A dual participation of ZAP-70 and scr protein tyrosine kinases is required for TCR-induced tyrosine phosphorylation of Sam68 in Jurkat T cells

Sam68 has been initially described as a substrate of src kinases during mitosis in fibroblasts. Recent evidence suggests that in T lymphocytes Sam68 may act as an adaptor protein and participate in the early biochemical cascade triggered after CD3 stimulation. A direct interaction between Sam68 and the two src kinases involved in T cell activation, p59^fyn and p56^lck, as well as a partnership of Sam68 with various key downstream signaling molecules, like phospholipase Cγ-1 and Grb2, has been shown. In this study we analyze the contribution of p56^lck, as well as the role of ZAP-70, the second class of protein tyrosine kinase involved in T cell activation, in Sam68 tyrosine phosphorylation in the human Jurkat T cell line. Using the src inhibitor PP1 [4-amino-5-(4-methylphenyl)7-(t-butyl) pyrazolo [3,4-d] pyrymidine] and cell variants with defective expression of p56^lck or expressing a dominant negative form of ZAP-70, we demonstrate that, while both p56^lck and ZAP-70 are dispensable for the low constitutive phosphorylation of Sam68 observed in Jurkat cells, a cooperation between the two kinases is required to increase its rapid phosphorylation observed in vivo after CD3 stimulation. We also show that recombinant forms of both p56^lck and ZAP-70 phosphorylate Sam68 in vitro. However, using CD2 stimulated cells, we observe that p56^lck activation by itself does not induce Sam68 tyrosine phosphorylation. We conclude that p59^lck and p56^lck differently participate in regulating the phosphorylation state of Sam68 in T cells and that ZAP-70 may contribute to Sam68 tyrosine phosphorylation and to the specific recruitment of this molecule after CD3 stimulation.     

Nature of Rec+ revertants isolated from Escherichia coli K-12 cultures with recA- mutations

The nature of Rec⁺ revertants isolated previously from cultures of recombinationally defective strainEscherichia coli K-12 AB 2463 recA13 was studied. With the aid of phage P1 vira the chromosome region of the recA gene in cells of strain JC2915F^- were transduced, after which the recombination capacity of the transductants was determined by crossing with JC158Hfr cells and their resistance to ultraviolet radiation was established. Sensitivity of the transductants to suppressor phages was determined. The Rec⁺ revertants were shown to differ with respect to the recA gene. In some Rec⁺ revertants the Rec⁺ phenotype appeared as the result of a back mutation in this gene from rec^- to rec⁺, whereas in other revertants the Rec⁺ phenotype was due to indirect suppression.Department of Biology and General Genetics, Patrice Lumumba Peoples' Friendship University, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR V. M. Zhdanov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 82, No. 12, pp. 1487–1488, December, 1976.     

Ampullary electroreceptors in catfish (Teleostei): temperature dependence of stimulus transduction

The response properties of ampullary electroreceptors have been studied in the catfish Ictalurus nebulosus at skin temperatures between 5 and 35 °C. A unimodal relationship between spontaneous activity and temperature was obtained. Mean (±SEM) peak discharge rate was 57.3 ±1.8 impulses s^–1 at 25 ° C; the receptors were active at 5 °C (15.0 impulses s^–1) and at 35 °C (31.5 impulses s^–1). There were no dynamic responses to temperature changes in either the warming or cooling direction. The shape of the frequency characteristic depended on temperature: the peak of the gain curve shifted to low frequencies at low temperatures. There was a concomitant change of the phase characteristic: the intersection at zero degree phase angle shifted to higher frequencies with an increase of temperature, thus increasing the lead at lower frequencies and decreasing the lag at higher frequencies. Latency after combined excitatory and inhibitory impulse stimulation was temperature dependent, ranging from 16.4 ms (5 °C) to 5.6 ms (35 °C). Application of the specific calcium channel blocker menthol (0.2 mM) suppressed spontaneous activity, the effect becoming more prominent at higher temperatures. Sensitivity to sinusoidal electrical stimulation was also impaired, but to a lesser degree and mainly at lower temperatures. We conclude that the filter properties of the receptor organ can be modelled by a band-pass filter in series with a latency, both of which are temperature dependent. These filter properties might be partially based on the activation kinetics of the tranduction channels.     

