beta-1,6-N-acetylglucosaminyltransferase V (GnT-V) (EC 2.4.1.155) that catalyzes beta-1,6 branching in asparagine-linked oligosaccharides is activated on viral or oncogenic transformation and is associated with tumor metastasis. To study the molecular mechanisms involved in regulation of expression of the GnT-V gene, we cloned cDNA and genomic DNA for the enzyme (Saito, H., Nishikawa, A., Gu, J., Ihara, Y., Soejima, Y., Sekiya, C., Niikawa, N., and Taniguchi, N. (1994) Biochem. Biophys. Res. Commun. 198, 318-327). We found that transforming growth factor beta (TGF beta) specifically induced GnT-V expression in mouse melanoma cells. The activity of GnT-V was increased 24 h after the addition of TGF beta and remained at high levels up to 72 h. Northern blot analysis showed that the mRNA levels of GnT-V were consistent with the increased activity. To further investigate the nature of the induction, mRNA stability and transcriptional activity were assayed. The enhancement of the GnT-V mRNA expression resulted from prolonged mRNA stability, not from increased transcription. Consequently, elevated mRNA levels were observed even 72 h after the addition of TGF beta. Lectin blot analysis involving leukoagglutinin showed newly synthesized beta-1,6 branching structures in the sugar chains of a protein of approximately 130 kDa at 48 h after TGF beta treatment. These results suggested that TGF beta caused changes in the sugar chains of proteins in melanoma cells by up-regulating GnT-V expression.