To analyze the direct effects of O-GlcNAcylation on Notch activation and Nrg1 levels in breast cancer cells, we used O-(2-Acetamido-2-deoxy-D-glucopyranosylidene) amino-Z-N-phenylcarbamate (PUGNAc), an inhibitor of O-GlcNAcase (OGA) that causes a global increase in O-GlcNAcylation of substrate proteins. The gene discussed is OGA; the disease is breast cancer.