Transglutaminase 2 suppresses apoptosis by modulating caspase 3 and NF-κB activity in hypoxic tumor cells

Abstract

The expression of hypoxia-inducible factor-1 (HIF-1) correlates with poor clinical outcomes and confers resistance to the apoptosis of the tumor cells that are exposed to hypoxia. Presently, the mechanism underlying this phenomenon is poorly understood. In this study we provide evidence that transglutaminase 2 (TG2), an enzyme that catalyses protein crosslinking reactions, is a transcriptional target of HIF-1 to enhance the survival of hypoxic cells. We found that hypoxia induces TG2 expression through an HIF-1 dependent pathway and concurrently activates intracellular TG2. The hypoxic cells overexpressing TG2 showed resistance to apoptosis. Conversely, the hypoxic cells treated with either TG2 inhibitor or small interfering RNA (siRNA) became sensitive to apoptosis. Activation of TG2 in response to hypoxic stress inhibited caspase-3 activity by forming crosslinked multimer, resulting in insoluble aggregates. TG2 also activates nuclear factor (NF)-jB pathway after hypoxic stress, and thereby induces the expression of cellular inhibitor of apoptosis 2. The anti-apoptotic role of TG2 was further confirmed in vivo using xenografts in athymic mice. Our results indicate that TG2 is an antiapoptotic mediator of HIF-1 through modulating both apoptosis and survival pathways and may confer a selective growth advantage to tumor cells. These findings suggest that the inhibition of TG2 may offer a novel strategy for anticancer therapy.

Cancer cells promote survival through depletion of the von Hippel–Lindau tumor suppressor by protein crosslinking

“…This may well be possible that in the same conditions TGase 2 could contribute to activation of the NF-kB cascade via VHL depletion. As VHL has a clear role in the degradation of HIF-1a, increased expression of TGase 2 via HIF-1a binding to its promoter would result into VHL depletion, thus raising the stability of HIF-1a and further increasing TGase 2 transcription in a positive activation loop (Jang et al, 2010).…”

“…In situ TGase 2 activity in cells TGase 2 enzyme activity in TGase-2-transfected cells was detected by labeling cells with 0.2 mM 5 0 -(biotinamido) pentylamine for 24 h (Jang et al, 2010). After labeling, the 5 0 -(biotinamido) pentylamine-incorporated cellular proteins was analyzed by cytochemistry using streptavidin Alexa Flour 546 conjugated (Invitrogen Life Technologies, 1:500 dilution).…”

Expression Profile of Genes Modulated by Aloe emodin in Human U87 Glioblastoma Cells

“…The reduced TGM2 level is a potential target in the treatment of highly metastatic cancer cells (Mehta et al, 2004). In contrast, activation of TGM2 has been suggested as a mediator for anti-apoptotic event in hypoxic tumour cells by inhibiting both caspase-3 activation and apoptosis induction (Jang et al, 2010). The increased expression of TGM2 in glioblastoma suggests a highly malignant glioma (Fu et al, 2013).…”

Metastasis-associated S100A4 is a specific amine donor and an activity-independent binding partner of transglutaminase-2

“…An inactive TG2 mutant (that has still preserved its guanine nucleotide binding ability) is a useful tool in studying TG2 interaction partners and substrates. One extensively used TG2 mutant is Cys277Ser where the cysteine residue that is part of the catalytic triad is mutated to serine [21,22]. However, this mutation results in a conformational change that impairs GTP binding capability [23].…”