Human thyroid carcinoma cell invasion is controlled by the low density lipoprotein receptor-related protein-mediated clearance of urokinase plasminogen activator

Multi-faceted role of LRP1 in the immune system

Graft versus host disease (GVHD) represents the major complication after allogeneic hematopoietic stem cell transplantation (Allo-SCT). GVHD-prone patients rely on GVHD prophylaxis (e.g. methotrexate) and generalized anti-GVHD medical regimen (glucocorticoids). New anti-GVHD therapy strategies are being constantly explored, however there is an urgent need to improve current treatment, since GVHD-related mortality reaches 22% within 5 years in patients with chronic GVHD. This review is an attempt to describe a very well-known receptor in lipoprotein studies - the low-density lipoprotein receptor related protein 1 (LRP1) - in a new light, as a potential therapeutic target for GVHD prevention and treatment. Our preliminary studies demonstrated that LRP1 deletion in donor murine T cells results in significantly lower GVHD-related mortality in recipient mice with MHC (major histocompatibility complex) -mismatched HSCT. Given the importance of T cells in the development of GVHD, there is a significant gap in scientific literature regarding LRP1's role in T cell biology. Furthermore, there is limited research interest and publications on this classical receptor molecule in other immune cell types. Herein, we endeavor to summarize existing knowledge about LRP1's role in various immune cells to demonstrate the possibility of this receptor to serve as a novel target for anti-GVHD treatment.

LRP-1-dependent control of calpain expression and activity: A new mechanism regulating thyroid carcinoma cell adhesion

The low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional endocytic receptor mediating the clearance of various molecules from the extracellular matrix. LRP1 also regulates cell surface expression of matrix receptors by modulating both extracellular and intracellular signals, though current knowledge of the underlying mechanisms remains partial in the frame of cancer cells interaction with matricellular substrates. In this study we identified that LRP1 downregulates calpain activity and calpain 2 transcriptional expression in an invasive thyroid carcinoma cell model. LRP1-dependent alleviation of calpain activity limits cell-matrix attachment strength and contributes to FTC133 cells invasive abilities in a modified Boyden chamber assays. In addition, using enzymatic assays and co-immunoprecipitation experiments, we demonstrated that LRP1 exerts post-translational inhibition of calpain activity through PKA-dependent phosphorylation of calpain-2. This LRP-1 dual mode of control of calpain activity fine-tunes carcinoma cell spreading. We showed that LRP1-mediated calpain inhibition participates in talin-positive focal adhesions dissolution and limits β1-integrin expression at carcinoma cell surface. In conclusion, we identified an additional and innovative intracellular mechanism which demonstrates LRP-1 pro-motile action in thyroid cancer cells. LRP-1 ability to specifically control calpain-2 expression and activity highlights a novel facet of its de-adhesion receptor status.

Amblyomin-X, a recombinant Kunitz-type inhibitor, regulates cell adhesion and migration of human tumor cells

In a tumor microenvironment, endothelial cell migration and angiogenesis allow cancer to spread to other organs causing metastasis.  Indeed, a number of molecules that are involved in cytoskeleton re-organization and intracellular signaling have been investigated for their effects on tumor cell growth and metastasis. Alongside that, Amblyomin-X, a recombinant Kunitz-type protein, has been shown to reduce metastasis and tumor growth in in vivo experiments. In the present report, we provide a mechanistic insight to these antitumor effects, this is,  Amblyomin-X modulates Rho-GTPases and uPAR signaling, and reduces the release of MMPs, leading to disruption of the actin cytoskeleton and decreased cell migration of tumor cell lines. Altogether, our data support a role for Amblyomin-X as a novel potential antitumor drug.

ABBREVIATIONS

Amb-X: Amblyomin-X; ECGF: endotelial cell growth factor; ECM: extracellular matrix; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; HUVEC: human umbilical vein endothelial cell; LRP1: low-density lipoprotein receptor-related protein; MMP: matrix metalloproteinase; HPI-4: hedgehog pathway inhibitor 4; PAI-1: plasminogen activator inhibitor 1; PMA: phorbol 12-myristate-13-acetate; TFPI: tissue factor pathway inhibitor; uPA: urokinase plasminogen activator; uPAR: uPA receptor.

