AK2 activates a novel apoptotic pathway through formation of a complex with FADD and caspase-10

Abstract

Mitochondrial proteins function as essential regulators in apoptosis. Here, we show that mitochondrial adenylate kinase 2 (AK2) mediates mitochondrial apoptosis through the formation of an AK2-FADD-caspase-10 (AFAC10) complex. Downregulation of AK2 attenuates etoposide- or staurosporine-induced apoptosis in human cells, but not that induced by tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL) or Fas ligand (FasL). During intrinsic apoptosis, AK2 translocates to the cytoplasm, whereas this event is diminished in Apaf-1 knockdown cells and prevented by Bcl-2 or Bcl-X(L). Addition of purified AK2 protein to cell extracts first induces activation of caspase-10 via FADD and subsequently caspase-3 activation, but does not affect caspase-8. AFAC10 complexes are detected in cells undergoing intrinsic cell death and AK2 promotes the association of caspase-10 with FADD. In contrast, AFAC10 complexes are not detected in several etoposide-resistant human tumour cell lines. Taken together, these results suggest that, acting in concert with FADD and caspase-10, AK2 mediates a novel intrinsic apoptotic pathway that may be involved in tumorigenesis.

Intracellular cleavage of osteopontin by caspase-8 modulates hypoxia/reoxygenation cell death through p53

“…These data suggest that OPN cleavage by caspase-8 during Hyp/RO is differently regulated from substrate cleavage by caspase-8 activated by DISC formation. Recent studies showed distinct apoptotic complexes containing caspase-8 or caspase-10, and diverse roles of those proximal caspases (32,33).…”

“…pOPN shRNAs were constructed using forward and reverse 64-nucleotides (#1, 679-ACGAGTCAGCTG-GATGACC-697, #2, 805-GTCAGCCGTGAATTCCACA-823) were synthesized, annealed, and cloned into the BglII and HindIII sites of pSuper mammalian expression vector (Oligoengine). pCasp-8 shRNA and pCasp-10 shRNA were generated as described (15,33).…”

FLIP and the death effector domain family

“…At another level, undoubtedly more proteins will be added to the mix that comprise DED-mediated signaling platforms (such as TRAF1, TRAF2 and Raf1 as mentioned above and others), and elucidating if and how these proteins integrate with any of the core DED family members to activate various signaling pathways will represent another initial yet crucial step in answering the posed questions. Along with these challenges, new and exciting frontiers involving DED family members are being discovered and a few examples include: induction of programmed cell death from locations outside of death receptors including unligated integrins (Stupack et al, 2001(Stupack et al, , 2006 and the mitochondria (Lee et al, 2007), regulation of autophagy (and autophagic cell death) by caspase-8 and FADD (Yu et al, 2004;Pyo et al, 2005;Thorburn et al, 2005), regulation of JNK (Nakajima et al, 2006) and WNT signaling by c-FLIP L (Naito et al, 2004;Nakagiri et al, 2005), and modulation of gene expression from the androgen receptor (Qi et al, 2007) and p53 by procaspase-8 (Yao et al, 2007). The increasingly complex involvement of DED proteins in different pathways and cellular processes is indeed unfolding from ongoing effort, and additional answers that verify and map out these new connections lie ahead.…”

Reticular dysgenesis–associated AK2 protects hematopoietic stem and progenitor cell development from oxidative stress

“…In particular, AK2 deficiency in Drosophila melanogaster is embryonically lethal (Fujisawa et al, 2009;Chen et al, 2012). Moreover, it has been suggested that AK2 deficiency may induce the unfolded protein response (Burkart et al, 2011) and apoptosis (Single et al, 1998;Köhler et al, 1999;Lee et al, 2007). The intracellular localization of AK2 is strictly limited to the mitochondrial intermembrane space (Dzeja et al, 2007) where it is required to generate ADP.…”