Kim Hun-Taek, Tasca Serban, Qiang Wenan, Wong Paul K Y, Stoica George
Department of Veterinary Pathobiology, Texas A&M University, College Station, Texas.
Lab Invest. 2002 Jun;82(6):693-702. doi: 10.1097/01.lab.0000017373.82871.45.
We previously reported that Moloney murine leukemia virus-ts1-mediated neuronal degeneration in mice is likely a result of both loss of glial support and release of cytokines and neurotoxins from ts1-infected glial cells. Viral infection in some cell types regulates expression of p53 protein, a key regulator of cell proliferation and death. Therefore, we hypothesized that p53 and its dependent genes may be linked with ts1-mediated neuropathology. We examined the presence of p53 and its dependent gene product, a proapoptotic protein bax-alpha, in ts1-induced spongiform encephalomyelopathy. Compared with controls, the lesions of infected animals contained increased levels of p53 and bax-alpha in astrocytes, as shown by strong nuclear p53 and cytoplasmic bax-alpha immunoreactivity in astrocytes. To determine how ts1 affects p53 expression in astrocytes, we then assessed the expression of p53 and its dependent genes, such as bax-alpha and p21, in infected and uninfected immortalized C1 astrocytes and studied possible pathways responsible for p53 accumulation in infected astrocytes. In these studies using mitogen-activated protein kinase inhibitors, infection-induced increases in the p53 level were partially blocked by PD98059, a synthetic inhibitor of MEK1 that is the immediate upstream kinase of extracellular signal-regulated kinases 1/2 (ERK1/2), but not by SB202190, a potent p38 kinase inhibitor. Furthermore, treatment with PD98059 significantly decreased the level of p21 protein, a p53-dependent gene product. These results suggest that ts1 infection may stabilize p53 protein through activation of ERKs in C1 astrocytes, leading to increased expression of the p21 and bax-alpha proteins, both of which induce cell cycle arrest and apoptosis. Our studies suggest that ts1 neuropathology in mice may result from changes in expression and activity of p53, brought about in part by ts1 activation of ERK.
我们之前报道过，莫洛尼鼠白血病病毒ts1介导的小鼠神经元变性可能是神经胶质支持丧失以及ts1感染的神经胶质细胞释放细胞因子和神经毒素共同作用的结果。某些细胞类型中的病毒感染会调节p53蛋白的表达，p53蛋白是细胞增殖和死亡的关键调节因子。因此，我们推测p53及其依赖基因可能与ts1介导的神经病理学有关。我们检测了ts1诱导的海绵状脑脊髓炎中p53及其依赖基因产物——促凋亡蛋白bax-α的存在情况。与对照组相比，感染动物的病变部位星形胶质细胞中p53和bax-α水平升高，星形胶质细胞中p53强核免疫反应性和bax-α细胞质免疫反应性表明了这一点。为了确定ts1如何影响星形胶质细胞中p53的表达，我们随后评估了感染和未感染的永生化C1星形胶质细胞中p53及其依赖基因（如bax-α和p21）的表达，并研究了感染星形胶质细胞中p53积累的可能途径。在这些使用丝裂原活化蛋白激酶抑制剂的研究中，感染诱导的p53水平升高被PD98059部分阻断，PD98059是MEK1的合成抑制剂，MEK1是细胞外信号调节激酶1/2（ERK1/2）的直接上游激酶，但未被有效的p38激酶抑制剂SB202190阻断。此外，用PD98059处理显著降低了p21蛋白的水平，p21蛋白是一种p53依赖的基因产物。这些结果表明，ts1感染可能通过激活C1星形胶质细胞中的ERK来稳定p53蛋白，导致p21和bax-α蛋白表达增加，这两种蛋白都会诱导细胞周期停滞和凋亡。我们的研究表明，小鼠中的ts1神经病理学可能是由p53表达和活性的变化导致的，部分原因是ts1对ERK的激活。
