A single amino acid substitution in the cyclin D binding domain of the infected cell protein no. 0 abrogates the neuroinvasiveness of herpes simplex virus without affecting its ability to replicate

The infected cell protein no, 0 (ICP0) of herpes simplex virus 1 is a promi scuous transactivator shown to enhance the expression of genes introduced i nto cells by infection or transfection. The protein interacts with several viral and cellular proteins. Earlier studies have shown that ICP0 binds and stabilizes cyclin D3 but does interfere with the phosphorylation of retino blastoma protein, its major function. Cyclin D3 plays a key role in the tra nsition from GI to S phase. To define the role of cyclin D3 in productive i nfection, the ICP0 binding site for cyclin D3 was mapped and mutagenized by substitution of aspartic acid codon 199 with the alanine codon. We report that the substitution precluded the interaction of this protein with cyclin D3 in the yeast two-hybrid system and the stabilization of cyclin D3 in in fected cells, A recombinant virus carrying this mutation could not be diffe rentiated from wild-type parent with respect to replication in dividing cel ls but yielded 10-fold less progeny from infected resting cells and serum-d eprived or contact-inhibited human fibroblasts, In mice, the mutant was onl y slightly less pathogenic than the wild-type parent by intracerebral route but was significantly less neuroinvasive after peripheral inoculation. Rep lacement of the mutated amino acid with aspartic acid restored wild-type ph enotype. Stabilization of cyclin D3 therefore is linked to higher:virus yie lds in nondividing cells and potentially higher virulence in experimental a nd natural hosts, One function of ICP0 is to scavenge the cell for proteins that could bolster viral replication.