Identification of putative functional motifs in viral proteins essential for human cytomegalovirus DNA replication.

Six of the eleven genes essential for Human cytomegalovirus (HCMV) DNA synthesis have been analyzed for putative structural motifs that may have a significant functional role in DNA replication. The genes studied encode for the DNA polymerase accessory protein (UL44), single-stranded DNA binding protein (UL57), primase-helicase complex (UL70, UL102, and UL105), and the putative initiator protein (UL84). The full-length open reading frames of these genes were highly conserved between ten isolates with amino acid sequence identity of >97% for all genes. Using ScanProsite software from the Expert Protein Analysis System (ExPASy) proteomics server, we have mapped putative motifs throughout these HCMV replication genes. Interesting motifs identified include casein kinase-2 (CKII) phosphorylation sites, a microbodies signal motif in UL57, and an ATP binding site in the putative UL105 helicase. Our investigations have also elucidated motif-rich regions of the UL44 DNA polymerase accessory protein and identified cysteine motifs that have potential implications for UL57 and UL70 primase. Taken together, these findings provide insights to regions of these HCMV replication proteins that are important for post-translation modification, activation, and overall function, and this information can be utilized to target further research into these proteins and advance the development of novel antiviral agents that target these processes.

The induction and suppression of the apoptotic response of HSV-1 in human corneal epithelial cells.

PURPOSE: HSV-1 has been shown to block apoptosis in some cell lines when the cells are exposed to exogenous agents (e.g., sorbitol). The purpose of this study was to determine whether HSV-1 infection of human corneal epithelial (HCE) cells alone induces an early proapoptotic response and whether this response is subsequently downregulated during the infection. METHODS: HCE cells were infected with HSV-1 or subjected to osmotic shock (sorbitol). Fluorescent staining for annexin V binding, mitochondrial membrane potential, and DNA condensation and assays for caspase 8, 9, and 3 activity and cytokeratin 18 cleavage were performed, to assess the apoptotic pathway. RESULTS: HSV-1 infection of HCE cells induced a rapid proapoptotic response, characterized by translocation of phosphatidylserine to the external membrane, activation of caspases 8 and 3 within 2 hours, and cleavage of cytokeratin 18. However, the induced response was downregulated during the infection, and later stages of the apoptotic responses (e.g., DNA condensation) were not produced. Sorbitol treatment led to terminal apoptosis by 12 hours, as indicated by DNA condensation of treated cells and reduction in the number of viable cells. CONCLUSIONS: HSV-1 can induce and subsequently suppress the apoptotic pathway in HCE. Suppression of apoptosis occurred only during HSV-1 infection and not after treatment with sorbitol, suggesting that the suppression of apoptosis may be a mechanism of viral survival.

The role of CXC chemokine receptor 2 in Pseudomonas aeruginosa corneal infection.

Pseudomonas is one of the leading causes of contact lens-related microbial keratitis. Despite the use of antibiotics, the host inflammatory response continues to cause damage to the cornea, which may lead to blindness. CXCR2-binding chemokines have been implicated in the pathogenesis of Pseudomonas keratitis, and the exact role of this receptor remains to be elucidated. Corneas of CXCR2 knockout and wild-type mice (Cmkar 2-/- and Cmkar 2+/+) were scratched, and 2x10(6) CFU/mL Pseudomonas 6294 or 6206 was added to corneas. Twenty-four hours postinfection, mice were killed, and eyes were harvested for enumeration of bacteria, myeloperoxidase (MPO) levels, and inflammatory mediators. Cmkar 2-/- had 20- to 100-fold more bacteria than Cmkar 2+/+ mice. There were no differences in MPO levels between gene knockout and Cmkar 2+/+ mice. Histology revealed PMN were restricted to the limbal area. Levels of CXCR2 chemokines (keratinocyte-derived chemokine and MIP-2) were elevated significantly in gene knockout mice. A lack of CXCR2 leads to an inability to control bacterial numbers as a result of the inability of PMN to reach the site of infection in the avascular cornea. These results imply that CXCR2 is critical to the extravasation of neutrophils into the avascular cornea.

Ocular and neuronal cell apoptosis during HSV-1 infection: a review.

HSV-1 may activate or suppress the apoptotic pathway in various cells. This review will discuss this apparent dichotomy and place particular emphasis on the different strategies HSV-1 uses to block or suppress the apoptotic pathway in various cell lines and tissues.