTH-producing cells contain very little Ca²⁺-dependent proteinases (calpain), but a remarkable amount of their inhibitor, calpastatin. Pituitary gland cells producing hormones other than ACTH contained calpains, but no detectable calpastatin. These results collectively suggest that intracellular substrate proteins in ACTH-producing cells are protected from Ca²⁺-dependent degradation and are substrates for Ca²⁺-dependent cross-linking catalyzed by the tissue-type transglutaminase. In other pituitary gland cells, conversely, the intracellular substrate proteins are more likely to undergo Ca²⁺-dependent degradation than cross-linking.

^* This work was supported in part by Grants-in-Aid for Scientific and Cancer Research from the Ministry of Education, Science, and Culture, Japan.

Received April 6, 1987.