RNA interference and retinoblastoma-related genes are required for repression of endogenous siRNA targets in Caenorhabditis elegans

In Caenorhabditis elegans, a vast number of endogenous short RNAs corresponding to thousands of genes have been discovered recently. This finding suggests that these short interfering RNAs (siRNAs) may contribute to regulation of many developmental and other signaling pathways in addition to silencing viruses and transposons. Here, we present a microarray analysis of gene expression in RNA interference (RNAi)-related mutants rde-4, zfp-1, and alg-1 and the retinoblastoma (Rb) mutant lin-35. We found that a component of Dicer complex RDE-4 and a chromatin-related zinc finger protein ZFP-1, not implicated in endogenous RNAi, regulate overlapping sets of genes. Notably, genes a) up-regulated in the rde-4 and zfp-1 mutants and b) up-regulated in the lin-35(Rb) mutant, but not the down-regulated genes are highly represented in the set of genes with corresponding endogenous siRNAs (endo-siRNAs). Our study suggests that endogenous siRNAs cooperate with chromatin factors, either C. elegans ortholog of acute lymphoblastic leukemia-1 (ALL-1)-fused gene from chromosome 10 (AF10), ZFP-1, or tumor suppressor Rb, to regulate overlapping sets of genes and predicts a large role for RNAi-based chromatin silencing in control of gene expression in C. elegans.     

Differential expression of cell cycle regulators in HCV-infection and related hepatocellular carcinoma

AIM: To investigate cell cycle proteins in chronic hepatitis C virus infection in order to analyze their role in the process of hepatocyte transformation and to characterize their prognostic properties.METHODS: Subjects of the current study included 50 cases of chronic hepatitis C (CHC) without cirrhosis, 30 cases of CHC with liver cirrhosis (LC), and 30 cases of hepatitis C-related hepatocellular carcinoma (HCC) admitted to the Department of Hepato-Gastroenterology, Theodor Bilharz Research Institute (TBRI), Giza, Egypt. Fifteen wedge liver biopsies, taken during laparoscopic cholecystectomy, were also included as normal controls. Laboratory investigations including urine and stool analysis, liver function tests and prothrombin concentration; serologic markers for viral hepatitis and ultrasonography were done for all cases of the study together with immunohistochemical analysis using primary antibodies against Cyclin D1, Cyclin E, p21, p27 and Rb/p105 proteins.RESULTS: Normal wedge liver biopsies didn’t express Cyclin E or Rb/p105 immunostaining but show positive staining for Cyclin D1, p21 and p27. Cyclin D1 expressed nuclear staining that was sequentially increased from CHC to LC (P < 0.01) to HCC (P < 0.001) cases; meanwhile, Cyclin E revealed nuclear positivity only in the case of HCCs patients that was directly correlated to Rb/p105 immuno-reactivity. The expression of p21 and p27 was significantly increased in CHC and LC cases compared to normal controls and HCCs with no significant difference between well- and poorly-differentiated tumors. p21 showed only a nuclear pattern of staining, while, p27 presented with either cytoplasmic and/or nuclear reactivity in all studied cases. Correlation analysis revealed a direct relation between Cyclin D1 and p21 in CHC cases (P < 0.001), between Cyclin D1 and Cyclin E in HCCs (P < 0.01); however, an inverse relationship was detected between Cyclin D1 and p21 or p27 (P < 0.001) and between p21 and Rb/p105 (P < 0.05) in HCCs.CONCLUSION: Upregulation of Cyclin D1 in CHC plays a vital role in the development and differentiation of HCC; while, Cyclin E may be a useful marker formonitoring tumor behavior. p21 and p27 can be used as predictive markers for HCC. Furthermore, higher expression of Rb/p105 as well as inverse relation with p21 and histologic grades suggests its important role in hepatic carcinogenesis.     

A polymorphism in the alpha4 nicotinic receptor gene (Chrna4) modulates enhancement of nicotinic receptor function by ethanol

BACKGROUND: Several studies indicate that ethanol enhances the activity of alpha4beta2 nicotinic acetylcholine receptors (nAChR). Our laboratory has identified a polymorphism in the alpha4 gene that results in the substitution of an alanine (A) for threonine (T) at amino acid position 529 in the second intracellular loop of the alpha4 protein. Mouse strains expressing the A variant have, in general, greater nAChR-mediated 86Rb+ efflux in response to nicotine than strains with the T variant. However, the possibility of the polymorphism modulating the effects of ethanol on the 86Rb+ efflux response has not been investigated. METHODS: We have used the 86Rb+ efflux method to study the acute effects of ethanol on the function of the alpha4beta2 nAChR in the thalamus in six different mouse strains. Experiments were also performed on tissue samples taken from F2 intercross animals. The F2 animals were derived from A/J mice crossed with a substrain of C57BL/6J mice that carried a null mutation for the gene encoding the beta2 nAChR subunit. RESULTS: In strains carrying the A polymorphism (A/J, AKR/J, C3H/Ibg), coapplication of ethanol (10-100 mM) with nicotine (0.03-300 microM) increased maximal ion flux when compared with nicotine alone with no effect on agonist potency. In contrast, ethanol had little effect on the nicotine concentration-response curve in tissue prepared from strains carrying the T polymorphism (Balb/Ibg, C57BL/6J, C58/J). Experiments with the F2 hybrids demonstrated that one copy of the A polymorphism was sufficient to produce a significant enhancement of nAChR function by ethanol (50 mM) in animals that were also beta2 +/+. Ethanol had no effect on nicotine concentration-response curves in T/T beta2 +/+ animals. CONCLUSIONS: The results suggest that the A/T polymorphism influences the initial sensitivity of the alpha4beta2 nAChR to ethanol.     

