Transgelin Silencing Induces Different Processes in Different Breast Cancer Cell Lines

Transgelin is a protein reported to be a marker of several cancers. However, previous studies have shown both up‐ and down‐regulation of transgelin in tumors when compared with non‐tumor tissues and the mechanisms whereby transgelin may affect the development of cancer remain largely unknown. Transgelin is especially abundant in smooth muscle cells and is associated with actin stress fibers. These contractile structures participate in cell motility, adhesion, and the maintenance of cell morphology. Here, the role of transgelin in breast cancer is focused on. Initially, the effects of transgelin on cell migration of the breast cancer cell lines, BT 549 and PMC 42, is studied. Interestingly, transgelin silencing increased the migration of PMC 42 cells, but decreased the migration of BT 549 cells. To clarify these contradictory results, the changes in protein abundances after transgelin silencing in these two cell lines are analyzed using quantitative proteomics. The results confirmed the role of transgelin in the migration of BT 549 cells and suggest the involvement of transgelin in apoptosis and small molecule biochemistry in PMC 42 cells. The context‐dependent function of transgelin reflects the different molecular backgrounds of these cell lines, which differ in karyotypes, mutation statuses, and proteome profiles.     

Loss of transgelin in breast and colon tumors and in RIE-1 cells by Ras deregulation of gene expression through Raf-independent pathways.

Activated Ras but not Raf can transform RIE-1 and other epithelial cells, indicating the critical importance of Raf-independent effector function in Ras transformation of epithelial cells. To elucidate the nature of these Raf-independent activities, we utilized representational difference analysis to identify genes aberrantly expressed by Ras through Raf-independent mechanisms in RIE-1 cells. We identified a total of 22 genes, both known and novel, whose expression was either activated or abolished by Ras but not Raf. The genes up-regulated encode proteins involved in protein or DNA synthesis, regulation of protease activity, or ligand binding, whereas those genes down-regulated encode actin cytoskeletal-, extracellular matrix-, and gap junction-associated proteins, and transmembrane receptor- or cytokine-like proteins. These results suggest that a key function of Raf-independent signaling involves deregulation of gene expression. We further characterized transgelin as a gene whose expression was abolished by Ras. Transgelin was identified previously as a protein whose expression was lost in virally transformed cell lines. We show that this loss is regulated at the level of gene expression and that both Raf-dependent and Raf-independent pathways are required to cause Ras down-regulation of transgelin in RIE-1 cells, whereas Raf alone is sufficient to cause its loss in NIH 3T3 fibroblasts. We also found that Ras-dependent and Ras-independent mechanisms can cause the down-regulation of transgelin in human breast and colon carcinoma cells lines and patient-derived tumor samples. We conclude that loss of transgelin gene expression may be an important early event in tumor progression and a diagnostic marker for breast and colon cancer development.     

Crystal structure of human transgelin

Transgelin (TAGLN), also known as smooth muscle protein 22 (SM22), is a highly conserved protein found in smooth muscle tissues of adult vertebrates. Abolition of transgelin gene expression by the oncogenic Ras may be an important early event in tumor progression and a diagnostic marker for breast and colon cancer development. Transgelin contains a single calponin homology (CH) domain. However, the question of whether this single CH domain can bind actin remains open. Here we report the 2.3 A resolution crystal structure of full length human transgelin, whose main structural feature is confirmed to be a CH domain. Secondary structures of CH domains from different proteins were analyzed and conserved residues were identified that maintain similar tertiary structures.     

Transgelin: an actin-binding protein and tumour suppressor

Transgelin is a shape change sensitive 22 kDa actin-binding protein of the calponin family. It contains a C-terminal calponin-like module (CLIK(23)) and an upstream positively charged amino acid region required for actin binding. Transgelin is ubiquitous to vascular and visceral smooth muscle and is an early marker of smooth muscle differentiation, where its expression is driven by CArG box, smooth muscle gene promoter. It is also present in fibroblasts, and some epithelium where expression is likely driven by TGF-beta1. Transgelin null mice reveal that, whilst it is not required for smooth muscle development, transgelin may be involved in calcium-independent smooth muscle contraction. Recent evidence suggests that transgelin acts as a tumour suppressor. Its expression is lost in prostate, breast and colon cancers. This is consistent with suppression of the metallo matrix protease-9 (MMP-9) by transgelin, where MMP-9 is upregulated in these common cancers.     

