Gibbs Peter E M, Maines Mahin D
Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, NY 14642, USA.
Int J Cancer. 2007 Dec 1;121(11):2567-74. doi: 10.1002/ijc.22978.
hBVR functions in the cell as a reductase and as a kinase. In the first capacity, it reduces biliverdin, the product of HO activity, to the effective intracellular antioxidant, bilirubin; as a dual-specificity kinase (S/T/Y) it activates the MAPK and IGF/IRK receptor signal transduction pathways. NF-kappaB and the MAPK pathway are activated by ROS, which results in the activation of stress-inducible genes, including ho-1. Presently, we report on the negative effect of biliverdin on NF-kappaB activation and the converse effect of hBVR. Biliverdin, in a concentration- and time-dependent manner, inhibited transcriptional activity of NF-kappaB in HEK293A cells. Nuclear extracts from biliverdin-treated cells show reduced DNA binding of NF-kappaB in an electromobility shift assay, whereas extracts from cells treated with TNF-alpha showed enhanced binding. Coimmunoprecipitation data show hBVR binds to the 65 kDa subunit of NF-kappaB, and that this is dependent on activation by TNF-alpha. Overexpression of hBVR enhanced both the basal and TNF-alpha-mediated activation of NF-kappaB and also that of the NF-kappaB-activated iNOS gene. Also, overexpression of hBVR arrested the cell cycle in the G(1)/G(0) phase and reduced the number of cells in S phase. Similar results were observed with MCF-7 cells. Because of the Janus nature of NF-kappaB activity in the cell and the inhibitory action of biliverdin, the present findings provide a foundation for therapeutic intervention in inflammatory diseases and cancer that may be attained by preventing reduction of biliverdin. On the other hand, by increasing BVR levels beneficial functions of NF-kappaB might be augmented.
hBVR在细胞中作为还原酶和激酶发挥作用。作为还原酶，它将HO活性产物胆绿素还原为有效的细胞内抗氧化剂胆红素；作为双特异性激酶（S/T/Y），它激活MAPK和IGF/IRK受体信号转导途径。NF-κB和MAPK途径由ROS激活，这导致包括ho-1在内的应激诱导基因的激活。目前，我们报道了胆绿素对NF-κB激活的负面影响以及hBVR的相反作用。胆绿素以浓度和时间依赖性方式抑制HEK293A细胞中NF-κB的转录活性。在电泳迁移率变动分析中，胆绿素处理细胞的核提取物显示NF-κB的DNA结合减少，而用TNF-α处理的细胞提取物显示结合增强。免疫共沉淀数据显示hBVR与NF-κB的65 kDa亚基结合，并且这依赖于TNF-α的激活。hBVR的过表达增强了NF-κB的基础激活和TNF-α介导的激活以及NF-κB激活的iNOS基因的激活。此外，hBVR的过表达使细胞周期停滞在G(1)/G(0)期并减少S期细胞数量。在MCF-7细胞中也观察到了类似结果。由于细胞中NF-κB活性的两面性以及胆绿素的抑制作用，本研究结果为通过防止胆绿素还原来治疗炎症性疾病和癌症提供了治疗干预的基础。另一方面，通过增加BVR水平，NF-κB的有益功能可能会增强。
