选择性剪接与肿瘤靶向治疗

RNA剪接过程受到多种调节因子作用,以保证前体mRNA剪接的准确性。但是大量研究发现,在人类肿瘤中经常发生选择性剪接的异常或者来自特定癌症基因的剪接调控元件的突变。因此,RNA剪接调节剂作为一类新的癌蛋白和肿瘤抑制因子而逐渐受到关注,并有望通过调节参与致癌基因的RNA而达到治疗肿瘤的效果。改变RNA的异常剪接是治疗相关癌症的基础,这也为靶向治疗提供了更加丰富的靶点。本文综述了新发现的和预测的不同的剪接事件导致癌症的相关基因,并且对它们如何促成疾病的发病机制进行讨论。最后,我们总结了最新的针对可变剪接而发展的癌症诊断和治疗方法,包括使用小分子的剪接抑制剂来阻断剪接体或转录因子修饰酶,以调节特异性剪接导致的癌症。     

Alternative splicing of glucokinase mRNA in rat liver.

The sequences of two near full-length cDNAs encoding rat liver glucokinase are reported. One of the cDNAs is essentially identical to the cDNA cloned by Andreone, Printz, Pilkis, Magnuson & Granner. [(1989) J. Biol. Chem. 264, 363-369]. The other cDNA contains a 151 bp insertion and a downstream 52 bp deletion. The inserted block of bases has been shown to originate from an optional cassette exon, termed 2A, between the previously described exons 1 and 2. The conceptual translation product from the variant mRNA is identical to the original glucokinase protein for the first 15 amino acids. Next there is a novel polypeptide sequence of 87 residues, comprising 50 residues encoded by the cassette exon and 37 residues specified by an altered reading frame in exon 2. Due to the 52 bp deletion, 17 amino acids of the reference sequence are then missing, after which the sequence reverts to the original. Northern blot analysis with oligonucleotide probes has shown that alternatively spliced mRNA represents about 5% of total glucokinase mRNA. Alternative splicing of glucokinase mRNA in liver may explain earlier findings of minor isoforms of hepatic glucokinase.     

Alternative splicing of mRNA of mouse interleukin-4 and interleukin-6

Interleukin-4 and interleukin-6 are multifunctional regulatory proteins, which participate both in haemopoiesis and in immunopoiesis. The alternative splicing of these interleukins in humans is known to proceed in a tissue-specific manner. Additionally, changes in splicing can also be dependent on tissue pathology. In this work, we report on the presence of alternatively spliced mRNA (IL-4delta2mRNA), lacking exon 2, in mouse bone marrow and spleen cells. We find that in unstimulated cells IL-4mRNA levels strongly dominate over IL-4delta2mRNA levels. Both increase in response to stimulation, with the concentration of the alternative variant rising earlier and faster than that of the full-length variant. In all other tissues studied dominance of IL-4delta2mRNA over the full-length variant was not observed. In addition, we find expression of three forms of IL-6 mRNA: the full-length IL-6 mRNA, IL-6Delta3 mRNA, and IL-6Delta5 mRNA in the second and third trimester placenta tissue and in the spleen of mice immunized with a high dose of sheep erythrocytes. It is anticipated that translation of these mRNA variants can generate proteins capable of binding to some subunits of the IL-6 receptor, thus possessing effector function. Alternative splicing is discussed as a source of cytokines with new regulatory properties.     

Alternative splicing creates two new architectures for human tyrosyl-tRNA synthetase

Many human tRNA synthetases evolved alternative functions outside of protein synthesis. These functions are associated with over 200 splice variants (SVs), most of which are catalytic nulls that engender new biology. While known to regulate non-translational activities, little is known about structures resulting from natural internal ablations of any protein. Here, we report analysis of two closely related, internally deleted, SVs of homodimeric human tyrosyl-tRNA synthetase (TyrRS). In spite of both variants ablating a portion of the catalytic core and dimer-interface contacts of native TyrRS, each folded into a distinct stable structure. Biochemical and nuclear magnetic resonance (NMR) analysis showed that the internal deletion of TyrRSΔE2–4 SV gave an alternative, neomorphic dimer interface ‘orthogonal’ to that of native TyrRS. In contrast, the internal C-terminal splice site of TyrRSΔE2–3 prevented either dimerization interface from forming, and yielded a predominantly monomeric protein. Unlike ubiquitous TyrRS, the neomorphs showed clear tissue preferences, which were distinct from each other. The results demonstrate a sophisticated structural plasticity of a human tRNA synthetase for architectural reorganizations that are preferentially elicited in specific tissues.     

Differentiation strategies of alternative splicing variants mRNA estrogen receptor-alpha

From the clinical point of view recognizing the concentrations and type profile of isoforms could be of significant practical importance. The aim of the study is designed QRT-PCR reaction to assess profile of mRNA ER-alpha and their isoforms. Theoretical part of the study was made according to computer program and available Genbank database. To detect a isoform one of the primer was designed to hybridize within exon-border linked in alternative splicing. The study presents the differentiation strategies in isoforms coming about as the alternative splicing result. Designed oligonucleotide probes and primers allow to distinguish mRNA isoforms of ER-alpha and their quantification in assessed tissues.     

Amyloidosis: new strategies for treatment

Amyloidosis is a disorder of protein folding in which normally soluble proteins are deposited extracellularly as insoluble fibrils, impairing tissue structure and function. Over 20 unrelated proteins form amyloid fibrils in vivo, with fibrils sharing a lamellar cross-β sheet structure, composed of non-covalently associated protein or peptide subunits. Amyloidosis may be acquired or hereditary and local or systemic, and is defined according to the precursor protein. Of note, local amyloid deposition occurs in Alzheimer’s disease (AD) and maturity onset diabetes but their precise role in the pathogenesis of these diseases remains uncertain. Glycosaminoglycans (GAG) and the pentraxin protein, serum amyloid P (SAP) component, are universal non-fibrillar constituents of amyloid deposits that contribute to fibrillogenesis. We review potential therapies for amyloidosis, which include measures to reduce the production of amyloidogenic precursor proteins, interference with fibrillogenesis, and enhancement of amyloid clearance, either by active or passive immunisation or by destabilising deposits through removal of serum amyloid P component.     

Drag reduction in wave-swept macroalgae: Alternative strategies and new predictions

? Premise of the study: Intertidal macroalgae must resist extreme hydrodynamic forces imposed by crashing waves. How does frond flexibility mitigate drag, and how does flexibility affect predictions of drag and dislodgement in the field? ? Methods: We characterized flexible reconfiguration of six seaweed species in a recirculating water flume, documenting both shape change and area reduction as fronds reorient. We then used a high-speed gravity-accelerated water flume to test our ability to predict drag under waves based on extrapolations of drag recorded at slower speeds. We compared dislodgement forces to drag forces predicted from slow- and high-speed data to generate new predictions of survivorship and maximum sustainable frond size along wave-swept shores. ? Key results: Bladed algae were generally "shape changers", limiting drag by reducing drag coefficients, whereas the branched alga Calliarthron was an "area reducer", limiting drag by reducing projected area in flow. Drag predictions often underestimated actual drag measurements at high speeds, suggesting that slow-speed data may not reflect the performance of flexible seaweeds under breaking waves. Several seaweeds were predicted to dislodge at similar combinations of velocity and frond size, suggesting common scaling factors of dislodgement strength and drag. ? Conclusions: Changing shape and reducing projected area in flow are two distinct strategies employed by flexible seaweeds to resist drag. Flexible reconfiguration contributes to the uncertainty of drag extrapolation, and researchers should use caution when predicting drag and dislodgement of seaweeds in the field.