Contents of Volume 53

Plant Molecular Biology -     

The Stress Hormone Corticosterone Increases Synaptic ��-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors via Serum- and Glucocorticoid-inducible Kinase (SGK) Regulation of the GDI-Rab4 Complex

Corticosterone, the major stress hormone, plays an important role in regulating neuronal functions of the limbic system, although the cellular targets and molecular mechanisms of corticosteroid signaling are largely unknown. Here we show that a short treatment of corticosterone significantly increases α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated synaptic transmission and AMPAR membrane trafficking in pyramidal neurons of prefrontal cortex, a key region involved in cognition and emotion. This enhancing effect of corticosterone is through a mechanism dependent on Rab4, the small GTPase-controlling receptor recycling between early endosome and plasma membrane. Guanosine nucleotide dissociation inhibitor (GDI), which regulates the cycle of Rab proteins between membrane and cytosol, forms an increased complex with Rab4 after corticosterone treatment. Corticosterone also triggers an increased GDI phosphorylation at Ser-213 by the serum- and glucocorticoid-inducible kinase (SGK). Moreover, AMPAR synaptic currents and surface expression and their regulation by corticosterone are altered by mutating Ser-213 on GDI. These results suggest that corticosterone, via SGK phosphorylation of GDI at Ser-213, increases the formation of GDI-Rab4 complex, facilitating the functional cycle of Rab4 and Rab4-mediated recycling of AMPARs to the synaptic membrane. It provides a potential mechanism underlying the role of corticosteroid stress hormone in up-regulating excitatory synaptic efficacy in cortical neurons.     

色氨酸残基在磷酸烯醇式丙酮酸羧化酶催化功能中的作用

在pH7.5条件下,用NBS对PEP羧化酶中色氨酸残基进行共价修饰表明,PEP羧化酶中48个色氨酸残基均能被NBS修饰。用邹承鲁图解法求得,其中4个残基为酶表现催化活性所必需的。 PEP羧化酶的变构效应剂G6P、Gly及Mal分别与酶预保温后,再经NBS修饰,前两种处理中,同样浓度的NBS所用修饰的色氨酸残基数和处理后的残存酶活与对照相比有很大的差异,而用Mal处理的,两者与对照相差无几。     

马齿苋叶片PEP羧化酶的分子特性

马齿苋叶片PEPCase由四个相同的亚基组成,亚基分子量为83kD。远紫外CD光谱分析表明,此酶含有36.6％α—螺旋结构。马齿苋叶片PEPCase可被G6P激活,但不能被Gly、Ser激活。G6P可防止酶的尿素变性和枯草杆菌蛋白酶的作用。这种保护效应与G6P诱导的酶构象变化有关。 从酶对低温、高温及尿素的反应来看,马齿苋叶片PEPCase的稳定性高于高粱叶片PEP—Case,两者的免疫特性和电泳特性亦不同。     

垂体在刺激脑内渗透压感受器引起的肾脏反应中的作用

实验在α氯醛糖和氨基甲酸乙酯混合麻醉的大鼠中进行。脑室内注射高张盐水(icv.HS)后,肾血浆流量、肾小球滤过率、尿量、尿钠排出量、尿钾排出量和渗透物质清除率均增加,游离水清除率下降。去除垂体后,icv.HS不再能引起上述肾脏反应。另外给大鼠静脉注射血管升压素(VP)拮抗剂(V_1和V_2受体拮抗剂),并不能削弱上述icv.HS引起的肾脏反应。脑室内注射高张盐水后,尿中多巴胺(DA)排出量无显著增多;给予多巴脱羧酶抑制剂苄丝肼也不能削弱icv.HS引起的肾脏反应。上述实验结果表明,在本实验条件下刺激脑内渗透压感受器引起的肾脏反应依赖于垂体的完整性,但看来并不依赖于外周的VP和DA,故垂体通过何种机制介导icv.HS引起上述肾脏反应,有待于进一步的研究。     

B7-2胚胎性癌细胞诱导分化过程中的表型转变

胚胎性癌细胞(简称EC细胞)作为一类肿瘤(畸胎瘤)的干细胞近年受到广泛的重视,从胚胎学、肿瘤学和分子生物学等许多学科领域都应用它作为实验材料,离体诱导分化研究是其中的一个方面。B 7-2 EC细胞是我们从129品系小鼠的自发睾丸畸胎瘤中分离克隆得到的一株多能EC细胞,它在同种同基因小鼠     

体外分化的人体巨噬细胞抑制天然杀伤(NK)细胞的研究

本文继先前工作后,进一步应用正常健康人外周血单个核细胞(PBMNC)经塑料培皿粘附技术把单核细胞分离出来,经培养进一步纯化,随后动态观察培养0,2,4,6和8天的单核-巨噬细胞的形态变化和对新鲜分离同种异基因个体PBMNC中NK活性的影响。实验表明,体外分化6天和8天的巨噬细胞质/核比例和胞浆内空泡显著增加,细胞直径约为0天时的2倍。这些细胞和PBMNC之比为0.5:1时,引起了NK细胞活性的50%以上抑制(4小时~(51)Cr标记K 562肿瘤的同位素释放试验)。这种抑制效应不为过氧化氢酶(Catalase 4000单位/毫升)和前列腺素合成酶的抑制剂(Indom 1×10~(-5)M)所阻断。实验证明,同种异基因个体的NK细胞不能识别巨噬细胞表面抗原,从而排除了巨噬细胞和K562肿瘤抗原竞争的可能性。实验还表明,巨噬细胞对NK活性的抑制是不受HLA约束的。应用高频超声振荡破碎巨噬细胞膜方法和免疫调变技术进一步提示,人体巨噬细胞对NK活性的抑制与巨噬细胞体积无关,而与体外分化所赋有的固有特性和它们分泌的免疫调节分子有关。