High Throughput siRNA Screening Identifies Phosphatidylinositol 3-kinase Class II Alpha as Important for Production of Human Cytomegalovirus Virions.

High throughput siRNA screening is a useful methodology to identify cellular factors required for virus replication. Here we utilized a high throughput siRNA screen based on detection of a viral antigen by microscopy to interrogate cellular protein kinases and phosphatases for their importance during human cytomegalovirus (HCMV) replication, and identified the Class II Phosphatidylinositol 3-kinase PI3K-C2A as being involved in HCMV replication. Confirming this observation, infected cells treated with either pooled or individual siRNAs targeting PI3K-C2A mRNA produced approximately 10-fold less infectious virus compared to controls. Western blotting and quantitative PCR analysis of infected cells treated with siRNAs indicated that depletion of PI3K-C2A slightly reduced accumulation of late, but not immediate-early or early, viral antigens and had no appreciable effect of viral DNA synthesis. Analysis of siRNA treated cells by electron microscopy and western blotting indicated that PI3K-C2A was not required for production of viral capsids, but did lead to increased numbers of enveloped capsids in the cytoplasm that had undergone secondary envelopment and reduction of viral particles exiting the cell. Therefore, PI3K-C2A is a factor important for HCMV replication and has a role in production of HCMV virions. IMPORTANCE: There is limited information about the cellular factors required for human cytomegalovirus (HCMV) replication. Therefore, to identify proteins involved in HCMV replication we developed a methodology to conduct a high throughput siRNA screen in HCMV infected cells. From our screening data we focused our studies on the top "hit" from our screen, the lipid kinase phosphatidylinositol 3-kinase Class II Alpha (PI3K-C2A), as its role in HCMV replication was unknown. Interestingly, we found that PI3K-C2A is important for the production of HCMV virions and is involved in virion production after secondary envelopment of viral capsids, the encapsidation of HCMV capsids by a lipid bilayer that occurs before virions exit the cell