TRANSFORMING GROWTH-FACTOR-BETA UP-REGULATES EXPRESSION OF THE N-ACETYLGLYCOSAMINYLTRANSFERASE-V GENE IN MOUSE MELANOMA-CELLS

beta-1,6-N acetylglucosaminyltransferase V (GnT-V) (EC 2.4.1.155) that catalyzes beta-1,6 branching in asparaginelinked oligosaccharides is activated on viral or oncogenic transformation and is associated with tumor metastasis. To study the molecular mechanisms involved in regula tion of expression of the GnT-V gene, we cloned cDNA and genomic DNA f or 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 melanom a cells. The activity of GnT-V was increased 24 h after the addition o f TGF beta and remained at high levels up to 72 h. Northern blot analy sis showed that the mRNA levels of GnT-V were consistent with the incr eased activity. To further investigate the nature of the induction, mR NA stability and transcriptional activity were assayed. The enhancemen t 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 an alysis involving leukoagglutinin showed newly synthesized beta-1,6 bra nching structures in the sugar chains of a protein of approximately 13 0 kDa at 48 h after TGF beta treatment. These results suggested that T GF beta caused changes in the sugar chains of proteins in melanoma cel ls by upregulating GnT-V expression.