Modification of multiple transcriptional regulatory elements in a Moloney murine leukemia virus gene transfer vector circumvents silencing in fibroblast grafts and increases levels of expression of the transferred enzyme

Abstract

Down-regulation of retroviral vector expression occurs in a number of cell types after transplantation. Although a num-

Α genetic fusion construct between the tetanus toxin C fragment and the lysosomal acid hydrolase β‐glucuronidase expresses a bifunctional protein with enhanced secretion and neuronal uptake

“…2e). The detection of a low level of intracellular activity in GTCL cells was consistent with the histochemical staining intensity, which has been shown to correlate with the levels of biochemical activity (Taylor and Wolfe 1994; Prasad Alur et al . 2002).…”

Targeting recombinant adeno-associated virus vectors to enhance gene transfer to pancreatic islets and liver

“…The relative specificity of the insulin promoter for beta cells also adds another level of precision to the gene delivery process, in that other cells transduced with insulin promoter-driven constructs are not likely to express the transgene at significant levels. It is also unlikely that the insulin promoter will undergo transcriptional silencing [26][27][28][29] in beta cells of the pancreatic islets, although it is possible that the promoter cassette could be selectively silenced in the context of the vector, while the endogenous insulin promoter remains active in the context of its chromosomal locus. Overall, these studies make it much more practical to consider ex vivo islet cell transduction in the context of islet cell transplantation.…”

Enhancing GABAAReceptor α1 Subunit Levels in Hippocampal Dentate Gyrus Inhibits Epilepsy Development in an Animal Model of Temporal Lobe Epilepsy

“…The reduction of ␣1 expression at 4 weeks suggests that the GABRA4 promoter in AAV vector is either silenced or transcriptionally downregulated. Although gene silencing has been reported in the CNS for integrated retrovirus vectors (Prasad-Alur et al, 2002;Rosenquist et al, 2005), it is less likely to alter AAV-mediated expression because AAV vector genomes are both episomal and associated with high-molecular-weight DNA in the brain, and robust gene expression has been documented from AAV using various promoters for much longer than 4 weeks (Skorupa et al, 1999;Xu et al, 2001;Passini et al, 2002). Our previous work strongly suggests that BDNF and Egr3 (early growth response 3) are major regulators of enhanced ␣4 expression after SE (Roberts et al, 2005(Roberts et al, , 2006, so downregulation of these transcription factors could explain our findings.…”