Identification of LRP-1 as an endocytosis and recycling receptor for β1-integrin in thyroid cancer cells

LRP-1 is a large endocytic receptor mediating the clearance of various molecules from the extracellular matrix. LRP-1 was reported to control focal adhesion turnover to optimize the adhesion-deadhesion balance to support invasion. To better understand how LRP-1 coordinates cell-extracellular matrix interface, we explored its ability to regulate cell surface integrins in thyroid carcinomas. Using an antibody approach, we demonstrated that β1-integrin levels were increased at the plasma membrane under LRP1 silencing or upon RAP treatment, used as LRP-1 antagonist. Our data revealed that LRP-1 binds with both inactive and active β1-integrin conformations and identified the extracellular ligand-binding domains II or IV of LRP-1 as sufficient to bind β1-integrin. Using a recombinant β1-integrin, we demonstrated that LRP-1 acts as a regulator of β1-integrin intracellular traffic. Moreover, RAP or LRP-1 blocking antibodies decreased up to 36% the number of β1-integrin-containing endosomes. LRP-1 blockade did not significantly affect the levels of β1-integrin-containing lysosomes while decreasing localization of β1-integrin within Rab-11 positive vesicles. Overall, we identified an original molecular process in which LRP-1 acts as a main regulator of β1-integrin internalization and recycling in thyroid cancer cells.

Role of LRP-1 in cancer cell migration in 3-dimensional collagen matrix

The low-density lipoprotein receptor-related protein-1 (LRP-1) is a member of Low Density Lipoprotein Receptor (LDLR) family, which is ubiquitously expressed and which is described as a multifunctional endocytic receptor which mediates the clearance of various extracellular matrix molecules including serine proteinases, proteinase-inhibitor complexes, and matricellular proteins. Several studies showed that high LRP-1 expression promotes breast cancer cell invasiveness, and LRP-1 invalidation leads to cell motility abrogation in both tumor and non-tumor cells. Furthermore, our group has reported that LRP-1 silencing prevents the invasion of a follicular thyroid carcinoma despite increased pericellular proteolytic activities from MMP2 and uPA using a 2D-cell culture model. As the use of 3D culture systems is becoming more and more popular due to their promise as enhanced models of tissue physiology, the aim of the present work is to characterize for the first time how the 3D collagen type I matrix may impact the ability of LRP-1 to regulate the migratory properties of thyroid carcinoma using as a model FTC-133 cells. Our results show that inhibition of LRP-1 activity or expression leads to morphological changes affecting cell-matrix interactions, reorganizations of the actin-cytoskeleton especially by inhibiting FAK activation and increasing RhoA activity and MLC-2 phosphorylation, thus preventing cell migration. Taken together, our results suggest that LRP-1 silencing leads to a decrease of cell migratory capacity in a 3D configuration.

Analysis of the effect of LRP-1 silencing on the invasive potential of cancer cells by nanomechanical probing and adhesion force measurements using atomic force microscopy

Low-density lipoprotein receptor-related protein 1 (LRP-1) can internalize proteases involved in cancer progression and is thus considered a promising therapeutic target. However, it has been demonstrated that LRP-1 is also able to regulate the endocytosis of membrane-anchored proteins. Thus, strategies that target LRP-1 to modulate proteolysis could also affect adhesion and cytoskeleton dynamics. Here, we investigated the effect of LRP-1 silencing on parameters reflecting cancer cells' invasiveness by atomic force microscopy (AFM). The results show that LRP-1 silencing induces changes in the cells' adhesion behavior, particularly the dynamics of cell attachment. Clear alterations in morphology, such as more pronounced stress fibers and increased spreading, leading to increased area and circularity, were also observed. The determination of the cells' mechanical properties by AFM showed that these differences are correlated with an increase in Young's modulus. Moreover, the measurements show an overall decrease in cell motility and modifications of directional persistence. An overall increase in the adhesion force between the LRP-1-silenced cells and a gelatin-coated bead was also observed. Ultimately, our AFM-based force spectroscopy data, recorded using an antibody directed against the β1 integrin subunit, provide evidence that LRP-1 silencing modifies the rupture force distribution. Together, our results show that techniques traditionally used for the investigation of cancer cells can be coupled with AFM to gain access to complementary phenotypic parameters that can help discriminate between specific phenotypes associated with different degrees of invasiveness.

