THE HIGHLY INDUCIBLE MEMBER OF THE 70 KDA FAMILY OF HEAT-SHOCK PROTEINS INCREASES CANINE-DISTEMPER VIRUS POLYMERASE-ACTIVITY

The cellular stress response is characterized by the production of hea t shock proteins (HSP) which serve important cytoprotective functions, Paradoxically, in vitro induction of the stress response promotes cyt opathic effect mediated by infection with canine distemper virus (CDV) . The stress-mediated increase in cytopathic effect is correlated to t he formation of complexes between the viral nucleocapsid (NC) and the major inducible member of the approximate to 70 kDa family of HSP (hsp 72), The objective of the present study was to document the functional significance of CDV NC-HSP interaction, Cytoplasmic NC was purified f rom Vero cells lytically infected with the Onderstepoort strain of CDV , Both ultrastructural variants of CDV NC interacted with both hsp72 a nd the constitutively expressed member of the approximate to 70 kDa fa mily of HSP (hsp73) in a reversible and ATP-dependent manner, An effec t of hsp72/73 on NC polymerase activity was demonstrated using cell-fr ee assays derived from either Vero or HeLa cell lines. Antibody specif ic to hsp72 suppressed both basal and stress-enhanced polymerase activ ity whereas hsp73-specific antibody had no affect, Supplementation of purified hsp72/73, but not hsp73 alone, enhanced basal polymerase acti vity in a dosage-dependent manner, Using purified NC variants, polymer ase activity was demonstrated in pre-formed hsp72/73-NC complexes but not in NC devoid of HSP. These results suggest that the stimulatory ef fect of the stress response upon CDV gene expression may, in part, be mediated by a reversible and direct interaction between hsp72 and the viral core particle.