Intracellular distribution of the ORF4 gene product of varicella-zoster virus is influenced by the IE62 protein

Abstract

Varicella-zoster virus (VZV) open reading frame 4-encoded protein (IE4) possesses transactivatingproperties for VZV genes as well as for genes of heterologous viruses. The major regulatory immediate-early protein of VZV (IE62) is a transactivator of VZV gene expression. In transfection assays, IE4 has been shown to enhance activation induced by IE62. To investigate the functional interactions underlying this observation, indirect immunofluorescence studies were undertaken to determine whether IE62 could influence IE4 intracellular localization in transfected cells. In single transfections, IE4 was predominantly found in cytoplasm. In cotransfection with IE62, the IE4 localization pattern was altered, with nuclear staining predominating over cytoplasmic staining. This effect was specific to the IE62 protein since the gene products of ORF63 and ORF61, which are also regulatory proteins, did not influence IE4 distribution. The use of IE62 mutants indicated that IE62 influence is independent of its transactivation function and that the integrity of regions 3 and 4 is required. IE62 remained nuclear whether IE4 was present or not. These observations underline differences in the regulation of gene expression between VZV proteins and their herpes simplex virus type 1 homoIogues. In infected cells, IE4 was only sometimes found to colocalize with IE62 in nuclei. This observation suggests that when all VZV proteins are present, complex interactions probably occur which could diminish the influence of IE62.

Identification and Analysis of the K5 Gene of Kaposi's Sarcoma-Associated Herpesvirus

“…Almost all other known herpesvirus IE antigens are found in the nucleus and are involved in regulation of the expression of other genes (e.g., E and L genes). One exception is the varicella-zoster virus IE-4 antigen, which, like K5, is localized in the cytoplasm (10,11). On the other hand, the varicella-zoster virus IE-4 antigen has transactivational activity toward homologous and heterologous promoters (10,11) and during very early stages of infection, it is detectable in the nucleus (11).…”

“…One exception is the varicella-zoster virus IE-4 antigen, which, like K5, is localized in the cytoplasm (10,11). On the other hand, the varicella-zoster virus IE-4 antigen has transactivational activity toward homologous and heterologous promoters (10,11) and during very early stages of infection, it is detectable in the nucleus (11). We observed no apparent transactivational activity toward homologous and heterologous promoters on the part of K5; nevertheless, by analogy, K5 may exert a regulatory effect on gene expression at times earlier than those at which we were first able to detect the protein in the present study.…”

Varicella-Zoster Virus ORF4 Latency-Associated Protein Is Important for Establishment of Latency

“…VZV ORF4 protein is present in the nucleus early in infection and later localizes predominantly to the cytoplasm. When ORF4 protein is coexpressed with ORF62 protein, the former localizes to the nucleus (10,27).…”

La régulation des cycles infectieux du virus de la varicelle et du zona.

“…Les interactions existant entre l'IE62 et l'IE4 suscitent un intérêt croissant puisque la protéine IE4 augmente l'effet transactivateur de l'IE62 [15]. L'IE62 transporte la protéine IE4 du cytoplasme vers le noyau [22] et la région carboxy-terminale (région 4) de l'IE62 semble impliquée dans cette propriété. Néanmoins, l'interaction physique directe entre ces deux protéines n'a pas encore été démontrée.…”

“…Il est actuellement difficile de corréler cette observation avec ses fonctions. La seule donnée expérimentale dont nous disposons concerne la capacité de la protéine IE62 d'entraîner l'IE4 dans le noyau dans lequel cette dernière pourrait exercer une partie de ses fonctions [22]. Il se peut que cet effet soit lié aux propriétés de transactivation synergique de ces deux protéines.…”