Transgelin functions as a suppressor via inhibition of ARA54-enhanced androgen receptor transactivation and prostate cancer cell growth

The androgen receptor (AR) requires coregulators for its optimal function. However, whether AR coregulators further need interacting protein(s) for their proper function remains unclear. Here we describe transgelin as the first ARA54-associated negative modulator for AR. Transgelin suppressed ARA54-enhanced AR function in ARA54-positive, but not in ARA54-negative, cells. Transgelin suppressed AR transactivation via interruption of ARA54 homodimerization and AR-ARA54 heterodimerization, resulting in the cytoplasmic retention of AR and ARA54. Stable transfection of transgelin in LNCaP cells suppressed AR-mediated cell growth and prostate-specific antigen expression, whereas this suppressive effect was abolished by the addition of ARA54-small interfering RNA. Results from tissue surveys showing decreased expression of transgelin in prostate cancer specimens further strengthened the suppressor role of transgelin. Our findings reveal the novel mechanisms of how transgelin functions as a suppressor to inhibit prostate cancer cell growth. They also demonstrate that AR coregulators, like ARA54, might have dual in vivo roles functioning as both a direct coactivator and as an indirect mediator in AR function. The finding that a protein can modulate AR function without direct interaction with AR might provide a new therapeutic approach, with fewer side effects, to battle prostate cancer by targeting AR indirectly.     

Transgelin 2 Participates in Lovastatin-Induced Anti-Angiogenic Effects in Endothelial Cells through a Phosphorylated Myosin Light Chain-Related Mechanism

Background

Anti-angiogenic activity is considered to play a key role in the statin-induced anti-tumor effects. We aimed to identify new targets underlying this pleiotropic effect of lovastatin.

Methodology/Principal Findings

We investigated the inhibitory effects of lovastatin on endothelial cell biology and angiogenesis in vitro. Lovastatin at high doses inhibited endothelial cell migration and tube formation. Using two-dimensional gel electrophoresis followed by mass spectrometry, we identified the up-regulation of the actin-binding protein transgelin 2 in endothelial cells following treatment with lovastatin. Changes in transgelin 2 levels were confirmed by Western blot and confocal microscopy. We further demonstrated that the Rho signaling inactivation and actin depolymerization contributed to the up-regulation of transgelin 2. The knockdown of transgelin 2 by siRNA dramatically enhanced endothelial migration and tube formation, and meanwhile attenuated the inhibitory effects of lovastatin on cell motility. Moreover, the lovastatin-induced inhibition of myosin light chain phosphorylation was also reversed by transgelin 2 knockdown. The activation of Rho GTPase in the absence of transgelin 2 may represent a mechanism underlying the regulation of phosphorylated myosin light chain by transgelin 2.

Conclusions/Significance

These results strongly imply a novel role for transgelin 2 in the angiostatic activities of lovastatin.     

A role for the actin cytoskeleton in cell death and aging in yeast

Several determinants of aging, including metabolic capacity and genetic stability, are recognized in both yeast and humans. However, many aspects of the pathways leading to cell death remain to be elucidated. Here we report a role for the actin cytoskeleton both in cell death and in promoting longevity. We have analyzed yeast strains expressing mutants with either increased or decreased actin dynamics. We show that decreased actin dynamics causes depolarization of the mitochondrial membrane and an increase in reactive oxygen species (ROS) production, resulting in cell death. Important, however, is the demonstration that increasing actin dynamics, either by a specific actin allele or by deletion of a gene encoding the actin-bundling protein Scp1p, can increase lifespan by over 65%. Increased longevity appears to be due to these cells producing lower than wild-type levels of ROS. Homology between Scp1p and mammalian SM22/transgelin, which itself has been isolated in senescence screens, suggests a conserved mechanism linking aging to actin stability.     

Crystallization and preliminary crystallographic analysis of transgelin

Transgelin was solubly expressed in E. coli. Crystals of transgelin have been grown at 291K using sodium formate or PEG-4000 as precipitants. X-ray diffraction by the crystal extends to 2.3 A resolution. The crystal belongs to the space group P2(1), with the unit cell parameters a=39.3, b=61.9, c=56.0 A and beta=90.2 degrees .     

