Phenotype-genotype studies in kuru: Implications for new variant Creutzfeldt–Jakob disease

The PRNP polymorphic (methionine/valine) codon 129 genotype influences the phenotypic features of transmissible spongiform encephalopathy. All tested cases of new variant Creutzfeldt–Jakob disease (nvCJD) have been homozygous for methionine, and it is conjectural whether different genotypes, if they appear, might have distinctive phenotypes and implications for the future “epidemic curve” of nvCJD. Genotype-phenotype studies of kuru, the only other orally transmitted transmissible spongiform encephalopathy, might be instructive in predicting the answers to these questions. We therefore extracted DNA from blood clots or sera from 92 kuru patients, and analyzed their codon 129 PRNP genotypes with respect to the age at onset and duration of illness and, in nine cases, to detailed clinical and neuropathology data. Homozygosity at codon 129 (particularly for methionine) was associated with an earlier age at onset and a shorter duration of illness than was heterozygosity, but other clinical characteristics were similar for all genotypes. In the nine neuropathologically examined cases, the presence of histologically recognizable plaques was limited to cases carrying at least one methionine allele (three homozygotes and one heterozygote). If nvCJD behaves like kuru, future cases (with longer incubation periods) may begin to occur in older individuals with heterozygous codon 129 genotypes and signal a maturing evolution of the nvCJD “epidemic.” The clinical phenotype of such cases should be similar to that of homozygous cases, but may have less (or at least less readily identified) amyloid plaque formation.

Comparison of intron-containing and intron-lacking human genes elucidates putative exonic splicing enhancers

Of the rules used by the splicing machinery to precisely determine intron–exon boundaries only a fraction is known. Recent evidence suggests that specific short sequences within exons help in defining these boundaries. Such sequences are known as exonic splicing enhancers (ESE). A possible bioinformatical approach to studying ESE sequences is to compare genes that harbor introns with genes that do not. For this purpose two non-redundant samples of 719 intron-containing and 63 intron-lacking human genes were created. We performed a statistical analysis on these datasets of intron-containing and intron-lacking human coding sequences and found a statistically significant difference (P = 0.01) between these samples in terms of 5–6mer oligonucleotide distributions. The difference is not created by a few strong signals present in the majority of exons, but rather by the accumulation of multiple weak signals through small variations in codon frequencies, codon biases and context-dependent codon biases between the samples. A list of putative novel human splicing regulation sequences has been elucidated by our analysis.

CD147 facilitates HIV-1 infection by interacting with virus-associated cyclophilin A

Cyclophilin A (CyPA) is specifically incorporated into the virions of HIV-1 and has been shown to enhance significantly an early step of cellular HIV-1 infection. Our preliminary studies implicated CD147 as a receptor for extracellular CyPA. Here, we demonstrate a role for CyPA–CD147 interaction during the early steps of HIV-1 infection. Expression of human CD147 increased infection by HIV-1 under one-cycle conditions. However, susceptibility to infection by viruses lacking CyPA (simian immunodeficiency virus or HIV-1 produced in the presence of cyclosporin A) was unaffected by CD147. Virus-associated CyPA coimmunoprecipitated with CD147 from infected cells. Antibody to CD147 inhibited HIV-1 entry as evidenced by the delay in translocation of the HIV-1 core proteins from the membrane and inhibition of viral reverse transcription. Viruses whose replication did not require CyPA (SIV or mutant HIV-1) were resistant to the inhibitory effect of anti-CD147 antibody. These results suggest that HIV-1 entry depends on an interaction between virus-associated CyPA and CD147 on a target cell.