Class III adenylyl cyclases: molecular mechanisms of catalysis and regulation

Class III adenylyl cyclases are the most abundant type of cyclic AMP-producing enzymes. The adjustment of the cellular levels of this second messenger is achieved by a variety of regulatory mechanisms which couple signals to adenylyl cyclase activity. Because of the divergent nature of stimuli which impinge on these enzymes, highly individualized class III adenylyl cyclases have evolved in metazoans, eukaryotic unicells and bacteria. Regulation usually exploits the dimeric structure of the catalyst, whose active centres form at the dimer interface. The fold of the catalytic domains and the basic catalytic mechanisms are similar in all class III adenylyl cyclases, and substrate binding generally closes the active site by an induced-fit mechanism. Regulatory inputs can result in dramatic rearrangements of the catalytic domains within the dimer, which often are based on rotational movements. Received 13 February 2006; received after revision 16 March 2006; accepted 20 April 2006     

大枣cAMP的大孔吸附树脂分离工艺研究

筛选分离大枣cAMP的最佳树脂,确定树脂分离大枣cAMP的工艺参数.以cAMP含量为指标,从6种不同型号大孔树脂中筛选出分离大枣cAMP的最佳树脂,并优化该树脂分离工艺条件.结果XAD 7HP型树脂的吸附分离性能最佳,在所确定的工艺条件下,提取物cAMP含量可达到3.55%.     

DNG1, a Dictyostelium homologue of tumor suppressor ING1 regulates differentiation of Dictyostelium cells

dng1 is a Dictyostelium homologue of the mammalian tumor suppressor ING gene. DNG1 protein localizes in the nucleus, and has a highly conserved PHD finger domain found in chromatin-remodeling proteins. Both dng1 disruption and overexpression impaired cell proliferation. In dng1-null cells, the progression of differentiation was delayed in a cell-density-dependent manner, and many tiny aggregates were formed. Exogenously applied cAMP pulses reversed the inhibitory effect caused by dng1 disruption on the aggregation during early development, but formation of tiny aggregates was not restored. dng1-overexpressing cells acquired the ability to undergo chemotaxis to cAMP earlier and exhibited enhanced differentiation. These phenotypes were found to be coupled with altered expressions of early genes such as cAMP receptor 1 (car1) and contact site A (csA). Furthermore, disordered histone modifications were demonstrated in dng1-null cells. These results suggest a regulatory role of dng1 in the transition of cells from growth to differentiation.Received 29 December 2004; received after revision 24 May 2005; accepted 26 May 2005     

Protein kinase C-dependent NF-κB activation is altered in T cells by chronic stress

Chronic stress has been associated with impaired immune function. In this work we studied the effect of chronic mild stress (CMS) exposure on the early intracellular pathways involved in T cells after stimulation with mitogen. We found that mitogen stimulation of T lymphocytes from CMS-exposed mice resulted in a reduction of the intracellular [Ca²⁺] rise, an impairment of growth-promoting protein kinase C (PKC) activation, a lower NF-κB activation and an increase in the inhibitory cAMP-protein kinase A (PKA) pathway activity with respect to those found in control lymphocytes. However, T cell activation with the direct PKC activator phorbol 12-myristate 13-acetate plus calcium ionophore led to a similar proliferative response in both CMS and control lymphocytes, indicating that signals downstream of PKC would not be affected by stress. In summary, our results show that chronic stress induced an alteration in T cell early transduction signals that result in an impairment of the proliferative response.Received 11 February 2005; received after revision 20 May 2005; accepted 6 June 2005     

Microinjection of synthetic protein kinase inhibitor into single barnacle muscle fibers before and after cyclic AMP

Summary Single muscle fibers from the barnacleBalanus nubilus have been used as a preparation to see if a synthetic 20-residue PKI (5-24)-peptide is able to block or reverse the stimulatory response of the ouabain-insensitive Na efflux to injected cAMP. The results obtained show that this peptide behaves as a powerful inhibitor of the cAMP-mediated response and is also able to partially reverse the sustained stimulation of the Na efflux observed in ouabain-poisoned fibers following the injection of subunit A of cholera toxin.Warmest thanks to Prof. E. H. Fischer and Kurt Diltz for a sample of sPK1. This work received support from NSF, the Graduate School Research Committee and from NIH through a General Research Support Grant to the University of Wisconsin Medical School.     

