Involvement of S100-related calcium-binding protein pEL98 (or mts1) in cell motility and tumor cell invasion

S100A4/TCF Complex Transcription Regulation Drives Epithelial-Mesenchymal Transition in Chronic Sinusitis Through Wnt/GSK-3β/β-Catenin Signaling

Epithelial-mesenchymal transition (EMT) is thought to be involved in the tissue remodeling and long-term inflammatory process of chronic sinusitis (CRS), but the driving mechanism is still unclear. Using high-resolution mass spectrometry, we performed a proteomic screen of CRS nasal mucosal tissue to identify differentially expressed proteins. Data are available via ProteomeXchange with identifier PXD030884. Specifically, we identified S100 calcium binding protein A4 (S100A4), an effective factor in inflammation-related diseases, and its downstream protein closely related to tissue fibrosis collagen type I alpha 1 chain (COL1A1), which suggested its involvement in nasal mucosal tissue remodeling. In addition, stimulation of human nasal epithelial cells (HNEpCs) with lipopolysaccharide (LPS) mimicked the inflammatory environment of CRS and showed that S100A4 is involved in regulating EMT and thus accelerating tissue remodeling in the nasal mucosa, both in terms of increased cell motility and overexpression of mesenchymal-type proteins. Additionally, we further investigated the regulation mechanism of S100A4 involved in EMT in CRS. Our research results show that in the inflammatory environment of CRS nasal mucosal epithelial cells, TCF-4 will target to bind to S100A4 and regulate its transcription. The transcription of S100A4 in turn affects the execution of the important signaling pathway in EMT, the Wnt/GSK-3β/β-catenin pathway, through the TCF-4/β-catenin complex. In conclusion, this study confirmed that the expression of S100A4 was significantly increased during the progressive EMT process of CRS mucosal epithelial cells, and revealed that the transcriptional regulation of S100A4 plays an important role in the occurrence and development of EMT. This finding will help us to better understand the pathogenesis behind the remodeling in CRS patients, and identify target molecules for the treatment of CRS.

The Multifaceted S100A4 Protein in Cancer and Inflammation

The metastasis-promoting S100A4 protein, a member of the S100 family, has recently been discovered as a potent factor implicated in various inflammation-associated diseases. S100A4 is involved in a range of biological functions such as angiogenesis, cell differentiation, apoptosis, motility, and invasion. Moreover, S100A4 is also a potent trigger of inflammatory processes and induces the release of cytokines and growth factors under different pathological conditions.Indeed, the release of S100A4 upon stress and mainly its pro-inflammatory role emerges as the most decisive activity in disease development, such as rheumatoid arthritis (RA), systemic sclerosis (SSc) allergy, psoriasis, and cancer. In the scope of this review, we will focus on the role of S100A4 as a mediator of pro-inflammatory pathways and its associated biological processes involved in the pathogenesis of various human noncommunicable diseases (NCDs) including cancer.

Correlation of two distinct metastasis-associated proteins, MTA1 and S100A4, in angiogenesis for promoting tumor growth

Extensive studies on metastasis-associated proteins, S100A4 and MTA1, have been carried out for over two decades, but correlation of both proteins remains obscure. Here we show evidence for the correlation in angiogenesis. First, silencing of each protein by siRNA-mediated knockdown in mouse endothelial MSS31 cells resulted in the inhibition of tube formation. Unexpectedly, the knockdown of MTA1 affected not only its own expression but also the expression of S100A4, whereas silencing of S100A4 did not affect the MTA1 expression. Additionally, non-muscle myosin IIA (NMIIA) phosphorylation, which was partly controlled by S100A4, was found to be upregulated by knockdown of both proteins in MSS31 cells. Moreover, cycloheximide treatment of MSS31 cells revealed that the rate of S100A4 degradation was accelerated by MTA1 knockdown. This finding, together with our observation that cytoplasmic MTA1, but not nuclear MTA1, was colocalized with S100A4, suggested the involvement of MTA1 in S100A4 stability. The direct in vivo angiogenesis assay showed that both protein siRNAs provoked a significant inhibition of new blood vessel formation induced by angiogenic factors, indicating their anti-angiogenic activities. Treatment of human pancreatic tumor (PANC-1) xenograft in mice with mMTA1 siRNA resulted in tumor regression via suppression of angiogenesis in vivo, as also observed in the case of human prostate cancer xenograft treated with mS100A4 siRNA. Taken together, these data led us to conclude that the MTA1-S100A4-NMIIA axis exists in endothelial cells as a novel pathway in promoting tumor vascular formation and could be a target for suppressing tumor growth and metastasis.

Prognostic significance of S100A4-expression and subcellular localization in early-stage breast cancer

PURPOSE

Prognostic factors are useful in order to identify early-stage breast cancer patients who might benefit from adjuvant treatment. The metastasis-promoting protein S100A4 has previously been associated with poor prognosis in breast cancer patients. The protein is expressed in diverse subcellular compartments, including the cytoplasm, extracellular space, and nucleus. Nuclear expression is an independent predictor of poor outcome in several cancer types, but the significance of subcellular expression has not yet been assessed in breast cancer.

METHODS

Nuclear and cytoplasmic expression of S100A4 was assessed by immunohistochemistry in prospectively collected tumor samples from early-stage breast cancer patients using tissue microarrays.

RESULTS

In patients not receiving adjuvant systemic therapy, nuclear or cytoplasmic expression was found in 44/291 tumors (15%). Expression of either nuclear or cytoplasmic S100A4 was associated with histological grade III, triple-negative subtype, and Ki-67-expression. Patients with S100A4-positive tumors had inferior metastasis-free and overall survival compared to S100A4-negative. When expression was analyzed separately, nuclear S100A4 was a significant predictor of outcome, while cytoplasmic was not. In patients who received adjuvant treatment 23/300 tumors (8%) were S100A4-positive, but no tumors displayed nuclear staining alone. S100A4-expression was strongly associated with histological grade III and triple-negative subtype. Although not significant, metastasis-free and overall survival was numerically reduced in patients with S100A4-positive tumors.

CONCLUSION

S100A4-expression was associated with poor outcome in early-stage breast cancer, but the low percentage of positive tumors and the modest survival differences imply that the clinical utility in selection of patients for adjuvant treatment is limited.