Roles of low-density lipoprotein receptor-related protein 1 in tumors

Low-density lipoprotein receptor-related protein 1 (LRP1, also known as CD91), a multifunctional endocytic and cell signaling receptor, is widely expressed on the surface of multiple cell types such as hepatocytes, fibroblasts, neurons, astrocytes, macrophages, smooth muscle cells, and malignant cells. Emerging in vitro and in vivo evidence demonstrates that LRP1 is critically involved in many processes that drive tumorigenesis and tumor progression. For example, LRP1 not only promotes tumor cell migration and invasion by regulating matrix metalloproteinase (MMP)-2 and MMP-9 expression and functions but also inhibits cell apoptosis by regulating the insulin receptor, the serine/threonine protein kinase signaling pathway, and the expression of Caspase-3. LRP1-mediated phosphorylation of the extracellular signal-regulated kinase pathway and c-jun N-terminal kinase are also involved in tumor cell proliferation and invasion. In addition, LRP1 has been shown to be down-regulated by microRNA-205 and methylation of LRP1 CpG islands. Furthermore, a novel fusion gene, LRP1-SNRNP25, promotes osteosarcoma cell invasion and migration. Only by understanding the mechanisms of these effects can we develop novel diagnostic and therapeutic strategies for cancers mediated by LRP1.

Genome-wide expression analysis suggests a crucial role of dysregulation of matrix metalloproteinases pathway in undifferentiated thyroid carcinoma

Background

Thyroid cancer (TC) is the most common malignant cancer of the Endocrine System. Histologically, there are three main subtypes of TC: follicular, papillary and anaplastic. Diagnosing a thyroid tumor subtype with a high level of accuracy and confidence is still a difficult task because genetic, molecular and cellular mechanisms underlying the transition from differentiated to undifferentiated thyroid tumors are not well understood.

A genome-wide analysis of these three subtypes of thyroid carcinoma was carried out in order to identify significant differences in expression levels as well as enriched pathways for non-shared molecular and cellular features between subtypes.

Results

Inhibition of matrix metalloproteinases pathway is a major event involved in thyroid cancer progression and its dysregulation may result crucial for invasiveness, migration and metastasis. This pathway is drastically altered in ATC while in FTC and PTC, the most important pathways are related to DNA-repair activation or cell to cell signaling events.

Conclusion

A progression from FTC to PTC and then to ATC was detected and validated on two independent datasets. Moreover, PTX3, COLEC12 and PDGFRA genes were found as possible candidates for biomarkers of ATC while GPR110 could be tested to distinguish PTC over other tumor subtypes. The genome-wide analysis emphasizes the preponderance of pathway-dysregulation mechanisms over simple gene-malfunction as the main mechanism involved in the development of a cancer phenotype.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1372-0) contains supplementary material, which is available to authorized users.

Emerging molecular markers for the prognosis of differentiated thyroid cancer patients

Epithelial thyroid cancers are represented by the differentiated papillary and follicular thyroid carcinomas which, following dedifferentiation, are thought to give rise to the highly aggressive and incurable anaplastic thyroid carcinomas. Although derived from the same cell type, the different thyroid tumors show specific histological features, biological behavior and degree of differentiation as a consequence of different genetic alterations. Over the last few years, our knowledge regarding the molecular alterations underlying thyroid cell malignant transformation and cancer progression has considerably increased; however, the prognosis of differentiated thyroid cancer patients still relies on high-risk clinic-pathological variables. In particular, the actual staging systems provides only a rough prediction for cancer mortality and risk of recurrences, including in each risk group patients with highly different tumor-specific progression, disease-free interval and survival time. In order to improve DTC patient's risk stratification, both the European and the American Thyroid Associations proposed practical guidelines to integrate the actual staging systems with additional clinical features such as the tumor histological variant, the results of post-ablative whole body scan and the serum thyroglobulin levels. Despite that, patients within the same risk group still show a very heterogeneous behavior in terms of disease-free interval. As a consequence, the identification of new prognostic molecular biomarkers able to testify tumor aggressiveness is highly required. Here we'll review recently characterized new molecular markers potentially able to ameliorate the prognosis in DTC patients.

