Gelsolin-induced epithelial cell invasion is dependent on Ras-Rac signaling

Role and therapeutic potential of gelsolin in atherosclerosis

Atherosclerosis is the major pathophysiological basis of a variety of cardiovascular diseases and has been recognized as a lipid-driven chronic inflammatory disease. Gelsolin (GSN) is a member of the GSN family. The main function of GSN is to cut and seal actin filaments to regulate the cytoskeleton and participate in a variety of biological functions, such as cell movement, morphological changes, metabolism, apoptosis and phagocytosis. Recently, more and more evidences have demonstrated that GSN is Closely related to atherosclerosis, involving lipid metabolism, inflammation, cell proliferation, migration and thrombosis. This article reviews the role of GSN in atherosclerosis from inflammation, apoptosis, angiogenesis and thrombosis.

Rhabdomyosarcomas are oncogene addicted to the activation of AVIL

Rhabdomyosarcoma (RMS) is one of the most common pediatric soft-tissue cancer. Previously, we discovered a gene fusion, MARS-AVIL formed by chromosomal inversion in RMS. Suspecting that forming a fusion with a housekeeping gene may be one of the mechanisms to dysregulate an oncogene, we investigated AVIL expression and its role in RMS. We first showed that MARS-AVIL translates into an in-frame fusion protein, which is critical for RMS cell tumorigenesis. Besides forming a gene fusion with the housekeeping gene, MARS, the AVIL locus is often amplified, and its RNA and protein expression are overexpressed in the majority of RMSs. Tumors with AVIL dysregulation exhibit evidence of oncogene addiction: Silencing MARS-AVIL in cells harboring the fusion, or silencing AVIL in cells with AVIL overexpression, nearly eradicated the cells in culture, as well as inhibited in vivo xenograft growth in mice. Conversely, gain-of-function manipulations of AVIL led to increased cell growth and migration, enhanced foci formation in mouse fibroblasts, and most importantly transformed mesenchymal stem cells in vitro and in vivo. Mechanistically, AVIL seems to serve as a converging node functioning upstream of two oncogenic pathways, PAX3-FOXO1 and RAS, thus connecting two types of RMS associated with these pathways. Interestingly, AVIL is overexpressed in other sarcoma cells as well, and its expression correlates with clinical outcomes, with higher levels of AVIL expression being associated with worse prognosis. AVIL is a bona fide oncogene in RMS, and RMS cells are addicted to its activity.

Regulation of Mitochondrial Function by the Actin Cytoskeleton

The regulatory role of actin cytoskeleton on mitochondrial function is a growing research field, but the underlying molecular mechanisms remain poorly understood. Specific actin-binding proteins (ABPs), such as Gelsolin, have also been shown to participate in the pathophysiology of mitochondrial OXPHOS disorders through yet to be defined mechanisms. In this mini-review, we will summarize the experimental evidence supporting the fundamental roles of actin cytoskeleton and ABPs on mitochondrial trafficking, dynamics, biogenesis, metabolism and apoptosis, with a particular focus on Gelsolin involvement in mitochondrial disorders. The functional interplay between the actin cytoskeleton, ABPs and mitochondrial membranes for the regulation of cellular homeostasis thus emerges as a new exciting field for future research and therapeutic approaches.

The molecular chaperone CCT sequesters gelsolin and protects it from cleavage by caspase-3

The actin filament severing and capping protein gelsolin plays an important role in modulation of actin filament dynamics by influencing the number of actin filament ends. During apoptosis, gelsolin becomes constitutively active due to cleavage by caspase-3. In non-apoptotic cells gelsolin is activated by the binding of Ca²⁺. This activated form of gelsolin binds to, but is not a folding substrate of the molecular chaperone CCT/TRiC. Here we demonstrate that in vitro, gelsolin is protected from cleavage by caspase-3 in the presence of CCT. Cryoelectron microscopy and single particle 3D reconstruction of the CCT:gelsolin complex reveals that gelsolin is located in the interior of the chaperonin cavity, with a placement distinct from that of the obligate CCT folding substrates actin and tubulin. In cultured mouse melanoma B16F1 cells, gelsolin co-localises with CCT upon stimulation of actin dynamics at peripheral regions during lamellipodia formation. These data indicate that localised sequestration of gelsolin by CCT may provide spatial control of actin filament dynamics.

Reactive Oxygen Species and Oncoprotein Signaling-A Dangerous Liaison

SIGNIFICANCE

There is evidence to implicate reactive oxygen species (ROS) in tumorigenesis and its progression. This has been associated with the interplay between ROS and oncoproteins, resulting in enhanced cellular proliferation and survival. Recent Advances: To date, studies have investigated specific contributions of the crosstalk between ROS and signaling networks in cancer initiation and progression. These investigations have challenged the established dogma of ROS as agents of cell death by demonstrating a secondary function that fuels cell proliferation and survival. Studies have thus identified (onco)proteins (Bcl-2, STAT3/5, RAS, Rac1, and Myc) in manipulating ROS level as well as exploiting an altered redox environment to create a milieu conducive for cancer formation and progression.

CRITICAL ISSUES

Despite these advances, drug resistance and its association with an altered redox metabolism continue to pose a challenge at the mechanistic and clinical levels. Therefore, identifying specific signatures, altered protein expressions, and modifications as well as protein-protein interplay/function could not only enhance our understanding of the redox networks during cancer initiation and progression but will also provide novel targets for designing specific therapeutic strategies.

FUTURE DIRECTIONS

Not only a heightened realization is required to unravel various gene/protein networks associated with cancer formation and progression, particularly from the redox standpoint, but there is also a need for developing more sensitive tools for assessing cancer redox metabolism in clinical settings. This review attempts to summarize our current knowledge of the crosstalk between oncoproteins and ROS in promoting cancer cell survival and proliferation and treatment strategies employed against these oncoproteins. Antioxid. Redox Signal.

Plasma Gelsolin: Indicator of Inflammation and Its Potential as a Diagnostic Tool and Therapeutic Target

Gelsolin, an actin-depolymerizing protein expressed both in extracellular fluids and in the cytoplasm of a majority of human cells, has been recently implicated in a variety of both physiological and pathological processes. Its extracellular isoform, called plasma gelsolin (pGSN), is present in blood, cerebrospinal fluid, milk, urine, and other extracellular fluids. This isoform has been recognized as a potential biomarker of inflammatory-associated medical conditions, allowing for the prediction of illness severity, recovery, efficacy of treatment, and clinical outcome. A compelling number of animal studies also demonstrate a broad spectrum of beneficial effects mediated by gelsolin, suggesting therapeutic utility for extracellular recombinant gelsolin. In the review, we summarize the current data related to the potential of pGSN as an inflammatory predictor and therapeutic target, discuss gelsolin-mediated mechanisms of action, and highlight recent progress in the clinical use of pGSN.

Oncogenic Epstein-Barr virus recruits Nm23-H1 to regulate chromatin modifiers

In cancer progression, metastasis is a major cause of poor survival of patients and can be targeted for therapeutic interventions. The first discovered metastatic-suppressor Nm23-H1 possesses nucleoside diphosphate kinase, histidine kinase, and DNase activity as a broad-spectrum enzyme. Recent advances in cancer metastasis have opened new ways for the development of therapeutic molecular approaches. In this review, we provide a summary of the current understanding of Nm23/NDPKs in the context of viral oncogenesis. We also focused on Nm23-H1-mediated cellular events with an emphasis on chromatin modifications. How Nm23-H1 modulates the activities of chromatin modifiers through interaction with Epstein-Barr virus-encoded oncogenic antigens and related crosstalks are discussed in the context of other oncogenic viruses. We also described the current understanding of the cellular and viral interactions of Nm23-H1 and their reference to transcription regulation and metastasis. Further, we summarized the recent therapeutic approaches targeting Nm23 and its potential links to pathways that can be exploited by oncogenic viruses.

