Apoptosis of epithelial cells in vivo involves tissue transglutaminase upregulation

Tissue transglutaminase (tTG) has been implicated in producing some of the cytoplasmic changes seen in apoptosis in vitro. The aim of this study was to investigate tTg protein and mRNA expression in three different epithelia induced experimentally in vivo to undergo apoptosis. They were castration-induced prostatic atrophy with subsequent testosterone-induced prostatic hyperplasia, apoptosis induced by mild ischaemia in the liver from ligation of the distal portal vein, and hydronephrosis due to ureteric ligation. tTG protein was consistently expressed with apoptosis in all three models, whereas the mRNA levels were different in each model. tTG mRNA was elevated in the later stages of hydronephrosis, when apoptosis was still occurring. In the prostate, the levels remained unchanged during the process of involution, but increased early in association with testosterone-induced proliferation. In the liver model, the mRNA levels remained unchanged. tTG protein expression may be a universal feature of apoptosis of epithelial tissues, whereas changes in tTG mRNA expression appear to be unique to each apoptosis-inducing agent.