LRP1-dependent pepsin clearance induced by 2'-hydroxycinnamaldehyde attenuates breast cancer cell invasion

2'-Hydroxycinnamaldehyde inhibits breast cancer cell invasion. This study examined whether 2'-hydroxycinnamaldehyde, acting as a Michael acceptor, interferes with the ligand binding of low-density lipoprotein receptor-related protein 1 to mediate breast cancer cell invasion. Low-density lipoprotein receptor-related protein 1, one of the direct molecular targets of 2'-hydroxycinnamaldehyde, is a multifunctional endocytic receptor. Changes in the thiol oxidation status of cell surface receptor proteins may function as a molecular switch, influencing ligand(s) binding. The oxidation status of extracellular cysteine thiol groups in MCF-7 and MDA-MB-231 cells was examined using a fluorescence-activated cell sorter with thiol-specific fluorescent probes; Matrigel invasion and wound-healing assays were performed to determine the effects of 2'-hydroxycinnamaldehyde on in vitro cell migration. The molecular mechanisms by which 2'-hydroxycinnamaldehyde acts were evaluated by transient knockdown using siRNA or inhibition of low-density lipoprotein receptor-related protein 1 by receptor-associated protein treatment. 2'-Hydroxycinnamaldehyde increased α-2-macroglobulin binding to low-density lipoprotein receptor-related protein 1, which was alleviated by pretreatment of cells with N-acetylcystein. 2'-Hydroxycinnamaldehyde decreased the extracellular pepsin concentration significantly in a low-density lipoprotein receptor-related protein 1- and α-2-macroglobulin-dependent manner. The anti-invasive effect of 2'-hydroxycinnamaldehyde was mitigated with receptor-associated protein pretreatment, suggesting that low-density lipoprotein receptor-related protein 1 is essential for the effects of 2'-hydroxycinnamaldehyde. From these data, we suggest that 2'-hydroxycinnamaldehyde increases the cysteine thiol oxidation status of low-density lipoprotein receptor-related protein 1 extracellular domains, which results in α-2-macroglobulin ligand binding stimulation. Therefore, pepsin clearance in a low-density lipoprotein receptor-related protein 1-α-2-macroglobulin-dependent manner might be an important molecular mechanism in 2'-hydroxycinnamaldehyde exerting its anti-invasive action on breast cancer cells. Furthermore, our data may provide an opportunity to promote the importance of the thiol oxidation status of cell surface receptor proteins for regulating cellular signaling pathways that are important in cancer progression.

Regulation of LRP-1 expression: make the point

The low-density lipoprotein receptor-related protein-1 (LRP-1) is a membrane receptor displaying both scavenging and signaling functions. The wide variety of extracellular ligands and of cytoplasmic scaffolding and signaling proteins interacting with LRP-1 gives it a major role not only in physiological processes, such as embryogenesis and development, but also in critical pathological situations, including cancer and neurological disorders. In this review, we describe the molecular mechanisms involved at distinct levels in the regulation of LRP-1, from its expression to the proper location and stability at the cell surface.

Comprehensive profiling of metastasis-related proteins in paired hepatocellular carcinoma cells with different metastasis potentials

Precise and comprehensive identifications of the proteins associated with metastasis are critical for early diagnosis and therapeutic intervention of hepatocellular carcinoma (HCC). Therefore, we investigated the proteomic differences between a pair of HCC cell lines, originating from the same progenitor, with different metastasis potential using amino acid-coded mass tagging-based LC-MS/MS quantitative proteomic approach. Totally the relative abundance of 336 proteins in these cell lines were quantified, in which 121 proteins were upregulated by >30%, and 64 proteins were downregulated by >23% in the cells with high metastasis potential. Further validation studies by Western blotting in a series of HCC cell types with progressively increasing trend of metastasis showed that peroxiredoxin 4, HSP90β and HSP27 were positively correlated with increasing metastasis while prohibitin was negatively correlated with metastasis potential. These validation results were also consistent with that obtained from comparative analysis of clinic tissues samples. Function annotations of differentially expressed HCC proteome suggested that the emergence and development of high metastasis involved the dysregulation of cell migration, cell cycle and membrane traffics. Together our results revealed a much more comprehensive profile than that from 2-DE-based method and provided more global insights into the mechanisms of HCC metastasis and potential markers for clinical diagnosis.

