Henle K J, Stone A, Chatterjee S K
Department of Medicine, University of Arkansas for Medical Sciences, Little Rock 72205.
Cancer Res. 1988 Oct 15;48(20):5717-21.
We measured activities of three glycosyltransferases at various times during heat-induced thermotolerance development. Glycosyltransferases are normally located in the Golgi apparatus and catalyze cellular glycosylation reactions. UDP-Gal:N-acetylglucosamine beta 1,4-galactosyltransferase (beta 1,4-GalT) is known to participate in the formation of N-linked glycoproteins; when compared to cell survival, beta 1,4-GalT activity was significantly more heat resistant (50% loss of activity: 80 min, 45 degrees C) and showed little elevation at a time when thermotolerance was fully expressed. However, beta 1,4-GalT activity increased twofold by 24-h postheating when thermotolerance had begun to decay. Activity of beta 1,4-GalT was compared with glycosyltransferase activities that are considered to be specific for O-linked glycoproteins: UDP-Gal:N-acetylgalactosamine-beta 1,3-galactosyltransferase (beta 1,3-GalT), and UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase (Gal-NAcT). Heat-inactivation experiments with heating times up to 60 min at 45 degrees C failed to reduce either activity below that of unheated control cells. Instead both beta 1,3-GalT and GalNAcT activity increased approximately twofold immediately after 10 min at 45 degrees C. Activity of beta 1,3-GalT rapidly decreased with time after heating and returned to control levels by 6-h postheating. In contrast, GalNAcT activity continued to increase with time after 10 min at 45 degrees C, and was 4.5-fold above unheated controls by 6-h postheating. GalNAcT activity returned to control levels 24- to 48-h postheating. A comparison with the cellular survival response showed that GalNAcT activity preceded thermotolerance expression by 2-4 h and also decayed more rapidly than heat resistance in thermotolerant cells. These data, together with other published results, suggest that expression of thermotolerance may be associated with enhanced glycosylation of intracellular proteins.
我们在热诱导耐热性形成的不同时间测量了三种糖基转移酶的活性。糖基转移酶通常位于高尔基体中，催化细胞糖基化反应。已知UDP-半乳糖：N-乙酰葡糖胺β1,4-半乳糖基转移酶（β1,4-GalT）参与N-连接糖蛋白的形成；与细胞存活率相比，β1,4-GalT活性具有显著更高的耐热性（活性丧失50%：45℃下80分钟），并且在耐热性充分表达时几乎没有升高。然而，在耐热性开始衰退的加热后24小时，β1,4-GalT活性增加了两倍。将β1,4-GalT活性与被认为对O-连接糖蛋白具有特异性的糖基转移酶活性进行了比较：UDP-半乳糖：N-乙酰半乳糖胺-β1,3-半乳糖基转移酶（β1,3-GalT）和UDP-GalNAc：多肽N-乙酰半乳糖胺基转移酶（Gal-NAcT）。在45℃下加热时间长达60分钟的热失活实验未能将任何一种活性降低到未加热对照细胞以下。相反，在45℃下处理10分钟后，β1,3-GalT和GalNAcT活性立即增加了约两倍。加热后，β1,3-GalT活性随时间迅速下降，并在加热后6小时恢复到对照水平。相比之下，在45℃下处理10分钟后，GalNAcT活性随时间持续增加，并且在加热后6小时比未加热对照高4.5倍。GalNAcT活性在加热后24至48小时恢复到对照水平。与细胞存活反应的比较表明，GalNAcT活性比耐热性表达提前2至4小时，并且在耐热细胞中的衰减也比耐热性更快。这些数据与其他已发表的结果一起表明，耐热性的表达可能与细胞内蛋白质糖基化增强有关。
