Hemin Reduces HMGB1 Release by UVB in an AMPK/HO-1-dependent Pathway in Human Keratinocytes HaCaT Cells

High mobility group box 1 (HMGB1) plays an important role as a pro-inflammatory cytokine that regulates inflammation in various diseases. We hypothesized that hemin might reduce HMGB1 release through the induction of HO-1 in UVB-induced HaCaTs. The effects of hemin on the release of HMGB1 in UVB exposure were evaluated. The mechanisms were investigated using various signal inhibitors and small interfering RNA techniques. Treatment with hemin inhibited reactive oxygen species (ROS) in UVB-induced HaCaTs in a dose-dependent manner. HMGB1 release by UVB was significantly reduced by hemin, N-acetyl-cysteine and DPI (NADPH oxidase inhibitor). Hemin increased HO-1 induction followed by phosphorylation of AMPK in a time- and dose-dependent manner. Additionally, hemin significantly increased the NAD+/NADH ratio in HaCaTs. The inhibitory effects of UVB-induced HMGB1 release by hemin were significantly reversed not only with pharmacological inhibitors of AMPK (compound c) or HO-1 (ZnPPIX) but also through transfection of small interfering RNAs (siRNAs) for AMPK or HO-1. Interestingly, hemin decreased phosphor-AMPK expression by HO-1 siRNA transfection, but it failed to induce HO-1 in AMPK siRNA-transfected cells, which suggested that HO-1 was involved in AMPK activation by hemin in HaCaT. Moreover, recombinant HMGB1 induced Snail and inhibited E-Cadherin in HaCaTs, whereas hemin reversed those effects through rHMGB1. It is concluded that the increased activity of HO-1/AMPK and scavenging ROS are, at least in part, responsible for the inhibition of UVB-induced HMGB1 release in keratinocyte HaCaTs. Therefore, hemin may be a useful agent for preventing UVB-induced skin cancer.