LRP-1--CD44, a new cell surface complex regulating tumor cell adhesion

The low-density lipoprotein receptor-related protein 1 (LRP-1) is a large endocytic receptor mediating the clearance of various molecules from the extracellular matrix. In the field of cancer, LRP-1-mediated endocytosis was first associated with antitumor properties. However, recent results suggested that LRP-1 may coordinate the adhesion-deadhesion balance in malignant cells to support tumor progression. Here, we observed that LRP-1 silencing or RAP (receptor-associated protein) treatment led to accumulation of CD44 at the tumor cell surface. Moreover, we evidenced a tight interaction between CD44 and LRP-1, not exclusively localized in lipid rafts. Overexpression of LRP-1-derived minireceptors indicated that the fourth ligand-binding cluster of LRP-1 is required to bind CD44. Labeling of CD44 with EEA1 and LAMP-1 showed that internalized CD44 is routed through early endosomes toward lysosomes in a LRP-1-dependent pathway. LRP-1-mediated internalization of CD44 was highly reduced under hyperosmotic conditions but poorly affected by membrane cholesterol depletion, revealing that it proceeds mostly via clathrin-coated pits. Finally, we demonstrated that CD44 silencing abolishes RAP-induced tumor cell attachment, revealing that cell surface accumulation of CD44 under LRP-1 blockade is mainly responsible for the stimulation of tumor cell adhesion. Altogether, our data shed light on the LRP-1-mediated internalization of CD44 that appeared critical to define the adhesive properties of tumor cells.

Low level of low-density lipoprotein receptor-related protein 1 predicts an unfavorable prognosis of hepatocellular carcinoma after curative resection

BACKGROUND

Low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional receptor involved in receptor-mediated endocytosis and cell signaling. The aim of this study was to elucidate the expression and mechanism of LRP1 in hepatocellular carcinoma (HCC).

METHODS

LRP1 expression in 4 HCC cell lines and 40 HCC samples was detected. After interruption of LRP1 expression in a HCC cell line either with specific lentiviral-mediated shRNA LRP1 or in the presence of the LRP1-specific chaperone, receptor-associated protein (RAP), the role of LRP1 in the migration and invasion of HCC cells was assessed in vivo and in vitro, and the expression of matrix metalloproteinase (MMP) 9 in cells and the bioactivity of MMP9 in the supernatant were assayed. The expression and prognostic value of LRP1 were investigated in 327 HCC specimens.

RESULTS

Low LRP1 expression was associated with poor HCC prognosis, with low expression independently related to shortened overall survival and increased tumor recurrence rate. Expression of LRP1 in non-recurrent HCC samples was significantly higher than that in early recurrent samples. LRP1 expression in HCC cell lines was inversely correlated with their metastatic potential. After inhibition of LRP1, low-metastatic SMCC-7721 cells showed enhanced migration and invasion and increased expression and bioactivity of MMP9. Correlation analysis showed a negative correlation between LRP1 and MMP9 expression in HCC patients. The prognostic value of LRP1 expression was validated in the independent data set.

CONCLUSIONS

LRP1 modulated the level of MMP9 and low level of LRP1 expression was associated with aggressiveness and invasiveness in HCCs. LRP1 offered a possible strategy for tumor molecular therapy.

LRP-1 promotes cancer cell invasion by supporting ERK and inhibiting JNK signaling pathways

Background

The low-density lipoprotein receptor-related protein-1 (LRP-1) is an endocytic receptor mediating the clearance of various extracellular molecules involved in the dissemination of cancer cells. LRP-1 thus appeared as an attractive receptor for targeting the invasive behavior of malignant cells. However, recent results suggest that LRP-1 may facilitate the development and growth of cancer metastases in vivo, but the precise contribution of the receptor during cancer progression remains to be elucidated. The lack of mechanistic insights into the intracellular signaling networks downstream of LRP-1 has prevented the understanding of its contribution towards cancer.

Methodology/Principal Findings

Through a short-hairpin RNA-mediated silencing approach, we identified LRP-1 as a main regulator of ERK and JNK signaling in a tumor cell context. Co-immunoprecipitation experiments revealed that LRP-1 constitutes an intracellular docking site for MAPK containing complexes. By using pharmacological agents, constitutively active and dominant-negative kinases, we demonstrated that LRP-1 maintains malignant cells in an adhesive state that is favorable for invasion by activating ERK and inhibiting JNK. We further demonstrated that the LRP-1-dependent regulation of MAPK signaling organizes the cytoskeletal architecture and mediates adhesive complex turnover in cancer cells. Moreover, we found that LRP-1 is tethered to the actin network and to focal adhesion sites and controls ERK and JNK targeting to talin-rich structures.

