In a cell-based firefly-luciferase reporter assay, an inhibitory ligand can stabilize the reporter enzyme, allowing more reporter protein to accumulate during incubation. If the detection reagent's substrate conditions reduce competitive inhibition, the accumulated enzyme can produce increased luminescence despite the compound's inhibitory activity against luciferase. This measurement effect can resemble reporter activation without establishing increased transcription.

Sources:

• https://www.ncbi.nlm.nih.gov/sites/books/NBK374281/