The transcriptional promoter of the cytomegalovirus (CMV) immediate early genes has been extensively exploited in mammalian vectors used for in vitro and in vivo transgene delivery. Transcriptional activation by the CMV promoter is dependent on the presence of certain cellular transcription factors, several of which are known to be altered in response to cellular stimuli. However, the stability of transgene expression in model systems that depend on coincident stimuli has not previously been addressed. Here we monitored the activity of the CMV promoter in an adeno-associated virus (AAV) vector used to deliver constitutively secreted Gaussia luciferase (GLuc) to primary cortical neurons in vitro and the rat striatum in vivo. Using a technique for repeated sampling of cerebral spinal fluid (CSF) in rats, we observed a methamphetamine-dependent increase in GLuc activity in the CSF. We also found a methamphetamine-dependent increase in GLuc mRNA levels in the striatum where the AAV-GLuc was injected. In cultured primary cortical neurons, glutamate and kainic acid treatment caused an increase in the CMV-dependent expression of GLuc following viral transduction. Our results suggest that variations in transgene expression can serve as a confounding factor in studies where stimulatory substances are applied on biological systems that use the CMV promoter to drive transgene expression. However, the observed effect on CMV-driven transcription could also be exploited for therapeutic purposes. As an example, we provide evidence that methamphetamine administration induces upregulation of a previously characterized antibody designed to mediate virus-based passive immunization against methamphetamine toxicity, leading to higher concentrations of the antibody in the presence of its antigen (methamphetamine). Collectively, our data emphasize that the use of a CMV promoter for constitutive, stable viral vector-mediated transgene expression should be empirically evaluated in the model system.
