N-糖蛋白去糖基化酶（PNGase）的研究进展

N-糖蛋白去糖基化酶（PNGase）是一种广泛存在于真菌、植物、哺乳动物中的去糖基化酶，可以水解N-糖蛋白或 N-糖肽上天冬酰胺与寡糖链连接的化学键，并释放出完整的N-寡糖。PNGase在生物体内参与蛋白质降解、器官发育、个体生长等过程。人PNGase基因功能缺陷会导致先天性去糖基化障碍，小鼠PNGase缺陷会导致胚胎致死性，线虫PNGase缺陷使其寿命下降。本文对PNGase在不同物种的分布、蛋白质结构、酶学功能及生物学功能进行阐述，为PNGase的生理病理功能及致病机制的基础研究提供思路，为PNGase作为糖生物学工具酶或药物开发的创新应用研究奠定基础。     

Modification in Cell Shape Unrelated to Cellulose Microfibril Orientation in Growing Thallus Cells of Chaetomorpha moniligera

Cellulose microfibril orientation patterns in thallus cellsof Chaetomorpha moniligera were studied, and the relationshipbetween the microfibril and the peripheral microtubule arrangementsduring cell-shape modification by colchicine was examined. Inthe cuttings from growing thalli, linearly arranged cylindricalcells developed into cask-shaped cells during 4–6 daysof culture at 27?C. In the cylindrical cells, microfibrils formingthe innermost portion of the wall were arranged alternatelyin longitudinal and transverse directions, but peripheral microtubuleswere always arranged only in a longitudinal direction. Thesefeatures were also noted in the cask-shaped cells. Colchicineat 10^–3M and 3?10^–3M accelerated both cell expansionand wall thickening with matrix deposition, but the directionsin which both microfibrils and microtubules were arranged werethe same as those of the cylindrical cells. These results indicatethat (1) the microfibril and microtubule arrangements of Chaetomorphaare not necessarily correlated, (2) changes in cell shape ofChaetomorpha are not necessarily accompanied by changes in thearrangement of cell-wall microfibrils, and (3) colchicine playsa role in the loosening and thickening of cell walls by enhancingmatrix deposition. (Received June 2, 1986; Accepted February 13, 1987)     

促性腺激素诱导猕猴排卵周期中卵巢纤溶酶原激活因子与抑制因子的变化

在用 PMSG 和 hUG 诱导猕猴排卵过程中,我们研究了 pA 和它的抑制因子 PAI-1与排卵的关系。实验结果表明,由促性腺激素所诱导出的卵巢 tPA 活性的增加与排卵密切相关,在排卵前达到高峰,而排卵后明显下降;uPA 只在排卵后的颗粒细胞大量出现;PAI-1分泌高峰比 tPA 峰值早出现12—24小时;排卵来临时,tPA 的明显上升导致 PAl-1的空然下降。上述实验结果说明,卵巢中 tPA 和 PAI-1活性的这种平衡性的变化可能在排卵机制和维持卵巢的正常生理功能中起重要作用,而 uPA 或许与黄体形成的调节有某些关系。     

Biochemical Characterization of α-Adrenergic Receptors in Human Brain and Changes in Alzheimer-Type Dementia

Abstract Using ligand binding techniques, we studied α-adrenergic receptors in brains obtained at autopsy from seven histologically normal controls and seven patients with histopathologically verified Alzheimer-type dementia (ATD). Binding of the α-adrenergic antagonists [³H]prazosin and [³H]yohimbine to membranes of human brains exhibited characteristics compatible with α₁- and α₂-adrenergic receptors, respectively. Binding of both ligands was saturable and reversible, with dissociation constants of 0.15 nM for [³H]prazosin and 5.5 nM for [³H]yohimbine. [³H]Prazosin binding was highest in the hippocampus and frontal cortex and lowest in the caudate and putamen in the control brains. [³H]Yohimbine binding was highest in the nucleus basalis of Meynert (NbM) and frontal cortex and lowest in the caudate and cerebellar hemisphere in the control brains. Compared with values for the controls, [³H]prazosin binding sites were significantly reduced in number in the hippocampus and cerebellar hemisphere, and [³H]yohimbine binding sites were significantly reduced in number in the NbM in the ATD brains. These results suggest that α₁ and α₂-adrenergic receptors are present in the human brain and that there are significant changes in numbers of both receptors in selected regions in patients with ATD.     

