Transglutaminase 2 ablation leads to mitophagy impairment associated with a metabolic shift towards aerobic glycolysis

Abstract

Macroautophagy selectively degrades dysfunctional mitochondria by a process known as mitophagy. Here we demonstrate the involvement of transglutaminase 2 (TG2) in the turnover and degradation of damaged mitochondria. In TG2-ablated cells we observed the presence of a large number of fragmented mitochondria that display decreased membrane potential, downregulation of IF1 along with increased Drp1 and PINK1 levels, two key proteins regulating the mitochondrial fission. Of note, we demonstrate that in healthy mitochondria, TG2 interacts with the dynamic proteins Drp1 and Fis1; interestingly, their interaction is largely reduced upon induction of the fission process by carbonyl cyanide m-chlorophenyl hydrazine (CCCP). In keeping with these findings, mitochondria lacking TG2 are more susceptible to CCCP treatment. As a consequence of accumulation of damaged mitochondria, cells lacking TG2 increased their aerobic glycolysis and became sensitive to the glycolytic inhibitor 2-deoxy-D-glucose (2-DG). In contrast, TG2-proficient cells are more resistant to 2-DG-induced apoptosis as the caspase 3 is inactivated through the enzyme's crosslinking activity. The data presented in this study show that TG2 plays a key role in cellular dynamics and consequently influences the energetic metabolism.

Vascular ageing and endothelial cell senescence: Molecular mechanisms of physiology and diseases

“…Selected VEGF isoforms bind the receptor VEGFR2 and heparan sulfate proteoglycans to stimulate angiogenesis, recently it has been shown that transglutaminase 2 (TG2) enzyme play a role in VEGF165-heparan sulfate proteoglycans interaction (Beckouche et al, 2015). TG2 is a Ca2+-dependent cross-linking enzyme that catalyzes the formation of -␥-glutamyl isopeptide bonds between peptide-bounds glutamine and lysine (Candi et al, 2005;De Laurenzi and Melino, 2001;Liu et al, 2002;Myneni et al, 2015;Rossin et al, 2015;Shrestha et al, 2015). TG2 is highly expressed in endothelial cells, it is located in the cytoplasm and in extracellular space.…”

Insights into Transglutaminase 2 Function Gained from Genetically Modified Animal Models

“…This was proposed to be the result of impaired recruitment of Bax to TG2 À/À mitochondria, resulting in decreased Bax/ANT1 interaction relative to wild-type mitochondria (Malorni et al 2009). A later study from the same group reported that under basal conditions TG2 À/À MEFs (source nor strain background defined) had a large number of fragmented, dysfunctional mitochondria due to an impairment in mitophagy (clearance of defective mitochondria) compared with wild-type MEFs (Rossin et al 2014). TG2…”

Transglutaminase 2, a double face enzyme

“…p53 is a well-known oncogene suppressor, and its degradation prevents apoptosis and favors conversely tumor survival and growth (Kang et al 2016). In addition, it must be mentioned that also the metabolism of cancer cells is apparently dependent on the action of Tgase2, as it happens in mammary cancer, in which expression and activity of Tgase2 is eventually relevant for triggering the Warburg effect (Kumar et al 2014;Rossin et al 2015) through NFκB and HIF signaling and more recently through its interplay with PKM2 a key rate limiting enzyme of glycolysis (Altuntas et al 2015). The involvement of Tgase2 in EMT and in angiogenesis is of special relevance for the relationships between Tgase2 and tumor growth.…”