MOLECULAR MECHANISMS REGULATING COPPER BALANCE IN HUMAN CELLS

Precise copper balance is essential for normal growth, differentiation, and function of human cells. Loss of copper homeostasis is associated with heart hypertrophy, liver failure, neuronal de-myelination and other pathologies. The copper-transporting ATPases ATP7A and ATP7B maintain cellular copper homeostasis. In response to copper elevation, they traffic from the trans-Golgi network (TGN) to vesicles where they sequester excess copper for further export. The mechanisms regulating activity and trafficking of ATP7A/7B are not well understood. Our studies focused on determining the role of kinase-mediated phosphorylation in copper induced trafficking of ATP7B, and identifying and characterizing novel regulators of ATP7A. We have shown that Ser-340/341 region of ATP7B plays an important role in interactions between the N-terminus and the nucleotide-binding domain and that mutations in these residues result in vesicular localization of the protein independent of the intracellular copper levels. We have determined that structural changes that alter the inter-domain interactions initiate exit of ATP7B from the TGN and that the role of copper-induced kinase-mediated hyperphosphorylation might be to maintain an open interface between the domains of ATP7B. In a separate study, seven proteins were identified, which upon knockdown result in increased intracellular copper levels. We performed an initial characterization of the knock-downs and obtained intriguing results indicating that these proteins regulate ATP7A protein levels, post-translational modifications, and copper-dependent trafficking. None of these proteins has been previously linked to copper homeostasis. Our studies have pointed to novel kinase inhibitors (IBTK and CAMK2N2), a novel relationship between copper transport and organic anion/bile acid transport (ABCC3), a likely mechanism of ATP7A regulation through changes in glycosylation levels, and identified an adaptor protein (ankyrin repeat domain protein 9 (ANKRD9)) that might be involved in stabilizing the Golgi structure. ANKRD9 depletion led to increase of intracellular copper levels, Golgi fragmentation, and defects in protein glycosylation. Additionally, the mRNA and protein levels of the human copper uptake protein Ctr1 were increased significantly despite high copper levels in the cells. We are facing challenging questions related to Golgi fragmentation and copper homeostasis. Further characterization of the above-mentioned novel regulatory modes will greatly expand our understanding of copper metabolism in human cells

Genome-wide RNAi ionomics screen reveals new genes and regulation of human trace element metabolism

Trace elements are essential for human metabolism and dysregulation of their homoeostasis is associated with numerous disorders. Here we characterize mechanisms that regulate trace elements in human cells by designing and performing a genome-wide high-throughput siRNA/ionomics screen, and examining top hits in cellular and biochemical assays. The screen reveals high stability of the ionomes, especially the zinc ionome, and yields known regulators and novel candidates. We further uncover fundamental differences in the regulation of different trace elements. Specifically, selenium levels are controlled through the selenocysteine machinery and expression of abundant selenoproteins; copper balance is affected by lipid metabolism and requires machinery involved in protein trafficking and post-translational modifications; and the iron levels are influenced by iron import and expression of the iron/haeme-containing enzymes. Our approach can be applied to a variety of disease models and/or nutritional conditions, and the generated data set opens new directions for studies of human trace element metabolism

Genome-Wide RNAi Ionomics Screen Reveals New Genes and Regulation of Human Trace Element Metabolism

Trace elements are essential for human metabolism and dysregulation of their homeostasis is associated with numerous disorders. Here we characterize mechanisms that regulate trace elements in human cells by designing and performing a genome-wide high-throughput siRNA/ionomics screen, and examining top hits in cellular and biochemical assays. The screen reveals high stability of the ionomes, especially the zinc ionome, and yields known regulators and novel candidates. We further uncover fundamental differences in the regulation of different trace elements. Specifically, selenium levels are controlled through the selenocysteine machinery and expression of abundant selenoproteins; copper balance is affected by lipid metabolism and requires machinery involved in protein trafficking and posttranslational modifications; and the iron levels are influenced by iron import and expression of the iron/heme-containing enzymes. Our approach can be applied to a variety of disease models and/or nutritional conditions, and the generated dataset opens new directions for studies of human trace element metabolism