ATF4在内质网应激调控成骨分化中的作用

为避免内质网中未折叠蛋白质的过度累积,真核细胞能激活一系列信号通路来维持内质网稳态,这个过程称为内质网应激。在骨生长发育中,适宜的内质网应激有助于成骨细胞、破骨细胞和软骨细胞的生长,可以促进骨髓间充质干细胞向成骨细胞分化。而过度的内质网应激会抑制成骨分化,严重的甚至导致骨质疏松、成骨不全等相关骨病的发生。内质网应激时可激活未折叠蛋白质反应,其主要是通过PERK/eIF2α/ATF4信号通路,上调转录激活因子4(ATF4)的表达。ATF4位于许多成骨分化调节因子的下游,是促进成骨分化的关键因子,在内质网应激对成骨分化的调节中发挥重要作用。在成骨分化过程中,适宜的内质网应激能通过激活PERK信号通路,诱导ATF4表达增加,进而上调骨钙素、骨涎蛋白等成骨所必需基因的表达,促进成骨分化。过度的内质网应激会激活ATF4/CHOP促凋亡途径,并导致Bax、胱天蛋白酶等凋亡信号分子的大量产生,进而导致细胞凋亡,抑制成骨分化。由于ATF4在ERS和成骨分化中的重要作用,ATF4在骨质疏松、成骨不全等骨相关疾病的治疗中具有重要意义。本文通过综述ATF4在内质网应激调控成骨分化中的作用机制,为相关骨性疾病治疗提供理论依据。     

用试管-玻片培养技术研究铵对木麻黄根瘤形成的影响

用植物试管玻片培养技术研究NH_4~ 对细枝木麻黄及Frankia菌株Co01共生体系建立过程的影响。NH_4~ (100,150ppm(NH_4)_2SO_4)通过阻止菌株Cc01与其宿主细枝木麻黄根毛壁的亲和作用来影响结瘤。但NH_4~ 不能阻抑菌株Cc01中结瘤基因pel和cel的表达及纤维素酶和果胶酶活性,且菌丝一旦侵入宿主皮层细胞,并形成根瘤原基及前根瘤,则NH_4~ (250ppm(NH_4)_2SO_4)就不再阻止原基进一步发育为成熟的根瘤。但在这种情况下,NH_4~ 能抑制根瘤的固氮活性。     

Ras-Regulated Hypophosphorylation of the Retinoblastoma Protein Mediates Neuronal Differentiation in PC12 Cells

Abstract: To investigate the role of the retinoblastoma protein pRB in neuronal differentiation, we have measured the accumulation of hypophosphorylated pRB in PC12 cells stimulated by nerve growth factor (NGF). NGF induced the accumulation of hypophosphorylated pRB within 30 min and the level peaked after 12 h. Viral Kiras, cyclic AMP (cAMP), and 12- O -tetradecanoylphorbol 13-acetate (TPA) also induced the hypophosphorylation of pRB, but epidermal growth factor and interleukin-6 did not. The extent of hypophosphorylation of pRB correlated well with the capacity of these factors to stimulate neurite outgrowth. The constitutively activated Ras induced persistent shift of the phosphorylation state of pRB toward hypophosphorylation. A dominant negative form of cHa-Ras suppressed significantly induction of the hypophosphorylation of pRB by NGF, but not by cAMP. Taken together, these results suggest that the hypophosphorylation of pRB triggered by NGF is mediated by a Ras-dependent pathway. Furthermore, microinjection of a monoclonal antibody specific for the hypophosphorylated form of pRB blocked the neurite outgrowth initiated by NGF. These results suggest a crucial role of pRB in withdrawal of cells from the cell cycle and in neuronal differentiation of PC12 cells.     

肝再生的调控及原癌基因表达

肝脏再生过程中受到多种体液因素的调控。肝细胞生长因子（ＨＧＦ）、肝刺激因子（ＨＳＳ）等对肝细胞有促分裂作用;转化生长因子β１（ＴＧＦβ１）等则具有抑制作用。此外,肝再生还需要去甲肾上腺素（ＮＥ）、胰岛素等辅助分裂原的存在,共同调节肝再生。肝细胞分裂增殖与原癌基因表达密切相关。肝细胞从静息期进入细胞周期,以及在整个细胞周期中,某些原癌基因有特征性的表达。