Miyoshi E, Ihara Y, Nishikawa A, Saito H, Uozumi N, Hayashi N, Fusamoto H, Kamada T, Taniguchi N
Department of Biochemistry, Osaka University Medical School, Suita, Japan.
Hepatology. 1995 Dec;22(6):1847-55.
N-acetylglucosaminyltransferases III and V (GnT-III and -V) are key enzymes in the synthesis of the branches of asparagine-linked oligosaccharides. Although their messenger RNAs (mRNAs) are expressed in various rat tissues, they are not detected in normal rat liver. Expression of the GnT-III and -V mRNAs, however, increased in regenerating liver after two-thirds partial hepatectomy compared with sham-operated rats. The enzymatic activities of GnT-III and -V increased in proportion to mRNA expression. To determine which type of cells in the liver have high activities of these glycosyltransferases, hepatocytes and nonparenchymal cells were separated by means of a two-step collagenase perfusion technique. GnT-III activity was only detected in nonparenchymal cells of normal rat liver. However, during liver regeneration, GnT-III activity increased and thus was also detectable in hepatocytes. GnT-V activity was detected in both types of cells. These data were supported by reverse transcription-polymerase chain reaction results. Although the mechanism underlying the induction of these glycosyltransferases is unknown, lectin blot analysis showed that oligosaccharides in many glycoproteins, including hepatocyte growth factor, a major growth factor associated with liver regeneration, were newly synthesized during liver regeneration. This is the first report on the expression of glycosyltransferases during liver regeneration and suggests that there are different mechanisms involved in regulation of the genes of GnT-III and -V during liver regeneration.
N-乙酰葡糖胺基转移酶III和V（GnT-III和-V）是天冬酰胺连接的寡糖分支合成中的关键酶。尽管它们的信使核糖核酸（mRNA）在大鼠的各种组织中均有表达，但在正常大鼠肝脏中却检测不到。然而，与假手术大鼠相比，在三分之二部分肝切除术后的再生肝脏中，GnT-III和-V的mRNA表达增加。GnT-III和-V的酶活性与mRNA表达成比例增加。为了确定肝脏中哪种类型的细胞具有这些糖基转移酶的高活性，采用两步胶原酶灌注技术分离肝细胞和非实质细胞。GnT-III活性仅在正常大鼠肝脏的非实质细胞中检测到。然而，在肝脏再生过程中，GnT-III活性增加，因此在肝细胞中也可检测到。在这两种类型的细胞中均检测到GnT-V活性。这些数据得到逆转录-聚合酶链反应结果的支持。尽管这些糖基转移酶诱导的潜在机制尚不清楚，但凝集素印迹分析表明，包括肝细胞生长因子（一种与肝脏再生相关的主要生长因子）在内的许多糖蛋白中的寡糖在肝脏再生过程中重新合成。这是关于肝脏再生过程中糖基转移酶表达的首次报道，并表明在肝脏再生过程中，GnT-III和-V的基因调控涉及不同的机制。
