Svetlana Lutsenko Laboratory, Johns Hopkins University

Research in the Svetlana Lutsenko Laboratory

Numerous cellular processes are controlled by proteins that rely on small metal cofactors to perform their essential roles in cell physiology. Fine balance of metals such as copper is essential for brain maturation and development, respiration, antimicrobial defense, heart and blood vessels formation. In humans, genetic disruptions of copper transport and distribution result in severe and often lethal disorders. We are interested in how copper is transported within and between the cells, how biosynthesis of copper-dependent enzymes is controlled and how copper metabolism interact with other processes such as lipid homeostasis, RNA biogenesis, and hormonal signaling in norm and disease.

Mechanism of copper transport in human cells

Copper is a redox active metal, which can readily donate and accept electrons. Copper-containing enzymes utilize this property to perform reactions necessary for utilization of oxygen, detoxification of radicals, formation of the tyrosyl quinone cofactor and other biochemical processes. For these reactions to take place in a cell, copper has to be transported to the appropriate compartments (cytosol, secretory pathway, mitochondria) in which the copper-requiring enzymes are located. This job is done by the copper transporters and small cytosolic proteins, copper chaperones, which were named so for their ability to bind copper and thus guard cells from copper reactivity, while delivering it to transporters and other acceptor proteins. In the laboratory, we study how the copper chaperone Atox1 transfers copper to the transporters ATP7A and ATP7B located in the trans-Golgi network and in the vesicles of the endocytic pathway. ATP7A and ATP7B are complex multi-domain proteins with at least 8 distinct copper binding sites. We study how copper is transferred to these metal-binding sites, how various domains in ATP7A and ATP7B communicate with each other to facilitate ion translocation across membranes and how copper is then incorporated into the acceptor enzymes within the secretory pathway.

Further reading:

"Schushan M, Bhattacharjee A, Ben-Tal N, Lutsenko S. (2012) A structural model of the copper ATPase ATP7B to facilitate analysis of Wilson disease-causing mutations and studies of the transport mechanism." Metallomics. 4(7):669-78. PMID: 22692182

Barry AN, Otoikhian A, Bhatt S, Shinde U, Tsivkovskii R, Blackburn NJ, Lutsenko S. (2011) The lumenal loop Met672-Pro707 of copper-transporting ATPase ATP7A binds metals and facilitates copper release from the intramembrane sites.J Biol Chem. 286(30):26585-94. PMID: 21646353

LeShane ES, Shinde U, Walker JM, Barry AN, Blackburn NJ, Ralle M, Lutsenko S.(2010) Interactions between copper-binding sites determine the redox status and conformation of the regulatory N-terminal domain of ATP7B. J Biol Chem.285(9):6327-36. PMID: 20032459

Barry AN, Shinde U, Lutsenko S. (2010) Structural organization of human Cu-transporting ATPases: learning from building blocks.J Biol Inorg Chem.15(1):47-59. PMID: 19851794

Gupta A, Lutsenko S. (2009) Human copper transporters: mechanism, role in human diseases and therapeutic potential. Future Med Chem. 1(6):1125-42. PMID: 20454597

The cross-talk between lipid and copper metabolisms mediated via regulation of RNA processing

The cross-talk between lipid and copper metabolisms mediated via regulation of RNA processing. Using Atp7b-/- mice, genomics and proteomics approaches, we discovered that lipid metabolism is especially sensitive to copper elevation in the liver. We have also found that this sensitivity can be linked to specific redistribution of copper to the nucleus and changes in the cellular RNA splicing machinery. Our current goal is to understand the roles of several RNA processing proteins in copper metabolism and, reciprocally, to dissect the mechanism through which copper triggers changes in the RNA splicing machinery.

Further reading:

Burkhead JL, Gray LW, Lutsenko S. (2011) Systems biology approach to Wilson's disease. Biometals. 24(3):455-66.

Burkhead JL, Ralle M, Wilmarth P, David L, Lutsenko S. (2011) Elevated copper remodels hepatic RNA processing machinery in the mouse model of Wilson's disease. J Mol Biol. 406(1):44-58.

