Transduction of foreign regulatory sequences by a replication-defective herpes simplex virus type 1: The rat neuron-specific enolase promoter

Herpes simplex virus type 1 (HSV-1) can transduce genes into non-proliferating cells such as neurons that are refractory to other means of gene transfer. We have been interested to examine the potential usefulness of HSV-1 as a gene transfer vehicle to analyze neuron-specific regulatory sequences. In this study, we have used a replication-defective HSV-1-based vector deleted for the essential immediate early gene 3 (IE3) to transduce a 1.8 kb promoter fragment from the rat neuron-specific enolase gene (nse) linked to the firefly luciferase reporter gene (luc). It has previously been shown that the same promoter fragment is capable of directing neuron-specific expression of a linked reporter gene in transgenic mice. As an internal control for infection and gene expression, we also inserted the chloramphenicol acetyltransferase (cat) gene driven by the SV40 early promoter/enhancer into the thymidine kinase locus of the same vector. We infected (i) non-neuronal BHK-C13 cells which do not express the endogenoous nse gene, (ii) differentiated and non-differentiated pheochromocytoma PC12 cells as well as (iii) N1E-115 neuroblastoma cells, all of which do express endogenous nse. All three cell types produced luciferase upon infection, indicating that the same nse promoter fragment that has previously been shown to be regulated in a cell-specific manner in transgenic mice, was not regulated cell type-specifically in the context of the HSV-1 genome. Therefore, the nse promoter fragment may either be incomplete (and genomic sequences in the transgenic mice may have compensated for this deficiency), or the function of the present control elements is affected by adjacent HSV sequences and is thus template-dependent.