Quantum Dot Erythropoietin Bioconjugates Enhance EPO-Receptor Clustering on Transfected Human Embryonic Kidney Cells

Erythropoietin (EPO)-induced cellular signaling through the EPO receptor (EPOR) is a fundamental pathway for the modulation of cellular behavior and activity. In our previous work, we showed in primary human astrocytes that the multivalent display of EPO on the surface of semiconductor quantum dots (QDs) mediates augmented JAK/STAT signaling, a concomitant 1.8-fold increase in the expression of aquaporin-4 (AQPN-4) channel proteins, and a 2-fold increase in the AQPN-4-mediated water transport activity. Our hypothesis is that this enhanced signaling involves the simultaneous ligation and clustering of EPOR by QD-EPO conjugates. Here, we utilized a human embryonic kidney (HEK 293T/17) cell line transfected with EPOR fused to enhanced green fluorescent protein (eGFP) to visualize EPOR clustering. We demonstrate that QDs displaying five copies of EPO (bearing a C-terminal 6-histidine tract) on the nanoparticle surface induce a 1.8-fold increase in EPOR clustering compared to monomeric EPO at the same concentration. Our findings confirm the critical role played by the multivalent display of EPO in mediating clustering of the EPOR. More generally, these results illustrate the capability of nanoparticle-growth factor bioconjugates to control the activity of cognate receptors and the important role played by multivalent display in the modulation of selective cellular delivery and signaling.