Plutonium interactions with cells in culture

Tatjana Paunesku, Baikuntha Aryal, Chuan He, Drew Gorman-Lewis, Stefan Vog, Barry Lai, Lynda Soderholm, Mark Jensen, and Gayle Woloschak

Department of Radiation Oncology, Northwestern University, Chicago, IL USADepartment of Chemistry, University of Chicago, Chicago, IL, USA

Chemical Science and Engineering Division, Argonne National Laboratory, Argonne, IL USAX-ray Sciences Division, Advanced Photon Source, Argonne National Laboratory, Argonne,

IL USA

The First International Conference on Radiation and Dosimetry in Various Fields of Research (RAD 2012), Niš, Serbia, April 25-27, 2012.

Biological effects of plutonium (Pu) exposure

•Regardless of the entry route, Pu deposition in the organism can last for decades.

•Pu effects on cells and organisms depend not only on alpha particle emission, but also on behavior of Pu as a heavy metal.

•Biochemical interactions of Pu are of great interest for investigation and interpretation of Pu effects on living cells and organisms.

Interaction of Pu with cells in culture

Short term interaction of Pu with cells was studied in vitro.

1. Cellular entry of Pu, and differentiation of different chemical states of Pu was investigated using synchrotron X-rays (Gorman-Lewis et al., 2011; Jensen et al., 2011; Jensen et al., 2012)

2.Transferrin bound Pu is taken up by the cells in the form of tetravalent Pu. (Jensen et al 2011)

3. Intracellular Pu(IV) interacting proteins were studied by metaloproteomics approaches . (Aryal et al., 2011)

(1) STUDY OF PLUTONIUM-CELLS INTERACTIONS USING X-RAY MICROSCOPY AND SPECTROSCOPY

X-ray microscopy and spectroscopy for Pu detection and chemical speciation

• X-ray fluorescence microscopy (XFM) with hard X-rays can be used to map and quantify elemental make-up of cells and tissue samples.

• Most native biological elements and trace elements are detected by their K alpha characteristic fluorescence.

• High Z elements including actinides such as plutonium (Pu) can be detected by hard X-ray XFM by their L lines characteristic fluorescence.

• Valence state of Pu can also be investigated by microspectroscopic techique microbeam X-ray absorption near edge structure (µ-XANES).

Advanced Photon Source: Argonne National Laboratory

Elemental distribution in cells is mapped by detecting element specific K (or L lines) X-ray fluorescence at one of the beamlines of the X-ray Operations and Research Collaborative Access Team (XOR-CAT) at the Advanced Photon Source of Argonne National Laboratory.

Example APS 2-ID-D:

• energy range E = 5 – 30 keV

• spatial resolution = 150 nm

• focussed flux 2·109 phot/s (can trade flux for resolution)

• stepscan sample through focused X-ray beam

• record full XRF spectrum at each scan point

•compare specimen counts/spectra to calibration curve, to quantify to area density

XFM schematic

Courtesy of S. Vogt, APS, Argonne National Laboratory, USA

X-ray induced X-ray fluorescence – a brief reminderphoto-electric absorption of incident hard X-rayemission of photo-electron

Emission of Auger e- - dominating low Z

X-ray fluoresence - dominating high Z

• Energy of X-ray fluorescence photons is characteristic for each element• XRF is quantitative, i.e., number of XRF photons is directly related to quantity of element• Photo-electric absorption crossection straightforward to calculate (monochomatic incident beam)

Detect XRF using energy dispersive detector

Energy

Inte

nsity

Jensen et al., 2011, Nature Chemistry

PC12 cells were treated with 242Pu. Two individual cell images show that:(1) Pu (red) and Fe (green) co-localize (yellow) --- initial hypothesis that Fe and Pu enter cell by the same mechanism(2) Pu (red) and Zn in upper cell (blue) or P (green) in lower cell do not co-localize --- since P and Zn are the highest in the nucleus, Pu apparently remains in the cytoplasm

Pu is localized in cytoplasm—overlap with Fe?

Gorman-Lewis et al., 2011 Inorganic ChemistryJensen et al., 2012. Analytica Chimica Acta

The intracellular oxidation state of plutonium was measured directly using microprobe X-ray absorption near edge spectroscopy. Despite the generally reducing conditions found inside living cells and regardless of the initial oxidation state or chemical form of plutonium presented to rat adrenal gland cells, the X-ray absorption spectra of the intracellular deposits were always consistent with tetravalent Pu.