Interaction between the human papillomavirus 16 E7 oncoprotein and gelsolin ignites cancer cell motility and invasiveness

The viral oncoprotein E7 from the “high-risk” Human Papillomavirus 16 (HPV16) strain is able, when expressed in human keratinocytes, to physically interact with the actin severing protein gelsolin (GSN). In a previous work it has been suggested that this protein-protein interaction can hinder GSN severing function, thus leading to actin network remodeling. In the present work we investigated the possible implications of this molecular interaction in cancer cell metastatic potential by analyzing two different human CC cell lines characterized by low or high expression levels of HPV16 DNA (SiHa and CaSki, respectively). In addition, a HPV-null CC cell line (C-33A), transfected in order to express the HPV16 E7 oncoprotein as well as two different deletion mutants, was also analyzed. We found that HPV16 E7 expression level was directly related with cervical cancer migration and invasion capabilities and that these HPV16 E7-related features were associated with Epithelial to Mesenchymal Transition (EMT) processes. These effects appeared as strictly attributable to the physical interaction of HPV16 E7 with GSN, since HPV16 E7 deletion mutants unable to bind to GSN were also unable to modify microfilament assembly dynamics and, therefore, cell movements and invasiveness. Altogether, these data profile the importance of the physical interaction between HPV16 E7 and GSN in the acquisition of the metastatic phenotype by CC cells, underscoring the role of HPV16 intracellular load as a risk factor in cancer.

Gelsolin-Cu/ZnSOD interaction alters intracellular reactive oxygen species levels to promote cancer cell invasion

The actin-binding protein, gelsolin, is a well known regulator of cancer cell invasion. However, the mechanisms by which gelsolin promotes invasion are not well established. As reactive oxygen species (ROS) have been shown to promote cancer cell invasion, we investigated on the hypothesis that gelsolin-induced changes in ROS levels may mediate the invasive capacity of colon cancer cells.

Herein, we show that increased gelsolin enhances the invasive capacity of colon cancer cells, and this is mediated via gelsolin's effects in elevating intracellular superoxide (O₂^.-) levels. We also provide evidence for a novel physical interaction between gelsolin and Cu/ZnSOD, that inhibits the enzymatic activity of Cu/ZnSOD, thereby resulting in a sustained elevation of intracellular O₂^.-. Using microarray data of human colorectal cancer tissues from Gene Omnibus, we found that gelsolin gene expression positively correlates with urokinase plasminogen activator (uPA), an important matrix-degrading protease invovled in cancer invasion. Consistent with the in vivo evidence, we show that increased levels of O₂^.- induced by gelsolin overexpression triggers the secretion of uPA. We further observed reduction in invasion and intracellular O₂^.- levels in colon cancer cells, as a consequence of gelsolin knockdown using two different siRNAs. In these cells, concurrent repression of Cu/ZnSOD restored intracellular O₂^.- levels and rescued invasive capacity.

Our study therefore identified gelsolin as a novel regulator of intracellular O₂^.- in cancer cells via interacting with Cu/ZnSOD and inhibiting its enzymatic activity. Taken together, these findings provide insight into a novel function of gelsolin in promoting tumor invasion by directly impacting the cellular redox milieu.

Gelsolin-mediated activation of PI3K/Akt pathway is crucial for hepatocyte growth factor-induced cell scattering in gastric carcinoma

In gastric cancer (GC), the main subtypes (diffuse and intestinal types) differ in pathological characteristics, with diffuse GC exhibiting early disseminative and invasive behaviour. A distinctive feature of diffuse GC is loss of intercellular adhesion. Although widely attributed to mutations in the CDH1 gene encoding E-cadherin, a significant percentage of diffuse GC do not harbor CDH1 mutations. We found that the expression of the actin-modulating cytoskeletal protein, gelsolin, is significantly higher in diffuse-type compared to intestinal-type GCs, using immunohistochemical and microarray analysis. Furthermore, in GCs with wild-type CDH1, gelsolin expression correlated inversely with CDH1 gene expression. Downregulating gelsolin using siRNA in GC cells enhanced intercellular adhesion and E-cadherin expression, and reduced invasive capacity. Interestingly, hepatocyte growth factor (HGF) induced increased gelsolin expression, and gelsolin was essential for HGF-medicated cell scattering and E-cadherin transcriptional repression through Snail, Twist and Zeb2. The HGF-dependent effect on E-cadherin was found to be mediated by interactions between gelsolin and PI3K-Akt signaling. This study reveals for the first time a function of gelsolin in the HGF/cMet oncogenic pathway, which leads to E-cadherin repression and cell scattering in gastric cancer. Our study highlights gelsolin as an important pro-disseminative factor contributing to the aggressive phenotype of diffuse GC.

Roles for RACK1 in cancer cell migration and invasion

Migration and invasion of cancer cells into surrounding tissue and vasculature is an important initial step in cancer metastasis. Metastasis is the leading cause of cancer related death and thus it is crucial that we improve our understanding of the mechanisms that promote this life-threatening phenomenon. Cell migration involves a complex, multistep process that leads to the actin-driven movement of cells on or through the tissues of the body. The multifunctional scaffolding protein RACK1 plays important roles in nucleating cell signalling hubs, anchoring proteins at specific subcellular locations and regulating protein activity. It is essential for cell migration and accumulating evidence now demonstrates multiple roles for RACK1 in regulating migration and invasion of tumour cells. The possibility of designing drugs that block the migratory and invasive capabilities of cancer cells represents an attractive therapeutic strategy for treating malignant disease with RACK1 being a potential target. In this review we summarize this evidence and examine the mechanisms that underlie the contribution of RACK1 to the various stages of cell migration and invasion.

Podocalyxin-like protein, linked to poor prognosis of pancreatic cancers, promotes cell invasion by binding to gelsolin

The cell‐adhesion glycoprotein PODXL is associated with an aggressive tumor phenotype in several forms of cancer. Here, we report that high PODXL expression was an independent predictor of worse overall survival of pancreatic cancer patients, and that PODXL promoted pancreatic cancer cell motility and invasion by physically binding to the cytoskeletal protein gelsolin. Suppression of PODXL or gelsolin decreased membrane protrusions with abundant peripheral actin structures, and in turn inhibited cell motility and invasion. Transfection of a PODXL‐rescue construct renewed the expression of gelsolin bound to peripheral actin structures in cell protrusions, and abrogated the decreased cell protrusions caused by the knockdown of PODXL. Furthermore, transfection of a PODXL‐rescue construct into pancreatic cancer cells in which both PODXL and gelsolin were suppressed failed to increase the formation of the protrusions. Thus, PODXL enhances motility and invasiveness through an increase in gelsolin–actin interactions in cell protrusions.