Enrichment of nuclear S100A4 during G2/M in colorectal cancer cells: possible association with cyclin B1 and centrosomes

S100A4 promotes metastasis in several types of cancer, but the involved molecular mechanisms are still incompletely described. The protein is associated with a wide variety of biological functions and it locates to different subcellular compartments, including nuclei, cytoplasm and extracellular space. Nuclear expression of S100A4 has been associated with more advanced disease stage as well as poor outcome in colorectal cancer (CRC). The present study was initiated to investigate the nuclear function of S100A4 and thereby unravel potential biological mechanisms linking nuclear expression to a more aggressive phenotype. CRC cell lines show heterogeneity in nuclear S100A4 expression and preliminary experiments revealed cells in G2/M to have increased nuclear accumulation compared to G1 and S cells, respectively. Synchronization experiments validated nuclear S100A4 expression to be most prominent in the G2/M phase, but manipulating nuclear levels of S100A4 using lentiviral modified cells failed to induce changes in cell cycle distribution and proliferation. Proximity ligation assay did, however, demonstrate proximity between S100A4 and cyclin B1 in vitro, while confocal microscopy showed S100A4 to localize to areas corresponding to centrosomes in mitotic cells prior to chromosome segregation. This might indicate a novel and uncharacterized function of the metastasis-associated protein in CRC cells.

Efficient inhibition of tumor angiogenesis and growth by a synthetic peptide blocking S100A4-methionine aminopeptidase 2 interaction

The prometastatic calcium-binding protein, S100A4, is expressed in endothelial cells, and its downregulation markedly suppresses tumor angiogenesis in a xenograft cancer model. Given that endothelial S100A4 can be a molecular target for inhibiting tumor angiogenesis, we addressed here whether synthetic peptide capable of blocking S100A4-effector protein interaction could be a novel antiangiogenic agent. To examine this hypothesis, we focused on the S100A4-binding domain of methionine aminopeptidase 2, an effector protein, which plays a role in endothelial cell growth. Overexpression of the domain in mouse endothelial MSS31 cells reduced DNA synthesis, and the corresponding synthetic peptide (named NBD) indeed interacted with S100A4 and inhibited capillary formation in vitro and new blood vessel formation in vivo. Intriguingly, a single intra-tumor administration of the NBD peptide in human prostate cancer xenografts significantly reduced vascularity, resulting in tumor regression. Mechanistically, the NBD peptide enhanced assembly of nonmuscle myosin IIA filaments along with Ser1943 phosphorylation, stimulated formation of focal adhesions without phosphorylation of focal adhesion kinase, and provoked G1/S arrest of the cell cycle. Altogether, the NBD peptide is a potent inhibitor for tumor angiogenesis, and is the first example of an anticancer peptide drug developed on the basis of an endothelial S100A4-targeted strategy.

Myosin II isoform co-assembly and differential regulation in mammalian systems

Non-muscle myosin 2 (NM2) is a major force-producing, actin-based motor in mammalian non-muscle cells, where it plays important roles in a broad range of fundamental biological processes, including cytokinesis, cell migration, and epithelial barrier function. This breadth of function at the tissue and cellular levels suggests extensive diversity and differential regulation of NM2 bipolar filaments, the major, if not sole, functional form of NM2s in vivo. Previous in vitro, cellular and animal studies indicate that some of this diversity is supported by the existence of multiple NM2 isoforms. Moreover, two recent studies have shown that these isoforms can co-assemble to form heterotypic filaments, further expanding functional diversity. In addition to isoform co-assembly, cells may differentially regulate NM2 function via isoform-specific expression, RLC phosphorylation, MHC phosphorylation or regulation via binding partners. Here, we provide a brief summary of NM2 filament assembly, summarize the recent findings regarding NM2 isoform co-assembly, consider the mechanisms cells might utilize to differentially regulate NM2 isoforms, and review the data available to support these mechanisms.

The heavy chain has its day: regulation of myosin-II assembly

Nonmuscle myosin-II is an actin-based motor that converts chemical energy into force and movement, and thus functions as a key regulator of the eukaryotic cytoskeleton. Although it is established that phosphorylation on the regulatory light chain increases the actin-activated MgATPase activity of the motor and promotes myosin-II filament assembly, studies have begun to characterize alternative mechanisms that regulate filament assembly and disassembly. These investigations have revealed that all three nonmuscle myosin-II isoforms are subject to additional regulatory controls, which impact diverse cellular processes. In this review, we discuss current knowledge on mechanisms that regulate the oligomerization state of nonmuscle myosin-II filaments by targeting the myosin heavy chain.

Activation of the PI3K/Akt/mTOR/p70S6K pathway is involved in S100A4-induced viability and migration in colorectal cancer cells

The S100 protein family member S100A4 regulates various cellular functions. Previous studies have shown that elevated expression of S100A4 is associated with progression and metastasis of colorectal cancer (CRC). However, little is known about whether and how S100A4 contributes to CRC development. In our present study, the elevated expression of S100A4 in CRC tissues compared to matched adjacent normal tissues was confirmed by immunohistochemistry, semi-quantitative RT-PCR and Western blot. Adenovirus-mediated S100A4 overexpression obviously enhanced viability and migration of CRC cells, which was detected by MTT assay and transwell assay, respectively. Additionally, S100A4 overexpression increased the phosphorylation levels of Akt, mTOR and p70S6K. These effects of S100A4 were abolished by treatment with either the specific PI3K/Akt inhibitor LY294002, or the specific mTOR/p70S6K inhibitor rapamycin. Furthermore, overexpression of S100A4 resulted in upregulation of VEGF and downregulation of E-cadherin, which were strongly reversed by either LY294002 or rapamycin. Altogether, our results demonstrate that activation of the PI3K/Akt/mTOR/p70S6K signaling pathway is involved in S100A4-induced viability, migration, upregulation of VEGF and downregulation of E-cadherin in CRC cells.

Silencing of S100A4, a metastasis-associated protein, in endothelial cells inhibits tumor angiogenesis and growth

Endothelial cells express S100A4, a metastasis-associated protein, but its role in angiogenesis remains to be elucidated. Here we show that knockdown of S100A4 in mouse endothelial MSS31 cells by murine specific small interference RNA (mS100A4 siRNA) markedly suppressed capillary-like tube formation in vitro, in early stage after the treatment, along with down- and up-regulation of some of the pro-angiogenic and anti-angiogenic gene expression, respectively. Of particular note is that intra-tumor administration of the mS100A4 siRNA in a human prostate cancer xenograft significantly reduced tumor vascularity and resulted in the inhibition of tumor growth. These findings show that S100A4 in endothelial cells is involved in tube formation, and suggest its potential as a molecular target for inhibiting tumor angiogenesis, which warrants further development of endothelial S100A4-based strategies for cancer treatment.

Structure of the S100A4/myosin-IIA complex

Background

S100A4, a member of the S100 family of Ca²⁺-binding proteins, modulates the motility of both non-transformed and cancer cells by regulating the localization and stability of cellular protrusions. Biochemical studies have demonstrated that S100A4 binds to the C-terminal end of the myosin-IIA heavy chain coiled-coil and disassembles myosin-IIA filaments; however, the mechanism by which S100A4 mediates myosin-IIA depolymerization is not well understood.