Pu X-ray absorption spectroscopy—only tetravalent Pu is inside cells

Gorman-Lewis et al., 2011 Inorganic Chemistry

Average plutonium content of individual cells incubated for 3 hours in complete media with serum containing 100 μM Pu added as Pu(III), Pu(IV), or Pu(VI). The corresponding average total Pu contents are Pu(III), 1.7 ± 0.2 fg per cell; Pu(IV), 15.8 ± 3.2 fg per cell; and Pu(VI), 2.1 ± 0.5 fg per cell. Uncertainties are given as the standard error of the mean for measurement of n cells.

Pu X-ray absorption spectroscopy—only tetravalent Pu is inside cells

(2) STUDY OF PLUTONIUM AND TRANSFERRIN INTERACTION BY SMALL ANGLE X-RAY SCATTERING

X-ray small angle scattering (SAX)

• SAX allows evaluation of proteins in solution• Rough protein structures reconstructed from

SAX data can be compared with existing protein crystal structures

• Testing hypothesis that Pu enters cells using same mechanism as Fe—SAX of transferrin molecules with different quantity and location of Pu and Fe

Structural models of transferrins with different quantities and locations of Fe and Pu derived from SAXS:--PuCFeNTf (green) adopts a conformation most similar to the native Fe2Tf (yellow)

(a)Orthogonal views of the three-dimensional molecular envelopes of metal–Tf structures reconstructed from the SAXS.

(b) Docking wireframe representations of the Tf structures superimposed onto each other

Jensen et al., 2011, Nature Chemistry

X-ray studies of cellular Pu: Conclusions

• Pu (IV) enters cells most abundantly• Pu (IV) can imitate Fe and enter cells using

transferrin uptake route• Once inside cells Pu is released from tranferrin

and can interact with intracellular proteins

METALOPROTEOMICS STUDY OF PLUTONIUM INTERACTING PROTEINS

Aryal et al., 2011, J. Proteome Res

A mixture of cellular proteins was loaded onto a Pu(IV) NTA (plutonium bound to nitrilotriacetic acid), after appropriate washes and elution steps many cellular proteins other than transferrin were found to bind to Pu.

Most Pu binding proteins detected by 2DE are metalloproteins binding Ca2+, Zn2+ or other divalent ions.

Computational MetaCore™ v.6.2 analysis shows that majority of the cellular proteins interacting with Pu have pro-neoplastic roles (same is true for transferin receptors which can bind Pu loaded transferrin).

Discovery of intracellular Pu(IV) interacting proteins: approach

Aryal et al., 2011, J. Proteome Res

Silver stained 2D PAGE of proteins isolated from rat pheochromocytoma PC12 cells previously panned on Pu(IV)-NTA IMAC. Proteins particularly discussed here are labeled as spots 1 to 7.

Proteins interacting with Pu(IV)-NTA3 pI 10

Mw

t

Aryal et al., 2011, J. Proteome Res

Plutonium binding proteins identified by LC-MS/MS analysis

Aryal et al., 2011, J. Proteome Res

MetaCore™ v.6.2 analysis was used to construct a "shortest distance pathway" connecting the proteins identified to be involved in Pu binding, directly or indirectly (via transferrin) (box). Every arrow represents a curated relationship between proteins connected; red arrows are inhibitory interactions, green arrows activations and gray arrows indicate unspecified (or more complex) relationships. One "upstream" and one "downstream" relationship from GRP78 are highlighted by light blue as examples.

Aryal et al., 2011, J. Proteome Res

MetaCore™ v.6.2 analysis : GO Processes for a "shortest distance" network including Pu binding proteins: GRP78, actin gamma1, NDPK B, pyruvate kinase and galectin 1.

Aryal et al., in press, J. Proteome Res

MetaCore™ v.6.2 analysis :Diseases associated with the collection of proteins involved in the "shortest distance" pathway

Pu metaloproteomics: Conclusions

• Pu (IV) interacting cellular proteins have pro-neoplastic roles

• Pu loaded proteins probably do not fulfill their cellular roles—competition with divalent metals (Ca2+ , Mg 2+, Zn 2+,…) as well as Fe

• Possible feedback loop where Pu caused neoplastic transformation leads to an increase of Pu interacting proteins and/or increased Pu load?

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