Pocket Protein p130/Rb2 Is Required for Efficient Herpes Simplex Virus Type 1 Gene Expression and Viral Replication

We have reported previously that herpes simplex virus type 1 (HSV-1) infection disrupts normal progression of the mammalian cell cycle, causing cells to enter a G(1)-like state. Infected cells were characterized by a decline in cyclin-dependent kinase 2 (CDK2) activities, loss of hyperphosphorylated retinoblastoma protein (pRb), accumulation of E2F-pocket protein complexes, and failure to initiate cellular DNA replication. In the present study, we investigated the role of the pocket proteins pRb, p107, and p130 in HSV-1-dependent cell cycle inhibition and cyclin kinase regulation by infecting murine 3T3 cells derived from wild-type (WT) mouse embryos or embryos with deletions of pRb (pRb(−/−)), p107 (p107(−/−)), p130 (p130(−/−)), or both p130 and p107 (p130(−/−)/p107(−/−)). With respect to CDK2 inhibition, viral protein accumulation, viral DNA replication, and progeny virus yield, WT, pRb(−/−), and p107(−/−) cells were essentially identical. In contrast, after infection of p130(−/−) cells, we observed no inhibition of CDK2 activity, a 5- to 6-h delay in accumulation of viral proteins, an impaired ability to form viral DNA replication compartments, and reduced viral DNA synthesis. As a result, progeny virus yield was reduced 2 logs compared to that in WT cells. Notably, p130(−/−)/p107(−/−) double-knockout cells had a virus replication phenotype intermediate between those of the p107(−/−) and p130(−/−) cells. We conclude from these studies that p130 is a key factor in regulating aspects of cell cycle progression, as well as the timely expression of viral genes and replication of viral DNA.