ABSTRACT

A single cycle of rituximab is an effective treatment for pemphigus. Because of its potentially severe side effects, its use should be limited to the most severe types of the disease. (ClinicalTrials.gov number, NCT00213512 [ClinicalTrials.gov].).

Pemphigus is a severe blistering condition of the skin and mucosa caused by autoantibodies directed against desmogleins, which are a type of keratinocyte adhesion protein. B cell depletion by rituximab has short-term efficacy against pemphigus. We aimed to assess the long-term course of pemphigus patients after B cell depletion and to understand the immunological mechanisms that mediate long-lasting remissions. We evaluated the clinical course of 22 pemphigus patients treated with rituximab after a 79-month median follow-up and compared the anti-desmoglein B cell response and B and T lymphocyte subpopulations and repertoire between patients who achieved complete remission (CR) and those who had incomplete remission (IR). Thirteen patients (59%) experienced CR during the study, including 10 patients off treatment and 3 patients with prednisone doses <10 mg/day; 9 patients had IR. A marked increase was observed in the ratio of CD19(+)CD27(-) naïve B cells to CD19(+)CD27(+) memory B cells. Indeed, patients in CR had a fourfold higher number of transitional B cells and interleukin-10-secreting regulatory B cells than those in IR. Furthermore, CR was associated with modification of the initial B cell repertoire and the disappearance of desmoglein-specific circulating immunoglobulin G-positive (IgG(+)) B lymphocytes, whereas a skewed B cell repertoire was observed in patients in IR. Thus, a blockage of B cell maturation, a prolonged repopulation with naïve B cells, and a delayed reappearance of memory B cells, which resulted in the disappearance of circulating desmoglein-specific IgG(+) B lymphocytes, contribute to the long-lasting effectiveness of rituximab for treating pemphigus.

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Chronic hepatitis C virus (HCV) infection frequently leads to liver cancer. To determine the viral factor(s)potentially involved in viral persistence, we focused our work on NS2, a viral protein of unknown function. To assign a role for NS2, we searched for cellular proteins that interact with NS2. Performing a two-hybrid screen on a human liver cDNA library, we found that NS2 interacted with the liver-specific pro-apoptotic CIDE-B protein. Binding specificity of NS2 for CIDE-B was confirmed by cell-free assays associated with colocalization studies and coprecipitation experiments on human endogenous CIDE-B. CIDE-B, a member of the novel CIDE family of apoptosis-inducing factors, has been reported to show strong cell death-inducing activity in its C-terminal domain. We show that this CIDE-B killing domain is involved in the NS2 interaction. NS2 binding was sufficient to inhibit CIDE-B-induced apoptosis because an NS2 deletion mutant unable to interact with CIDE-B in vitro lost its capacity to interfere with CIDE-B cell death activity. Although it has been reported that CIDE-Binduced apoptosis is characterized by mitochondrial localization, the precise apoptotic mechanism remained unknown. Here, we show that CIDE-B induced cell death in a caspase-dependent manner through cytochrome c release from mitochondria. Furthermore, we found that NS2 counteracted the cytochrome c release induced by CIDE-B. In vivo, the CIDE-B protein level was extremely low in adenovirus-infected transgenic mice expressing the HCV polyprotein compared with that in wild-type mice. We suggest that NS2 interferes with the CIDE-B-induced death pathway and participates in HCV strategies to subvert host cell defense.

Hepatitis C virus (HCV) nonstructural 2 (NS2) protein is a hydrophobic transmembrane protein, described to be involved in different functions, such as apoptosis inhibition and gene transcription modulation. We investigated here NS2 protein turnover and found that NS2 was rapidly degraded by the proteasome in different cell lines, as in primary human hepatocytes. Since posttranslational modifications can influence protein turnover, we looked for potential phosphoacceptor sites in NS2. Computational sequence analysis in combination with screening of NS2 point mutants revealed that serine residue 168 was critical for degradation. In the quest of a protein kinase for NS2, we identified by sequence analysis that the serine residue 168 was part of a consensus casein kinase 2 (CK2) recognition site (S/TXXE). This motif was highly conserved since it could be found in the NS2 primary consensus sequences from all HCV genotypes. To verify whether CK2 is involved in NS2 phosphorylation, we showed by an in vitro kinase assay that CK2 phosphorylated NS2, as far as this CK2 motif was conserved. Interestingly, NS2 became resistant to protein degradation when the CK2 motif was modified by a single point mutation. Furthermore, inhibition of CK2 activity by curcumin decreased NS2 phosphorylation in vitro and stabilized NS2 expression in HepG2 cells. Finally, we showed in Huh-7.5 replicon cells that NS2, expressed in the context of the HCV polyprotein, was also sensitive to both proteasome-mediated degradation and CK2 inhibitor treatment. We suggest that NS2 is a short-lived protein whose degradation by the proteasome is regulated in a phosphorylation-dependent manner through the protein kinase CK2.

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After completing this course, the reader will be able to:1. Describe the profile of severe toxicities in patients treated with sorafenib.2. Summarize the pharmacokinetics of sorafenib-induced toxicities.3. Identify predictive factors for early and delayed toxicities in patients treated with sorafenib.This article is available for continuing medical education credit at CME.TheOncologist.com. CME CME ABSTRACT Background. Sorafenib displays major interpatient pharmacokinetic variability. It is unknown whether the pharmacokinetics of sorafenib influence its toxicity.Methods. We analyzed the severity and kinetics of sorafenib-induced toxicities in unselected consecutive patients with cancer, as well as their relationship with biolog-