Ralle M, Huster D, Vogt S, Schirrmeister W, Burkhead JL, Capps TR, Gray L, Lai B, Maryon E, Lutsenko S. (2010) Wilson disease at a single cell level: intracellular copper trafficking activates compartment-specific responses in hepatocytes.J Biol Chem. 285(40):30875-83

Regulation of copper transport through hormonal signaling, intracellular trafficking, and kinase-mediated phosphorylation

Human copper metabolism is tightly coupled to other metabolic processes, as well as various signaling events. Changes in the environment inside and outside a cell require redistribution of copper between cellular compartments or export of excess copper from cells. Human copper transporting ATPases ATP7A and ATP7B play the key role in these processes. In response to various signals (such as changes in copper concentration, hormonal signaling, or inflammation), these transporters move from their basal location in trans-Golgi network to vesicles in order to regulate copper delivery to metalloenzymes as well as facilitate copper efflux. We discovered that the intracellular trafficking of ATP7B was coupled to changes in phosphorylation of this transporter by kinases, and we are now investigating the role of phosphorylation in targeting of ATP7B to distinct cellular compartments. We have also discovered a copper-independent trafficking of ATP7A in adipocytes, and we are interested in the role of this process in physiology of adipose tissue. Recently, using siRNA screening strategy, we identified a set of new regulators for copper-transporting ATPase ATP7A. By characterizing these proteins we hope to build a comprehensive regulatory network for ATP7A.

Further reading:

Hasan NM, Lutsenko S. (2012) Regulation of copper transporters in human cells. Curr Top Membr. 69:137-61

Hasan NM, Gupta A, Polishchuk E, Yu CH, Polishchuk R, Dmitriev OY, Lutsenko S. (2012) Molecular Events Initiating Exit of a Copper-transporting ATPase ATP7B from the Trans-Golgi Network. J Biol Chem. 287(43):36041-50

Barnes N, Bartee MY, Braiterman L, Gupta A, Ustiyan V, Zuzel V, Kaplan JH, Hubbard AL, Lutsenko S. (2009) Cell-specific trafficking suggests a new role for renal ATP7B in the intracellular copper storage. Traffic 10(6):767-79.

Metallochaperone Atox1, copper transfer mechanism

Another important direction in the laboratory is identification and characterization of proteins that regulate WNDP function and membrane targeting. In a cell, the Wilson's disease protein receives copper from a small cytosolic protein, copper-chaperone Atox1. Our current goal is to understand how the chaperone and copper-transporting ATPase find each other in a cell, how copper is transferred from the chaperone to the Wilson's disease protein, and what are the specific molecular consequences of copper transfer.

Understanding Wilson’s disease pathology

Wilson's disease is caused by mutations in copper-transporting ATPase ATP7B. Elevated copper gradually induces a large spectrum of severe abnormalities, including liver fibrosis, neuronal degeneration, and behavioral changes. At present, the molecular events that accompany copper accumulation in tissues are poorly understood. The goal of our studies is to dissect the biochemical basis of pathological changes associated with abnormal accumulation of copper in human cells. To understand these events we are currently identifying the major targets of inborn copper toxicity using the recently developed ATP7B knock-out mouse (an animal model for Wilson's disease (Buiakova et al., 1999) [PDF]), oligonucleotide microarray technology and real-time PCR.

Copper homeostasis in the brain (Coming soon)

Copper binds specifically to a number of proteins with important functions in the brain, including enzymes involved in neurotransmitter biosynthesis, prion protein, and amyloid precursor protein. Defects in copper transport in the brain result in neurological abnormalities and neurodegeneration. To understand how levels of copper are regulated in the brain we study distribution of human copper transporters using fluorescent in situ hybridization with single cell resolution.

Lutsenko Lab
Department of Physiology
Johns Hopkins University
725 N. Wolfe Street
203 Hunterian
Baltimore, MD 21205
(410) 614-4661 (tel)
(410) 955-0461 (fax)