Gregory Judson

Evolution Reversed : The Ability To Bind Iron Restored to the N-Lobe of the Murine Inhibitor of Carbonic Anhydrase by Strategic Mutagenesis

The murine inhibitor of carbonic anhydrase (mICA) is a member of the superfamily related to the bilobal iron transport protein transferrin (TF), which binds a ferric ion within a cleft in each lobe. Although the gene encoding ICA in humans is classified as a pseudogene, an apparently functional ICA gene has been annotated in mice, rats, cows, pigs, and dogs. All ICAs lack one (or more) of the amino acid ligands in each lobe essential for high-affinity coordination of iron and the requisite synergistic anion, carbonate. The reason why ICA family members have lost the ability to bind iron is potentially related to acquiring a new function(s), one of which is inhibition of certain carbonic anhydrase (CA) isoforms. A recombinant mutant of the mICA (W124R/S188Y) was created with the goal of restoring the ligands required for both anion (Arg124) and iron (Tyr188) binding in the N-lobe. Absorption and fluorescence spectra definitively show that the mutant binds ferric iron in the N-lobe. Electrospray ionization mass spectrometry confirms the presence of both ferric iron and carbonate. At the putative endosomal pH of 5.6, iron is released by two slow processes indicative of high-affinity coordination. Induction of specific iron binding implies that (1) the structure of mICA resembles those of other TF family members and (2) the N-lobe can adopt a conformation in which the cleft closes when iron binds. Because the conformational change in the N-lobe indicated by metal binding does not impact the inhibitory activity of mICA, inhibition of CA was tentatively assigned to the C-lobe. Proof of this assignment is provided by limited trypsin proteolysis of porcine ICA.

Circulating antioxidant levels and risk of prostate cancer by TMPRSS2:ERG

Few studies have considered etiological differences across molecular subtypes of prostate cancer, despite potential to improve opportunities for precision prevention of a disease for which modifiable risk factors have remained elusive. Factors that lead to DNA double‐strand breaks, such as oxidative stress, may promote the formation of the TMPRSS2:ERG gene fusion in prostate cancer. We tested the hypothesis that increasing levels of pre‐diagnostic circulating antioxidants, which may reduce oxidative stress, are associated with lower risk of developing TMPRSS2:ERG positive prostate cancer.

The Association of Five-Year Changes in the Levels of N-Terminal Fragment of the Prohormone Brain-Type Natriuretic Peptide (NT-proBNP) with Subsequent Heart Failure and Death in Patients with Stable Coronary Artery Disease: The Heart and Soul Study

Background: The N-terminal fragment of the prohormone brain-type natriuretic peptide (NT-proBNP) is a powerful predictor of adverse outcomes in patients with coronary artery disease (CAD). However, little is known regarding the prognostic significance of longitudinal changes in NT-proBNP levels. Methods: We evaluated the ability of 5-year changes in NT-proBNP levels to predict subsequent heart failure (HF) hospitalization or cardiovascular (CV) death in 635 participants with stable CAD enrolled in the Heart and Soul Study. Results: The median (IQR) 5-year change in NT-proBNP was 50 pg/mL (-5 to +222). During an average of 4.0 ± 1.4 years follow-up (i.e., 9 years from the baseline measurement), there were 67 events. Participants with 5-year changes in the highest quartile (≥ 223 pg/mL increase in NT-proBNP) had an almost 4-fold greater risk of subsequent HF or CV death than those in the lowest quartile of ≤-5 pg/mL (HR 3.8; 95% CI 2.0-7.3; p < 0.001). This association remained strong after adjustment for demographic variables, comorbidities, left ventricular mass index, systolic and diastolic function, and baseline and follow-up NT-proBNP levels (HR 3.9; 95% CI 1.1-13.4; p = 0.01). Conclusion: Changes in NT-proBNP levels at 5 years predict subsequent HF or CV death in patients with stable CAD, independent of other prognostic markers, including baseline and follow-up NT-proBNP levels. A stable NT-proBNP level predicts a low risk of subsequent events.

Longitudinal Blood Pressure Changes and Kidney Function Decline in Persons Without Chronic Kidney Disease: Findings From the MESA Study

