ORIGINAL ARTICLE TG2 transamidating activity acts as a reostat controlling the interplay between apoptosis and autophagy Federica Rossin • Manuela D’Eletto • Douglas Macdonald • Maria Grazia Farrace • Mauro Piacentini Received: 23 December 2010 / Accepted: 22 March 2011 / Published online: 10 April 2011 Ó Springer-Verlag 2011 Abstract Tissue transglutaminase (TG2) activity has been implicated in inflammatory disease processes such as Celiac disease, infectious diseases, cancer, and neu- rodegenerative diseases, such as Huntington’s disease. Furthermore, four distinct biochemical activities have been described for TG2 including protein crosslinking via transamidation, GTPase, kinase and protein disulfide isomerase activities. Although the enzyme plays a com- plex role in the regulation of cell death and autophagy, the molecular mechanisms and the putative biochemical activity involved in each is unclear. Therefore, the goal of the present study was to determine how TG2 modu- lates autophagy and/or apoptosis and which of its bio- chemical activities is involved in those processes. To address this question, immortalized embryonic fibroblasts obtained from TG2 knock-out mice were reconstituted with either wild-type TG2 or TG2 lacking its transami- dating activity and these were subjected to different treatments to induce autophagy or apoptosis. We found that knock out of the endogenous TG2 resulted in a significant exacerbation of caspase 3 activity and PARP cleavage in MEF cells subjected to apoptotic stimuli. Interestingly, the same cells showed the accumulation of LC3 II isoform following autophagy induction. These findings strongly suggest that TG2 transamidating activity plays a protective role in the response of MEF cells to death stimuli, because the expression of the wild-type TG2, but not its transamidation inactive C277S mutant, resulted in a suppression of caspase 3 as well as PARP cleavage upon apoptosis induction. Additionally, the same mutant was unable to catalyze the final steps in autophagosome formation during autophagy. Our findings clearly indicate that the TG2 transamidating activity is the primary biochemical function involved in the physi- ological regulation of both apoptosis and autophagy. These data also indicate that TG2 is a key regulator of cross-talk between autophagy and apoptosis. Keywords Transglutaminase 2 Á Apoptosis Á Autophagy Á Transamidating activity Introduction Transglutaminases (EC 2.3.2.13; TG) are a family of enzymes that catalyse thiol- and Ca 2? -dependent transa- midation reactions, through the formation of a covalent bond between the c-carboxamide group of a peptide bond glutamine residue and a primary amine group (Folk and Finlayson 1977). The most ubiquitous isoenzyme is rep- resented by type 2 transglutaminase (TG2), which has been found both intracellularly as well as on the cell surface in association with the extra-cellular matrix (Gaudry et al. 1999; Piacentini et al. 2002). TG2 has been implicated in a variety of cellular processes, such as differentiation, cell F. Rossin and M. D’Eletto contributed equally to this work. F. Rossin Á M. D’Eletto Á M. G. Farrace Á M. Piacentini (&) Department of Biology, University of Rome ‘‘Tor Vergata’’, Via della Ricerca Scientifica 1, 00133 Rome, Italy e-mail: mauro.piacentini@uniroma2.it M. Piacentini National Institute for Infectious Diseases IRCCS ‘‘Lazzaro Spallanzani’’, 00149 Rome, Italy D. Macdonald CHDI Management/CHDI Foundation, Los Angeles, CA, USA 123 Amino Acids (2012) 42:1793–1802 DOI 10.1007/s00726-011-0899-x