Herpes simplex virus type-1 (HSV-1) initially infects mucoepithelial tissues of the orofacial region, the eye and to a lesser extent the genitalia. We report here on dLAT1.5, a mutant with LAT nucleotides 76 to 1667 deleted. The latent cell population comprises primary-order neurons infected directly from peripheral tissues and cells infected following further virus spread within the ganglion. Cell survival was reduced minimally after repression of high multiplicity HSV type 1 (HSV-1) infection of human fibroblast cells with (E)-5-(2-bromovinyl)-2′-deoxyuridine in combination with human leukocyte interferon (IFN-alpha). For comparative purposes, latent infections were quantified by (i) quantitative PCR on DNA extracted from whole ganglia, (ii) the number of latency-associated transcript (LAT) promoter-positive neurons, using KOS and 17syn+ LAT promoter-beta-galactosidase reporter mutants, and (iii) contextual analysis of DNA. The factor-binding properties of each LP1 CRE element distinguish them from each other and from a highly related canonical CRE binding site and the TPA response element (TRE). Taken together, these data indicate that the regulation of expression and processing of LAT RNA within the mouse is highly cell-type specific and occurs in the absence of other viral cis- and trans-acting factors.
LP1 CRE-2 is more unusual in that it shares more features of a canonical CRE site than a TRE with two notable exceptions: it does not bind CREB-1 very well and it binds CREB-2 better than the canonical CRE. There is evidence suggesting that certain HSV-1 miRNAs can repress the expression of important HSV-1 activators of lytic gene expression (7, 9). In addition, we have demonstrated the two HSV-1 LP1 CRE sites to be unique with respect to their ability to bind neuronal AP1-related factors that are regulated by cAMP. These studies suggest that both factor binding and activation of bound factors may be involved in cAMP regulation of HSV-1 LP1 through the CRE elements, and indicate the necessity of investigating the expression and posttranslational modification of a variety of ATF/CREB and AP-1 factors during latency and reactivation.