GRHL2 and breast cancer: Since the effect of SUMO modification on transcriptional activity can depend on the target gene promoter and/or cellular context, we employed two distinct luciferase-based reporter assays and MDA-MB-231 breast cancer cells as a model system to demonstrate that SUMO modification enhances GRHL2 transcriptional activity, possibly through induction of structural changes, enhancement or inhibition of protein–protein interactions, or by influencing GRHL2 protein solubility.