Gelsolin Promotes Radioresistance in Non-Small Cell Lung Cancer Cells Through Activation of Phosphoinositide 3-Kinase/Akt Signaling

Gelsolin is an actin-binding protein and acts as an important regulator of cell survival. This study aimed to determine the function of gelsolin in the radioresistance of non-small cell lung cancer cells. We examined the expression of gelsolin in radioresistant A549 and H460 cells and their parental cells. The effects of gelsolin overexpression and knockdown on the clonogenic survival and apoptosis of non-small cell lung cancer cells after irradiation were studied. The involvement of phosphoinositide 3-kinase/Akt signaling in the action of gelsolin was checked. We found that gelsolin was significantly upregulated in radioresistant A549 and H460 cells. Overexpression of gelsolin significantly ( P < .05) increased the number of colonies from irradiated A549 and H460 cells compared to transfection of empty vector. In contrast, knockdown of gelsolin significantly ( P < .05) suppressed colony formation after irradiation. Gelsolin-overexpressing cells displayed reduced apoptosis in response to irradiation, which was coupled with decreased levels of cleaved caspase-3 and poly adenosine diphosphate-ribose polymerase. Ectopic expression of gelsolin significantly ( P < .05) enhanced the phosphorylation of Akt compared to nontransfected cells. Pretreatment with the phosphoinositide 3-kinase inhibitor LY294002 (20 μmol/L) significantly decreased clonogenic survival and enhanced apoptosis in gelsolin-overexpressing A549 and H460 cells after irradiation. Taken together, gelsolin upregulation promotes radioresistance in non-small cell lung cancer cells, at least partially, through activation of phosphoinositide 3-kinase/Akt signaling.

Gelsolin inhibits the proliferation and invasion of the 786-0 clear cell renal cell carcinoma cell line in vitro

The aim of the present study was to investigate the effect of gelsolin (GSN) on the proliferation and invasion of the 786-0 clear cell renal cell carcinoma (ccRCC) cell line in vitro. A GSN overexpression lentiviral vector was constructed and transfected into 786‑0 ccRCC cells in vitro. A 3-(4,5-dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT) assay was conducted to detect the effect of GSN on the proliferation and adhesion ability of the 786‑0 ccRCC cells, and a Transwell invasion assay was used to determine the effect of GSN on the invasion of 786‑0 ccRCC cells. In addition, the expression levels of invasion‑associated proteins, matrix metalloproteinase (MMP)2, MMP9 and E‑cadherin were analyzed by ELISA and western blotting. The MTT assay demonstrated a significantly lower optical density value for the 786‑0/GSN cells compared with that of the 786‑0/green fluorescent protein (GFP) and 786‑0 cells following 24‑ and 48‑h culture (P<0.05). The mean penetration rate of the 786‑0/GSN cells was significantly lower than that of the 786‑0/GFP and 786‑0 cells (P<0.05) according to the Transwell invasion assay. The expression levels of MMP2 and MMP9 were significantly decreased in the 786‑0/GSN cells, when compared with the 786‑0/GFP and 786‑0 cells following a 48‑h transfection, according to ELISA (P<0.001). Furthermore, in the 786‑0/GSN cells, the expression levels of MMP2 and MMP9 were markedly decreased, while the expression of E‑cadherin was markedly increased. Thus, the overexpression of GSN may inhibit the proliferation, adhesion ability and invasion of 786‑0 ccRCC cells. Additionally, GSN downregulated the expression of MMP2 and MMP9, and upregulated the expression of E‑cadherin in the 786‑0 ccRCC cells, which may have suppressed the invasion ability of the 786-0 ccRCC cells.

Role of gelsolin in cell proliferation and invasion of human hepatocellular carcinoma cells

OBJECTIVE

Gelsolin (GSN), one of the most important actin structure regulating proteins, has been implicated in the oncogenesis of some cancers. In this study, we investigated the expression of GSN in hepatocellular carcinoma (HCC) and revealed its potential mechanisms. The mRNA and protein levels of GSN were overexpressed in HCC cells and HCC tissues compared to adjacent noncancerous tissues. GSN expression was correlated with venous invasion (P=0.0199) and Edmonson grading (P=0.0344) expression in HCC. Overexpression of GSN in Huh7 and SMMC-7721 cells significantly promoted cell proliferation and the number of Matrigel™-invading cells compared with control cells, with increased expression of matrix metalloproteinase MCL-1, MMP-2 and MMP-9, a key regulator of growth and invasion. In contrast, knockdown of GSN expression with small interfering RNA (siRNA) in MHCC-97L and MHCC-97H cell lines resulted in decreased cell viability and cell invasion. Our findings indicated that GSN expression promoted tumor-associated phenotypes by facilitating proliferative and invasive capacities of HCC cells, which might serve as a potential therapeutic target for HCC treatment.

Plasma Proteomic Profiling in Hereditary Breast Cancer Reveals a BRCA1-Specific Signature: Diagnostic and Functional Implications

Background

Breast cancer (BC) is a leading cause of death among women. Among the major risk factors, an important role is played by familial history of BC. Germ-line mutations in BRCA1/2 genes account for most of the hereditary breast and/or ovarian cancers. Gene expression profiling studies have disclosed specific molecular signatures for BRCA1/2-related breast tumors as compared to sporadic cases, which might help diagnosis and clinical follow-up. Even though, a clear hallmark of BRCA1/2-positive BC is still lacking. Many diseases are correlated with quantitative changes of proteins in body fluids. Plasma potentially carries important information whose knowledge could help to improve early disease detection, prognosis, and response to therapeutic treatments. The aim of this study was to develop a comprehensive approach finalized to improve the recovery of specific biomarkers from plasma samples of subjects affected by hereditary BC.

Methods

To perform this analysis, we used samples from patients belonging to highly homogeneous population previously reported. Depletion of high abundant plasma proteins, 2D gel analysis, liquid chromatography-tandem mass spectrometry (LC-MS/MS) and bioinformatics analysis were used into an integrated approach to investigate tumor-specific changes in the plasma proteome of BC patients and healthy family members sharing the same BRCA1 gene founder mutation (5083del19), previously reported by our group, with the aim to identify specific signatures.

Results

The comparative analysis of the experimental results led to the identification of gelsolin as the most promising biomarker.

Conclusions

Further analyses, performed using a panel of breast cancer cell lines, allowed us to further elucidate the signaling network that might modulate the expression of gelsolin in breast cancer.

Gelsolin regulates proliferation, apoptosis, migration and invasion in human oral carcinoma cells

Gelsolin (GSN) is one of the most abundant actin-binding proteins, and is involved in several pathological processes, including Alzheimer's disease, cardiac injury and cancer. The aim of the present study was to assess the effect of GSN on the growth and motility of oral squamous cell carcinoma Tca8113 cells. The overexpression vector pcDNA3.1-GSN was transfected into Tca8113 cells and the stable GSN overexpression cell line was identified based on G418 antibiotic selection. The effect of GSN overexpression on the proliferation, apoptosis, migration and invasion of Tca8113 cells was examined using a cell counting kit-8 assay, flow cytometry and Transwell assays. The results revealed that GSN overexpression significantly promoted the cell proliferation and apoptosis of Tca8113 cells. In addition, Transwell assays demonstrated that the migration and invasion abilities of Tca8113 cells were enhanced by GSN overexpression. Therefore, the upregulation of GSN promotes cell growth and motility, indicating that it may perform a vital function in the progression of human oral cancers.

