A mathematical model for the hindered diffusion and competitive adsorption of two proteins in an agarose gel has been developed. In a simulation program the model has been used to study the competing and displacement effects on a single bead for lysozyme and bovine serum albumin (BSA) bound to the ligand Cibacron Blue in agarose gel. The model takes into account hindered diffusion described by the Renkin model, competitive Langmuir adsorption kinetics, pore size distribution of the gel, and a shrinking effective pore radius attributed to molecule‐to‐ligand binding. The simulation model can easily explain displacement of BSA or lysozyme dependent on the binding capacity, kinetics, and diffusion. The influence of a bimodal pore size distribution is demonstrated. It also provides insight into the phenomenon of static vs. dynamic binding capacity observed in experimental determinations of the isotherm. © 2004 American Institute of Chemical Engineers AIChE J, 50: 3006–3018, 2004

Nuclear export and translation of intron-containing viral mRNAs are required for HIV-1 gene expression and replication. In this report, we provide evidence to show that DDX3 regulates the translation of HIV-1 mRNAs. We found that knockdown of DDX3 expression effectively inhibited HIV-1 production. Translation of HIV-1 early regulatory proteins, Tat and rev, was impaired in DDX3-depleted cells. All HIV-1 transcripts share a highly structured 5’ untranslated region (UTR) with inhibitory elements on translation of viral mRNAs, yet DDX3 promoted translation of reporter mRNAs containing the HIV-1 5’ UTR, especially with the transactivation response (TAR) hairpin. Interestingly, DDX3 directly interacts with HIV-1 Tat, a well-characterized transcriptional activator bound to the TAR hairpin. HIV-1 Tat is partially targeted to cytoplasmic stress granules upon DDX3 overexpression or cell stress conditions, suggesting a potential role of Tat/DDX3 complex in translation. We further demonstrated that HIV-1 Tat remains associated with translating mRNAs and facilitates translation of mRNAs containing the HIV-1 5’ UTR. Taken together, these findings indicate that DDX3 is recruited to the TAR hairpin by interaction with viral Tat to facilitate HIV-1 mRNA translation.

Background: Only a fraction of cigarette smokers develop lung cancer, suggesting that people differ in their susceptibility to this disease. We investigated whether differences in DNA repair capacity (DRC) for repairing tobacco carcinogen-induced DNA damage are associated with differential susceptibility to lung cancer. Methods: From August 1, 1995, through April 30, 1999, we conducted a hospital-based, casecontrol study of 316 newly diagnosed lung cancer patients and 316 cancer-free control subjects matched on age, sex, and smoking status. DRC was measured in cultured lymphocytes with the use of the host-cell reactivation assay with a reporter gene damaged by a known activated tobacco carcinogen, benzo[a]pyrene diol epoxide. Statistical tests were two-sided. Results: Overall, lower DRC was observed in case patients than in control subjects (P<.001) and was associated with a greater than twofold increased risk of lung cancer.

Epidemiological studies have indicated that reduced DNA repair capacity and increased DNA adduct levels are associated with increased risk of lung cancer. Nucleotide excision repair (NER) is the major pathway in humans for repairing DNA adducts induced by smoking-related carcinogens, such as benzo[a]pyrene diol epoxide. We hypothesized that genetically determined baseline expression level of genes involved in NER is associated with risk of lung cancer. In a pilot case-control study, we measured the relative expression levels of five NER genes [ERCC1, XPB/ERCC3, XPG/ERCC5, CSB/ERCC6 and XPC (ERCC, excision repair cross-complementing; CSB, Cockayne's syndrome complementary group B)] in phytohemagglutinin-stimulated peripheral lymphocytes obtained from 75 lung cancer patients and 95 controls using a newly developed multiplex RT-PCR assay. Cases and controls were matched on age, sex, ethnicity and tobacco use. The expression level of the beta-actin gene was used as an internal control for the relative quantitation. We observed a 12.2 and 12.5% decrease in the baseline expression levels of XPG/ERCC5 and CSB/ERCC6, respectively, in cases compared with controls. These differences were statistically significant (P < 0.01) when the median expression level in the controls was used as the cut-off point, the lung cancer patients were significantly more likely than the controls to have reduced expression levels of XPG/ERCC5 [odds ratio (OR), 2.32; 95% confidence interval (CI), 1.22-4.43] and CSB/ERCC6 (OR, 2.49; 95% CI, 1.28-4.84). There was also a dose-response relationship between reduced expression levels and increased lung cancer risk (trend test: P< 0.01). Our results suggest that individuals whose expression levels of XPG/ERCC5 and CSB/ERCC6 are reduced may be at higher risk of lung cancer.

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