Differential roles of nitric oxide synthases in regulation of ultraviolet B light-induced apoptosis

Abstract

Ultraviolet B light (UVB) activates nitric oxide synthase(s) (NOS) and nitric oxide (NO•) production, which plays a role in regulation of apoptosis. However the role of NO• in UVB-induced apoptosis remains controversial. In this study, we analyzed expression and activation of constitutive NOSs (cNOSs) and their roles in UV-induced apoptosis of HaCaT keratinocytes. Our data showed that the expression of neuronal NOS (nNOS) was increased while endothelial NOS (eNOS) was uncoupled in the early phase (0–6 h) post-UVB. The expression of both cNOSs peaked at 12 h post-UVB and NO• was transiently elevated with 30 min and then steadily rose from 6–18 h post-UVB. The expression of iNOS was detected at 6 h post-UVB and then sturdily increased. Inhibition of cNOSs with L-NAME reduced the inducibility of NO• in the early and late phases of irradiation. Along with the eNOS uncoupling, an increased level of peroxynitrite (ONOO−) was detected in the early phase, but not in the late phase post-UVB. Inhibition of cNOSs reduced the production of ONOO− in the early time, but led to an increase of ONOO− in the late time after UVB-irradiation. The results indicate that cNOSs regulate NO•/ONOO− imbalance after UVB-irradiation. Our data suggested that the activation of cNOSs in the early phase post-UVB leads to NO•/ONOO− imbalance and promotes apoptosis via a caspase 3-independent pathway. The elevation of NO• in the late phase of UVB-irradiation is mainly produced by inducible NOS (iNOS). However, cNOSs also contribute to the NO• production and to maintain a higher NO•/ONOO− ratio, which reduces caspase 3 activity and protects cells from UVB-induced apoptosis.

Targeting Nitric Oxide Signaling with nNOS Inhibitors As a Novel Strategy for the Therapy and Prevention of Human Melanoma

“…UVB-induced nNOS occurred in a transient, short-duration manner; the induction of NO was evident shortly after UVB exposure and peaked at 4 h followed by a sharp drop. Although similar transient nNOS induction after UVB exposure was reported in HaCaT kerationcytes, the predominant elevation of NO levels was mediated by iNOS induction especially in the late phase post-UVB ( > 6 h) (31). We propose that the long-lasting nNOS induction by UVA might account for delayed chronic responses; the transient nNOS induction by UVB might contribute to acute reactions.…”

Protective Effects of Millettia Pulchra Flavonoids on Myocardial Ischemia In Vitro and In Vivo

“…Variation in the serum LDH isoenzyme pattern is considered a definitive diagnostic criterion for the assessment of myocardial damage because the rate of LDH appearance and disappearance in the blood indicates the size of the infarction [31]. In the present study, LDH activity was increased in the H/R model group compared with the blank control group, which is supported by previous findings [32].…”

“…Additionally, cardioprotection is related to the levels of different types of NOS [27,28]. It is widely accepted that iNOS induces apoptosis but that cNOS inhibits apoptosis [29,30,31]. In this study, we found that the iNOS activity was higher and the cNOS activity was lower in the H/R model group and that pretreatment with MPF could effectively reverse these changes.…”

The Role of Constitutive Nitric-oxide Synthase in Ultraviolet B Light-induced Nuclear Factor κB Activity

“…Thus when L-NAME inhibited NF-B, it also reduced the production of ONOO Ϫ , which promotes cell death (33,40,41). An elevation of ONOO Ϫ can lead to the oxidation of cholesterol (42), which plays a critical role in regulating UVB-induced apoptosis via induction of lipid rafts clustering and Fas aggregation (43,44); NF-B activation can induce iNOS expression (45), and an elevated NO⅐ production inhibits caspase 3 activation in late stage of UVB irradiation (14). Based on these studies and our findings, we propose that early activation of cNOS promotes apoptosis via induction of ONOO Ϫ elevation and inhibits apoptosis via activation of NF-B followed by induced expression of iNOS and escalated NO⅐ pro-FIGURE 9.…”

“…We previously showed that both nNOS and eNOS are expressed in HaCaT cells (14). To determine the contribution of each isoform of cNOS in regulation of UVB-induced reduction of IB, we analyzed the extent of the effect of nNOS and/or eNOS knockdown on IB expression after UVB irradiation.…”