Transgelin基因真核表达载体的构建及其对胃腺癌AGS细胞增殖的影响

目的 构建人肌动蛋白凝胶蛋白（Transgelin）基因编码区序列（cDNA）的真核表达载体,并观察其对胃腺癌细胞增殖的影响.方法 从健康人肠组织中提取总RNA,应用RT-PCR方法扩增TransgelincDNA的全长序列后克隆入pcDNA3.1/myc-His（-）A质粒中,构建成Transgelin基因的真核表达载体,然后转染入AGS细胞中,新霉素筛选稳定转染细胞克隆,通过MTT实验,研究转染Transgelin基因后细胞增殖的变化.结果 重组载体经酶切鉴定和测序证实目的 基因正确尤误,Western印迹检测结果显示Transgelin融合蛋白在AGS细胞中具有良好的表达,而转染空载体及未转染细胞对照则未见有此融合蛋白质条带;RT-PCR结果显示Transgelin基因在其稳定转染的AGS细胞克隆中表达上调,与空载体稳定转染及未转染细胞比较,差异具有统计学意义（P＜0.05）.Transgelin表达上调的稳定克隆组,AGS细胞的增殖活性明显降低,MTT结果显示其增殖活性显著低于空载体稳定转染组及未转染亲代细胞组,差异具有统计学意义（P＜0.05）,而后两者之间差异无统计学意义（P＞0.05）.结论 Transselin表达上调可导致胃腺癌细胞增殖降低.     

The Saccharomyces cerevisiae calponin/transgelin homolog Scp1 functions with fimbrin to regulate stability and organization of the actin cytoskeleton

Calponins and transgelins are members of a conserved family of actin-associated proteins widely expressed from yeast to humans. Although a role for calponin in muscle cells has been described, the biochemical activities and in vivo functions of nonmuscle calponins and transgelins are largely unknown. Herein, we have used genetic and biochemical analyses to characterize the budding yeast member of this family, Scp1, which most closely resembles transgelin and contains one calponin homology (CH) domain. We show that Scp1 is a novel component of yeast cortical actin patches and shares in vivo functions and biochemical activities with Sac6/fimbrin, the one other actin patch component that contains CH domains. Purified Scp1 binds directly to filamentous actin, cross-links actin filaments, and stabilizes filaments against disassembly. Sequences in Scp1 sufficient for actin binding and cross-linking reside in its carboxy terminus, outside the CH domain. Overexpression of SCP1 suppresses sac6Delta defects, and deletion of SCP1 enhances sac6Delta defects. Together, these data show that Scp1 and Sac6/fimbrin cooperate to stabilize and organize the yeast actin cytoskeleton.     

The cell surface structure of tumor endothelial marker 8 (TEM8) is regulated by the actin cytoskeleton

Tumor endothelial marker 8 (TEM8) is an integrin-like cell surface protein upregulated on tumor blood vessels and a potential vascular target for cancer therapy. Here, we found that the ability of an anti-TEM8 antibody, clone SB5, to recognize the extracellular domain of TEM8 on the cell surface depends on other host-cell factors. By taking advantage of SB5's ability to distinguish different forms of cell surface TEM8, we identified alpha-smooth muscle actin and transgelin, an actin binding protein, as intracellular factors able to alter TEM8 cell surface structure. Overexpression of either of these proteins in cells converted TEM8 from an SB5-exposed to an SB5-masked form and protected cells from SB5-saporin immunotoxins. Because the predominant form of TEM8 on the cell surface is not recognized by SB5, we also developed a new monoclonal antibody, called AF334, which is able to recognize both the SB5-exposed and the SB5-masked forms of TEM8. AF334-saporin selectively killed TEM8-positive cells independent of TEM8 cell surface structure. These studies reveal that TEM8 exists in different forms at the cell surface, a structure dependent on interactions with components of the actin cytoskeleton, and should aid in the rational design of the most effective diagnostic and therapeutic anti-TEM8 monoclonal antibodies.     

植物细胞中的前纤维蛋白

肌动蛋白组成的微丝骨架是真核细胞中的重要结构,在体内处于高度动态变化之中,受多种肌动蛋白结合蛋白（actin-binding proteins）的调节。前纤维蛋白（profilin）是一种单体肌动蛋白结合蛋白,存在于所有的真核细胞中,在植物细胞中也得到较多的研究。前纤维蛋白除可以结合单体肌动蛋白之外,还可以与磷脂酰肌醇及富含多聚脯氨酸的蛋白质等多种分子结合,在细胞信号转导中行使着重要的功能。本文结合本实验室的研究结果,概述了前纤维蛋白的最新研究进展。     

Stg 1 is a novel SM22/transgelin-like actin-modulating protein in fission yeast

We identified a novel actin-modulating protein Stg 1 in the fission yeast Schizosaccharomyces pombe. Stg 1 is similar to mammalian SM22/transgelin, and biochemical experiments showed that Stg 1 crosslinked F-actin. Microscopic observation suggested that Stg 1 was a component of actin patch. Overexpression of Stg 1 caused a defect in cytokinesis by suppressing the formation of a contractile ring and formation of abnormal aggregates of F-actin in the ends and mid-region of cells. Although distribution of the actin cytoskeleton was not affected by disrupting Stg 1(+), genetic interaction suggested that Stg 1 was likely involved in controlling the organization of the actin cytoskeleton in cell morphogenesis and cytokinesis in fission yeast.     

