Connecting peptide (C-peptide), a byproduct of insulin biosynthesis, has diverse cellular and biological functions. Particulate mat-ter 2.5 (PM2.5 ) adversely affects human skin, leading to skin thickening, wrinkle formation, skin aging, and inflammation. This study aimed to investigate the protective effects of C-peptide against PM2.5 -induced damage to skin cells, focusing on oxidative stressas a key mechanism. C-peptide mitigated NADPH oxidation and intracellular reactive oxygen species (ROS) production inducedby PM2.5 . It also suppressed PM2.5 -induced NADPH oxidase (NOX) activity and alleviated PM2.5 -induced NOX1 and NOX4 expression. C-peptide protected against PM2.5 -induced DNA damage, lipid peroxidation, and protein carbonylation. Additionally, C-peptide mitigated PM2.5 -induced apoptosis by inhibiting intracellular ROS production. In summary, our findings suggest that C-peptide mitigates PM2.5 -induced apoptosis in human HaCaT keratinocytes by inhibiting intracellular ROS production and NOX activity.

γ-Radiation resistance is a major obstacle to the success of radiotherapy in colorectal cancer. Antioxidant-related factors contribute to resistance to radiation therapy and, therefore, are targets for improving the therapeutic response. In this study, we evaluated the molecular mechanisms underlying γ-radiation resistance using the colorectal cancer cell line SNUC5 and γ-radiation-resistant variant SNUC5/RR, including analyses of the role of nuclear factor erythroid 2-related factor 2 (NRF2), a transcription factor that regulates antioxidant enzymes, and related epigenetic regulators. Reactive oxygen species (ROS) levels, antioxidant enzyme expression, NRF2 expression, and nuclear translocation were higher in SNUC5/RR cells irradiated with or without 8 Gy than in SNUC5 cells. The DNA demethylase ten-eleven translocation 1 (TET1) expression and TET1 binding to the NRF2 promoter in SNUC5/RR cells were stronger than those in SNUC5 cells, indicating lower methylation of CpG islands in the NRF2 promoter.TET1 knockdown in SNUC5/RR cells suppressed NRF2 expression significantly. Additionally, histone mixed-lineage leukemia (MLL), a histone methyltransferase, was upregulated, leading to increased trimethylation of histone H3 lysine 4, whereas enhancer of zeste homolog 2 (EZH2), a histone methyltransferase, was downregulated, leading to decreased trimethylation of histone H3 lysine 27. Histone deacetylase (HDAC) and histone acetyltransferase (HAT) levels were lower and higher in SNUC5/RR cells than in SNUC5 cells, respectively. MLL and HAT knockdown in SNUC5/RR cells irradiated with or without 8 Gy decreased levels of NRF2 and heme-oxygenase 1, resulting in enhanced γ-radiation sensitivity. These findings support NRF2 as a target for improving the response to radiotherapy in patients with colorectal cancer.

Connecting peptide (C-peptide), a byproduct of insulin biosynthesis, has diverse cellular and biological functions. Particulate mat-ter 2.5 (PM2.5 ) adversely affects human skin, leading to skin thickening, wrinkle formation, skin aging, and inflammation. This study aimed to investigate the protective effects of C-peptide against PM2.5 -induced damage to skin cells, focusing on oxidative stressas a key mechanism. C-peptide mitigated NADPH oxidation and intracellular reactive oxygen species (ROS) production inducedby PM2.5 . It also suppressed PM2.5 -induced NADPH oxidase (NOX) activity and alleviated PM2.5 -induced NOX1 and NOX4 expression. C-peptide protected against PM2.5 -induced DNA damage, lipid peroxidation, and protein carbonylation. Additionally, C-peptide mitigated PM2.5 -induced apoptosis by inhibiting intracellular ROS production. In summary, our findings suggest that C-peptide mitigates PM2.5 -induced apoptosis in human HaCaT keratinocytes by inhibiting intracellular ROS production and NOX activity.

