Bioluminescent CXCL12 fusion protein for cellular studies of CXCR4 and CXCR7

Chemokine CXCL12 and its two known receptors, CXCR4 and CXCR7, may play a role in diseases including tumor growth and metastasis, atherosclerosis, and HIV infection. Therefore, these molecules may be promising targets for drug development. While studies of cell signaling and high-throughput screening for drug discovery increasingly are based on luminescent assays because of their high sensitivity and signal-to-background ratio, there currently is no bioluminescent assay for chemokine-chemokine receptor binding. To develop a bioluminescent probe for chemokine binding and cellular uptake, we fused CXCL12 to Gaussia luciferase (GL), an ATP-independent enzyme that is the smallest known luciferase. Fusing CXCL12 to Gaussia luciferase (CXCL12-GL) did not alter the bioluminescence emission spectrum and only minimally affected enzyme function under varying conditions of pH, temperature, and NaCl concentration. CXCL12-GL also activated CXCR4-dependent signaling to a comparable extent as unfused CXCL12. Using multiwell plate assays, vie established that CXCR7 increases cell-associated CXCL12 to a significantly greater extent than CXCR4. We also showed that CXCL12-GL can be used to quantify inhibition of chemokine receptor binding by compounds that specifically target CXCR7. These data validate CXCL12-GL as a bioluminescent probe to investigate molecular functions of CXCR4 and CXCR7 and screen for compounds that modulate ligand-receptor binding.