Epidemiology of adult and pediatric Burkitt lymphoma in Canada: sequelae of the HIV epidemic.

Background: Although the pathogenesis and epidemiology of endemic Burkitt lymphoma (bl) have been extensively studied, the epidemiologic landscape of sporadic and immunodeficiency-associated bl in North America remains poorly understood. Methods: We used 3 distinct population-based cancer registries to retrospectively study bl incidence and mortality in Canada. Data for patient sex; age at the time of diagnosis; and reporting province, city, and forward sortation area (fsa, the first three characters of a postal code) were analyzed. Results: During 1992-2010, 1420 patients with bl in Canada were identified (incidence rate: 2.40 cases per million patient-years), of which 71.1% were male patients. Mean age at diagnosis was 55.5 ± 20.8 years. A bimodal incidence by age distribution was seen in both sexes, with pediatric- and adult-onset peaks. An analysis based on fsas identified select communities with statistically higher rates of adult bl. Several of those fsas were located within the 3 major metropolitan areas (Montreal, Vancouver, Toronto) and within self-identified lgbtq communities. The fsas with a higher socioeconomic status score were associated with lower rates of bl. Conclusions: Current results highlight the geographic and historic pattern of bl in Canada. The human immunodeficiency virus remains an important risk factor for adult bl.

Essential role of leucine222 in mediating signal transduction of the human angiotensin II type 1 receptor.

The angiotensin II (Ang II) type I receptor (AT1) is a member of the superfamily of heptahelical, G protein-coupled receptors (GPCRs) characterized by hydrophobic transmembrane domains connected by extra- and intracellular hydrophilic loops. The third intracellular loop (IC3) of many GPCRs is thought to directly interact with G proteins. We examined the molecular environment of the basic sequence KA221L222KK found in the IC3 of the human AT1 (hAT1) receptor by substituting Ala221 for Glu/Gln or Leu222 for Arg/Gln and determined the pharmacological properties of the resulting mutant receptors. Competitive binding experiments with the antagonist [Sar1,Ile8]Ang II revealed that COS-7 or stably expressing CHO cells transfected with either the wild-type or mutant receptors, produced a single population of high affinity binding sites (Kd of 0.5 nM) but variable receptor levels depending on cell type; Bmax approximately 100,000 sites/cell (COS-7), approximately 20,000 sites/cell (CHO). However, in competitive binding experiments using the agonist Ang II, both the wild type and the Ala-->Glu mutant displayed binding affinities of 1 nM, while the Leu-->Arg mutant had a significantly lower affinity (4 nM). When the functionality of the mutant receptors was examined, a lowered production of inositol-1,4,5-trisphosphate was obtained upon stimulation of the Ala-->Glu and Ala-->Gln mutants when compared to the wild-type receptor. However, no significant production of Ins(1,4,5)P3 was detected for the Leu-->Arg and leu-->Gln mutants. Our results suggest that Leu222 in the KALKK sequence of the IC3 of the hAT1 receptor, through not essential for antagonist binding, has an essential role in mediating interactions with G protein and in signal transduction.

Epitope tagging and immunoreactivity of the human angiotensin II type 1 receptor.

Structural analysis of G-protein-coupled receptors has largely been limited to photoaffinity labeling and site-directed mutagenesis. This is primarily due to the difficulty in the production of antibodies against this class of receptors. We were therefore interested in tagging the amino-terminal side of the human angiotensin II (AngII) type 1 receptor (AT1) with the FLAG epitope DYKDDDDK. Competitive binding experiments with [125I][Sar1,Ile8]AngII revealed that stably transfected Chinese hamster ovary (CHO) cells express 37,300 hAT1-FLAG receptors/cell with a high affinity of 0.53 nM, comparable with that of the wild-type hAT1. After photolabeling and solubilization, a significant proportion of hAT1-FLAG specifically immunoprecipitated with anti-FLAG M5 and M2 antibodies. The immunoprecipitated receptor comigrated on SDS-PAGE with photolabeled wild-type hAT1. Immunofluorescence studies by FACS scan analysis revealed that 11.9% of CHO cells expressing hAT1-FLAG receptor significantly increased their fluorescence level as a result of M5 specific reactivity. Western blot analysis failed to show any specific interaction between M5 antibody and denatured hAT1-FLAG receptor. These results demonstrate the efficiency of the epitope tagging approach for specific immunoreactivity against AT1 receptor. Appropriate refinements of this approach could improve the level of immunoreactivity.