γ-Radiation resistance is a major obstacle to the success of radiotherapy in colorectal cancer. Antioxidant-related factors contribute to resistance to radiation therapy and, therefore, are targets for improving the therapeutic response. In this study, we evaluated the molecular mechanisms underlying γ-radiation resistance using the colorectal cancer cell line SNUC5 and γ-radiation-resistant variant SNUC5/RR, including analyses of the role of nuclear factor erythroid 2-related factor 2 (NRF2), a transcription factor that regulates antioxidant enzymes, and related epigenetic regulators. Reactive oxygen species (ROS) levels, antioxidant enzyme expression, NRF2 expression, and nuclear translocation were higher in SNUC5/RR cells irradiated with or without 8 Gy than in SNUC5 cells. The DNA demethylase ten-eleven translocation 1 (TET1) expression and TET1 binding to the NRF2 promoter in SNUC5/RR cells were stronger than those in SNUC5 cells, indicating lower methylation of CpG islands in the NRF2 promoter.TET1 knockdown in SNUC5/RR cells suppressed NRF2 expression significantly. Additionally, histone mixed-lineage leukemia (MLL), a histone methyltransferase, was upregulated, leading to increased trimethylation of histone H3 lysine 4, whereas enhancer of zeste homolog 2 (EZH2), a histone methyltransferase, was downregulated, leading to decreased trimethylation of histone H3 lysine 27. Histone deacetylase (HDAC) and histone acetyltransferase (HAT) levels were lower and higher in SNUC5/RR cells than in SNUC5 cells, respectively. MLL and HAT knockdown in SNUC5/RR cells irradiated with or without 8 Gy decreased levels of NRF2 and heme-oxygenase 1, resulting in enhanced γ-radiation sensitivity. These findings support NRF2 as a target for improving the response to radiotherapy in patients with colorectal cancer.

Connecting peptide (C-peptide), a byproduct of insulin biosynthesis, has diverse cellular and biological functions. Particulate mat-ter 2.5 (PM2.5 ) adversely affects human skin, leading to skin thickening, wrinkle formation, skin aging, and inflammation. This study aimed to investigate the protective effects of C-peptide against PM2.5 -induced damage to skin cells, focusing on oxidative stressas a key mechanism. C-peptide mitigated NADPH oxidation and intracellular reactive oxygen species (ROS) production inducedby PM2.5 . It also suppressed PM2.5 -induced NADPH oxidase (NOX) activity and alleviated PM2.5 -induced NOX1 and NOX4 expression. C-peptide protected against PM2.5 -induced DNA damage, lipid peroxidation, and protein carbonylation. Additionally, C-peptide mitigated PM2.5 -induced apoptosis by inhibiting intracellular ROS production. In summary, our findings suggest that C-peptide mitigates PM2.5 -induced apoptosis in human HaCaT keratinocytes by inhibiting intracellular ROS production and NOX activity.

γ-Radiation resistance is a major obstacle to the success of radiotherapy in colorectal cancer. Antioxidant-related factors contribute to resistance to radiation therapy and, therefore, are targets for improving the therapeutic response. In this study, we evaluated the molecular mechanisms underlying γ-radiation resistance using the colorectal cancer cell line SNUC5 and γ-radiation-resistant variant SNUC5/RR, including analyses of the role of nuclear factor erythroid 2-related factor 2 (NRF2), a transcription factor that regulates antioxidant enzymes, and related epigenetic regulators. Reactive oxygen species (ROS) levels, antioxidant enzyme expression, NRF2 expression, and nuclear translocation were higher in SNUC5/RR cells irradiated with or without 8 Gy than in SNUC5 cells. The DNA demethylase ten-eleven translocation 1 (TET1) expression and TET1 binding to the NRF2 promoter in SNUC5/RR cells were stronger than those in SNUC5 cells, indicating lower methylation of CpG islands in the NRF2 promoter.TET1 knockdown in SNUC5/RR cells suppressed NRF2 expression significantly. Additionally, histone mixed-lineage leukemia (MLL), a histone methyltransferase, was upregulated, leading to increased trimethylation of histone H3 lysine 4, whereas enhancer of zeste homolog 2 (EZH2), a histone methyltransferase, was downregulated, leading to decreased trimethylation of histone H3 lysine 27. Histone deacetylase (HDAC) and histone acetyltransferase (HAT) levels were lower and higher in SNUC5/RR cells than in SNUC5 cells, respectively. MLL and HAT knockdown in SNUC5/RR cells irradiated with or without 8 Gy decreased levels of NRF2 and heme-oxygenase 1, resulting in enhanced γ-radiation sensitivity. These findings support NRF2 as a target for improving the response to radiotherapy in patients with colorectal cancer.

Rosmarinic acid (RA) is a phenolic ester that protects human keratinocytes against oxidative damage induced by ultraviolet B (UVB) exposure, however, the mechanisms underlying its effects remain unclear. This study aimed to elucidate the cell signaling mechanisms that regulate the antioxidant activity of RA and confirm its cyto-protective role. To explore the signaling mechanisms, we used the human keratinocyte cell line HaCaT and SKH1 hairless mouse skin. RA enhanced glutamate-cysteine ligase catalytic subunit (GCLC) and glutathione synthetase (GSS) expression in HaCaT cells in a dose- and time-dependent manner. Moreover, RA induced nuclear factor erythroid-2-related factor 2 (NRF2) nuclear translocation and activated the signaling kinases protein kinase B (AKT) and extracellular signal-regulated kinase (ERK). Treatment with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, the ERK inhibitor U0126, and small interfering RNA (siRNA) gene silencing suppressed RA-enhanced GCLC, GSS, and NRF2 expression, respectively. Cell viability tests showed that RA significantly prevented UVB-induced cell viability decrease, whereas the glutathione (GSH) inhibitors buthionine sulfoximine, LY294002, and U0126 significantly reduced this effect. Moreover, RA protected against DNA damage and protein carbonylation, lipid peroxidation, and apoptosis caused by UVB-induced oxidative stress in a concentration-dependent manner in SKH1 hairless mouse skin tissues. These results suggest that RA protects against UVB-induced oxidative damage by activating AKT and ERK signaling to regulate NRF2 signaling and enhance GSH biosynthesis. Thus, RA treatment may be a promising approach to protect the skin from UVB-induced oxidative damage.

