The HSV-1 immediate early protein ICP22 is a J-like protein required for Hsc70 reorganization during lytic infection

Abstract

Molecular chaperones and co-chaperones are the most abundant cellular effectors of protein homeostasis, assisting protein folding and preventing aggregation of misfolded proteins. We have previously shown that HSV-1 infection results in the drastic spatial reorganization of the cellular chaperone Hsc70 into nuclear domains called VICE (Virus Induced Chaperone Enriched) domains and that this recruitment is dependent on the viral immediate early protein ICP22. In this paper, we present several lines of evidence supporting the notion that ICP22 functions as a virally encoded co-chaperone (J-protein/Hsp40) functioning together with its Hsc70 partner to recognize and manage aggregated and misfolded proteins. We show that ICP22 results in (i) nuclear sequestration of non-native proteins, (ii) reduction of cytoplasmic aggresomes in cells expressing aggregation-prone proteins and (iii) thermoprotection against heat-inactivation of firefly luciferase. (iv) Sequence homology analysis indicated that ICP22 contains an N-terminal J-domain and a C-terminal substrate binding domain, similar to type II cellular J-proteins. ICP22 may, thus, be functionally similar to J-protein/Hsp40 co-chaperones that function together with their HSP70 partners to prevent aggregation of non-native proteins. This is not the first example of a virus hijacking a function of a cellular chaperone, as SV40 T Antigen was previously shown to contain a J-domain; however, this the first known example of the acquisition of a complete J-like protein by a virus and suggests that HSV has taken advantage of the adaptable nature of J-proteins to evolve a multi-functional co-chaperone that functions with Hsc70 to promote lytic infection.\n\nIMPORTANCEViruses have evolved a variety of strategies to succeed in a hostile environment. The HSV immediate early protein ICP22 plays several roles in the virus life cycle including down-regulation of cellular gene expression, up-regulation of late viral gene expression, inhibition of apoptosis, prevention of aggregation of non-native proteins and the recruitment of a cellular heat shock protein, Hsc70, to nuclear domains. We present evidence that ICP22 resembles a cellular J-protein/HSP40 family co-chaperone, interacting specifically with Hsc70. This is the first known example of the acquisition of a complete J-like protein by a virus and suggests that HSV has evolved to manipulate the host proteostatic machinery during the establishment of lytic infection.