Modulation of cytoskeletal dynamics by mammalian nucleoside diphosphate kinase (NDPK) proteins

Nucleoside diphosphate kinase (NDPK) proteins comprise a family of ten human isoforms that participate in the regulation of multiple cellular processes via enzymatic and nonenzymatic functions. The major enzymatic function of NDPKs is the generation of nucleoside triphosphates, such as guanosine triphosphate (GTP). Mechanisms behind the nonenzymatic NDPK functions are not clear but likely involve context-dependent signaling roles of NDPK within multi-protein complexes. This is most evident for NDPK-A, which is encoded by the human NME1 gene, the first tumor metastasis suppressor gene to be identified. Understanding which protein interactions are most relevant for the biological and metastasis-related functions of NDPK will be important in the potential utilization of NDPK as a disease target. Accumulating evidence suggests that NDPK interacts with and affects various components and regulators of the cytoskeleton, including actin-binding proteins, intermediate filaments, and cytoskeletal attachment structures (adherens junctions, desmosomes, and focal adhesions). We review the existing literature on this topic and highlight outstanding questions and potential future directions that should clarify the impact of NDPK on the different cytoskeletal systems.

Janus-faces of NME-oncoprotein interactions

Since the identification of Nm23 (NME1, NME/NM23 nucleoside diphosphate kinase 1) as the first non-metastatic protein, a great deal of research on members of the NME family of proteins has focused on roles in processes implicated in carcinogenesis and particularly their regulation of cellular motility and the process of metastatic spread. To date, there are ten identified members of this family of genes, and these can be dichotomized into groups both taxonomically and by the presence or absence of their nucleoside diphosphate kinase activity with NMEs 1-4 encoding nucleoside diphosphate kinases (NDPKs) and NMEs 5-9 plus RP2 displaying little if any NDPK activity. NMEs are relatively small proteins that can form hetero-oligomers (typically hexamers), and given the apparent genetic redundancy of some NMEs and the number of different isoforms, it is perhaps not surprising that there remains a great deal of uncertainty regarding their function and even more regarding cellular mechanisms of action. Since residues that contribute to NDPK activity span much of the protein, it seems likely that the consequences of NME expression must be mediated through their NDPK activity, through interactions with other structures in cells including protein-protein interactions or through combinations of these. Our goal in this review is to focus on some of the protein-protein interactions that have been identified and to highlight some of the challenges that face this area of research.

Modulation of cytoskeletal dynamics by mammalian nucleoside diphosphate kinase (NDPK) proteins

Nucleoside diphosphate kinase (NDPK) proteins comprise a family of ten human isoforms that participate in the regulation of multiple cellular processes via enzymatic and nonenzymatic functions. The major enzymatic function of NDPKs is the generation of nucleoside triphosphates, such as guanosine triphosphate (GTP). Mechanisms behind the nonenzymatic NDPK functions are not clear but likely involve context-dependent signaling roles of NDPK within multi-protein complexes. This is most evident for NDPK-A, which is encoded by the human NME1 gene, the first tumor metastasis suppressor gene to be identified. Understanding which protein interactions are most relevant for the biological and metastasis-related functions of NDPK will be important in the potential utilization of NDPK as a disease target. Accumulating evidence suggests that NDPK interacts with and affects various components and regulators of the cytoskeleton, including actin-binding proteins, intermediate filaments, and cytoskeletal attachment structures (adherens junctions, desmosomes, and focal adhesions). We review the existing literature on this topic and highlight outstanding questions and potential future directions that should clarify the impact of NDPK on the different cytoskeletal systems.

Regulation of the metastasis suppressor Nm23-H1 by tumor viruses

Metastasis is the most common cause of cancer mortality. To increase the survival of patients, it is necessary to develop more effective methods for treating as well as preventing metastatic diseases. Recent advancement of knowledge in cancer metastasis provides the basis for development of targeted molecular therapeutics aimed at the tumor cell or its interaction with the host microenvironment. Metastasis suppressor genes (MSGs) are promising targets for inhibition of the metastasis process. During the past decade, functional significance of these genes, their regulatory pathways, and related downstream effector molecules have become a major focus of cancer research. Nm23-H1, first in the family of Nm23 human homologues, is a well-characterized, anti-metastatic factor linked with a large number of human malignancies. Mounting evidence to date suggests an important role for Nm23-H1 in reducing virus-induced tumor cell motility and migration. A detailed understanding of the molecular association between oncogenic viral antigens with Nm23-H1 may reveal the underlying mechanisms for tumor virus-associated malignancies. In this review, we will focus on the recent advances to our understanding of the molecular basis of oncogenic virus-induced progression of tumor metastasis by deregulation of Nm23-H1.

Gelsolin regulates cisplatin sensitivity in human head-and-neck cancer

Chemoresistance is a major challenge in cancer therapy. Cisplatin is commonly used for chemotherapy in patients with head-and-neck cancer (HNC), but it increases control of the disease by only 10-15%. Downregulation of proapoptotic pathways is a key determinant for chemoresistance in which gelsolin (GSN) is critically involved. We analyzed the association between GSN expression and cisplatin resistance in HNC cell lines, animals with HNC and cancer tissue samples from 58 cisplatin-treated patients with HNC. GSN expression levels were positively associated with chemoresistance in vitro and in vivo. Cisplatin-induced GSN downregulation was associated with the cleavage of GSN and the promotion of apoptosis. GSN silencing facilitated cisplatin-induced apoptosis in chemoresistant cells. In contrast, intact gelsolin was prosurvival in the presence of cisplatin by interacting with X-linked inhibitor of apoptosis protein (XIAP). In chemosensitive cells, cisplatin suppressed GSN-XIAP interaction, promoted translocation of XIAP from the perinuclear region to the nucleus and induced apoptosis. In chemoresistant cells, GSN was highly expressed, and cisplatin had no significant effect on GSN-XIAP interaction and apoptosis. We conclude that GSN is important for chemoresistance in HNC and may be an appropriate therapeutic target in chemoresistant cancers.

L-plastin nanobodies perturb matrix degradation, podosome formation, stability and lifetime in THP-1 macrophages

Podosomes are cellular structures acting as degradation ‘hot-spots’ in monocytic cells. They appear as dot-like structures at the ventral cell surface, enriched in F-actin and actin regulators, including gelsolin and L-plastin. Gelsolin is an ubiquitous severing and capping protein, whereas L-plastin is a leukocyte-specific actin bundling protein. The presence of the capping protein CapG in podosomes has not yet been investigated. We used an innovative approach to investigate the role of these proteins in macrophage podosomes by means of nanobodies or Camelid single domain antibodies. Nanobodies directed against distinct domains of gelsolin, L-plastin or CapG were stably expressed in macrophage-like THP-1 cells. CapG was not enriched in podosomes. Gelsolin nanobodies had no effect on podosome formation or function but proved very effective in tracing distinct gelsolin populations. One gelsolin nanobody specifically targets actin-bound gelsolin and was effectively enriched in podosomes. A gelsolin nanobody that blocks gelsolin-G-actin interaction was not enriched in podosomes demonstrating that the calcium-activated and actin-bound conformation of gelsolin is a constituent of podosomes. THP-1 cells expressing inhibitory L-plastin nanobodies were hampered in their ability to form stable podosomes. Nanobodies did not perturb Ser5 phosphorylation of L-plastin although phosphorylated L-plastin was highly enriched in podosomes. Furthermore, nanobody-induced inhibition of L-plastin function gave rise to an irregular and unstable actin turnover of podosomes, resulting in diminished degradation of the underlying matrix. Altogether these results indicate that L-plastin is indispensable for podosome formation and function in macrophages.

