CYP2B6 genotype is a strong predictor of systemic exposure to efavirenz in HIV-infected Zimbabweans.

OBJECTIVE: Efavirenz, an antiretroviral medicine, is extensively metabolized by cytochrome P450 2B6 (CYP2B6), UDP-glucuronosyltransferase 2B7 (UGT2B7), and CYP2A6. In this study, we investigated the association of single nucleotide polymorphisms (SNPs) in these genes with plasma efavirenz levels in Zimbabwean human immunodeficiency virus (HIV)-positive patients treated with efavirenz. METHODS: The exon regions of the CYP2B6, CYP2A6, and UGT2B7 genes were re-sequenced in 49 HIV-infected Zimbabwean patients treated with a combination therapy including efavirenz. Associations of SNPs in these three genes with efavirenz plasma concentrations 11-16 h after the administration of treatment were evaluated. RESULTS: Eight patients carrying CYP2B6*6/*18 showed the highest plasma efavirenz levels, with a fourfold higher concentration than patients who carried CYP2B6*1/*1. Patients with CYP2B6*6/*6 also showed higher efavirenz plasma concentrations than those with CYP2B6*1/*1. Among the 17 and 12 SNPs identified in CYP2A6 and UGT2B7, respectively, no SNP showed a significant association with the plasma efavirenz concentration. CONCLUSION: Although based on only a limited number of subjects, our results suggest that the CYP2B6*6 and CYP2B6*18 alleles should affect hepatic metabolic activity and elevate the systemic circulation level of efavirenz, which may lead to toxicity in Zimbabwean HIV patients.

S-glycoprotein-like protein regulates defense responses in Nicotiana plants against Ralstonia solanacearum.

RsRGA4 (for Ralstonia solanacearum-responsive gene A4) encodes a polypeptide similar to S-locus glycoprotein (SGP) from Brassica rapa and SGP-like proteins from Ipomoea trifida and Medicago truncatula. Therefore, we designated RsRGA4 as NtSGLP (for Nicotiana tabacum SGP-like protein) and NbSGLP (its Nicotiana benthamiana ortholog). NbSGLP is expressed in root, leaf, petal, gynoecium, and stamen. Expression of NbSGLP was strongly induced by inoculation with an avirulent strain of R. solanacearum (Rs8107) and slightly enhanced by inoculation with virulent R. solanacearum (RsOE1-1). Expression of NbSGLP was induced by inoculation with an hrpY-deficient mutant of RsOE1-1 and Rs8107. Expression was also induced by aminocyclopropane carboxylic acid and salicylic acid. Virus-induced gene silencing of NbSGLP enhanced the growth of Rs8107. Growth of RsOE1-1 and appearance of wilt symptoms were also accelerated in silenced plants. Expression of PR-1a and EREBP was reduced, and markers for basal defense, such as callose deposition and reduced vascular flow, were compromised in NbSGLP-silenced plants. Moreover, growth of Pseudomonas cichorii, Pseudomonas syringae pv tabaci, and P. syringae pv mellea was also enhanced in the silenced plants. On the other hand, silencing of NbSGLP did not interfere with the appearance of the hypersensitive response. NbSGLP was secreted in a signal peptide-dependent manner. Agrobacterium tumefaciens-mediated expression of NbSGLP induced PR-1a and EREBP expression, callose deposition, and reduced vascular flow. NbSGLP-induced callose deposition and reduced vascular flow were not observed in salicylic acid-deficient N. benthamiana NahG plants. Taken together, SGLP might have a role in the induction of basal defense in Nicotiana plants.

Induction of a small heat shock protein and its functional roles in Nicotiana plants in the defense response against Ralstonia solanacearum.

In tobacco (Nicotiana tabacum), Ralstonia solanacearum OE1-1 (RsOE1-1) is pathogenic, whereas R. solanacearum 8107 (Rs8107) is nonpathogenic and induces the hypersensitive response (HR). To elucidate the molecular mechanisms of plant-R. solanacearum interactions, we used differential display to isolate a cDNA fragment, A6, regulated in tobacco by inoculation with RsOE1-1. The deduced amino acid sequence predicted from full-length A6-cDNA showed similarity to small heat shock proteins from Arabidopsis (Arabidopsis thaliana; hypothetical protein), Medicago truncatula, and Cucumis melo; we therefore designated A6 to correspond to Ntshsp17 (for tobacco small heat shock protein 17). Recombinant Ntshsp17 overproduced in Escherichia coli exhibited molecular chaperone function. Expression of Ntshsp17 was increased in tobacco leaves inoculated with both RsOE1-1 and Rs8107. Expression was induced by heat treatment and by treatment with aminocyclopropane carboxylic acid, hydrogen peroxide, methyl jasmonate, and salicylic acid. Ntshsp17 expression was induced by inoculation with a HR and pathogenicity gene mutant of Rs8107 that does not induce the HR, but not by Agrobacterium-mediated transient expression of INF1, an HR elicitor. In Nbshsp17-silenced plants (an Ntshsp17 ortholog in Nicotiana benthamiana), expression of ETHYLENE-RESPONSE ELEMENT-BINDING PROTEIN, PATHOGENESIS-RELATED1a (PR1a), and PR4 genes was compromised, but expression of ELONGATION FACTOR1alpha was scarcely affected. Appearance of the HR was not affected in the silenced plants. In the silenced plants, growth of Rs8107 was accelerated. Bacterial growth and wilt symptoms elicited by RsOE1-1 were also accelerated in the silenced plants. These results indicate that this small heat shock protein might have a role in HR-independent defenses in Nicotiana plants.