The STAT5 Reporter (Luc)-U937 cell line is designed for monitoring STAT5 signal transduction pathway in the U937 cell line. It contains a firefly luciferase gene driven by the STAT5 response element located upstream of the minimal TATA promoter. After activation by GM-CSF, endogenous STAT5 binds to the DNA response elements, inducing transcription of the luciferase reporter gene.