Nm23-h1 binds to gelsolin and inactivates its actin-severing capacity to promote tumor cell motility and metastasis

Nm23-H1 has been identified as a metastasis suppressor gene, but its protein interactions have yet to be understood with any mechanistic clarity. In this study, we evaluated the proteomic spectrum of interactions made by Nm23-H1 in 4T1 murine breast cancer cells derived from tissue culture, primary mammary tumors, and pulmonary metastases. By this approach, we identified the actin-severing protein Gelsolin as binding partner for Nm23-H1, verifying their interaction by coimmunoprecipitation in 4T1 cells as well as in human MCF7, MDA-MB-231T, and MDA-MB-435 breast cancer cells. In Gelsolin-transfected cells, coexpression of Nm23-H1 abrogated the actin-severing activity of Gelsolin. Conversely, actin severing by Gelsolin was abrogated by RNA interference-mediated silencing of endogenous Nm23-H1. Tumor cell motility was negatively affected in parallel with Gelsolin activity, suggesting that Nm23-H1 binding inactivated the actin-depolymerizing function of Gelsolin to inhibit cell motility. Using indirect immunoflourescence to monitor complexes formed by Gelsolin and Nm23-H1 in living cells, we observed their colocalization in a perinuclear cytoplasmic compartment that was associated with the presence of disrupted actin stress fibers. In vivo analyses revealed that Gelsolin overexpression increased the metastasis of orthotopically implanted 4T1 or tail vein-injected MDA-MB-231T cells (P = 0.001 and 0.04, respectively), along with the proportion of mice with diffuse liver metastases, an effect ablated by coexpression of Nm23-H1. We observed no variation in proliferation among lung metastases. Our findings suggest a new actin-based mechanism that can suppress tumor metastasis.

Nm23-h1 binds to gelsolin and inactivates its actin-severing capacity to promote tumor cell motility and metastasis

Nm23-H1 has been identified as a metastasis suppressor gene, but its protein interactions have yet to be understood with any mechanistic clarity. In this study, we evaluated the proteomic spectrum of interactions made by Nm23-H1 in 4T1 murine breast cancer cells derived from tissue culture, primary mammary tumors, and pulmonary metastases. By this approach, we identified the actin-severing protein Gelsolin as binding partner for Nm23-H1, verifying their interaction by coimmunoprecipitation in 4T1 cells as well as in human MCF7, MDA-MB-231T, and MDA-MB-435 breast cancer cells. In Gelsolin-transfected cells, coexpression of Nm23-H1 abrogated the actin-severing activity of Gelsolin. Conversely, actin severing by Gelsolin was abrogated by RNA interference-mediated silencing of endogenous Nm23-H1. Tumor cell motility was negatively affected in parallel with Gelsolin activity, suggesting that Nm23-H1 binding inactivated the actin-depolymerizing function of Gelsolin to inhibit cell motility. Using indirect immunoflourescence to monitor complexes formed by Gelsolin and Nm23-H1 in living cells, we observed their colocalization in a perinuclear cytoplasmic compartment that was associated with the presence of disrupted actin stress fibers. In vivo analyses revealed that Gelsolin overexpression increased the metastasis of orthotopically implanted 4T1 or tail vein-injected MDA-MB-231T cells (P = 0.001 and 0.04, respectively), along with the proportion of mice with diffuse liver metastases, an effect ablated by coexpression of Nm23-H1. We observed no variation in proliferation among lung metastases. Our findings suggest a new actin-based mechanism that can suppress tumor metastasis.

Gelsolin and ceruloplasmin as potential predictive biomarkers for cervical cancer by 2D-DIGE proteomics analysis

This study aimed to identify candidate proteins which may serve as potential biological markers for cervical cancer using 2D-DIGE. Serum samples of controls, patients with cervical intraepithelial neoplasia grade 3 (CIN 3), squamous cell carcinoma of early (SCC I and II) and late (SCC III and IV) stage were subjected to 2D-DIGE. Differentially expressed spots were identified by tandem mass spectrometry. Validation of candidate proteins in serum and tissue samples were then performed by ELISA and immunohistochemistry (IHC) analysis respectively. A total of 20 differentially expressed proteins were identified. These proteins were found to play key roles in the apoptosis pathway, complement system, various types of transportation such as hormones, fatty acids, lipid, vitamin E and drug transportation, coagulation cascade, regulation of iron and immunologic response. Based on their functional relevancy to the progression of various cancers, 4 proteins namely the complement factor H, CD5-like antigen, gelsolin and ceruloplasmin were chosen for further validation using ELISA. Biological network analysis showed that ceruloplasmin and gelsolin are closely interacted with the oncogene NF-κb. These two proteins were further validated using the IHC. Gelsolin and ceruloplasmin may serve as potential predictive biomarkers for the progression of high grade lesions.

Thyroid hormone actions in liver cancer

The thyroid hormone 3,3',5-triiodo-L-thyronine (T3) mediates several physiological processes, including embryonic development, cellular differentiation, metabolism, and the regulation of cell proliferation. Thyroid hormone receptors (TRs) generally act as heterodimers with the retinoid X receptor (RXR) to regulate target genes. In addition to their developmental and metabolic functions, TRs have been shown to play a tumor suppressor role, suggesting that their aberrant expression can lead to tumor transformation. Conversely, recent reports have shown an association between overexpression of wild-type TRs and tumor metastasis. Signaling crosstalk between T3/TR and other pathways or specific TR coregulators appear to affect tumor development. Since TR actions are complex as well as cell context-, tissue- and time-specific, aberrant expression of the various TR isoforms has different effects during diverse tumorigenesis. Therefore, elucidation of the T3/TR signaling mechanisms in cancers should facilitate the identification of novel therapeutic targets. This review provides a summary of recent studies focusing on the role of TRs in hepatocellular carcinomas (HCCs).

RACK1 promotes the proliferation, migration and invasion capacity of mouse hepatocellular carcinoma cell line in vitro probably by PI3K/Rac1 signaling pathway

Hca-P and Hca-F is a pair of synogenetic mouse hepatocarcinoma ascites cell lines, possessing different capacity of lymphatic metastasis. Receptor of activated C-kinase 1 (Rack1), together with Jnk1 and gelsolin (Gsn) were previously identified as differentially expressed proteins for lymphatic metastatic potential between the two cell lines. As an intracellular scaffold protein, Rack1 could recruit such signaling molecules as integrins, Src, PKC which are involved in many important biological processes and play key roles in cancer progression. In our present studies, pCDNA3.1(+)-Rack1, a eukaryotic expression plasmid, was constructed and stably transfected into Hca-P cells with a low metastatic potential. CCK8 assay and transwell system were used to evaluate the effects of Rack1 on proliferation, migration and invasion of Hca-P cells in vitro. Then, LY294002, an inhibitor of PI3K, was added into the culture medium of pCDNA3.1(+)-Rack1-Hca-P cells and their biological behaviors observed further. Moreover, the expression of Jnk1, Rac1 and Gsn of pCDNA3.1(+)-Rack1-Hca-P cells were detected by western blot after pretreated with various doses of LY294002. As a result, the proliferation, migration and invasion of pCDNA3.1(+)-Rack1-Hca-P cells were significantly enhanced and could be inhibited by LY294002. In addition, the expression of Gsn, Rac1 and Jnk1 of pCDNA3.1(+)-Rack1-Hca-P cells also decreased after pretreated with LY294002. The expression of Gsn can be inhibited by NSC33766 (an inhibitor of Rac1). Taken together, Rack1/PI3K/Rac1 signaling pathway may play a crucial role in malignant biological behaviors of mouse hepatocarcinoma cells with lymphatic metastasis potential. It may be a potential target for therapy of cancer lymphatic metastasis.

