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.