Conclusions

We identified ERK and JNK as the main molecular relays by which LRP-1 regulates focal adhesion disassembly of malignant cells to support invasion.

Inhibition of uPAR and uPA reduces invasion in papillary thyroid carcinoma cells

OBJECTIVES/HYPOTHESIS

We analyzed the expression of urokinase plasminogen activator (uPA) and its receptor (uPAR) in papillary thyroid carcinoma (PTC) and normal thyroid tissue and examined in vitro how uPA and uPAR contribute to an invasive/metastatic phenotype, and the functional consequences of inhibiting this system.

STUDY DESIGN

Retrospective chart review of PTC patients, followed by prospective study using previously obtained patient tissue and PTC cellular models.

METHODS

uPA and uPAR RNA and protein levels were analyzed in PTC patient tissue samples, PTC and normal thyroid tissue culture cells, and conditioned media (CM) using quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and/or Western blotting. The plasminogen-activating ability of CM was examined using dark-quenched casein fluorimetry and casein-plasminogen gel zymography. The invasive potentials of the PTC and normal thyroid epithelial cell lines were assessed using an in vitro cellular invasion/migration system.

RESULTS

uPA and uPAR RNA and protein levels were increased in PTC patient samples and PTC cells relative to controls. uPA and uPAR RNA were also significantly higher in patients with metastatic disease. Casein-plasminogen zymography and Western blotting demonstrated increased active uPA secreted by PTC cells compared with normal thyroid cells. Fluorimetric assays revealed that the PTC cells' CM was able to activate plasminogen, resulting in measurable casein hydrolysis. This casein hydrolysis was prevented by the addition of several specific uPA inhibitors. Finally, the in vitro invasion phenotypes of PTC cells were augmented by the addition of plasminogen, and this augmentation was reversed by inhibitory anti-uPA and anti-uPAR antibodies.

CONCLUSIONS

These data provide new functional evidence of the uPA/uPAR system's role in PTC invasion/metastasis and demonstrate the attractiveness of uPA and uPAR as molecular biomarkers and therapeutic targets.

LRP-1: a new modulator of cytoskeleton dynamics and adhesive complex turnover in cancer cells

The low-density lipoprotein receptor-related protein-1 (LRP-1)is a large scavenger receptor mediating the internalization and catabolism of various biological components from the extracellular matrix. In the past decade, LRP-1 appeared as an attractive receptor for targeting the invasive behavior of cancer cells since this protein is able to reduce the accumulation of extracellular proteinases by endocytosis. However, recent data suggest that LRP-1 could support carcinoma cell invasion depending on the cellular environment. Indeed, in addition to its well-determined role in ligand binding and endocytosis, LRP-1 emerges as a central molecular regulator of cytoskeleton organization and adhesive complex turnover in malignant cells. This commentary reviews the functions played by LRP-1 in cancer-related events and discusses the potential mechanisms whereby LRP-1 is able to control the cellular phenotype of cancer cells.

Low-density lipoprotein receptor-related protein 1 promotes cancer cell migration and invasion by inducing the expression of matrix metalloproteinases 2 and 9

The low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional endocytic receptor involved in the metabolism of various extracellular ligands, including proteinases, that play critical roles in tumor invasion. Although several studies have shown an increased expression of LRP1 in cancer cells, its function in tumor development and progression remains largely unclear. Here, we reveal a novel mechanism by which LRP1 induces the expression of matrix metalloproteinase 2 (MMP2) and MMP9 and thereby promotes the migration and invasion of human glioblastoma U87 cells. Knockdown of LRP1 expression greatly decreased U87 cell migration and invasion, which was rescued by the forced expression of a functional LRP1 minireceptor. Inhibition of ligand binding to LRP1 by a specific antagonist, receptor-associated protein, also led to reduced cancer cell migration and invasion. Because MMPs play critical roles in cancer cell migration and invasion, we examined the expression of several MMPs and found that the expression of functional MMP2 and MMP9 was selectively decreased in LRP1 knockdown cells. More importantly, decreased cell migration and invasion of LRP1 knockdown cells were completely rescued by exogenous expression of MMP2 or MMP9, suggesting that these MMPs are likely downstream targets of LRP1-mediated signaling. We further show that the level of phosphorylated extracellular signal-regulated kinase (ERK) was significantly decreased in LRP1-silenced cells, suggesting that ERK is a potential mediator of LRP1-regulated MMP2 and MMP9 expression in U87 cells. Together, our data strongly suggest that LRP1 promotes glioblastoma cell migration and invasion by regulating the expression and function of MMP2 and MMP9 perhaps via an ERK-dependent signaling pathway.

