Kalsi Kameljit, Lawson Charlotte, Dominguez Martin, Taylor Patricia, Yacoub Magdi H, Smolenski Ryszard T
Imperial College School of Medicine, National Heart and Lung Institute at Harefield Hospital, Middlesex, UK.
Mol Cell Biochem. 2002 Mar;232(1-2):113-9. doi: 10.1023/a:1014806916844.
Ecto-5'-nucleotidase (E5'N, CD73) is key enzyme responsible for formation of anti-inflammatory and immunosuppressive adenosine from extracellular nucleotides as well as an important surface molecule involved in cellular signalling. In this study we provide evidence that the pro-inflammatory cytokine, tumour necrosis factor-alpha (TNF-alpha) may reduce the capacity of human endothelial cells to produce adenosine by a decrease in surface expression and in the activity of E5'N. Human umbilical vein endothelial cells incubated for 24 h with TNF-alpha lost 54% of the activity of E5'N while activities of the other enzymes involved in adenosine metabolism remained unaffected. Immunofluorescence staining with anti-E5'N (1E9) following exposure to TNF-alpha, showed reduced numbers of positive cells. TNF-alpha induced down-regulation of E5'N was prevented by addition of the PLC inhibitor neomycin, but not by inhibitors of MAPK-like pathways (MEK and p38). Therefore, we conclude that TNF-alpha through activation of endogenous PLC leads to cleavage of the GPI-linkage of E5'N resulting in loss of E5'N from the extracellular surface. This change may lead to decrease in formation of adenosine and could be an important mechanism of endothelial activation during inflammation.
ecto-5'-核苷酸酶（E5'N，CD73）是负责从细胞外核苷酸形成抗炎和免疫抑制性腺苷的关键酶，也是参与细胞信号传导的重要表面分子。在本研究中，我们提供证据表明促炎细胞因子肿瘤坏死因子-α（TNF-α）可能通过降低E5'N的表面表达和活性来降低人内皮细胞产生腺苷的能力。用人脐静脉内皮细胞与TNF-α孵育24小时后，E5'N的活性丧失了54%，而参与腺苷代谢的其他酶的活性未受影响。用抗E5'N（1E9）进行免疫荧光染色，结果显示暴露于TNF-α后阳性细胞数量减少。添加PLC抑制剂新霉素可阻止TNF-α诱导的E5'N下调，但MAPK样途径（MEK和p38）的抑制剂则不能。因此，我们得出结论，TNF-α通过激活内源性PLC导致E5'N的GPI连接断裂，从而导致E5'N从细胞外表面丢失。这种变化可能导致腺苷形成减少，并且可能是炎症期间内皮细胞激活的重要机制。
