No abstract

We have previously demonstrated that cyclic ADP-ribose (cADPR) is a calcium signaling messenger in interleukin 8 (IL-8)-induced lymphokine-activated killer (LAK) cells. In this study we examined the possibility that IL-8 activates CD38 to produce another messenger, nicotinic acid adenine dinucleotide phosphate (NAADP), in LAK cells, and we showed that IL-8 induced NAADP formation after cADPR production. These calcium signaling messengers were not produced when LAK cells prepared from CD38 knock-out mice were treated with IL-8, indicating that the synthesis of both NAADP and cADPR is catalyzed by CD38 in LAK cells. Application of cADPR to LAK cells induced NAADP production, whereas NAADP failed to increase intracellular cADPR levels, confirming that the production of cADPR precedes that of NAADP in IL-8-treated LAK cells. Moreover, NAADP increased intracellular Ca 2؉ signaling as well as cell migration, which was completely blocked by bafilomycin A1, suggesting that NAADP is generated in lysosome-related organelles after cADPR production. A type II transmembrane protein, CD38, possesses ADP-ribosyl cyclase (ADPR cyclase) 3 and cyclic ADP-ribose hydrolase (cADPR hydrolase) activity (1, 2). These two enzyme activities are involved in the conversion of ␤-nicotinamide adenine dinucleotide (␤-NAD ϩ ) first to cADPR and then to ADPR (3-5). The metabolite cADPR is known to increase intracellular Ca 2ϩ concentration, [Ca 2ϩ ] i , by releasing Ca 2ϩ from intracellular stores or by Ca 2ϩ influx through plasma membrane Ca 2ϩ channels in a variety of cells (6 -10). It was shown that CD38 can also synthesize NAADP from NADP in the presence of nicotinic acid by a base exchange reaction in vitro (11). However, it still remains unclear whether the base exchange reaction occurs physiologically as intracellular nicotinic acid concentration is less than the millimolar concentration that is required for the enzymatic synthesis of nicotinic acid adenine dinucleotide phosphate (NAADP) in vitro (12).NAADP is a potent Ca 2ϩ -releasing messenger in a variety of cell types, including mammalian cells (13-15). Although D-myo-inositol 1,4,5-trisphosphate (IP 3 ) and cADPR are firmly established as secondary Ca 2ϩ messengers, receptor-mediated formation of NAADP has been shown in a limited number of cellular systems (16 -18). It has been demonstrated that NAADP triggers Ca 2ϩ release from thapsigargin-insensitive Ca 2ϩ stores through the activation of channels distinct from those sensitive to ryanodine and IP 3 (19). In sea urchin eggs, NAADP releases Ca 2ϩ from acidic Ca 2ϩ stores, lysosome-related organelles (20). However, NAADP can also release Ca 2ϩ from the endoplasmic reticulum (21-23).Previously, we have reported that IL-8 stimulated cADPR formation by activation of CD38 via cGMP/protein kinase G and induced an increase of [Ca 2ϩ ] i and migration of LAK cells (24). In this study we investigated whether NAADP is involved in IL-8-induced Ca 2ϩ signaling and migration of LAK cells. We showed that NAADP plays a key role in IL-8-stimul...

Carbon monoxide (CO) can confer protection against cellular stress, whereas the potential involvement of autophagy and lysosomal biogenesis remains incompletely understood. We demonstrate here that the activation of protein kinase R (PKR)-like endoplasmic reticulum (ER) kinase (PERK) with CO increased the nuclear translocation of transcription factor EB (TFEB). PERK activation by CO increased intracellular Ca2+ concentration and the phosphatase activity of calcineurin against TFEB. Moreover, we found that in the deficiency of TFEB, CO not only failed to recruit Parkin to the mitochondria but also failed to increase expression of lysosomal genes such as Lamp1, CathB, and TPP1. Therefore, we suggest that CO increases mitophagy through TFEB nuclear translocation by PERK-calcinuerin activation. In addition, the inhibition of TFEB with siRNA against TFEB abrogated the increase of mtDNA with CO, markers of mitochondrial biogenesis such as PGC1α, NRF1, and TFAM, and the mitochondrial proteins COX II, COX IV, and cytochrome c. To investigate the effects of CO on mitochondrial homeostasis in vivo, mice were treated with lipopolysaccharide (LPS)/d-galactosamine (D-GalN). CO inhalation reduced liver injury after challenge with LPS/GalN. Furthermore, CO inhalation increased TFEB activation, mitophagy and mitochondrial biogenesis in mice treated with LPS/GalN. Our findings describe novel mechanisms underlying CO-dependent cytoprotection in hepatocytes and liver tissue via activation of TFEB-dependent mitophagy and associated induction of both lysosomal and mitochondrial biogenesis.

CD38 is an ADP-ribosyl cyclase, producing a potent

No abstract