Functional proteomic analysis of long-term growth factor stimulation and receptor tyrosine kinase coactivation in Swiss 3T3 fibroblasts

In Swiss 3T3 fibroblasts, long-term stimulation with PDGF, but not insulin-like growth factor 1 (IGF-1) or EGF, results in the establishment of an elongated migratory phenotype, characterized by the formation of retractile dendritic protrusions and absence of actin stress fibers and focal adhesion complexes. To identify receptor tyrosine kinase-specific reorganization of the Swiss 3T3 proteome during phenotypic differentiation, we compared changes in the pattern of protein synthesis and phosphorylation during long-term exposure to PDGF, IGF-1, EGF, and their combinations using 2DE-based proteomics after (35)S- and (33)P-metabolic labeling. One hundred and five differentially regulated proteins were identified by mass spectrometry and some of these extensively validated. PDGF stimulation produced the highest overall rate of protein synthesis at any given time and induced the most sustained phospho-signaling. Simultaneous activation with two or three of the growth factors revealed both synergistic and antagonistic effects on protein synthesis and expression levels with PDGF showing dominance over both IGF-1 and EGF in generating distinct proteome compositions. Using signaling pathway inhibitors, PI3K was identified as an early site for signal diversification, with sustained activity of the PI3K/AKT pathway critical for regulating late protein synthesis and phosphorylation of target proteins and required for maintaining the PDGF-dependent motile phenotype. Several proteins were identified with novel PI3K/Akt-dependent synthesis and phosphorylations including eEF2, PRS7, RACK-1, acidic calponin, NAP1L1, Hsp73, and fascin. The data also reveal induction/suppression of key F-actin and actomyosin regulators and chaperonins that enable PDGFR to direct the assembly of a motile cytoskeleton, despite simultaneous antagonistic signaling activities. Together, the study demonstrates that long-term exposure to different growth factors results in receptor tyrosine kinase-specific regulation of relatively small subproteomes, and implies that the strength and longevity of receptor tyrosine kinase-specific signals are critical in defining the composition and functional activity of the resulting proteome.

Gelsolin induces colorectal tumor cell invasion via modulation of the urokinase-type plasminogen activator cascade

Gelsolin is a cytoskeletal protein which participates in actin filament dynamics and promotes cell motility and plasticity. Although initially regarded as a tumor suppressor, gelsolin expression in certain tumors correlates with poor prognosis and therapy-resistance. In vitro, gelsolin has anti-apoptotic and pro-migratory functions and is critical for invasion of some types of tumor cells. We found that gelsolin was highly expressed at tumor borders infiltrating into adjacent liver tissues, as examined by immunohistochemistry. Although gelsolin contributes to lamellipodia formation in migrating cells, the mechanisms by which it induces tumor invasion are unclear. Gelsolin's influence on the invasive activity of colorectal cancer cells was investigated using overexpression and small interfering RNA knockdown. We show that gelsolin is required for invasion of colorectal cancer cells through matrigel. Microarray analysis and quantitative PCR indicate that gelsolin overexpression induces the upregulation of invasion-promoting genes in colorectal cancer cells, including the matrix-degrading urokinase-type plasminogen activator (uPA). Conversely, gelsolin knockdown reduces uPA levels, as well as uPA secretion. The enhanced invasiveness of gelsolin-overexpressing cells was attenuated by treatment with function-blocking antibodies to either uPA or its receptor uPAR, indicating that uPA/uPAR activity is crucial for gelsolin-dependent invasion. In summary, our data reveals novel functions of gelsolin in colorectal tumor cell invasion through its modulation of the uPA/uPAR cascade, with potentially important roles in colorectal tumor dissemination to metastatic sites.

Maintenance of acinar cell organization is critical to preventing Kras-induced acinar-ductal metaplasia

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers owing to a number of characteristics including difficulty in establishing early diagnosis and the absence of effective therapeutic regimens. A large number of genetic alterations have been ascribed to PDAC with mutations in the KRAS2 proto-oncogene thought to be an early event in the progression of disease. Recent lineage-tracing studies have shown that acinar cells expressing mutant Kras^G12D are induced to transdifferentiate, generating duct-like cells through a process known as acinar-ductal metaplasia (ADM). ADM lesions then convert to precancerous pancreatic intraepithelial neoplasia (PanIN) that progresses to PDAC over time. Thus, understanding the earliest events involved in ADM/PanIN formation would provide much needed information on the molecular pathways that are instrumental in initiating this disease. Since studying the transition of acinar cells to metaplastic ductal cells in vivo is complicated by analysis of the entire organ, an in vitro 3D culture system was employed to model ADM outside the animal. Kras^G12D-expressing acinar cells rapidly underwent ADM in 3D culture, forming ductal cysts that silenced acinar genes and activated duct genes, characteristics associated with in vivo ADM/PanIN lesions. Analysis of downstream KRAS signaling events established a critical importance for the Raf/MEK/ERK pathway in ADM induction. Additionally, forced expression of the acinar-restricted transcription factor Mist1, which is critical to acinar cell organization, significantly attenuated Kras^G12D-induced ADM/PanIN formation. These results suggest that maintaining MIST1 activity in Kras^G12D-expressing acinar cells can partially mitigate the transformation activity of oncogenic KRAS. Future therapeutics that target both the MAPK pathway and Mist1 transcriptional networks may show promising efficacy in combating this deadly disease.

Quantitative and robust assay to measure cell-cell contact assembly and maintenance

Epithelial junction formation and maintenance are multistep processes that rely on the clustering of macromolecular complexes. These events are highly regulated by signalling pathways that involve Rho small GTPases. Usually, when analysing the contribution of different components of Rho-dependent pathways to cell-cell adhesion, the localisation of adhesion receptors at junctions is evaluated by immunofluorescence. However, we find that this method has limitations on the quantification (dynamic range), ability to detect partial phenotypes and to differentiate between the participation of a given regulatory protein in assembly and/or maintenance of cell-cell contacts.In this chapter, we describe a suitable method, the aggregation assay, in which we adapted a quantitative strategy to allow objective and reproducible detection of partial phenotypes. Importantly, this methodology estimates the ability of cells to form junctions and their resistance to mechanical shearing forces (stabilisation).

New approaches to targeting the actin cytoskeleton for chemotherapy

The actin cytoskeleton is indispensable for normal cellular function. In particular, several actin-based structures coordinate cellular motility, a process hijacked by tumor cells in order to facilitate their propagation to distant sites. The actin cytoskeleton, therefore, represents a point for chemotherapeutic intervention. The challenge in disrupting the actin cytoskeleton is in preserving actin-driven contraction of cardiac and skeletal muscle. By targeting actin-binding proteins with altered expression in malignancy, it may be possible to achieve tumor-specific toxicity. A number of actin-binding proteins act cooperatively and synergistically to regulate actin structures required for motility. The actin cytoskeleton is characterized by a significant degree of plasticity. Targeting specific actin-binding proteins for chemotherapy will only be successful if no other compensatory mechanisms exist.