Contrasting effects of vasopressin,desglycinamide-vasopressin and amphetamine on a delayed matching to position task in rats

The effects of peripherally injected arginine vasopressin (AVP: 0–25 g/kg), its desglycinamide analogue (DGAVP: 0–25 g/kg), which is practically devoid of pressor activity, and d-amphetamine (AMP: 0–1.25 mg/kg) were studied using a delayed (0–32 s) matching to position task (Dunnett 1985). A limited hold for responding (20 s) was in operation. This task enables an accurate assessment of forgetting in rats. AVP reliably improved per cent correct performance, and this effect was substantiated by accuracy indices derived from signal detection theory (TSD). DGAVP, however, was inactive, suggesting that the parent peptide's pressor properties were responsible for its beneficial effects. AMP disrupted performance in a dose-related manner, and was the only substance to alter a TSD bias index (responsivity index, RI), indicating a degree of response repetition at the highest dose. These results are consistent with some earlier reports, and suggest that AVP may enhance memory by peripheral action, while AMP disrupts performance. Closer inspection of the data, however, suggested that the peptide reduced general responsiveness. A new index to measure bias (Sahgal 1987) suggested that AVP-treated subjects restricted their sample and choice responses to one side of the operant chamber, thereby achieving a spuriously high detection rate with few errors of commission (incorrect responses). It is concluded that AVP does not, after all, improve performance: on the contrary it has detrimental effects, and produces errors of omission (failure to respond).     

肝脏局灶性小占位的磁共振信号强度比与病灶性质的相关性

目的 计算肝细胞癌、肝转移瘤、肝脏海绵状血管瘤和肝囊肿的病灶／肝脏磁共振信号强度比（SIR）,并评价其与病灶性质的关系。方法 随机选择经确诊的肝细胞癌、肝转移瘤、肝海绵状血管瘤和肝囊肿病例共92例（148个病灶）行前瞻性磁共振成像（0．5T）研究。计算4种病灶的SIR,并进行统计学分析。结果 在T1W图像上,肝海绵状血管瘤与恶性肿瘤的SIR值间差异无显著性（t=1.799,P=0.075);质子加权像上,良恶性肿瘤的SIR之间无统计学意义（t=0.691,P=0.491);T2WI上,良性病变的SIR显著高于恶性肿瘤（P＜0．01）,且4种病变的SIR值与回波时间（TE）之间均存在线性正向相关关系。结论 在T2WI个测得的SIR可用于区分肝脏占位性病灶的性质。     

Stat3磷酸化与c-fos和c-jun蛋白表达在肝细胞癌发生中的作用

利用SP免疫组织化学技术检测 5 5例肝细胞癌 (HCC)及其癌旁组织中p Stat3(Tyr70 5 ) ,c fos和c jun蛋白的表达。结果显示 :HCC中p Stat3,c fos和c jun蛋白阳性率和阳性强度均高于癌旁组织 (P <0 .0 1) ,且p Stat3与c fos和c jun蛋白表达强度均呈明显正相关 ,而在癌旁组织中p Stat3仅与c jun蛋白表达相关 ,提示Stat3蛋白的磷酸化可能是HCC发生的早期事件 ,并通过激活c jun和c fos基因使肝细胞恶性转化 ;癌旁肝组织中 ,p Stat3,c jun或c fos呈阳性表达的肝细胞可能是一种具有恶性潜能的癌前细胞群。     

肝癌组织中β—和p^120—连环蛋白的表达

目的 揭示连环蛋白与肝癌的发生发展的关系。方法 应用RT－PCT和免疫组织化学观察细胞黏附与信号转导分子β－和p^120－连环蛋白在正常肝组织、肝癌旁结节性肝硬化组织和肝癌组织中p^120ctn mRNA的蛋白质表达情况及其与β－连环蛋白的关系。结果 所有肝组织中均表达p^120 ctn mRNA同工蛋白1A和3A。2例正常肝组织中β－和p^120-连环蛋白分子表现为胞膜表达而胞质无表达;17例癌旁结节性肝硬化组织表现为胞膜和胞质均有表达,以胞质为主,且胞膜表达有所增强。17例HCC组织中表现为胞膜表达明显减弱或消失,而胞质表达则增强。多数细胞胞膜表达呈现不连续性。结论 肝组织中可检测到p^120ctn同工蛋白1A和3A mRNA。此外,正常肝组织中β－和p^120-连环蛋白分布在胞膜,对维持正常的细胞黏附和信号转导起重要作用;结节性肝硬化肝组织中此2种分子出现了分布变化,而肝癌细胞中此2种分子发生了明显的转位现象,提示肝癌细胞在一定程度上改变了细胞黏附分子的正常功能和其所介导的信号转导作用。