8-Oxo-7,8-dihydroguanosine triphosphate(8-oxoGTP) down-regulates respiratory burst of neutrophils by antagonizing GTP toward Rac, a small GTP binding protein

Abstract

8-oxo-7,8-dihydroguanosine triphosphate (8-oxoGTP) has been regarded simply as a oxidative mutagenic byproduct. The results obtained in this study imply that it may act as a down-regulator of respiratory burst of neutrophils. Human neutrophils treated with PMA produced superoxides and at the same time, the cytosol of these cells was intensely immunostained by 8-oxo-7,8-dihydroguanosine(8-oxoG) antibody, indicating that 8-oxoG-containing chemical species including 8-oxoGTP are produced. Human neutrophil lysates treated with PMA also produced superoxides, which was stimulated by GTPgammaS but inhibited by 8-oxoGTPgammaS. Moreover, 8-oxoGTPgammaS suppressed the stimulatory action of GTPgammaS. Likewise, GTPgammaS stimulated Rac activity in neutrophil lysates but 8-oxoGTPgammaS and GDP inhibited it. The inhibitory effect of GDP was one tenth that of 8-oxoGTPgammaS. Here again, 8-oxoGTPgammaS also suppressed the stimulatory action of GTPgammaS on Rac activity. These results imply the possibility that 8-oxoGTP is formed during respiratory burst of neutrophils and limits neutrophil production of superoxides by antagonizing GTP toward Rac.

8-Oxoguanine DNA glycosylase-1 links DNA repair to cellular signaling via the activation of the small GTPase Rac1

“…2H, lower panels). 8-OxodG slightly lowered Rac1-GTP levels (data not shown) as documented previously [41]. As shown by immunoblot analysis, Rac1 is abundantly expressed in lung tissues (Fig.…”

“…Importantly, the guanine base, FapyG (another BER product of OGG1) and 8-OH-Ade or uric acid did not increase Rac1-GTP levels in MRC5 and A549 cells (data not shown). On the other hand, 8-oxodG slightly inhibited Rac1 activation (data not shown), as shown in previous studies [41]. MRC5 and A549 cells abundantly express Rac1, whereas the expression of Rac3 (closely related to Rac1 in functions and nucleotide binding; rev in [42]) was approximately 22- and 43-times lower than that of Rac1 in MRC-5 and A549 cells, respectively (Fig.…”

“…These observations are consistent with those showing that both A549 and MRC5 cells express NOX4 [42, 55]. We found that 8-oxodG decreased Rac1-GTP levels (data not shown) – an observation in good agreement with previous studies showing a decrease in NOX activity by 8-oxodG [41]. …”

The Mutyh Base Excision Repair Gene Influences the Inflammatory Response in a Mouse Model of Ulcerative Colitis

“…The anti-inflammatory activity exerted in vivo by 8-oxoGTP or 7,8-dihydro-8-oxo-deoxyguanosine (but not by 8-oxoG) indicates that some oxidation by-products can modulate immune functions [34], [35]. The mechanism by which Mutyh influences the inflammatory response remains however to be ascertained.…”

Oxidation in the nucleotide pool, the DNA damage response and cellular senescence: Defective bricks build a defective house

“…However whether endogenous levels of 8-oxo-GTP effect the same enhancement of such mitogenic signaling is not known. On the other hand, addition of 8-oxoGTP␥S appears to inhibit Rac signaling relative to GTP␥S [129], suggesting oxidized GTP exerts diverse effects on signaling via Ras-related proteins. Thus, the role of oxidized GTP in oncogenic G-protein mediated signal transduction is likely to be complex and a potentially promising area of study.…”