Interaction of canine distemper virus nucleocapsid variants with 70K heat-shock proteins

Cytoplasmic nucleocapsid (NC) isolated from Vero (V) cells infected in the logarithmic phase of growth with Onderstepoort canine distemper virus consists of light-NC (L-NC) and dense-NC (D-NC), encapsidating full-length genomic RNA, and defective-NC (Df-NC), encapsidating variably truncated RNAs. The 70K host cell protein constituent of L-NC and Df-NC was shown to be a member of the 70K heat-shock protein (70K hsp) family. Specifically, 72K hsp is associated with L-NC, and 72K and 73K hsp are associated with Df-NC. Variable L-NC production by three different Vero cell sublines was compared to cellular 70K hsp levels. V141 supported the highest level of L-NC production and expressed high basal levels of 70K hsp in uninfected cells. These high basal levels correspond to a large distribution of log phase V141s in the S phase of the cell cycle. V138-L and V138-H cells produced lower amounts of L-NC and exhibited similar low basal levels of 70K hsp expression, corresponding to low percentages of log phase cells in the S phase cell cycle compartment. Heat shock was effective in inducing L-NC expression in V138-H, which otherwise produced D-NC. Similar cell subline differences in L-NC production were obtained for eight different virus pools derived from the same plaque-purified parental stock. Enhanced biological activity was associated with L-NC based on correlation between L-NC production, viral titre, and plaque areas measured over infected cells.