Results

We determined the X-ray crystal structure of the S100A4Δ8C/MIIA^1908-1923 peptide complex, which showed an asymmetric binding mode for the myosin-IIA peptide across the S100A4 dimer interface. This asymmetric binding mode was confirmed in NMR studies using a spin-labeled myosin-IIA peptide. In addition, our NMR data indicate that S100A4Δ8C binds the MIIA^1908-1923 peptide in an orientation very similar to that observed for wild-type S100A4. Studies of complex formation using a longer, dimeric myosin-IIA construct demonstrated that S100A4 binding dissociates the two myosin-IIA polypeptide chains to form a complex composed of one S100A4 dimer and a single myosin-IIA polypeptide chain. This interaction is mediated, in part, by the instability of the region of the myosin-IIA coiled-coil encompassing the S100A4 binding site.

Conclusion

The structure of the S100A4/MIIA^1908-1923 peptide complex has revealed the overall architecture of this assembly and the detailed atomic interactions that mediate S100A4 binding to the myosin-IIA heavy chain. These structural studies support the idea that residues 1908–1923 of the myosin-IIA heavy chain represent a core sequence for the S100A4/myosin-IIA complex. In addition, biophysical studies suggest that structural fluctuations within the myosin-IIA coiled-coil may facilitate S100A4 docking onto a single myosin-IIA polypeptide chain.

Novel interactions of the TRTK12 peptide with S100 protein family members: specificity and thermodynamic characterization

The S100 protein family consists of small, dimeric proteins that exert their biological functions in response to changing calcium concentrations. S100B is the best-studied member and has been shown to interact with more than 20 binding partners in a calcium-dependent manner. The TRTK12 peptide, derived from the consensus binding sequence for S100B, has previously been found to interact with S100A1 and has been proposed to be a general binding partner of the S100 family. To test this hypothesis and gain a better understanding of the specificity of binding for the S100 proteins, 16 members of the human S100 family were screened against this peptide and its alanine variants. Novel interactions were found with only two family members, S100P and S100A2, indicating that TRTK12 selectively interacts with a small subset of the S100 proteins. Substantial promiscuity was observed in the binding site of S100B thereby accommodating variations in the peptide sequence, while S100A1, S100A2, and S100P exhibited larger differences in the binding constants for the TRTK12 alanine variants. This suggests that single-point substitutions can be used to selectively modulate the affinity of TRTK12 peptides for individual S100 proteins. This study has important implications for the rational drug design of inhibitors for the S100 proteins, which are involved in a variety of cancers and neurodegenerative diseases.

Anti-S100A4 antibody suppresses metastasis formation by blocking stroma cell invasion

The small Ca-binding protein, S100A4, has a well-established metastasis-promoting activity. Moreover, its expression is tightly correlated with poor prognosis in patients with numerous types of cancer. Mechanistically, the extracellular S100A4 drives metastasis by affecting the tumor microenvironment, making it an attractive target for anti-cancer therapy. In this study, we produced a function-blocking anti-S100A4 monoclonal antibody with metastasis-suppressing activity. Antibody treatment significantly reduced metastatic burden in the lungs of experimental animals by blocking the recruitment of T cells to the site of the primary tumor. In vitro studies demonstrated that this antibody efficiently reduced the invasion of T cells in a fibroblast monolayer. Moreover, it was capable of suppressing the invasive growth of human and mouse fibroblasts. We presume therefore that the antibody exerts its activity by suppressing stroma cell recruitment to the site of the growing tumor. Our epitope mapping studies suggested that the antibody recognition site overlaps with the target binding interface of human S100A4. We conclude here that this antibody could serve as a solid basis for development of an efficient anti-metastatic therapy.

Bay11-7082 inhibits the disintegration of the lymphendothelial barrier triggered by MCF-7 breast cancer spheroids; the role of ICAM-1 and adhesion

Background:

Many cancers spread through lymphatic routes, and mechanistic insights of tumour intravasation into the lymphatic vasculature and targets for intervention are limited. The major emphasis of research focuses currently on the molecular biology of tumour cells, while still little is known regarding the contribution of lymphatics.

Methods:

Breast cancer cell spheroids attached to lymphendothelial cell (LEC) monolayers were used to investigate the process of intravasation by measuring the areas of ‘circular chemorepellent-induced defects' (CCID), which can be considered as entry gates for bulky tumour intravasation. Aspects of tumour cell intravasation were furthermore studied by adhesion assay, and siRNA-mediated knockdown of intracellular adhesion molecule-1 (ICAM-1). Replacing cancer spheroids with the CCID-triggering compound 12(S)-hydroxyeicosatetraenoic acid (HETE) facilitated western blot analyses of Bay11-7082- and baicalein-treated LECs.

Results:

Binding of LECs to MCF-7 spheroids, which is a prerequisite for CCID formation, was mediated by ICAM-1 expression, and this depended on NF-κB and correlated with the expression of the prometastatic factor S100A4. Simultaneous inhibition of NF-κB with Bay11-7082 and of arachidonate lipoxygenase (ALOX)-15 with baicalein prevented CCID formation additively.

Conclusion:

Two mechanisms contribute to CCID formation: ALOX15 via the generation of 12(S)-HETE by MCF-7 cells, which induces directional migration of LECs, and ICAM-1 in LECs under control of NF-κB, which facilitates adhesion of MCF-7 cells to LECs.

S100A4 calcium-binding protein is key player in tumor progression and metastasis: preclinical and clinical evidence

The fatality of cancer is mainly bestowed to the property of otherwise benign tumor cells to become malignant and invade surrounding tissues by circumventing normal tissue barriers through a process called metastasis. S100A4 which is a member of the S100 family of calcium-binding proteins has been shown to be able to activate and integrate pathways both intracellular and extracellular to generate a phenotypic response characteristic of cancer metastasis. A large number of studies have shown an increased expression level of S100A4 in various types of cancers. However, its implications in cancer metastasis in terms of whether an increased expression of S100A4 is a causal factor for metastasis or just another after effect of several other physiological and molecular changes in the body resulting from metastasis are not clear. Here we describe the emerging preclinical and clinical evidences implicating S100A4 protein, in both its forms (intracellular and extracellular) in the process of tumorigenesis and metastasis in humans. Based on studies utilizing S100A4 as a metastasis biomarker and molecular target for therapies such as gene therapy, we suggest that S100A4 has emerged as a promising molecule to be tested for anticancer drugs. This review provides an insight in the (1) molecular mechanisms through which S100A4 drives the tumorigenesis and metastasis and (2) developments made in the direction of evaluating S100A4 as a cancer biomarker and drug target.

