酪氨酸蛋白激酶和蛋白激酶C对N-乙酰氨基葡萄糖转移酶V的双重调控

在人肝癌细胞７７２１中研究了酪氨酸蛋白激酶（ＴＰＫ）和蛋白激酶Ｃ（ＰＫＣ）的激活剂［分别为表皮生长因子（ＥＧＦ）和佛波酯（ＰＭＡ）］和各种蛋白激酶抑制剂对Ｎ－乙酰氨基葡萄糖转移酶Ｖ（ＧｎＴ－Ｖ）活力的影响，以探讨ＴＰＫ和ＰＫＣ对ＧｎＴ－Ｖ的调节。结果发现，ＥＧＦ或ＰＭＡ处理细胞４８ｈ后，ＧｎＴ－Ｖ的活力明显增高；蛋白激酶的非特异性抑制剂槲皮素和染料木黄酮（ｇｅｎｉｓｔｅｉｎ）在抑制ＴＰＫ和ＰＫＣ的同时，抑制ＧｎＴ－Ｖ的基础活力，并完全阻断ＥＧＦ或ＰＭＡ对ＧｎＴ－Ｖ的增高作用；ＴＰＫ的特异性抑制剂Ｔｙｒｐｈｏｓｔｉｎ－２５和ＰＫＣ的特异性抑制剂Ｄ－鞘氨醇分别应用时，各自只能部分地取消ＥＧＦ或ＰＭＡ对ＧｎＴ－Ｖ的诱导。但当Ｔｙｒｐｈｏｓｔｉｎ－２５和Ｄ－鞘氨醇同时加入培养基中则可完全阻断ＥＧＦ或ＰＭＡ对ＧｎＴ－Ｖ的诱导激活。蛋白质合成抑制剂环己亚胺和蛋白激酶抑制剂作用相仿，不但可抑制ＧｎＴ－Ｖ的基础活力，也可完全消除ＥＧＦ或ＰＭＡ对ＧｎＴ－Ｖ的激活。以上结果提示ＥＧＦ或ＰＭＡ通过蛋白激酶调节ＧｎＴ－Ｖ的酶蛋白合成，并且ＧｎＴ－Ｖ受到膜性ＴＰＫ和ＰＫＣ的双重调节，其中ｍ－ＴＰＫ较ｍ－ＰＫＣ更为重要。

Dual Regulation of Tyrosine Protein Kinase and Protein Kinase C on N-acetylglucosaminyltransferase V

The effects of the epidermal growth factor(EGF), a stimulator of tyrosine protein kinase(TPK), and phorbol 12 myristate 13 acetate(PMA), a stimulator of protein kinase C(PKC), on the activity of N acetylglucosaminyltransferase V(GnT V) were studied in human hepatocarcinoma cell line 7721 in order to elucidate the regulation of TPK and PKC on GnT V. It was found that the GnT V activity obviously increased after treatment of the cells with EGF or PMA for 48 h. A non specific protein kinase inhibitor, quercetin, inhibited the activities of TPK and PKC(inhibited mainly the membranous TPK and PKC) as well as GnT V simultanously. Moreover, quercetin completely eliminated the stimulating effect of EGF or PMA on GnT V. When Tyrohostin 25, a specific inhibitor of TPK, or sphingosine, the specific inhibitor of PKC, was used separately to substitute for quercetin, the induction effect of EGF or PMA on GnT V was only partially eliminated. However, when both Tyrphostin 25 and sphingosine were added to the culture medium, the elevation of GnT V caused by EGF or PMA was entirely blocked. Cycloheximide, a well known inhibitor of protein synthesis, showed an effect similar to the inhibition of protein kinases; it not only inhibited the basal activity of GnT V, but also abolished the inducing stimulation of GnT V by EGF or PMA. These results indicate that EGF or PMA regulates the activity of GnT V via protein kinases, and GnT V is regulated by dual mechanism of membranous TPK and PKC. Membranous TPK is more important than membranous PKC in the regulation of GnT V.