Bioinformatics analysis of metastasis-related proteins in hepatocellular carcinoma

AIM: To analyze the metastasis-related proteins in hepatocellular carcinoma (HCC) and discover the biomarker candidates for diagnosis and therapeutic intervention of HCC metastasis with bioinformatics tools.

METHODS: Metastasis-related proteins were determined by stable isotope labeling and MS analysis and analyzed with bioinformatics resources, including Phobius, Kyoto encyclopedia of genes and genomes (KEGG), online mendelian inheritance in man (OMIM) and human protein reference database (HPRD).

RESULTS: All the metastasis-related proteins were linked to 83 pathways in KEGG, including MAPK and p53 signal pathways. Protein-protein interaction network showed that all the metastasis-related proteins were categorized into 19 function groups, including cell cycle, apoptosis and signal transduction. OMIM analysis linked these proteins to 186 OMIM entries.

CONCLUSION: Metastasis-related proteins provide HCC cells with biological advantages in cell proliferation, migration and angiogenesis, and facilitate metastasis of HCC cells. The bird’s eye view can reveal a global characteristic of metastasis-related proteins and many differentially expressed proteins can be identified as candidates for diagnosis and treatment of HCC.

Vitronectin inhibits plasminogen activator inhibitor-1-induced signalling and chemotaxis by blocking plasminogen activator inhibitor-1 binding to the low-density lipoprotein receptor-related protein

We have previously reported that the serpin plasminogen activator inhibitor-1 activates the Janus kinase (Jak)/signal transducer and activator of transcription (Stat) signalling pathway and stimulates cell migration by binding to the low-density lipoprotein receptor-related protein. All the free forms (cleaved, latent or active) of this inhibitor were shown to be motogenic. However, the plasminogen activator inhibitor-1 can also interact with vitronectin which acts as a cofactor by increasing the half-life of the active form of the serpin. Since vitronectin influences most of the biological functions of the plasminogen activator inhibitor-1, we explored the effects of vitronectin on signalling and cell migration induced by this serpin. We found that the interaction between vitronectin and the plasminogen activator inhibitor-1 suppressed signalling and cell migration. In fact, a purified vitronectin(1-97)/plasminogen activator inhibitor-1 complex was not chemotactic. Vitronectin interaction with the plasminogen activator inhibitor-1 blocks the binding of this serpin to its motogenic receptor, the low-density lipoprotein receptor-related protein. Consequently, vitronectin inhibits the activation of the Janus kinase/signal transducer and activator of transcription signalling pathway by the plasminogen activator inhibitor-1 and subsequent cell migration. In conclusion, we have unveiled a new inhibitory role of vitronectin, which turns off the intracellular signalling and migration-promoting activity of the plasminogen activator inhibitor-1. Thus, the motogenic (cleaved, latent or active) and non-motogenic (in complex with vitronectin) forms of the plasminogen activator inhibitor-1 have different properties that may explain the rather contrasting physiological and pathological roles of this serpin.

LDL receptor-related protein 1: unique tissue-specific functions revealed by selective gene knockout studies

The LDL receptor-related protein (originally called LRP, but now referred to as LRP1) is a large endocytic receptor that is widely expressed in several tissues. LRP1 is a member of the LDL receptor family that plays diverse roles in various biological processes including lipoprotein metabolism, degradation of proteases, activation of lysosomal enzymes, and cellular entry of bacterial toxins and viruses. Deletion of the LRP1 gene leads to lethality in mice, revealing a critical, but as of yet, undefined role in development. Tissue-specific gene deletion studies reveal an important contribution of LRP1 in the vasculature, central nervous system, macrophages, and adipocytes. Three important properties of LRP1 dictate its diverse role in physiology: 1) its ability to recognize more than 30 distinct ligands, 2) its ability to bind a large number of cytoplasmic adaptor proteins via determinants located on its cytoplasmic domain in a phosphorylation-specific manner, and 3) its ability to associate with and modulate the activity of other transmembrane receptors such as integrins and receptor tyrosine kinases.