Expression of S100A4, ephrin-A1 and osteopontin in non-small cell lung cancer

Background

The metastasis-promoting protein S100A4 induces expression of ephrin-A1 and osteopontin in osteosarcoma cell lines. The aim of this study was to investigate S100A4-mediated stimulation of ephrin-A1 and osteopontin in non-small cell lung cancer (NSCLC) cell lines, and to characterize the expression of these biomarkers in primary tumor tissue from NSCLC patients.

Methods

Four NSCLC cell lines were treated with extracellular S100A4, and ephrin-A1 and osteopontin expression was analyzed by real time RT-PCR and Western blotting. Immunohistochemical staining for S100A4, ephrin-A1 and osteopontin was performed on tissue microarrays containing primary tumor samples from a cohort of 217 prospectively recruited NSCLC patients, and associations with clinicopathological parameters were investigated.

Results

S100A4 induced ephrin-A1 mRNA and protein expression in adenocarcinoma, but not in squamous carcinoma cell lines, whereas the level of osteopontin was unaffected by S100A4 treatment. In primary tumors, moderate or strong immunoreactivity was observed in 57% of cases for cytoplasmic S100A4, 46% for nuclear S100A4, 86% for ephrin-A1 and 77% for osteopontin. Interestingly, S100A4 expression was associated with ephrin-A1 also in vivo, but there was no association between S100A4 and osteopontin. Expression levels of S100A4 and ephrin-A1 were significantly higher in adenocarcinomas compared to other histological subtypes, and S100A4-positive tumors were smaller and more differentiated than tumors without expression.

Conclusions

Our findings suggest that S100A4, ephrin-A1 and osteopontin are involved in the biology of NSCLC, and further investigation of their potential use as biomarkers in NSCLC is warranted.

S100A4 downregulates filopodia formation through increased dynamic instability

Cell migration requires the initial formation of cell protrusions, lamellipodia and/or filopodia, the attachment of the leading lamella to extracellular cues and the formation and efficient recycling of focal contacts at the leading edge. The small calcium binding EF-hand protein S100A4 has been shown to promote cell motility but the direct molecular mechanisms responsible remain to be elucidated. In this work, we provide new evidences indicating that elevated levels of S100A4 affect the stability of filopodia and prevent the maturation of focal complexes. Increasing the levels of S100A4 in a rat mammary benign tumor derived cell line results in acquired cellular migration on the wound healing scratch assay. At the cellular levels, we found that high levels of S100A4 induce the formation of many nascent filopodia, but that only a very small and limited number of those can stably adhere and mature, as opposed to control cells, which generate fewer protrusions but are able to maintain these into more mature projections. This observation was paralleled by the fact that S100A4 overexpressing cells were unable to establish stable focal adhesions. Using different truncated forms of the S100A4 proteins that are unable to bind to myosin IIA, our data suggests that this newly identified functions of S100A4 is myosin-dependent, providing new understanding on the regulatory functions of S100A4 on cellular migration.

NF-κB mediates the 12(S)-HETE-induced endothelial to mesenchymal transition of lymphendothelial cells during the intravasation of breast carcinoma cells

Background:

The intravasation of breast cancer into the lymphendothelium is an early step of metastasis. Little is known about the mechanisms of bulky cancer invasion into lymph ducts.

Methods:

To particularly address this issue, we developed a 3-dimensional co-culture model involving MCF-7 breast cancer cell spheroids and telomerase-immortalised human lymphendothelial cell (LEC) monolayers, which resembles intravasation in vivo and correlated the malignant phenotype with specific protein expression of LECs.

Results:

We show that tumour spheroids generate ‘circular chemorepellent-induced defects’ (CCID) in LEC monolayers through retraction of LECs, which was induced by 12(S)-hydroxyeicosatetraenoic acid (HETE) secreted by MCF-7 spheroids. This 12(S)-HETE-regulated retraction of LECs during intravasation particularly allowed us to investigate the key regulators involved in the motility and plasticity of LECs. In all, 12(S)-HETE induced pro-metastatic protein expression patterns and showed NF-κB-dependent up-regulation of the mesenchymal marker protein S100A4 and of transcriptional repressor ZEB1 concomittant with down-regulation of the endothelial adherence junction component VE-cadherin. This was in accordance with ∼50% attenuation of CCID formation by treatment of cells with 10 μM Bay11-7082. Notably, 12(S)-HETE-induced VE-cadherin repression was regulated by either NF-κB or by ZEB1 since ZEB1 siRNA knockdown abrogated not only 12(S)-HETE-mediated VE-cadherin repression but inhibited VE-cadherin expression in general.

Interpretation:

These data suggest an endothelial to mesenchymal transition-like process of LECs, which induces single cell motility during endothelial transmigration of breast carcinoma cells. In conclusion, this study demonstrates that the 12(S)-HETE-induced intravasation of MCF-7 spheroids through LECs require an NF-κB-dependent process of LECs triggering the disintegration of cell–cell contacts, migration, and the generation of CCID.

S100A4 protects gastric cancer cells from anoikis through regulation of αv and α5 integrin

Detachment from the extracellular matrix induces a form of programmed cell death termed anoikis. Resistance to anoikis permits cancer cells to survive in systemic circulation and facilitates their metastasis to distant organs. It is well known that S100A4 is overexpressed in many tumors and involved in tumor metastasis, but the mechanisms of the metastasis-promoting function of S100A4 are not fully understood. We hypothesized that S100A4 might play a role in anoikis of gastric cancer cells and further affects their metastasis. To test this hypothesis, we changed the expression of S100A4 by means of RNA interference or experimental overexpression and investigated the effect on anoikis. We found that knockdown of S100A4 by RNA interference led to significantly increased anoikis, whereas overexpression of S100A4 resulted in inhibition of anoikis. Furthermore, we provide evidence that inhibition of S100A4 resulted in the downregulation of α5 and αv integrin expression. These findings suggest that S100A4 protects gastric cancer cells from anoikis by regulation of αv and α5 integrin expression, which sheds a novel light for the role of S100A4 in cancer metastasis.

S100A4 regulates macrophage chemotaxis

Using a targeted genetic deletion, we show that the S100A4 metastasis factor is required for macrophage recruitment to sites of inflammation in vivo. S100A4^−/− primary macrophages display defects in chemotaxis due to myosin-IIA overassembly and altered CSF-1 receptor signaling. These studies establish S100A4 as a regulator of macrophage motility.

