No abstract

Reactivation of the human polyomavirus JC (JCV) in the CNS results in a fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). The lytic destruction of oligodendrocytes, which occurs at the terminal stage of the viral infection cycle, is considered a critical factor in the development of demyelination and the pathogenesis of PML. However, knowledge is limited about interaction of JCV with oligodendrocytes and its impact on the denudation of axons at the early stage of viral reactivation and prior to the destruction of the infected cells. We have developed an in vitro neuroprogenitor cell culture using human fetal brain that can be differentiated to the oligodendrocyte lineage to investigate interactions of JCV with its host cells. Results show that infection with JCV delays oligodendrocyte maturation as shown by reduced levels of oligodendrocytic markers, including myelin basic protein, proteolipid protein, and platelet-derived growth factor receptor-α. Furthermore, replication of JCV in these cells caused substantial dysregulation of several chemokines, including CCL5/RANTES, GRO, CXCL1/GROα, CXCL16, CXCL8/IL-8, CXCL5/ENA-78, and CXCL10/IP-10, all of which play a role in cell growth and differentiation.

No abstract

Examination of signal transduction pathways that modulate neuronal cell differentiation and protection against apoptosis has revealed a central role for the MAPK/Erk cascade. The activation of MAPK/Erk through the TrkA NGF signaling pathway is critical for growth and survival of neuronal cells. Here, we investigate the impact of HIV-1 Tat on the NGF-signaling pathway in SK-N-MC neuroblastoma cells. Expression of Tat decreased cell growth and induced apoptosis. Our results revealed dysregulation of various steps involved in the NGF pathway including suppression of MAPK, and inhibition of the promoter activity of Egr-1, a key pleiotropic mediator of the expression of genes involved in cell growth upon expression of Tat in SK-N-MC cells. Similarly, exposure of SK-N-MC to conditioned media derived from cells expressing Tat decreased phosphorylation of MAPK and reduced the level of Egr-1 protein expression in SK-N-MC cells. Furthermore, MAPK was able to phosphorylate Puralpha, a cellular protein that plays an important role in neuronal cell function and differentiation, and this was inhibited by Tat. The ability of Puralpha to interact with a GA/GC-rich sequence positioned upstream from the transcription start site of the Egr-1 promoter provided a rationale to examine Egr-1 expression. Expression of Tat decreased NGF-induced Egr-1 levels in SK-N-MC cells and reduced binding of Puralpha to the Egr-1 promoter. All of these observations support a model where the interplay between Tat and Puralpha dysregulates the NGF pathway including the MAPK/Erk network, resulting in reduced expression and activity of Egr-1 in neuronal cells.