Effects of fetal bovine serum on ferrous ion-induced oxidative stress in pheochromocytoma (PC12) cells

AKR1C1 connects autophagy and oxidative stress by interacting with SQSTM1 in a catalytic-independent manner

Targeting autophagy might be a promising anticancer strategy; however, the dual roles of autophagy in cancer development and malignancy remain unclear. NSCLC (non-small cell lung cancer) cells harbour high levels of SQSTM1 (sequestosome 1), the autophagy receptor that is critical for the dual roles of autophagy. Therefore, mechanistic insights into SQSTM1 modulation may point towards better approaches to treat NSCLC. Herein, we used multiple autophagy flux models and autophagy readouts to show that aldo-keto reductase family 1 member C1 (AKR1C1), which is highly expressed in NSCLC, promotes autophagy by directly binding to SQSTM1 in a catalytic-independent manner. This interaction may be strengthened by reactive oxygen species (ROS), important autophagy inducers. Further mechanistic research demonstrated that AKR1C1 interacts with SQSTM1 to augment SQSTM1 oligomerization, contributing to the SQSTM1 affinity for binding cargo. Collectively, our data reveal a catalytic-independent role of AKR1C1 for interacting with SQSTM1 and promoting autophagy. All these findings not only reveal a novel functional role of AKR1C1 in the autophagy process but also indicate that modulation of the AKR1C1-SQSTM1 interaction may be a new strategy for targeting autophagy.

Direct effect of sodium iodate on neurosensory retina

PURPOSE

To systematically characterize the effects of NaIO3 on retinal morphology and function.

METHODS

NaIO3 at 10, 20, or 30 mg/kg was administered by retro-orbital injection into adult C57BL/6J mice. Phenotypic and functional changes of the retina were assessed at 1, 3, 5, and 8 days postinjection by fundus imaging, optical coherence tomography (OCT), ERG, and histology. Direct NaIO3 cytotoxicity on ARPE-19 and 661W cells was quantified using lactate dehydrogenase (LDH) apoptosis assay. Effect of NaIO3 on RPE and photoreceptor gene expression was assessed in vitro and in vivo by quantitative PCR.

RESULTS

While little to no change was observed in the 10 mg/kg NaIO3-injected group, significant retinal anomalies, such as RPE atrophy and retinal thinning, were observed in both 20 and 30 mg/kg NaIO3-injected groups. Gene expression analysis showed rapid downregulation of RPE-specific genes, increase in heme oxygenase 1 expression, and induction of the ratio of Bax to Bcl-2. Electroretinographic response loss and photoreceptor gene repression preceded gross morphological changes. High NaIO3 toxicity on 661W cells was observed in vitro along with reactive oxygen species (ROS) induction. NaIO3 treatment also disrupted oxidative stress, phototransduction, and apoptosis gene expression in 661W cells. Exposure of ARPE-19 cells to NaIO3 increased expression of neurotrophins and protected photoreceptors from direct NaIO3 cytotoxicity.

CONCLUSIONS

Systematic characterization of changes associated with NaIO3 injection revealed a large variability in the severity of toxicity induced. Treatment with >20 mg/kg NaIO3 induced visual dysfunction associated with rapid suppression of phototransduction genes and induced oxidative stress in photoreceptors. These results suggest that NaIO3 can directly alter photoreceptor function and survival.

Catalase reverses tumorigenicity in a malignant cell line by an epidermal growth factor receptor pathway

We have used a keratinocyte in vivo/in vitro cell model to test the hypothesis that hydrogen peroxide acts as a signaling molecule, contributing to proliferation and tumorigenesis. A cell line, 6M90, that produces squamous cell carcinoma (SCC), has high levels of ROS and low levels of catalase. A new cell line, MTOC2, generated from parental 6M90 cells by introduction of a Tet-responsive catalase transgene, effectively expressed higher peroxisomal catalase. Increased catalase expression diminished constitutive ROS and enhanced viability after treatment with hydrogen peroxide. Protein tyrosine phosphatase activity was higher in the MTOC2 cells with high catalase, consistent with detection of a lower level of phosphorylation at tyrosine 1068 of the epidermal growth factor receptor (EGF-R). Transcription of downstream c-fos, AP-1 transactivation and cell proliferation were higher in the low catalase cells. An EGF-R inhibitor, AG1478, blocks the higher AP-1 transactivation and cell proliferation of the low catalase 6M90 cells. Tumorigenesis in SCID mice was greatly diminished in the high catalase cells. Our data suggest that hydrogen peroxide functions as a signaling molecule that can modulate activity of a protein tyrosine phosphatase/(s) resulting in phosphorylation of tryrosine/(s) on the EGF-R. Therefore, catalase acts as a tumor-suppressor gene in part by decreasing EGF-R signaling.

Regulation of apoptosis by glutathione redox state in PC12 cells exposed simultaneously to iron and ascorbic acid

We previously reported that the levels of non-protein-bound iron (NPBI) and ascorbic acid (AA) are markedly increased in the cerebrospinal fluid of infants with perinatal asphyxia. The present study showed that FeSO4 and AA synergistically induced apoptosis of PC12 cells, which was prevented by alpha-tocopherol and glutathione (GSH) ethyl ester. Markers of free radical damage, such as ortho-tyrosine, meta-tyrosine, and F(2alpha)-isoprostane, showed a gradual increase. AA and ferrous NPBI disappeared rapidly from the culture medium, but exposure for only a few hours was sufficient to trigger apoptosis. Intracellular GSH decreased progressively along with a concomitant increase of glutathione disulfide (GSSG). The baseline half-cell reduction potential (Ehc) for GSSG, 2H+/2GSH couple was -246 mV and an Ehc of -200 mV was the critical level to switch on apoptosis, although some cells escaped this fate by transient increase of intracellular GSH. Once Ehc reached around -165 mV (81 mV oxidation from the baseline), all cells lost the ability to maintain an adequate intracellular GSH level and subsequently underwent apoptosis. These findings at least partly explain the mechanism of Fe-AA cytotoxicity, in that ferrous iron catalyzes hydroxyl radical generation and induces lipid peroxidation, after which subsequent depletion of GSH raises Ehc to the critical level for triggering or potentiating the apoptotic cascade.