Interactions between the actin filament capping and severing protein gelsolin and the molecular chaperone CCT: evidence for nonclassical substrate interactions

CCT is a member of the chaperonin family of molecular chaperones and consists of eight distinct subunit species which occupy fixed positions within the chaperonin rings. The activity of CCT is closely linked to the integrity of the cytoskeleton as newly synthesized actin and tubulin monomers are dependent upon CCT to reach their native conformations. Furthermore, an additional role for CCT involving interactions with assembling/assembled microfilaments and microtubules is emerging. CCT is also known to interact with other proteins, only some of which will be genuine folding substrates. Here, we identify the actin filament remodeling protein gelsolin as a CCT-binding partner, and although it does not behave as a classical folding substrate, gelsolin binds to CCT with a degree of specificity. In cultured cells, the levels of CCT monomers affect levels of gelsolin, suggesting an additional link between CCT and the actin cytoskeleton that is mediated via the actin filament severing and capping protein gelsolin.

Aldolase directly interacts with ARNO and modulates cell morphology and acidic vesicle distribution

Previously, we demonstrated that the vacuolar-type H(+)-ATPase (V-ATPase) a2-subunit functions as an endosomal pH sensor that interacts with the ADP-ribosylation factor (Arf) guanine nucleotide exchange factor, ARNO. In the present study, we showed that ARNO directly interacts not only with the a2-subunit but with all a-isoforms (a1-a4) of the V-ATPase, indicating a widespread regulatory interaction between V-ATPase and Arf GTPases. We then extended our search for other ARNO effectors that may modulate V-ATPase-dependent vesicular trafficking events and actin cytoskeleton remodeling. Pull-down experiments using cytosol of mouse proximal tubule cells (MTCs) showed that ARNO interacts with aldolase, but not with other enzymes of the glycolytic pathway. Direct interaction of aldolase with the pleckstrin homology domain of ARNO was revealed by pull-down assays using recombinant proteins, and surface plasmon resonance revealed their high avidity interaction with a dissociation constant: K(D) = 2.84 × 10(-10) M. MTC cell fractionation revealed that aldolase is also associated with membranes of early endosomes. Functionally, aldolase knockdown in HeLa cells produced striking morphological changes accompanied by long filamentous cell protrusions and acidic vesicle redistribution. However, the 50% knockdown we achieved did not modulate the acidification capacity of endosomal/lysosomal compartments. Finally, a combination of small interfering RNA knockdown and overexpression revealed that the expression of aldolase is inversely correlated with gelsolin levels in HeLa cells. In summary, we have shown that aldolase forms a complex with ARNO/Arf6 and the V-ATPase and that it may contribute to remodeling of the actin cytoskeleton and/or the trafficking and redistribution of V-ATPase-dependent acidic compartments via a combination of protein-protein interaction and gene expression mechanisms.

Multifunctional roles of gelsolin in health and diseases

Gelsolin, a Ca(2+) -regulated actin filament severing, capping, and nucleating protein, is an ubiquitous, multifunctional regulator of cell structure and metabolism. More recent data show that gelsolin can act as a transcriptional cofactor in signal transduction and its own expression and function can be influenced by epigenetic changes. Here, we review the functions of the plasma and cytoplasmic forms of gelsolin, and their manifold impacts on cancer, apoptosis, infection and inflammation, cardiac injury, pulmonary diseases, and aging. An improved understanding of the functions and regulatory mechanisms of gelsolin may lead to new considerations of this protein as a potential biomarker and/or therapeutic target.

A llama-derived gelsolin single-domain antibody blocks gelsolin-G-actin interaction

RNA interference has tremendously advanced our understanding of gene function but recent reports have exposed undesirable side-effects. Recombinant Camelid single-domain antibodies (VHHs) provide an attractive means for studying protein function without affecting gene expression. We raised VHHs against gelsolin (GsnVHHs), a multifunctional actin-binding protein that controls cellular actin organization and migration. GsnVHH-induced delocalization of gelsolin to mitochondria or the nucleus in mammalian cells reveals distinct subpopulations including free gelsolin and actin-bound gelsolin complexes. GsnVHH 13 specifically recognizes Ca(2+)-activated gelsolin (K (d) approximately 10 nM) while GsnVHH 11 binds gelsolin irrespective of Ca(2+) (K (d) approximately 5 nM) but completely blocks its interaction with G-actin. Both GsnVHHs trace gelsolin in membrane ruffles of EGF-stimulated MCF-7 cells and delay cell migration without affecting F-actin severing/capping or actin nucleation activities by gelsolin. We conclude that VHHs represent a potent way of blocking structural proteins and that actin nucleation by gelsolin is more complex than previously anticipated.

Granzyme B-induced and caspase 3-dependent cleavage of gelsolin by mouse cytotoxic T cells modifies cytoskeleton dynamics

Granule-associated perforin and granzymes (gzms) are key effector molecules of cytotoxic T lymphocytes (Tc cells) and natural killer cells and play a critical role in the control of intracellular pathogens and cancer. Based on the notion that many gzms, including A, B, C, K, H, and M exhibit cytotoxic activity in vitro, all gzms are believed to serve a similar function in vivo. However, more recent evidence supports the concept that gzms are not unidimensional but, rather, possess non-cytotoxic potential, including stimulation of pro-inflammatory cytokines and anti-viral activities. The present study shows that isolated mouse gzmB cleaves the actin-severing mouse protein, cytoplasmic gelsolin (c-gelsolin) in vitro. However, when delivered to intact target cells by ex vivo immune Tc cells, gzmB mediates c-gelsolin proteolysis via activation of caspases 3/7. The NH(2)-terminal c-gelsolin fragment generated by either gzmB or caspase 3 in vitro constitutively severs actin filaments without destroying the target cells. The observation that gzmB secreted by Tc cells initiates a caspase cascade that disintegrates the actin cytoskeleton in target cells suggests that this intracellular process may contribute to anti-viral host defense.

Molecular aspects of thyroid hormone actions

Cellular actions of thyroid hormone may be initiated within the cell nucleus, at the plasma membrane, in cytoplasm, and at the mitochondrion. Thyroid hormone nuclear receptors (TRs) mediate the biological activities of T(3) via transcriptional regulation. Two TR genes, alpha and beta, encode four T(3)-binding receptor isoforms (alpha1, beta1, beta2, and beta3). The transcriptional activity of TRs is regulated at multiple levels. Besides being regulated by T(3), transcriptional activity is regulated by the type of thyroid hormone response elements located on the promoters of T(3) target genes, by the developmental- and tissue-dependent expression of TR isoforms, and by a host of nuclear coregulatory proteins. These nuclear coregulatory proteins modulate the transcription activity of TRs in a T(3)-dependent manner. In the absence of T(3), corepressors act to repress the basal transcriptional activity, whereas in the presence of T(3), coactivators function to activate transcription. The critical role of TRs is evident in that mutations of the TRbeta gene cause resistance to thyroid hormones to exhibit an array of symptoms due to decreasing the sensitivity of target tissues to T(3). Genetically engineered knockin mouse models also reveal that mutations of the TRs could lead to other abnormalities beyond resistance to thyroid hormones, including thyroid cancer, pituitary tumors, dwarfism, and metabolic abnormalities. Thus, the deleterious effects of mutations of TRs are more severe than previously envisioned. These genetic-engineered mouse models provide valuable tools to ascertain further the molecular actions of unliganded TRs in vivo that could underlie the pathogenesis of hypothyroidism. Actions of thyroid hormone that are not initiated by liganding of the hormone to intranuclear TR are termed nongenomic. They may begin at the plasma membrane or in cytoplasm. Plasma membrane-initiated actions begin at a receptor on integrin alphavbeta3 that activates ERK1/2 and culminate in local membrane actions on ion transport systems, such as the Na(+)/H(+) exchanger, or complex cellular events such as cell proliferation. Concentration of the integrin on cells of the vasculature and on tumor cells explains recently described proangiogenic effects of iodothyronines and proliferative actions of thyroid hormone on certain cancer cells, including gliomas. Thus, hormonal events that begin nongenomically result in effects in DNA-dependent effects. l-T(4) is an agonist at the plasma membrane without conversion to T(3). Tetraiodothyroacetic acid is a T(4) analog that inhibits the actions of T(4) and T(3) at the integrin, including angiogenesis and tumor cell proliferation. T(3) can activate phosphatidylinositol 3-kinase by a mechanism that may be cytoplasmic in origin or may begin at integrin alphavbeta3. Downstream consequences of phosphatidylinositol 3-kinase activation by T(3) include specific gene transcription and insertion of Na, K-ATPase in the plasma membrane and modulation of the activity of the ATPase. Thyroid hormone, chiefly T(3) and diiodothyronine, has important effects on mitochondrial energetics and on the cytoskeleton. Modulation by the hormone of the basal proton leak in mitochondria accounts for heat production caused by iodothyronines and a substantial component of cellular oxygen consumption. Thyroid hormone also acts on the mitochondrial genome via imported isoforms of nuclear TRs to affect several mitochondrial transcription factors. Regulation of actin polymerization by T(4) and rT(3), but not T(3), is critical to cell migration. This effect has been prominently demonstrated in neurons and glial cells and is important to brain development. The actin-related effects in neurons include fostering neurite outgrowth. A truncated TRalpha1 isoform that resides in the extranuclear compartment mediates the action of thyroid hormone on the cytoskeleton.

