The Exonuclease TREX1 Is in the SET Complex and Acts in Concert with NM23-H1 to Degrade DNA during Granzyme A-Mediated Cell Death

Abstract

Granzyme A (GzmA) activates a caspase-independent cell death pathway with morphological features of apoptosis. Single-stranded DNA damage is initiated when the endonuclease NM23-H1 becomes activated to nick DNA after granzyme A cleaves its inhibitor, SET. SET and NM23-H1 reside in an endoplasmic reticulum-associated complex (the SET complex) that translocates to the nucleus in response to superoxide generation by granzyme A. We now find the 3'-to-5' exonuclease TREX1, but not its close homolog TREX2, in the SET complex. TREX1 binds to SET and colocalizes and translocates with the SET complex. NM23-H1 and TREX1 work in concert to degrade DNA. Silencing NM23-H1 or TREX1 inhibits DNA damage and death of cells treated with perforin (PFN) and granzyme A, but not of cells treated with perforin and granzyme B (GzmB). After granzyme A activates NM23-H1 to make single-stranded nicks, TREX1 removes nucleotides from the nicked 3' end to reduce the possibility of repair by rejoining the nicked ends.

Translocation of human ribosomal protein S3 to sites of DNA damage is dependant on ERK-mediated phosphorylation following genotoxic stress

“…Notably, NM23-H1 is part of the SET complex that is activated by Granzyme A (GzmA) and translocated from the endoplasmic reticulum to the nucleus [41]. GzmA generates reactive oxygen species and activates a caspase-independent cell death pathway by cleaving SET [42] that in turn activates the endonuclease possessed by NM23-H1, which in concert with TREX1 degrades DNA, leading to cell death with morphological features similar to apoptosis [43].…”

Cell Death Mechanisms Induced by Cytotoxic Lymphocytes

“…It cleaves single-stranded DNA, and hydrolyzes proteins containing basic amino acids such as arginine or lysine (74,75). Grz-A activates an endoplasmic reticulum associated complex (the SET complex), which is conformed by two tumor-suppressor proteins, phosphoprotein 32 (pp32) and nonmetastatic protein 23 homologue 1 (NM23-H1), and three Grz-A substrates: oncoprotein SET, high mobility group 2 (HMG-2) protein, and apurinic endonuclease 1 (Ape1) (74,76,77). A characteristic of apoptosis is the increase of reactive oxygen species (ROS) and decrease of the mitochondrial membrane potential, a process that seems to play a pivotal role in the SET translocation into cell nucleus via mechanism that is not fully understood (Figure 3) (74,75,78).…”

“…A characteristic of apoptosis is the increase of reactive oxygen species (ROS) and decrease of the mitochondrial membrane potential, a process that seems to play a pivotal role in the SET translocation into cell nucleus via mechanism that is not fully understood (Figure 3) (74,75,78). Once inside the cell nucleus, Grz-A cleaves SET (specific inhibitor for NM23-H1), and the cleavage of SET releases NM23-H1, which degrades chromosomal DNA (Figure 3) (74,76). It is also postulated that Grz-A cleaves to histone 1, modifying the nucleosomal center, so chromatin is relaxed and DNA is fragmented by endonucleases (79).…”

“…It is also postulated that Grz-A cleaves to histone 1, modifying the nucleosomal center, so chromatin is relaxed and DNA is fragmented by endonucleases (79). Extracellular activity of Grz-A has been also reported by either fragmenting the IL-1 pro-peptide at the Asp116 site to give rise to the active form of IL-1 or activating fibroblasts to secrete cytokines, such as IL-6, IL-8 and IFN- (74,76,80,81).…”

The role of DNA exonucleases in protecting genome stability and their impact on ageing

“…Furthermore, it participates in Granzyme-A-mediated cell death in concert with the NM23-H1 nuclease (Chowdhury et al 2006), resulting in DNA fragmentation characteristic of apoptosis. As loss-of-function (Zhang et al 2010), as such factors closely resemble 'pathogen-associated molecular patterns' (PAMPS) to which the innate immune system is tuned.…”