Bystander macrophages silence transgene expression driven by the retroviral long terminal repeat.
The Moloney murine leukemia virus (MLV)-based retroviral vector has been widely used for transfer of exogenous genes to various organs and tissues. Although the long terminal repeat (LTR) of MLV allows for transgene expression in a wide range of cell type, its activity is often silenced in vivo. In reporter macrophages transduced with a MLV-based retroviral vector, activity of the LTR was transiently and reversibly suppressed following stimulation by lipopolysaccharide (LPS). When unstimulated reporter macrophages were co-cultured with LPS-stimulated, untransduced macrophages, the LTR activity was similarly depressed. Activity of the LTR in retrovirus-transduced, mesangial cells was also down-regulated when co-cultured with activated macrophages. This suppressive effect was reproduced by cross-feeding with culture media conditioned by activated macrophages. LPS-stimulated macrophages abundantly expressed cytokines including IL-1beta, tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1). When externally added, TNF-alpha and/or TGF-beta1, but not IL-1beta, depressed activity of the LTR in reporter macrophages and reporter mesangial cells. These results raise a possibility that expression of transgenes driven by the MLV-LTR may be silenced in vivo when the retrovirally-transduced cells are co-localized with activated macrophages.
Kitamura
M
M
Department of Medicine, University College London Medical School, The Rayne Institute, 5 University Street, London, WC1E 6JJ, United Kingdom. m.kitamura@medicine.ucl.ac.uk
D000818:Animals; D001374:Azacitidine / Q000494:pharmacology; D018920:Coculture Techniques; D017077:Culture Media, Conditioned; D015536:Down-Regulation / Q000187:drug effects; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007375:Interleukin-1 / Q000235:genetics / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008262:Macrophage Activation / Q000187:drug effects; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008979:Moloney murine leukemia virus / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020079:Terminal Repeat Sequences / Q000235:genetics*; D014161:Transduction, Genetic; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000494:pharmacology; D019076:Transgenes / Q000235:genetics*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000494:pharmacology
D017077:Culture Media, Conditioned; D007375:Interleukin-1; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D014409:Tumor Necrosis Factor-alpha; D001374:Azacitidine