Quick preparation of nanoluciferase-based tracers for novel bioluminescent receptor-binding assays of protein hormones: Using erythropoietin as a model.

Nanoluciferase (NanoLuc) is a newly developed small luciferase reporter with the so far brightest bioluminescence. In recent studies, we developed NanoLuc as an ultrasensitive probe for novel bioluminescent receptor-binding assays of some protein/peptide hormones. In the present study, we proposed a simple method for quick preparation of the NanoLuc-based protein tracers using erythropoietin (Epo) as a model. Epo is a glycosylated cytokine that promotes erythropoiesis by binding and activating the cell membrane receptor EpoR. For quick preparation of a bioluminescent Epo tracer, an Epo-Luc fusion protein carrying a NanoLuc-6 × His-tag at the C-terminus was secretorily overexpressed in transiently transfected human embryonic kidney (HEK) 293 T cells. The Epo-Luc fusion protein retained high-binding affinities with EpoR either overexpressed in HEK293T cells or endogenously expressed in mouse erythroleukemia cells, representing a novel ultrasensitive bioluminescent tracer for non-radioactive receptor-binding assays. Sufficient Epo-Luc tracer for thousands of assays could be quickly obtained within 2 days through simple transient transfection. Thus, our present work provided a simple method for quick preparation of novel NanoLuc-based bioluminescent tracers for Epo and some other protein hormones to facilitate their ligand-receptor interaction studies.