Inhibition of bone cell metabolism increases strontium-85 uptake

Summary Experiments have been performed on the canine tibia to investigate whether perturbation of the energy metabolism of bone cells can influence the short-term exchange of bone mineral. Simultaneous injection of three radioactive tracers,¹²⁵I-albumin,⁸⁵Sr, and⁸⁶Rb, into the tibial nutrient artery was followed immediately by measurement of the concentration of these tracers in the venous outflow from the bone for a period of 5 minutes. This procedure was performed before and after the injection of potassium cyanide into the bone. From the measured concentrations, extraction ratios for⁸⁵Sr and⁸⁶Rb with respect to¹²⁵I-albumin were calculated. It was found that net extraction after 5 minutes of⁸⁵Sr was significantly increased. This result indicates that efflux of ions from exchangeable mineral is dependent to a significant extent on the metabolic activity of bone cells.     

9-顺维A酸诱导肺癌细胞L78凋亡及其与Rb和Cyclin D1基因表达的关系

目的研究9-顺维A酸(9-cis-retinoic acid, 9-cis RA)诱导肺鳞癌细胞株L78凋亡作用及其与Rb、Cyclin D1基因表达的关系,初步探讨其作用机制. 方法体外培养肺鳞癌细胞株L78,随机分为两组,实验组加入浓度为5 μmol/L的9-cis RA;对照组加入浓度为0.1%二甲亚砜.两组均培养48小时后用免疫组织化学法检测L78细胞中Rb基因表达率,用流式细胞仪技术分别检测Rb、Cyclin D1基因表达率和肿瘤细胞凋亡率, 并研究三者之间的相关关系. 结果实验组肺鳞癌细胞株L78细胞Rb基因表达明显增强,Cyclin D1基因表达降低,细胞凋亡率增高(P＜0.01).Rb基因表达率与细胞凋亡发生率呈正相关(r=0.854,P＜0.05),Cyclin D1基因表达率与细胞凋亡发生率呈负相关(r=-0.812,P＜0.05). 结论 9-cis RA可能通过Rb基因表达增强和Cyclin D1基因表达降低途径,使细胞明显阻滞在G0/G1期,并诱导肺鳞癌细胞株L78细胞凋亡.     

人参皂甙单体Rb1对多药耐药细胞系 K562/HHT的耐药逆转作用

目的：探讨中药钙离子通道拮抗剂人参皂甙单体Ｒｂ１,对白血病多药耐药细胞系（Ｋ－５６２／ＨＨＴ）的耐药逆转作用。方法：药物敏感试验采用四唑氮盐（ＭＴＴ）比色试验法。结果：Ｒｂ１在０～８０ μｍ ｏｌ／Ｌ浓度范围内对Ｋ５６２／ＨＨＴ未见明显毒性作用;２０ μｍ ｏｌ／Ｌ、４０ μｍ ｏｌ／ＬＲｂ１ 耐药逆转倍数分别为４．４、７．９ 倍。结论：Ｒｂ１ 可以逆转Ｋ５６２／ＨＨＴ的多药耐药性,并呈剂量依赖性     

Rb intrinsically promotes erythropoiesis by coupling cell cycle exit with mitochondrial biogenesis

Regulation of the cell cycle is intimately linked to erythroid differentiation, yet how these processes are coupled is not well understood. To gain insight into this coordinate regulation, we examined the role that the retinoblastoma protein (Rb), a central regulator of the cell cycle, plays in erythropoiesis. We found that Rb serves a cell-intrinsic role and its absence causes ineffective erythropoiesis, with a differentiation block at the transition from early to late erythroblasts. Unexpectedly, in addition to a failure to properly exit the cell cycle, mitochondrial biogenesis fails to be up-regulated concomitantly, contributing to this differentiation block. The link between erythropoiesis and mitochondrial function was validated by inhibition of mitochondrial biogenesis. Erythropoiesis in the absence of Rb resembles the human myelodysplastic syndromes, where defects in cell cycle regulation and mitochondrial function frequently occur. Our work demonstrates how these seemingly disparate pathways play a role in coordinately regulating cellular differentiation.     

Effects of selective α1 and α2 adrenoceptor active drugs on 86Rb+ efflux from pieces of rat parotid gland

Minute pieces of rat parotid gland were used in studies of adrenergic regulation of K+ efflux using ⁸⁶Rb+ as a probe for K+. Noradrenaline induced a concentration-dependent Rb+ efflux, whereas the β₁-selective agonist prenalterol was without effect. On the other hand, the β₂-selective drug, terbutaline, at high concentrations displayed a small enhancement of Rb+ -secretion. The selective α₁-adrenoceptor drug, phenylephrine, was as potent as noradrenaline, whereas the α₂-agonist clonidine had only a small effect. The noradrenaline-induced Rb+-efflux was effectively inhibited in the presence of prazosin, an α₁-blocker, whereas the α₂-antagonist, yohimbine, was roughly 50 times less potent. The results suggest that catecholamine-induced K+-secretion from the rat parotid gland is mediated via activation of post-synaptic α-adrenoceptors of the α₁-subtype.