Scapinin,the Protein Phosphatase 1 Binding Protein,Enhances Cell Spreading and Motility by Interacting with the Actin Cytoskeleton

Scapinin, also named phactr3, is an actin and protein phosphatase 1 (PP1) binding protein, which is expressed in the adult brain and some tumor cells. At present, the role(s) of scapinin in the brain and tumors are poorly understood. We show that the RPEL-repeat domain of scapinin, which is responsible for its direct interaction with actin, inhibits actin polymerization in vitro. Next, we established a Hela cell line, where scapinin expression was induced by tetracycline. In these cells, expression of scapinin stimulated cell spreading and motility. Scapinin was colocalized with actin at the edge of spreading cells. To explore the roles of the RPEL-repeat and PP1-binding domains, we expressed wild-type and mutant scapinins as fusion proteins with green fluorescence protein (GFP) in Cos7 cells. Expression of GFP-scapinin (wild type) also stimulated cell spreading, but mutation in the RPEL-repeat domain abolished both the actin binding and the cell spreading activity. PP1-binding deficient mutants strongly induced cell retraction. Long and branched cytoplasmic processes were developed during the cell retraction. These results suggest that scapinin enhances cell spreading and motility through direct interaction with actin and that PP1 plays a regulatory role in scapinin-induced morphological changes.     

Purification and properties of transgelin: a transformation and shape change sensitive actin-gelling protein

We have purified the transformation and shape change sensitive isoform of an actin associated polypeptide doublet previously described by us (Shapland, C., P. Lowings, and D. Lawson. 1988. J. Cell Biol. 107:153- 161) and have shown that it is evolutionarily conserved as far back as yeast. The purified protein: (a) binds directly to actin filaments at a ratio of 1:6 actin monomers, with a binding constant (Ka) of approximately 7.5 x 10(5) M-1; and (b) causes actin filament gelation within 2 min. Although these activities are controlled by ionic strength (and may be mediated by positively charged amino acid residues) the molecule remains as a monomer irrespective of ionic conditions. EM reveals that the addition of this protein to actin filaments converts them from a loose, random distribution into a tangled, cross-linked meshwork within 1 min, and discrete tightly aggregated foci after 10 min. By use of an "add-back" cell permeabilization system we can rebind this molecule specifically to actin filaments in cells from which it has previously been removed. Since the protein is transformation sensitive and gels actin, we have named it transgelin.     

Identification of vascular breast tumor markers by laser capture microdissection and label-free LC-MS

Blood vessels in tumors frequently show abnormal characteristics, such as tortuous morphology or leakiness, but very little is known about protein expression in tumor vessels. In this study, we have used laser capture microdissection (LCM) to isolate microvessels from clinical samples of invasive ductal carcinoma (IDC), the most common form of malignant breast cancer, and from patient-matched adjacent nonmalignant tissue. This approach eliminates many of the problems associated with the heterogeneity of clinical tumor tissues by controlling for differences in protein expression between both individual patients and different cell types. Proteins from the microvessels were trypsinized and the resulting peptides were quantified by a label-free nanoLC-MS method. A total of 86 proteins were identified that are overexpressed in tumor vessels relative to vessels isolated from the adjacent nonmalignant tissue. These proteins include well-known breast tumor markers such as Periostin and Tenascin C but also proteins with lesser-known or emerging roles in breast cancer and tumor angiogenesis (i.e., Serpin H1, Clic-1, and Transgelin 2). We also identified 40 proteins that were relatively under-expressed in IDC tumor vessels, including several components of the basement membrane whose lower expression could be responsible for weakening tumor vessels. Lastly, we show that a subset of 29 proteins, derived from our list of differentially expressed proteins, is able to predict survival in three publicly available clinical breast cancer microarray data sets, which suggests that this subset of proteins likely plays a functional role in cancer progression and outcome.