Tissue-type transglutaminase expression in the Dunning tumor.

Transglutaminases with different functions and tissue distribution patterns can be distinguished by specific antibodies and by inhibition of enzyme activity in the presence of guanosine triphosphate (GTP). The most common form is the so-called tissue-type transglutaminase that is apparently involved in membrane stabilization processes, e.g. during apoptosis, and can be inhibited by incubation with GTP at low calcium concentrations. A secretory transglutaminase that cannot be inhibited by GTP is synthesized in an androgen-dependent manner in the dorsal prostate of the rat, the site suggested to represent the origin of the Dunning tumor used as an experimental model in prostate cancer research. Here we studied the expression of transglutaminases in different Dunning tumor lines--mainly in the highly differentiated H subline--and characterized the enzyme both biochemically and immunocytochemically. A very high enzyme activity was found only in the less well differentiated HI-F tumor line. Immunohistochemical reactions and Western blot analysis showed that there is no secretory transglutaminase present in any of the Dunning tumor lines studied. Transglutaminase activity of the Dunning tumor results from the so-called tissue-type enzyme that is non-organ specific. The absence of a secretory form of transglutaminase does not support the contention of a prostatic origin of the Dunning tumor.