Engineering an effective Mn-binding MRI reporter protein by subcellular targeting

Magn Reson Med. 2015 Dec;74(6):1750-7. doi: 10.1002/mrm.25566. Epub 2014 Dec 17.


Purpose: Manganese (Mn) is an effective contrast agent and biologically active metal, which has been widely used for Mn-enhanced MRI (MEMRI). The purpose of this study was to develop and test a Mn binding protein for use as a genetic reporter for MEMRI.

Methods: The bacterial Mn-binding protein, MntR was identified as a candidate reporter protein. MntR was engineered for expression in mammalian cells, and targeted to different subcellular organelles, including the Golgi Apparatus where cellular Mn is enriched. Transfected HEK293 cells and B16 melanoma cells were tested in vitro and in vivo, using immunocytochemistry, MR imaging and relaxometry.

Results: Subcellular targeting of MntR to the cytosol, endoplasmic reticulum and Golgi apparatus was verified with immunocytochemistry. After targeting to the Golgi, MntR expression produced robust R1 changes and T1 contrast in cells, in vitro and in vivo. Co-expression with the divalent metal transporter DMT1, a previously described Mn-based reporter, further enhanced contrast in B16 cells in culture, but in the in vivo B16 tumor model tested was not significantly better than MntR alone.

Conclusion: This second-generation reporter system both expands the capabilities of genetically encoded reporters for imaging with MEMRI and provides important insights into the mechanisms of Mn biology which create endogenous MEMRI contrast.

Keywords: DMT1; Mn-enhanced MRI (MEMRI); MntR; manganese (Mn); molecular imaging.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Cell Line, Tumor
  • Contrast Media / metabolism
  • Genes, Reporter / genetics*
  • HEK293 Cells
  • Humans
  • Magnetic Resonance Imaging / methods*
  • Manganese / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Molecular Probe Techniques
  • Molecular Probes / genetics
  • Molecular Probes / pharmacokinetics
  • Neoplasms, Experimental / metabolism*
  • Neoplasms, Experimental / pathology
  • Protein Binding
  • Protein Engineering / methods
  • Repressor Proteins / chemistry
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Subcellular Fractions / metabolism*


  • Bacterial Proteins
  • Contrast Media
  • MntR protein, bacteria
  • Molecular Probes
  • Repressor Proteins
  • Manganese