BACKGROUND While changes in blood pressure (BP) are independently associated with cardiovascular events, less is known about the association between changes in BP and subsequent changes in renal function in adults with an estimated glomerular filtration rate (eGFR) of >60 ml/min/1.73 m2. METHODS The present study included 3,920 participants in the Multi-Ethnic Study of Atherosclerosis (MESA) study who had ≥2 BP measurements during the first 5 years of MESA and had eGFR measurements at both year 5 and 10. Change in BP was estimated as the annualized slope of BP between year 0 and 5 based on linear mixed models (mean number of measurements = 4.0). Participants were then grouped into 1 of 3 categories based on the distribution of systolic BP (SBP), diastolic BP (DBP), and pulse pressure (PP) change (top 20%, middle 21-79%, bottom 20%). We calculated eGFR from cystatin C (ml/min/1.73 m2), estimated annual change in eGFR (ml/min/1.73 m2/year), and defined rapid kidney function decline as a >30% decrease in eGFR from year 5 to 10. We used multivariable logistic regression adjusting for year 0 demographic and clinical characteristics, including eGFR and BP, to determine associations of BP change with rapid kidney function decline. RESULTS Median age was 59 [interquartile range (IQR): 52, 67] and median eGFR at year 0 was 95.5 (IQR: 81.7, 105.9) ml/min/1.73 m2. Median SBP at year 0 was 111, 121, and 147 mm Hg for increasing, stable, and decreasing SBP change, respectively. Increasing SBP and widening PP change were each associated with higher odds of rapid kidney function decline compared with stable SBP and PP groups, respectively [odds ratio, OR 1.7 (95% confidence interval, CI 1.3, 2.4) for SBP; OR 1.4 (95% CI 1.1, 1.9) for PP]. Decreasing SBP was associated with rapid kidney function decline after adjusting for all covariates except for year 0 BP [OR 1.4 (95% CI 1.0, 1.8)], but this association was no longer statistically significant after adjustment for year 0 BP. There were no significant associations between DBP change and rapid decline in the fully adjusted models. Similar findings were seen with annual change in eGFR. CONCLUSIONS Increasing SBP and widening PP over time were associated with greater risk for accelerated kidney function decline even at BP levels below established hypertension thresholds.

Expression of IGF/insulin receptor in prostate cancer tissue and progression to lethal disease

Circulating insulin-like growth factor-1 (IGF-1) is consistently associated with prostate cancer risk. IGF-1 binds to IGF-1 receptor (IGF1R) and insulin receptor (IR), activating cancer hallmark pathways. Experimental evidence suggests that TMPRSS2:ERG may interact with IGF/insulin signaling to influence progression. We investigated IGF1R and IR expression and its association with lethal prostate cancer among 769 men. Protein expression of IGF1R, IR and ERG (i.e. a surrogate of ERG fusion genes) were assayed by immunohistochemistry. Cox models estimated hazard ratios (HR) and 95% confidence intervals (CI) adjusted for clinical characteristics. Among patients, 29% had strong tumor IGF1R expression and 10% had strong IR expression. During a mean follow-up of 13.2 years through 2012, 80 men (11%) developed lethal disease. Tumors with strong IGF1R or IR expression showed increased cell proliferation, decreased apoptosis and a higher prevalence of ERG. In multivariable models, strong IGF1R was associated with a borderline increased risk of lethal prostate cancer (HR 1.7; 95% CI 0.9-3.1). The association appeared greater in ERG-positive tumors (HR 2.8; 95% CI 0.9-8.4) than in ERG-negative tumors (HR 1.3; 95% CI 0.6-3.0, p-heterogeneity 0.08). There was no association between IR and lethal prostate cancer (HR 0.8; 95% CI 0.4-1.9). These results suggest that tumor IGF1R expression may play a role in prostate cancer progression to a lethal phenotype and that ERG-positive tumors may be more sensitive to IGF signaling. These data may improve our understanding of IGF signaling in prostate cancer and suggest therapeutic options for disease subtypes.

Abstract A76: Nuclear androgen receptor expression is linked to two SNPs in prostate tumor tissue

A76 Introduction The androgen receptor (AR) plays a critical role in the pathogenesis of prostate cancer (PCa), and down-regulated expression in prostatic epithelium is linked to decreased differentiation and increased proliferation of tumors cells. Genetic variation in the AR gene, located on the X-chromosome, has previously been linked with PCa risk. Whether the effect of AR variants on cancer risk is explained through regulation of prostate AR expression is not well understood. This study examines whether six SNPs located in AR, as well as the CAG repeat, are related to expression of cytoplasmic and nuclear AR in prostate tumor tissue. Methods We genotyped 6 SNPs with minor allele frequencies greater than 5% located in a 310 kb region overlapping the AR gene and the CAG repeat in 270 PCa cases diagnosed among participants in the Health Professionals Follow-up Study and the Physicians Health Study. AR expression was assessed by immunohistochemistry in tumor tissue obtained from archival prostatectomy blocks. To determine if expression levels varied by genotype, we conducted an ANOVA analysis with AR expression modeled as the dependent variable. Results We found two SNPs that were significantly associated with AR nuclear expression. Men who carried the rs1337082 variant allele (18.2% of men) had reduced AR nuclear expression (p= 0.03) compared to wild-type in the non-adjusted analysis. In addition, men with the rs6152 variant allele (13.6% of men) also had decreased AR expression (p= 0.04) when adjusted for age at diagnosis. When adjusting for age, the association between rs1337082 and AR expression also became stronger (p= 0.02). The linkage disequilibrium R2 value was 0.63. Approximately 2% of the variation in AR expression can be explained by these two SNPs. The four other SNPs examined were weakly but not significantly associated with AR expression. CAG repeat length was not correlated with expression of AR. Discussion rs1337082 (approximately 40 kb downstream of AR) is an A/G polymorphism while rs6152 (exon 1) is a silent G/A polymorphism. The link between nuclear AR expression and these two non-coding SNPs provides evidence of novel genetic factors that may influence AR expression. Citation Information: Cancer Prev Res 2008;1(7 Suppl):A76.