S100A4, a member of the S100 family of Ca²⁺-binding proteins, is directly involved in tumor metastasis. In addition to its expression in tumor cells, S100A4 is expressed in normal cells and tissues, including fibroblasts and cells of the immune system. To examine the contribution of S100A4 to normal physiology, we established S100A4-deficient mice by gene targeting. Homozygous S100A4^−/− mice are fertile, grow normally and exhibit no overt abnormalities; however, the loss of S100A4 results in impaired recruitment of macrophages to sites of inflammation in vivo. Consistent with these observations, primary bone marrow macrophages (BMMs) derived from S100A4^−/− mice display defects in chemotactic motility in vitro. S100A4^−/− BMMs form unstable protrusions, overassemble myosin-IIA, and exhibit altered colony-stimulating factor-1 receptor signaling. These studies establish S100A4 as a regulator of physiological macrophage motility and demonstrate that S100A4 mediates macrophage recruitment and chemotaxis in vivo.

The basic C-terminal amino acids of calcium-binding protein S100A4 promote metastasis

The calcium-binding protein S100A4 can induce a metastatic phenotype in animal model systems and its expression in various human cancers has been shown to be associated with metastasis and reduced patient survival. Using a series of nested deletion mutants, it is now shown that the two C-terminal lysine residues are required for the enhanced metastasis, invasion and migration abilities that S100A4 confers on cells in a model system of metastasis. Basic C-terminal residues enhance the affinity between S100A4 and its best characterized target, a recombinant C-terminal fragment of non-muscle myosin II heavy chain isoform A (NMMHC-IIA). In wild-type S100A4 protein, the presence of the C-terminal lysine, residue 101, enhances the rate of association between S100A4 and NMMHC-IIA. These results identify the amino acids of S100A4 that are involved in metastasis induction and show that the C-terminal region of S100A4 is a possible target for inhibitors of its metastatic action.

S100A4 overexpression proves to be independent marker for breast cancer progression

BACKGROUND

Breast cancer is the most common cancer and cause of deaths in women around the world. Oncogene amplification usually occurs late in tumor progression and correlates well with aggressiveness of tumor. In fact the function of the S100A4 protein and its role in metastasis is unclear at present. The purpose of the study was to determine the expression of S100A4 protein in the invasion status and metastatic potential of breast cancer by using tissue microarray and to determine its role in breast cancer based on the expression of S100A4 gene product.

METHODS

S100A4 protein expression was examined by immunohistochemistry (IHC) using commercially available tissue microarray containing malignant and normal breast tissue cores from 216 patients.

RESULTS

S100A4 was absent in normal breast tissues while positive in 45.1% of infiltrating ductal carcinoma (IDC) node negative and 48.8% of infiltrating lobular carcinoma node negative. In paired samples, S100A4 protein was expressed in 13.5% of IDC node positive cases and 35.1% of matched lymph node metastasis.

CONCLUSION

S100A4 protein expression appears widely expressed in early and advanced breast cancer stages compared with normal breast. Our study suggests S100A4 may play a role in breast cancer progression and may prove to be an independent marker of breast cancer which appears to be down regulated in more advanced stages of breast cancer.

The metastasis-associated protein S100A4 exists in several charged variants suggesting the presence of posttranslational modifications

Background

S100A4 is a metastasis-associated protein which has been linked to multiple cellular events, and has been identified extracellularly, in the cytoplasm and in the nucleus of tumor cells; however, the biological implications of subcellular location are unknown. Associations between a variety of posttranslational protein modifications and altered biological functions of proteins are becoming increasingly evident. Identification and characterization of posttranslationally modified S100A4 variants could thus contribute to elucidating the mechanisms for the many cellular functions that have been reported for this protein, and might eventually lead to the identification of novel drugable targets.

Methods

S100A4 was immuoprecipitated from a panel of in vitro and in vivo sources using a monoclonal antibody and the samples were separated by 2D-PAGE. Gels were analyzed by western blot and silver staining, and subsequently, several of the observed spots were identified as S100A4 by the use of MALDI-TOF and MALDI-TOF/TOF.

Results

A characteristic pattern of spots was observed when S100A4 was separated by 2D-PAGE suggesting the presence of at least three charge variants. These charge variants were verified as S100A4 both by western immunoblotting and mass spectrometry, and almost identical patterns were observed in samples from different tissues and subcellular compartments. Interestingly, recombinant S100A4 displayed a similar pattern on 2D-PAGE, but with different quantitative distribution between the observed spots.

Conclusion

Endogenously expressed S100A4 were shown to exist in several charge variants, which indicates the presence of posttranslational modifications altering the net charge of the protein. The different variants were present in all subcellular compartments and tissues/cell lines examined, suggesting that the described charge variants is a universal phenomenon, and cannot explain the localization of S100A4 in different subcellular compartments. However, the identity of the specific posttranslational modification and its potential contribution to the many reported biological events induced by S100A4, are subject to further studies.

Amplification and overexpression of PPFIA1, a putative 11q13 invasion suppressor gene, in head and neck squamous cell carcinoma

Chromosomal amplifications of the 11q13 genomic region are frequent in head and neck squamous cell carcinoma (HNSCC). To identify novel 11q13 amplification targets, we integrated high-resolution array-based comparative genomic hybridization and Affymetrix gene-expression profiling of eight HNSCC cell lines. We found that PPFIA1 was the highest upregulated gene in the 11q13 amplicon of HNSCC cell lines when compared with HNSCC lines without 11q13 amplification and confirmed the upregulation of PPFIA1 in primary HNSCCs by real-time PCR. Using siRNA knockdown, we investigated PPFIA1 function in three HNSCC lines using both in vitro invasion assays and wound-healing assays. Surprisingly, we found that cancer cells become more invasive when the PPFIA1 protein levels were reduced, suggesting that PPFIA1 may act as an invasion inhibitor in HNSCC. This unexpected result suggests that the 11q13 amplicon may comprise both positive and negative regulators involved in HNSCC. Our study is the first to evaluate the role of PPFIA1 in head and neck carcinogenesis and suggests a potential link between PPFIA1 activity and cell-extracellular matrix interactions. This article contains supplementary material available via the Internet at http://www.interscience.wiley.com/jpages/1045-2257/suppmat.

Expression of S100A4 by a variety of cell types present in the tumor microenvironment of human breast cancer

The S100A4 protein, which is involved in the metastasis process, is a member of the S100 superfamily of Ca-binding proteins. Members of this family are multifunctional signaling proteins with dual extra and intracellular functions involved in the regulation of diverse cellular processes. Several studies have established a correlation between S100A4 protein expression and worse prognosis for patients with various malignancies including breast cancer. In this article, we have used specific antibodies in combination with immunohistochemistry (IHC) to identify the cell types that express S100A4 in human breast cancer biopsies obtained from high-risk patients. IHC analysis of 68 tumor biopsies showed that the protein is expressed preferentially by various cell types present in the tumor microenvironment (macrophages, fibroblasts, activated lymphocytes), rather than by the tumor cells themselves. Moreover, we show that the protein is externalized by the stroma cells to the fluid that bathes the tumor microenvironment, where it is found in several forms that most likely correspond to charge variants. Using a specific ELISA test, we detected a significant higher concentration of S100A4 in the tumor interstitial fluid (TIF) as compared to their corresponding normal counterparts (NIF).

