Systematic analysis of enhancer and critical cis-acting RNA elements in the protein-encoding region of the hepatitis C virus genome.

Hepatitis C virus (HCV) causes chronic hepatitis, cirrhosis, and liver cancer. cis-acting RNA elements of the HCV genome are critical for translation initiation and replication of the viral genome. We hypothesized that the coding regions of nonstructural proteins harbor enhancer and essential cis-acting replication elements (CRE). In order to experimentally identify new cis RNA elements, we utilized an unbiased approach to introduce synonymous substitutions. The HCV genome coding for nonstructural proteins (nucleotide positions 3872 to 9097) was divided into 17 contiguous segments. The wobble nucleotide positions of each codon were replaced, resulting in 33% to 41% nucleotide changes. The HCV genome containing one of each of 17 mutant segments (S1 to S17) was tested for genome replication and infectivity. We observed that silent mutations in segment 13 (S13) (nucleotides [nt] 7457 to 7786), S14 (nt 7787 to 8113), S15 (nt 8114 to 8440), S16 (nt 8441 to 8767), and S17 (nt 8768 to 9097) resulted in impaired genome replication, suggesting CRE structures are enriched in the NS5B region. Subsequent high-resolution mutational analysis of NS5B (nt 7787 to 9289) using approximately 51-nucleotide contiguous subsegment mutant viruses having synonymous mutations revealed that subsegments SS8195-8245, SS8654-8704, and SS9011-9061 were required for efficient viral growth, suggesting that these regions act as enhancer elements. Covariant nucleotide substitution analysis of a stem-loop, JFH-SL9098, revealed the formation of an extended stem structure, which we designated JFH-SL9074. We have identified new enhancer RNA elements and an extended stem-loop in the NS5B coding region. Genetic modification of enhancer RNA elements can be utilized for designing attenuated HCV vaccine candidates.

Efficacy of Antibody Delivery to the Retina and Optic Nerve by Topical Administration.

PURPOSE: The purpose of this study was to determine whether nonspecific and ICAM-1-specific IgG1 antibodies can accumulate in the rat retina following topical application, and to develop a model system to show that antibodies that reach the posterior segment retain their pharmacological properties. METHODS: Eye drops containing mouse IgG1 or anti-ICAM-1 and the permeation enhancer saponin were topically applied to the eyes of Lewis rats. Concentrations were determined in the retina and optic nerve up to 30 min later using ELISA assays. We also developed an in vitro model to assess the pharmacologic activity of topically delivered antibodies in the retina based on the requirement of human umbilical vein endothelial cells (HUVECs) for vascular endothelial growth factor (VEGF) for growth. Rat eyes were treated with anti-VEGF antibody in the same manner as above; their retinas, harvested shortly thereafter, were added to HUVECs cultured in VEGF-containing media. The effect of these retinal homogenates on HUVEC proliferation was then assessed. RESULTS: Significant concentrations of IgG1 were detected in the optic nerve (P < 0.001) and retina (P < 0.0001) following topical application. Anti-ICAM-1 antibody also accumulated in the retina after topical application, though levels were less than those seen with IgG1 probably owing to a lower starting concentration. Retinal homogenates from eyes treated with anti-VEGF antibody significantly suppressed HUVEC proliferation (P < 0.0001). CONCLUSIONS: Our data support the contention that topically applied antibodies can accumulate in the posterior segment, and suggest they retain their pharmacological properties.