Regular oscillations in suspensions of a putatively chaotic mutant ofDictyostelium discoideum

Summary We have tested the light-scattering properties of suspensions of theDictyostelium discoideum mutantHH201 derived from the mutantFr17. Previous studies indicated thatHH201 andFr17 possess highly irregular rhythmic properties which might represent aperiodic oscillations, i.e. chaos. We report that the former mutant can display regular oscillatory behavior. Possible explanations for this result are discussed, including that of a transition from chaotic to periodic behavior resulting from some parameter change or from strong intercellular coupling in cell suspensions.     

山羊血浆环核苷酸在感染肝片吸虫前后的变化

用放射免疫方法测定山羊血浆ｃＡＭＰ,ｃＧＭＰ和ｃＡＭＰ／ｃＧＭＰ正常水平值以及感染肝片吸虫后的动态变化。结果表明：山羊血浆ｃＡＭＰ,ｃＧＭＰ和ｃＡＭＰ／ｃＧＭＰ的正常值分别为（０．８０±０．０３）,（０．８３±０．０３） ｐｍ ｏｌ·ｍ Ｌ－ １,（０．６９±０．０４）,感染１ 组和２ 组山羊在感染后第１～６ 周,血液中ｃＡＭＰ水平显著低于或低于对照组,以后两组水平相当。感染１ 组的ｃＧＭＰ水平在感染后５～９ 周期间低于对照组,而感染２ 组山羊的ｃＧＭＰ水平在感染后１～４ 周高于对照组。感染１ 组和２ 组山羊的ｃＡＭＰ／ｃＧＭＰ比值分别在感染后１～４ 周和１～６ 周呈现低于对照组的趋势,但差异不明显。因而,肝片吸虫感染可导致宿主的ｃＡＭＰ,ｃＧＭＰ和ｃＡＭＰ／ｃＧＭＰ紊乱。     

双丁酰环腺苷酸对人胃腺癌体外培养细胞DNA合成的影响

应用~3H-TdR光镜和电镜放射自显影观察表明,MGc80-3 细胞标记指数达31.51％,标记银粒集中于分裂间期的S期细胞核中,细胞核呈重标记状态,绝大多数标记银粒分布于细胞核常染色质区域,少数见于核孔附近的常染色质或核孔附近的细胞质中,核仁未见标记,显示细胞内 DNA合成十分活跃。但经 dBcAMP诱导后,标记指数则降至 4.35％,细胞核呈弱标记状态,电镜放射自显影则未在细胞核内见到标记银粒,表明其DNA合成受到明显抑制。这种变化是由于dBcAMP诱导胃癌细胞内cAMP水平提高而实现的,认为DNA合成抑制是导致MGc80-3细胞走向分化的一个重要原因,对于癌变细胞恶性表型逆转具有重要作用。     

大鼠肝大部分切除对血及肝组织中cAMP、ATP含量变化的影响

目的：观察大鼠大部分肝切除后3天时血浆及肝组织中cAMP、ATP含量变化与肝再生的影响。方法：用液体闪烁计数仪和高效液相色谱仪分别测定cAMP及ATP含量。结果：大鼠大部分肝切除后血中和肝组织中cAMP含量明显高于正常对照组,肝组织ATP含量也明显增高,与肝重增长呈明显正相关关系。结论：肝再生时许多物质参与调控,可能与cAMP的传递密切相关,同时与能量代谢也有一定的关系。