LRP-1 silencing prevents malignant cell invasion despite increased pericellular proteolytic activities

The scavenger receptor low-density lipoprotein receptor-related protein 1 (LRP-1) mediates the clearance of a variety of biological molecules from the pericellular environment, including proteinases which degrade the extracellular matrix in cancer progression. However, its accurate functions remain poorly explored and highly controversial. Here we show that LRP-1 silencing by RNA interference results in a drastic inhibition of cell invasion despite a strong stimulation of pericellular matrix metalloproteinase 2 and urokinase-type plasminogen activator proteolytic activities. Cell migration in both two and three dimensions is decreased by LRP-1 silencing. LRP-1-silenced carcinoma cells, which are characterized by major cytoskeleton rearrangements, display atypical overspread morphology with a lack of membrane extensions. LRP-1 silencing accelerates cell attachment, inhibits cell-substrate deadhesion, and induces the accumulation, at the cell periphery, of abundant talin-containing focal adhesion complexes deprived of FAK and paxillin. We conclude that in addition to its role in ligand binding and endocytosis, LRP-1 regulates cytoskeletal organization and adhesive complex turnover in malignant cells by modulating the focal complex composition, thereby promoting invasion.

Thrombospondin-1 enhances human thyroid carcinoma cell invasion through urokinase activity

Previous studies reported that modification in the expression of the matricellular multidomain glycoprotein thrombospondin-1 (TSP-1) could play a critical role in the control of tumor progression and metastasis development. The function of this multimodular protein in cancers appears highly dependent on the cellular context and thus remains to date very difficult to accurately characterize. Controversial results indeed exist reporting either pro- or anti-invasive properties of TSP-1. Since it appeared that TSP-1 could be of prognostic value for certain specific types of cancers, we examined in this study the prospective function of TSP-1 in the control of human follicular thyroid carcinoma (FTC) cell invasiveness. First, we established that the aggressive behavior of human thyroid malignant cells is closely correlated to the TSP-1 amount. We demonstrated that exogenously added TSP-1 stimulates by two-fold the capacity of FTC cells to invade Matrigel-coated wells. The use of specific anti-TSP-1 blocking antibodies led to a drastic inhibition of the basal FTC cell invasion. Zymography experiments revealed that the uPA-dependent proteolytic activity is directly controlled by TSP-1, MMPs activity is not. The TSP-1-mediated stimulation of uPA appears to occur at post-transcriptional level. Finally, we established that the TSP-1-stimulated FTC cell invasion is wholly abolished under anti-uPA blocking antibodies or aprotinin treatments whereas MMP inhibitors have no effect. All together, we evidenced in the present study that TSP-1 promotes human follicular thyroid carcinoma cell invasion mainly through up-regulation of the urokinase-dependent activity.

Gene expression and the biological phenotype of papillary thyroid carcinomas

The purpose of this paper is to correlate the molecular phenotype of papillary thyroid carcinoma (PTC) to their biological pathology. We hybridized 26 PTC on microarrays and showed that nearly 44% of the transcriptome was regulated in these tumors. We then combined our data set with two published PTC microarray studies to produce a platform- and study-independent list of PTC-associated genes. We further confirmed the mRNA regulation of 15 genes from this list by quantitative reverse transcription-PCR. Analysis of this list with statistical tools led to several conclusions: (1) there is a change in cell population with an increased expression of genes involved in the immune response, reflecting lymphocyte infiltration in the tumor compared to the normal tissue. (2) The c-jun N-terminal kinase pathway is activated by overexpression of its components. (3) The activation of ERKK1/2 by genetic alterations is supplemented by activation of the epidermal growth factor but not of the insulin-like growth factor signaling pathway. (4) There is a downregulation of immediate early genes. (5) We observed an overexpression of many proteases in accordance with tumor remodeling, and suggested a probable role of S100 proteins and annexin A2 in this process. (6) Numerous overexpressed genes favor the hypothesis of a collective migration mode of tumor cells.