Cadmium (Cd) is an ecotoxic heavy metal that predominantly causes renal failure. Proximal tubular cell damage is typical of chronic Cd toxicity. Proximal tubular cells play important roles in maintaining a stable balance of body chemicals through the functions of various transporters. ABC transporter subfamily B member 1 [ABCB1; also called MDR1 (multiple drug resistance 1)], one of the ATP binding cassette (ABC) multidrug efflux transporters, is expressed in the proximal tubular epithelium and is involved in the extracellular clearance of various chemicals. In this study, we demonstrate that Cd significantly increases the levels of ABCB1 mRNA and P-glycoprotein protein (the ABCB1 gene product) in the HK-2 human proximal tubular cells. Our results suggest that Cd affects the transportation function in the proximal tubules. However, ABCB1 knockdown did not affect Cd toxicity in the HK-2 cells. Therefore, the Cd-induced increase in ABCB1 may affect the transportation function in the kidney but not the Cd toxicity.

Cadmium (Cd) is an environmental hazardous heavy metal that causes renal dysfunction triggered by its toxicity to proximal tubular cells. Our previous study demonstrated that Cd changed the activities of various transcription factors (TFs) in the mouse kidney. In this study, we investigated whether long-term exposure to Cd affected the expression levels of downstream genes of these TFs. C57BL/6J female mice were fed chow containing 300 ppm Cd for 12 months. After 4, 8, and 12 months of Cd exposure, total RNA was extracted from the mouse kidney. The results confirmed that Cd exposure dramatically increased the expression of metallothionein-2 (Mt2) in the mouse kidney. Cd exposure increased the mRNA levels of Slc13a1, Vegfa, and Vegfb among the downstream genes regulated by Cd-activated TFs. Thy1 expression was decreased by Cd exposure, even though the upstream TF was activated by Cd. Furthermore, Cd exposure decreased the mRNA levels of Agtrap, Tert, Fgfr4, Foxq1, Abcb1b, Cd274, Pck1, and Egr1 among the downstream genes regulated by Cd-suppressed TFs. The expression of Pklr increased at 4-month Cd exposure, but decreased at 12-month exposure. Although our previous study indicated Cd exposure suppressed the retinoic acid receptor TF in the mouse kidney, in the present study, it was found that the downstream gene Tnfrsf10b was up-regulated by Cd exposure. For many of the genes whose expressions were affected by long-term Cd exposure, the relationship with Cd renal toxicity has not been reported so far. Our results may provide useful clues into the molecular mechanism of Cd renal toxicity.

Epidermal cells produce cytokines as a part of the body’s response to various external stimuli. Though extracellular ATP-induced activation of P2 receptors is involved in cytokine production in epidermal cells, it is not known whether activation of P1 receptors by extracellular adenosine leads to IL-6 production in epidermal cells. Here, we show that activation of adenosine A2B receptor induces IL-6 production via phosphorylation of epidermal growth factor receptor (EGFR) in human keratinocyte HaCaT cells. We found that treatment of HaCaT cells with 100 μM adenosine or with A2B receptor-specific agonist BAY60-6583 induced IL-6 production, and the production of IL-6 was suppressed by pretreatment with A2B receptor-specific antagonist PSB603. Adenosine- induced IL-6 production was also suppressed by A2B receptor knockdown. In addition, adenosine- and BAY60-6583-induced IL-6 production was suppressed by treatment with EGFR antagonist AG1478. Furthermore, adenosine and BAY60-6583 induced EGFR phosphorylation, and this phosphorylation was suppressed by A2B receptor knockdown. Thus, our data indicate that the A2B receptor-EGFR pathway has a role in IL-6 production. This in turn suggests that extracellular adenosine is involved in skin inflammation.

The controlled and moderate oxidative stress such as ozone induces both inflammatory and anti-inflammatory response. This balance is important for homeostasis of living organisms. Furthermore, it has been shown that this conflict response is mainly regulated by two transcriptional factors, nuclear transcriptional factor κB (NF-κB) and nuclear factor erythroid 2-related factor 2 (Nrf2). NF-κB is involved in inflammatory responses by regulating expression of cyclooxygenase-2 (COX-2) and various inflammatory cytokines while Nrf2 is involved in anti-inflammatory responses by controlling expression of numerous antioxidant enzymes such as heme oxygenase- 1 (HO-1). We here demonstrate the molecular mechanisms of the crosstalk between NF-κB and Nrf2 activation during the moderate oxidative stress induced by ozone. We first confirmed the activation of NF-κB and Nrf2 signaling during the moderate oxidative stress in HeLa cells. Induction of NF-κB-mediated COX-2 mRNA expression was observed at the early phase after stimulation (30-60 min after ozone treatment). However, induction of HO-1 mRNA expression was observed at the late phase of stimulation (6 h after stimulation). To reveal the crosstalk between NF-κB and Nrf2, we tested whether reduction of NF-κB expression affects ozone-induced Nrf2 activation by knocking down of NF-κB in HeLa cells. Importantly, the HO-1 induction by ozone was remarkably decreased by a reduction in NF-κB expression. These results suggest that the moderate oxidative stress by ozone initially induces NF-κB activation, and this NF-κB activation is required for HO-1 induction at the late phase of the moderate stress.

Some α-helical antimicrobial peptides enhance the activation of immune cells induced by the recognition of DNA containing unmethylated cytosine-guanine motifs (CpG DNA). We recently found that an α-helical antimicrobial peptide FIKRIARLLRKIF, known as Kn2-7, increased CpG DNA-dependent responses in mouse macrophage- like RAW264.7 cells, and we also found that enhanced cellular uptake of CpG DNA by Kn2-7 was necessary but insufficient to augment CpG DNA-dependent responses. In this study, we clarified the relationship between the affinity of Kn2-7 to CpG DNA and the ability of Kn2-7 to enhance cellular uptake of DNA. Electrophoretic mobility analysis on a polyacrylamide gel revealed that Kn2-7 binds to CpG DNA more effectively than Kn2-7RA in which arginine residues of Kn2-7 were substituted with alanine residues, and also found that Kn2-7 binds to CpG DNA less effectively than Kn2-7KR in which lysine residues of Kn2-7 were substituted with arginine residues. The DNA-binding abilities of Kn2-7, Kn2-7RA, and Kn2-7KR correlated well with their abilities to enhance the cellular uptake of CpG DNA. In contrast, Kn2-7LA in which leucine residues of Kn2-7 were substituted with alanine residues exhibited a similar DNA-binding ability to Kn2-7, but it did not enhance cellular uptake of CpG DNA. Our results indicate that affinity to DNA is necessary for the ability of Kn2-7 to enhance cellular uptake of CpG DNA, but hydrophobicity of Kn2-7 is also necessary for the enhancement of cellular uptake.