DataSheet1_Heterogeneous nuclear ribonucleoprotein hnRNPA2/B1 regulates the abundance of the copper-transporter ATP7A in an isoform-dependent manner.PDF

Copper (Cu) is an essential micronutrient with a critical role in mammalian growth and development. Imbalance of Cu causes severe diseases in humans; therefore, cellular Cu levels are tightly regulated. Major Cu-transport proteins and their cellular behavior have been characterized in detail, whereas their regulation at the mRNA level and associated factors are not well-understood. We show that the heterogeneous nuclear ribonucleoprotein hnRNPA2/B1 regulates Cu homeostasis by modulating the abundance of Cu(I)-transporter ATP7A. Downregulation of hnRNPA2/B1 in HeLa cells increases the ATP7A mRNA and protein levels and significantly decreases cellular Cu; this regulation involves the 3′ UTR of ATP7A transcript. Downregulation of B1 and B1b isoforms of hnRNPA2/B1 is sufficient to elevate ATP7A, whereas overexpression of either hnRNPA2 or hnRNPB1 isoforms decreases the ATP7A mRNA levels. Concurrent decrease in hnRNPA2/B1, increase in ATP7A, and a decrease in Cu levels was observed in neuroblastoma SH-SY5Y cells during retinoic acid-induced differentiation; this effect was reversed by overexpression of B1/B1b isoforms. We conclude that hnRNPA2/B1 is a new isoform-specific negative regulator of ATP7A abundance.</p

Promoter methylation of ADAMTS1 and BNC1 as potential biomarkers for early detection of pancreatic cancer in blood

Abstract Background Despite improvements in cancer management, most pancreatic cancers are still diagnosed at an advanced stage. We have recently identified promoter DNA methylation of the genes ADAMTS1 and BNC1 as potential blood biomarkers of pancreas cancer. In this study, we validate this biomarker panel in peripheral cell-free tumor DNA of patients with pancreatic cancer. Results Sensitivity and specificity for each gene are as follows: ADAMTS1 87.2% and 95.8% (AUC = 0.91; 95% CI 0.71–0.86) and BNC1 64.1% and 93.7% (AUC = 0.79; 95% CI 0.63–0.78). When using methylation of either gene as a combination panel, sensitivity increases to 97.3% and specificity to 91.6% (AUC = 0.95; 95% CI 0.77–0.90). Adding pre-operative CA 19-9 values to the combined two-gene methylation panel did not improve sensitivity. Methylation of ADAMTS1 was found to be positive in 87.5% (7/8) of stage I, 77.8% (7/9) of stage IIA, and 90% (18/20) of stage IIB disease. Similarly, BNC1 was positive in 62.5% (5/8) of stage I patients, 55.6% (5/9) of stage IIA, and 65% (13/20) of patients with stage IIB disease. The two-gene panel (ADAMTS1 and/or BNC1) was positive in 100% (8/8) of stage I, 88.9% (8/9) of stage IIA, and 100% (20/20) of stage IIB disease. The sensitivity and specificity of the two-gene panel for localized pancreatic cancer (stages I and II), where the cancer is eligible for surgical resection with curative potential, was 94.8% and 91.6% respectively. Additionally, the two-gene panel exhibited an AUC of 0.95 (95% CI 0.90–0.98) compared to 57.1% for CA 19-9 alone. Conclusion The methylation status of ADAMTS1 and BNC1 in cfDNA shows promise for detecting pancreatic cancer during the early stages when curative resection of the tumor is still possible. This minimally invasive blood-based biomarker panel could be used as a promising tool for diagnosis and screening in a select subset of high-risk populations

Analysis of Outcomes in Ischemic vs Nonischemic Cardiomyopathy in Patients With Atrial Fibrillation A Report From the GARFIELD-AF Registry

IMPORTANCE Congestive heart failure (CHF) is commonly associated with nonvalvular atrial fibrillation (AF), and their combination may affect treatment strategies and outcomes