Peroxisomal deficiencies are associated with altered activity of endothelial NOS in human fibroblasts

Loss of p53 in stromal fibroblasts promotes epithelial cell invasion through redox-mediated ICAM1 signal

Tumor microenvironment plays a major role in cancer development. Understanding how the stroma affects epithelial transformation will provide a basis for new preventive strategies. Recent evidence suggests that oxidative stress in stroma may play a role in cancer progression, and loss of p53 function in the stromal cells was associated with poor prognosis and high tumor recurrence. However, the underlying mechanisms remain poorly understood. Here, we investigated the role of p53 loss in fibroblasts in epithelial transformation and the mechanistic involvement of reactive species. Using 3D organotypic culture and other assays, we report that the stroma containing p53-deficient fibroblasts could induce the nontumorigenic epithelial cells of oral and ovarian tissue origins to become invasive through reactive nitrogen species (RNS)-mediated release of the cytokine ICAM1. The p53-deficient fibroblasts have increased RNS production and accumulation of oxidative DNA-damage products associated with specific upregulation of endothelial nitric oxide synthase (eNOS). Suppression of RNS production by siRNA of eNOS or the antioxidant NAC reduced ICAM1 expression and prevented the stroma-mediated epithelial invasion. Our study uncovers the novel mechanism by which redox alteration associated with loss of p53 in stromal fibroblasts functions as a key inducer of epithelial transformation and invasion via RNS-mediated ICAM1 signaling. Thus, the modulation of redox signaling in the microenvironment may serve as a new approach to preventing epithelial transformation and suppressing cancer invasion.

Elevated urinary excretion of nitric oxide metabolites in young infants with Zellweger syndrome

BACKGROUND

Children with Zellweger syndrome (ZS), a rare peroxisome deficiency disorder, excrete into the urine highly elevated amounts of urinary metabolites of the arachidonic acid cascade. This pathway may interact in vivo with the L-arginine/nitric oxide (NO) pathway. The aim of this study was to investigate NO production in ZS.

METHODS

We studied 11 infants aged 2-12 months with ZS and 30 healthy controls (HC) aged 1-12 months. Urinary excretion of nitrite plus nitrate (U(NO(x))), which is a reliable measure of whole body NO formation, was determined by gas chromatography-mass spectrometry (GC-MS) and corrected for creatinine excretion.

RESULTS

In the subjects aged 1-6 months, U(NO(x)) was more than twofolds higher in ZS (median, 666 micromol/mmol creatinine) as compared to HC (median, 257 micromol/mmol creatinine) (P=0.014 by Mann-Whitney U-test). In children aged 7-12 months, U(NO(x)) was similar for ZS subjects and HC (P=0.96). U(NO(x)) correlated negatively with age in ZS (Kendall's rank correlation coefficient, tau=-0.75, P=0.001). By contrast, no such correlation was found in HC (tau=0.06, P=0.6).

CONCLUSIONS

NO production is highly elevated during the first 6 months of life in infants with ZS and falls to normal levels within the following 6 months, suggesting a dramatic decrease in NO synthesis in ZS.

Autologous nitric oxide protects mouse and human keratinocytes from ultraviolet B radiation-induced apoptosis

Nitric oxide (NO) can either prevent or promote apoptosis, depending on cell type. In the present study, we tested the hypothesis that NO suppresses ultraviolet B radiation (UVB)-induced keratinocyte apoptosis both in vitro and in vivo. Irradiation with UVB or addition of the NO synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) increased apoptosis in the human keratinocyte cell line CCD 1106 KERTr, and apoptosis was greater when the two agents were given in combination. Addition of the chemical NO donor S-nitroso-N-acetyl-penicillamine (SNAP) immediately after UVB completely abrogated the rise in apoptosis induced by l-NAME. An adenoviral vector expressing human inducible NOS (AdiNOS) also reduced keratinocyte death after UVB. Caspase-3 activity, an indicator of apoptosis, doubled in keratinocytes incubated with l-NAME compared with the inactive isomer, d-NAME, and was reduced by SNAP. Apoptosis was also increased on addition of 1,H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase. Mice null for endothelial NOS (eNOS) exhibited significantly higher apoptosis than wild-type mice both in the dermis and epidermis, whereas mice null for inducible NOS (iNOS) exhibited more apoptosis than wild-type mice only in the dermis. These results demonstrate an antiapoptotic role for NO in keratinocytes, mediated by cGMP, and indicate an antiapoptotic role for both eNOS and iNOS in skin damage induced by UVB.

L-Carnitine alters nitric oxide synthase activity in fibroblasts depending on the peroxisomal status

Fibroblast cellular models are widely used for research on fatty acid metabolism. Due to the importance of L-carnitine in intermediary metabolism we studied the effects of L-carnitine on healthy human skin fibroblasts and fibroblasts without functional peroxisomes (Zellweger Syndrome) cultivated under carnitine deficiency, which is caused by standard media compositions. The application of physiological (0.1mM) or super-physiological (1mM) doses of L-carnitine causes a significant decrease of the specific activity of nitric oxide synthase (NOS, 2.25+/-0.10 to 1.36 pmol/(minmg)+/-0.09 pmol/(minmg) at 0.1mM), proliferation and a tendentious decrease of the antioxidant defence potential against hydrogen peroxide only in control cells. Simultaneous application of L-carnitine and 100 micro M N-acetylcysteine (NAC) prevents the alterations in control cells. Thus, L-carnitine alters the cellular regulation of the NOS probably by reactive oxygen species (ROS), which suggests that carnitine deficient media neither reflect physiological conditions for cellular models for fatty acid metabolism nor for the regulation of NOS.

Basic fibroblast growth factor activates endothelial nitric-oxide synthase in CHO-K1 cells via the activation of ceramide synthesis

In this study, we analyzed the intracellular mechanisms leading to basic fibroblast growth factor (bFGF)-dependent production of NO in Chinese hamster ovary (CHO)-K1 cells and a possible physiological role for such an effect. bFGF induces NO production through the activation of the endothelial form of NO synthase (eNOS), causing a subsequent increase in the cGMP levels. In these cells, the activation of eNOS by bFGF is Ca(2+)- and mitogen-activated protein kinase-independent. The translocation of the enzyme from the plasma membrane, where it is located in caveolae bound to caveolin 1, to the cytosol is the crucial step for the synthesis of NO through the eNOS isoform. We demonstrate that bFGF activates a sphingomyelinase to synthesize ceramide, which, in turn, allows the dissociation of eNOS from caveolin 1 and its translocation to the cytosol in the active form, where it catalyzes the synthesis of NO. In fact, drugs interfering with sphingomyelinase activity blocked bFGF activation of eNOS, and an increase in ceramide content was detected after bFGF treatment. Moreover, in fibroblasts derived from patients with Niemann-Pick disease, in which the enzyme is genetically inactive, bFGF is unable to elicit eNOS activation. The NO produced after bFGF treatment, through the activation of guanylyl cyclase and protein kinase G, mediates a mitogen-activated protein kinase-independent cell proliferation. In conclusion, our data show that, in CHO-K1 cells, bFGF regulates the activity of eNOS through a novel intracellular pathway, involving the induction of ceramide synthesis and that the NO released participates in bFGF proliferative activity.