BCL2 inhibits cell adhesion, spreading, and motility by enhancing actin polymerization

BCL2 is best known as a multifunctional anti-apoptotic protein. However, little is known about its role in cell-adhesive and motility events. Here, we show that BCL2 may play a role in the regulation of cell adhesion, spreading, and motility. When BCL2 was overexpressed in cultured murine and human cell lines, cell spreading, adhesion, and motility were impaired. Consistent with these results, the loss of Bcl2 resulted in higher motility observed in Bcl2-null mouse embryonic fibroblast (MEF) cells compared to wild type. The mechanism of BCL2 regulation of cell adhesion and motility may involve formation of a complex containing BCL2, actin, and gelsolin, which appears to functionally decrease the severing activity of gelsolin. We have observed that the lysate from MCF-7 and NIH3T3 cells that overexpressed BCL2 enhanced actin polymerization in cell-free in vitro assays. Confocal immunofluorescent localization of BCL2 and F-actin during spreading consistently showed that increased expression of BCL2 resulted in increased F-actin polymerization. Thus, the formation of BCL2 and gelsolin complexes (which possibly contain other proteins) appears to play a critical role in the regulation of cell adhesion and migration. Given the established correlation of cell motility with cancer metastasis, this result may explain why the expression of BCL2 in some tumor cell types reduces the potential for metastasis and is associated with improved patient prognosis.

Small G proteins in islet beta-cell function

Glucose-stimulated insulin secretion from the islet beta-cell involves a sequence of metabolic events and an interplay between a wide range of signaling pathways leading to the generation of second messengers (e.g., cyclic nucleotides, adenine and guanine nucleotides, soluble lipid messengers) and mobilization of calcium ions. Consequent to the generation of necessary signals, the insulin-laden secretory granules are transported from distal sites to the plasma membrane for fusion and release of their cargo into the circulation. The secretory granule transport underlies precise changes in cytoskeletal architecture involving a well-coordinated cross-talk between various signaling proteins, including small molecular mass GTP-binding proteins (G proteins) and their respective effector proteins. The purpose of this article is to provide an overview of current understanding of the identity of small G proteins (e.g., Cdc42, Rac1, and ARF-6) and their corresponding regulatory factors (e.g., GDP/GTP-exchange factors, GDP-dissociation inhibitors) in the pancreatic beta-cell. Plausible mechanisms underlying regulation of these signaling proteins by insulin secretagogues are also discussed. In addition to their positive modulatory roles, certain small G proteins also contribute to the metabolic dysfunction and demise of the islet beta-cell seen in in vitro and in vivo models of impaired insulin secretion and diabetes. Emerging evidence also suggests significant insulin secretory abnormalities in small G protein knockout animals, further emphasizing vital roles for these proteins in normal health and function of the islet beta-cell. Potential significance of these experimental observations from multiple laboratories and possible avenues for future research in this area of islet research are highlighted.

Myosin Va cooperates with PKA RIalpha to mediate maintenance of the endplate in vivo

Myosin V motor proteins facilitate recycling of synaptic receptors, including AMPA and acetylcholine receptors, in central and peripheral synapses, respectively. To shed light on the regulation of receptor recycling, we employed in vivo imaging of mouse neuromuscular synapses. We found that myosin Va cooperates with PKA on the postsynapse to maintain size and integrity of the synapse; this cooperation also regulated the lifetime of acetylcholine receptors. Myosin Va and PKA colocalized in subsynaptic enrichments. These accumulations were crucial for synaptic integrity and proper cAMP signaling, and were dependent on AKAP function, myosin Va, and an intact actin cytoskeleton. The neuropeptide and cAMP agonist, calcitonin-gene related peptide, rescued fragmentation of synapses upon denervation. We hypothesize that neuronal ligands trigger local activation of PKA, which in turn controls synaptic integrity and turnover of receptors. To this end, myosin Va mediates correct positioning of PKA in a postsynaptic microdomain, presumably by tethering PKA to the actin cytoskeleton.

Gelsolin regulates cardiac remodeling after myocardial infarction through DNase I-mediated apoptosis

Gelsolin, a calcium-regulated actin severing and capping protein, is highly expressed in murine and human hearts after myocardial infarction and is associated with progression of heart failure in humans. The biological role of gelsolin in cardiac remodeling and heart failure progression after injury is not defined. To elucidate the contribution of gelsolin in these processes, we randomly allocated gelsolin knockout mice (GSN(-/-)) and wild-type littermates (GSN(+/+)) to left anterior descending coronary artery ligation or sham surgery. We found that GSN(-/-) mice have a surprisingly lower mortality, markedly reduced hypertrophy, smaller late infarct size, less interstitial fibrosis, and improved cardiac function when compared with GSN(+/+) mice. Gene expression and protein analysis identified significantly lower levels of deoxyribonuclease (DNase) I and reduced nuclear translocation and biological activity of DNase I in GSN(-/-) mice. Absence of gelsolin markedly reduced DNase I-induced apoptosis. The association of hypoxia-inducible factor (HIF)-1alpha with gelsolin and actin filaments cleaved by gelsolin may contribute to the higher activation of DNase. The expression pattern of HIF-1alpha was similar to that of gelsolin, and HIF-1alpha was detected in the gelsolin complex by coprecipitation and HIF-1alpha bound to the promoter of DNase I in both gel-shift and promoter activity assays. Furthermore, the phosphorylation of Akt at Ser473 and expression of Bcl-2 were significantly increased in GSN(-/-) mice, suggesting that gelsolin downregulates prosurvival factors. Our investigation concludes that gelsolin is an important contributor to heart failure progression through novel mechanisms of HIF-1alpha and DNase I activation and downregulation of antiapoptotic survival factors. Gelsolin inhibition may form a novel target for heart failure therapy.