Specific sensitivity of the skin to ultraviolet B (UVB) rays is one of the mechanisms responsible for widespread skin damage. This study tested whether 1,3,5-trihydroxybenzene (THB), a compound abundant in marine products, might inhibit UVB radiationinduced NADPH oxidase 4 (NOX4) in both human HaCaT keratinocytes and mouse dorsal skin and explore its cytoprotective mechanism. The mechanism of action was determined using western blotting, immunocytochemistry, NADP + /NADPH assay, reactive oxygen species (ROS) detection, and cell viability assay. THB attenuated UVB-induced NOX4 expression both in vitro and in vivo, and suppressed UVB-induced ROS generation via NADP + production, resulting in increased cell viability with decreased apoptosis. THB also reduced the expression of UVB-induced phosphorylated AMP-activated protein kinase (AMPK) and phosphorylated c-Jun N-terminal kinase (JNK). THB suppressed UVB-induced NOX4 expression and ROS generation by inhibiting AMPK and JNK signaling pathways, thereby inhibiting cellular damage. These results showed that THB could be developed as a UV protectant.

Radiation resistance represents an imperative obstacle in the treatment of patients with colorectal cancer, which remains difficult to overcome. Here, we explored the anti-proliferative and migration-inhibiting properties of the natural product shikonin on a radiation-resistant human colon carcinoma cell line (SNU-C5RR). Shikonin reduced the viability of these cells in a dose-dependent manner; 38 μM of shikonin was determined as the half-maximal inhibitory concentration. Shikonin induced apoptotic cell death, as demonstrated by increased apoptotic body formation and the number of TUNEL-positive cells. Moreover, shikonin enhanced mitochondrial membrane depolarization and Bax expression and also decreased Bcl-2 expression with translocation of cytochrome c from mitochondria into the cytosol. In addition, shikonin activated mitogen-activated protein kinases, and their specific inhibitors reduced the cytotoxic effects of shikonin. Additionally, shikonin decreased the migration of SNU-C5RR cells via the upregulation of E-cadherin and downregulation of N-cadherin. Taken together, these results suggest that shikonin induces mitochondria-mediated apoptosis and attenuates epithelial-mesenchymal transition in SNU-C5RR cells.

Resistance to chemotherapeutic drugs is a significant problem in the treatment of colorectal cancer, resulting in low response rates and decreased survival. Recent studies have shown that shikonin, a naphthoquinone derivative, promotes apoptosis in colon cancer cells and cisplatin-resistant ovarian cells, raising the possibility that this compound may be effective in drug-resistant colorectal cancer. The aim of this study was to characterize the molecular mechanisms underpinning shikonin-induced apoptosis, with a focus on endoplasmic reticulum (ER) stress, in a 5-fluorouracil–resistant colorectal cancer cell line, SNU-C5/5-FUR. Our results showed that shikonin significantly increased the proportion of sub-G1 cells and DNA fragmentation and that shikonin-induced apoptosis is mediated by mitochondrial Ca 2+ accumulation. Shikonin treatment also increased the expression of ER-related proteins, such as glucose regulatory protein 78 (GRP78), phospho-protein kinase RNA-like ER kinase (PERK), phospho-eukaryotic initiation factor 2 (eIF2α), phospho-phosphoinositol-requiring protein-1 (IRE1), spliced X-box–binding protein-1 (XBP-1), cleaved caspase-12, and C/EBP-homologous protein (CHOP). In addition, siRNA-mediated knockdown of CHOP attenuated shikonininduced apoptosis, as did the ER stress inhibitor TUDCA. These data suggest that ER stress is a key factor mediating the cytotoxic effect of shikonin in SNU-C5/5-FUR cells. Our findings provide an evidence for a mechanism in which ER stress leads to apoptosis in shikonin-treated SNU-C5/5-FUR cells. Our study provides evidence to support further investigations on shikonin as a therapeutic option for 5-fluorouracil–resistant colorectal cancer.