CTGF enhances the motility of breast cancer cells via an integrin-alphavbeta3-ERK1/2-dependent S100A4-upregulated pathway

Connective tissue growth factor (CTGF) expression is elevated in advanced stages of breast cancer, but the regulatory role of CTGF in invasive breast cancer cell phenotypes is unclear. Presently, overexpression of CTGF in MCF-7 cells (MCF-7/CTGF cells) enhanced cellular migratory ability and spindle-like morphological alterations, as evidenced by actin polymerization and focal-adhesion-complex aggregation. Reducing the CTGF level in MDA-MB-231 (MDA231) cells by antisense CTGF cDNA (MDA231/AS cells) impaired cellular migration and promoted a change to an epithelial-like morphology. A neutralizing antibody against integrin alphavbeta3 significantly attenuated CTGF-mediated ERK1/2 activation and cellular migration, indicating that the integrin-alphavbeta3-ERK1/2 signaling pathway is crucial in mediating CTGF function. Moreover, the cDNA microarray analysis revealed CTGF-mediated regulation of the prometastatic gene S100A4. Transfection of MCF-7/CTGF cells with AS-S100A4 reversed the CTGF-induced cellular migratory ability, whereas overexpression of S100A4 in MDA231/AS cells restored their high migratory ability. Genetic and pharmacological manipulations suggested that the CTGF-mediated S100A4 upregulation was dependent on ERK1/2 activation, with expression levels of CTGF and S100A4 being closely correlated with human breast tumors. We conclude that CTGF plays a crucial role in migratory/invasive processes in human breast cancer by a mechanism involving activation of the integrin-alphavbeta3-ERK1/2-S100A4 pathway.

The S100A4 metastasis factor regulates cellular motility via a direct interaction with myosin-IIA

S100A4, a member of the Ca(2+)-dependent S100 family of proteins, is a metastasis factor that is thought to regulate the motility and invasiveness of cancer cells. Previously, we showed that S100A4 specifically binds to nonmuscle myosin-IIA and promotes the unassembled state. S100A4, thus, provides a connection between the actomyosin cytoskeleton and the regulation of cellular motility; however, the step or steps in the motility cycle that are affected by S100A4 expression have not been investigated. To examine how the biochemical properties of S100A4 affect cell motility, we determined the effect of S100A4 expression on protrusive behavior during chemoattractant-stimulated motility. Our studies show that S100A4 modulates cellular motility by affecting cell polarization, with S100A4 expressing cells displaying few side protrusions and extensive forward protrusions during chemotaxis compared with control cells. To establish a direct link between S100A4 and the regulation of myosin-IIA function, we prepared an antibody to the S100A4 binding site on the myosin-IIA heavy chain that has comparable effects on myosin-IIA assembly as S100A4. Microinjection experiments show that the antibody elicits the same effects on cell polarization as S100A4. Our studies show for the first time that S100A4 promotes directional motility via a direct interaction with myosin-IIA. These findings establish S100A4 as a critical regulator of myosin-II function and metastasis-associated motility.

The metastasis associated protein S100A4: role in tumour progression and metastasis

The metastasis associated protein S100A4 is a small calcium binding protein that is associated with metastatic tumors and appears to be a molecular marker for clinical prognosis. Below we discuss its biochemical properties and possible cellular functions in metastasis including cell motility, invasion, apoptosis, angiogenesis and differentiation.

Suppression of tumor development and metastasis formation in mice lacking the S100A4(mts1) gene

The S100A4(mts1) protein stimulates metastatic spread of tumor cells. An elevated expression of S100A4 is associated with poor prognosis in many human cancers. Dynamics of tumor development were studied in S100A4-deficient mice using grafts of CSML100, highly metastatic mouse mammary carcinoma cells. A significant delay in tumor uptake and decreased tumor incidences were observed in S100A4(-/-) mice compared with the wild-type controls. Moreover, tumors developed in S100A4(-/-) mice never metastasize. Immunohistochemical analyses of these tumors revealed reduced vascularity and abnormal distribution of host-derived stroma cells. Coinjection of CSML100 cells with immortalized S100A4(+/+) fibroblasts partially restored the dynamics of tumor development and the ability to form metastasis. These fibroblasts were characterized by an enhanced motility and invasiveness in comparison with S100A4(-/-) fibroblasts, as well as by the ability to release S100A4 into the tumor environment. Taken together, our results point to a determinative role of host-derived stroma cells expressing S100A4 in tumor progression and metastasis.

S100A4 antisense oligodeoxynucleotide suppresses invasive potential of neuroblastoma cells

BACKGROUND

S100A4 gene product has been implicated in tumor invasion and metastasis. The overall survival rate of children with neuroblastoma remains poor because of disease dissemination at the time of diagnosis. The purpose of this study was to investigate the effect and mechanism of S100A4 on invasion and metastasis of neuroblastoma.

METHODS

A 20-mer phosphorothioate antisense oligodeoxynucleotide (asODN) targeted against the S100A4 mRNA was transfected into the human neuroblastoma cell line LA-N-6 by Lipofectamine 2000. The expressions of S100A4 and MMP-2 mRNAs were quantified by the reverse transcription polymerase chain reaction. The capability of migration and invasion of LA-N-6 cells were evaluated by the transwell chamber assay.

RESULTS

The S100A4 mRNA and the MMP-2 mRNA levels in asODN-treated cells were decreased by 35.6% and 25.5%, respectively, compared with those in nontreated cells. The numbers of migrating and invading LA-N-6 cells were both significantly lower in the asODN-treated groups than those in the nontreated groups ( 9.33 +/- 4.73 vs 20.67 +/- 2.89 and 2.33 +/- 1.15 vs 9.00 +/- 2.65, respectively; both P = .03 ).

CONCLUSIONS

The S100A4 asODN significantly reduced the S100A4 mRNA levels and the motility and invasive ability of neuroblastoma cells, with concomitant decrease of the MMP-2 mRNA levels. Thus, S100A4 may exert its effect on invasion and metastasis of neuroblastoma cells by stimulating the motility of tumor cells as well as influencing the expression of MMP-2.

S100A4 Expression Is an Early Event of Papillary Carcinoma of the Thyroid

OBJECTIVES

S100A4 is a calcium-binding protein related to the metastatic potential of carcinoma. In order to elucidate its contribution to the progression of thyroid carcinoma, we investigated S100A4 expression in various thyroid neoplasms.

METHODS

We immunohistochemically examined S100A4 expression in 195 cases of thyroid neoplasms.

