Herpes simplex virus type 1 UL14 tegument protein regulates intracellular compartmentalization of major tegument protein VP16

Abstract

Background:Herpes simplex virus type 1 (HSV-1) has a complicated life-cycle, and its genome encodes manycomponents that can modify the cellular environment to facilitate efficient viral replication. The protein UL14 islikely involved in viral maturation and egress (Cunningham C. et al), and it facilitates the nuclear translocation ofviral capsids and the tegument protein VP16 during the immediate-early phase of infection (Yamauchi Y. et al,2008). UL14 of herpes simplex virus type 2 exhibits multiple functions (Yamauchi Y. et al, 2001, 2002, 2003). Methods:To better understand the function(s) of UL14, we generated VP16-GFP-incorporated UL14-mutant viruseswith either single (K51M) or triple (R60A, R64A, E68D) amino acid substitutions in the heat shock protein (HSP)-likesequence of UL14. We observed the morphology of cells infected with UL14-null virus and amino acid-substitutedUL14-mutant viruses at different time points after infection. Results:UL14(3P)-VP16GFP and UL14D-VP16GFP (UL14-null) viruses caused similar defects with respect to growthkinetics, compartmentalization of tegument proteins, and cellular morphology in the late phase. Both the UL14D-VP16GFP and UL14(3P)-VP16GFP viruses led to the formation of an aggresome that incorporated some tegumentproteins but did not include nuclear-egressed viral capsids. Conclusions:Our findings suggest that a cluster of charged residues within the HSP-like sequence of UL14 isimportant for the molecular chaperone-like functions of UL14, and this activity is required for the acquisition offunctionality of VP16 and UL46. In addition, UL14 likely contributes to maintaining cellular homeostasis followinginfection, including cytoskeletal organization. However, direct interactions between UL14 and VP16, UL46, or othercellular or viral proteins remain unclear.