Increased expression of N-acetylglucosaminyltransferase-V in human hepatoma cells by retinoic acid and 1α,25-dihydroxyvitamin D₃

UDP-N-acetylglucosamine: α-6-D-mannoside β-1,6N- acetylglucosaminyltransferase-V activities were determined in human hepatoma cell lines of Hep3B and HepG2, and also compared with those of normal liver tissues and primary hepatocytes. When GlcNAcβ1-2Manα1- 3(GlcNAcβ1-2Manα1-4)(Manβ1-4GlcNAc-2-amino pyridine (GlcN,GlcN-biant-PA) and UDP-GlcNAc were used as substrates, the enzymes displayed optimum temperatures of 50°C, optimum pHs of 6.5 in each case, K_m values for UDP-GlcNAc to be 5.8 (Hep3B) and 4.5 mM (HepG2) and K_m values for GlcN,GlcN-biant-PA (mM) to be 1.28 (Hep3B) and 2.4 (HepG2). This indicates that values of Hep3B GlcNAc-transferase-V were distinguishable with HepG2 enzyme. Furthermore, Hep3B enzyme in membrane fraction showed about 1.5-fold higher specific activity (1.423 pmol/(h mg) than that (1.066 pmol/(h mg)) of HepG2. Normal hepatocytes are characterized by very low level of GlcNAc-transferase-V activity whereas hepatoma cells contained high activities. Treatment of hepatoma cells with retinoic acid and 1α,2,5-dihydroxyvitamin D₃ (Vit-D₃) resulted in an increase in GlcNAc-transferase-V activity, while treatment with dimethyl sulfoxide and cytosine-arabinoside resulted in decrease in the enzyme activity. Although retinoic acid (RA) treated cells shows a changed GlcNAc-transferase-V mRNA expression, expression of marker proteins such as α-fetoprotein and albumin was not changed. This is the first demonstration of GlcNAc-transferase-V activity in RA and Vit-D₃-treated hepatoma cell lines.