RESULTS

Although S100A4 was absent in normal follicular cells and follicular adenoma, S100A4 was positive in all 115 cases of papillary carcinoma examined, including 58 microcarcinomas. However, a significant relationship could not be established between S100A4 expression and clinicopathological features of papillary carcinoma. In follicular carcinoma, the widely invasive type expressed S100A4 more frequently than the minimally invasive type (p = 0.0028). In anaplastic carcinoma, S100A4 was expressed in 61.9% of cases, but the incidence was significantly lower (p < 0.0001) than that in papillary carcinoma.

CONCLUSIONS

These findings suggest that (1) S100A4 plays a constitutive role in papillary carcinoma and (2) S100A4 may be a useful marker for early the detection of this carcinoma.

Role of intracellular S100A4 for migration of rat astrocytes

S100A4 is a member of the EF-hand family of calcium-binding proteins, first identified in tumor cells, and implicated in tumor invasion and metastasis. Intracellular upregulation of S100A4 is associated with increased motility of tumor cells. Extracellular application of S100A4 increases the motility of glioma cells in vitro. We showed previously that astrocytes in spinal cord and brain white matter also express S100A4. This expression is markedly increased in reactive white matter astrocytes after injury. Here, we have explored how changes in intracellular S100A4 affect migration of astrocytes. We produced cultures of white matter, S100A4 expressing astrocytes, and developed a small interfering (si) RNA approach to specifically eliminate S100A4 expression in these cells, and compared the migration of astrocytes expressing S100A4 with astrocytes transfected with S100A4 siRNA. As a "positive control" we used S100A4 expressing C6 glioma cells. In contrast to malignant cells, S100A4 expressing astrocytes increased their migration capacity after S100A4 siRNA treatment. At the same time, and in parallel with increased migration, white matter astrocytes increased their expression of metalloproteinases MMP-9 and MT1-MMP. The addition of MMP-2/MMP-9 inhibitor resulted in a significant inhibition of migration in S100A4 siRNA-treated astrocytes. These findings indicate that S100A4 has a stabilizing function in reactive white matter astrocytes, a function that may contribute to the development of a rigid, growth-inhibitory glial scar.

S100A4 inhibition by RNAi up-regulates osteoblast related genes in periodontal ligament cells

Periodontal ligament (PDL) is a thin fibrous connective tissue located between alveolar bone and cementum that remains unmineralized physiologically. It is thus thought that PDL cells possess mechanisms to inhibit mineralization. It has been demonstrated that S100A4, a member of the S100 calcium-binding protein family, is synthesized and secreted by PDL cells, and that it may act as an inhibitor of mineralization. However, the mechanisms of action of S100A4 in mineralization have not been thoroughly clarified. In the present study we investigated the effects of S100A4 inhibition by a short interfering RNA (siRNA) on the expression of osteoblast related genes by human PDL cells. Inhibition of S100A4 by siRNA resulted in increased expression of osteoblastic markers such as osteopontin and osteocalcin, and the osteoblast-specific transcription factors, Runx2/Cbfa1 and Osterix. These results indicate that S100A4 suppresses the expression of osteoblastic genes in PDL cells and may thus inhibit mineralization in the PDL.

Interaction of metastasis-inducing S100A4 protein in vivo by fluorescence lifetime imaging microscopy

Elevated levels of the calcium-binding regulatory protein, S100A4, have been shown to be causative of a metastatic phenotype in models of cancer metastasis and to be associated with reduced patient survival in breast cancer patients. Recombinant S100A4 protein interacts in vitro in a calcium-dependent manner with the heavy chain of non-muscle myosin isoform A at a protein kinase C phosphorylation site. At present, the mechanism of metastasis induction by S100A4 in vivo is almost completely unknown. The binding of S100A4 to a C-terminal recombinant fragment of non-muscle myosin heavy chain in living HeLa cells has now been shown using confocal microscopy, fluorescence lifetime imaging microscopy and time-correlated single-photon counting. The association between S100A4 and non-muscle myosin heavy chain was studied by determining fluorescence resonance energy transfer-derived changes in the fluorescence lifetime of enhanced cyan fluorescent protein fused to S100A4 in the presence of a recombinant fragment of the C-terminal region of non-muscle myosin heavy chain (rNMMHCIIA) fused to enhanced yellow fluorescent protein. There was no interaction between the non-muscle myosin heavy chain fragment and a calcium-binding-deficient mutant of S100A4 protein which has been shown to be defective in the induction of metastasis in model systems in vivo. The results demonstrate, for the first time, not only direct interaction between S100A4 and a target rNMMHCIIA in live mammalian cells, but also that the interaction between S100A4 and the non-muscle myosin heavy chain in vivo could contribute to the mechanism of metastasis induction by a high level of S100A4 protein.

Probing the S100 protein family through genomic and functional analysis

The EF-hand superfamily of calcium binding proteins includes the S100, calcium binding protein, and troponin subfamilies. This study represents a genome, structure, and expression analysis of the S100 protein family, in mouse, human, and rat. We confirm the high level of conservation between mammalian sequences but show that four members, including S100A12, are present only in the human genome. We describe three new members of the S100 family in the three species and their locations within the S100 genomic clusters and propose a revised nomenclature and phylogenetic relationship between members of the EF-hand superfamily. Two of the three new genes were induced in bone-marrow-derived macrophages activated with bacterial lipopolysaccharide, suggesting a role in inflammation. Normal human and murine tissue distribution profiles indicate that some members of the family are expressed in a specific manner, whereas others are more ubiquitous. Structure-function analysis of the chemotactic properties of murine S100A8 and human S100A12, particularly within the active hinge domain, suggests that the human protein is the functional homolog of the murine protein. Strong similarities between the promoter regions of human S100A12 and murine S100A8 support this possibility. This study provides insights into the possible processes of evolution of the EF-hand protein superfamily. Evolution of the S100 proteins appears to have occurred in a modular fashion, also seen in other protein families such as the C2H2-type zinc-finger family.

Mts1 regulates the assembly of nonmuscle myosin-IIA

The formation of myosin-II filaments is fundamental to contractile and motile processes in nonmuscle cells, and elucidating the mechanisms controlling filament assembly is essential for understanding how myosin-II rapidly responds to changing conditions within the cell. Several proteins including KRP and a novel 38 kDa protein (1, 2) have been shown to modulate filament assembly through the stabilization of myosin-II assemblies. In contrast, we demonstrate that mts1, a member of the Ca(2+)-regulated S100 family of proteins, may regulate the monomeric, unassembled state in an isoform-specific manner. Biochemical analyses demonstrate that mts1 has a 9-fold higher affinity for myosin-IIA filaments than for myosin-IIB filaments. At stoichiometric levels, mts1 inhibits the assembly of myosin-IIA monomers into filaments and promotes the disassembly of myosin-IIA filaments into monomers; however, mts1 has little effect on the assembly properties of myosin-IIB. Using a solution based-assay, we have demonstrated that mts1 binds to residues 1909-1924 of the myosin-IIA heavy chain, which is near the C-terminal tip of the alpha-helical coiled-coil. The observation that mts1 binds a linear sequence of approximately 16 amino acids is consistent with other S100 family members, which bind linear sequences of 13-22 residues in their protein targets. In addition, mts1 increases the critical monomer concentration for myosin-IIA filament assembly by approximately 11-fold. Kinetic assembly assays indicate that the elongation rate and the extent of polymerization depend on the initial myosin-IIA concentration; however, mts1 had only a small affect on the half-time for assembly and predominately affected the extent of myosin IIA polymerization. Altogether, these observations are consistent with mts1 regulating myosin IIA assembly by monomer sequestration and suggest that mts1 regulates cell shape and motility through the modulation of myosin-IIA function.

S100A4 regulates cell motility and invasion in an in vitro model for breast cancer metastasis

Elevated levels of the calcium-binding protein S100A4 are associated with poor patient survival in breast cancer patients and induce metastasis in rodent models. To investigate the effects of S100A4 on different components of the metastatic process, epithelial cells lines have been isolated from nonmalignant tumours in neu transgenic mice and from malignant tumours in neu/S100A4 double transgenic mice. Additional cell lines expressing both Neu and S100A4 have also been derived by transfection of rat S100A4 cDNA into tumour cell lines cloned from neu single transgenic mice. Using these cells in transfilter migration assays, it has been shown that increases in either motility or invasive properties correlate with each other and with the level of S100A4 protein. Injection of three of the cell lines separately into the mammary fat pads of nude mice showed that elevated levels of S100A4 correlated with the degree of metastasis to the lungs. In contrast, changes in cell proliferation and cell–substrate adhesion did not correlate with S100A4 levels. Neither motility nor invasiveness correlated with proteolytic degradation of gelatin as measured by zymography. Thus, the results suggest that the main effect of increases in S100A4 levels in metastasis is to generate increased cell motility and invasion and that this latter change is not dependent upon an increased ability to degrade the intercellular matrix.

Constitutive upregulation of hypoxia-inducible factor-1alpha mRNA occurring in highly metastatic lung carcinoma cells leads to vascular endothelial growth factor overexpression upon hypoxic exposure

Neoangiogenesis is crucial for tumor growth and metastasis and is regulated by various angiogenic factors including vascular endothelial growth factor (VEGF). However, little is known whether highly metastatic cells express higher level of VEGF in response to various stimuli, thereby increasing neoangiogenesis compared to low-metastatic cells. Here we report that hypoxia markedly induced the expression of VEGF mRNA in the cell lines with high-metastatic potential (A11 and D6 cells) compared to the cell lines with low-metastatic potential (P29 and P34 cells) established from Lewis lung carcinoma. A11 cells exhibited higher VEGF gene-promoter activity, produced a larger amount of VEGF and showed higher activity to induce neoangiogenesis than P29 cells. Although the degradation rate of VEGF mRNA under hypoxic conditions was similar in both cell lines, hypoxia-inducible factor-1alpha (HIF-1alpha) mRNA, but not HIF-1beta mRNA, was found to be constitutively upregulated in A11 cells compared to P29 cells. Accordingly, the level of HIF-1alpha protein in response to hypoxia was higher in A11 cells than in P29 cells. Upregulation of HIF-1alpha mRNA was also observed in D6 cells but not in P34 cells. Thus, the high-metastatic cells produced a larger amount of VEGF under hypoxic conditions through constitutive HIF-1alpha mRNA upregulation compared to the low-metastatic cells, thereby leading to extensive neoangiogenesis.

Characterization of the metastasis-associated protein, S100A4. Roles of calcium binding and dimerization in cellular localization and interaction with myosin

Elevated S100A4 protein expression is associated with metastatic tumor progression and appears to be a strong molecular marker for clinical prognosis. S100A4 is a calcium-binding protein that is known to form homodimers and interacts with several proteins in a calcium-dependent manner. Here we show that S100A4 localizes to lamellipodia structures in a migrating breast cancer-derived cell line and colocalizes with a known S100A4-interacting protein, myosin heavy chain IIA, at the leading edge. We demonstrate that S100A4 mutants that are defective in either their ability to dimerize or in calcium binding are unable to interact with myosin heavy chain IIA. An S100A4 mutant that is deficient for calcium binding retains the ability to form homodimers, suggesting that S100A4 can exist as calcium-free or calcium-bound dimers in vivo. However, a calcium-bound S100A4 monomer only interacts with another calcium-bound monomer and not with an S100A4 mutant that does not bind calcium. Interestingly, despite the calcium dependence for interaction with known protein partners, calcium binding is not necessary for localization to lamellipodia. Both wild type and a mutant that is deficient for calcium binding colocalize with known markers of actively forming leading edges of lamellipodia, Arp3 and neuronal Wiskott-Aldrich syndrome protein. These data suggest that S100A4 localizes to the leading edge in a calcium-independent manner, and identification of the proteins that are involved in localizing S100A4 to the lamellipodial structures may provide novel insight into the mechanism by which S100A4 regulates metastasis.

S100A4: a novel negative regulator of mineralization and osteoblast differentiation

S100A4 is an intracellular calcium-binding protein expressed by osteoblastic cells. However, its roles in bone physiology are unknown. Because before matrix mineralization, its expression is markedly diminished, we hypothesized that S100A4 negatively regulates the mineralization process. In this study, we investigated the effects of the inhibition of S100A4 synthesis on osteoblast differentiation and in vitro mineralized nodule formation. Inhibition of S100A4 synthesis was achieved by an antisense approach in the mouse osteoblastic cell line MC3T3-E1. Cell clones that synthesized low levels of S100A4 (AS clones) produced markedly increased number of mineralized nodules at much earlier stages in comparison with controls as demonstrated by Alizarin red S and von Kossa staining. The expression of type I collagen (COLI) and osteopontin (OPN) increased in AS clones compared with controls. Bone sialoprotein (BSP) and osteocalcin (OCN), molecules associated with mineralization and markers for mature osteoblastic phenotype, were expressed in AS clones before their detection in controls. Because S100A4 was not localized in the nucleus of MC3T3-E1 cells and AS clones, it is unlikely that S100A4 directly regulates the expression of these genes. Moreover, the expression of Cbfal/Osf-2 and Osx, transcription factors necessary for the expression of osteoblast-associated genes, remained unchanged in AS clones, indicating that S100A4 may be downstream to these transcription factors. These findings indicate that S100A4 is a novel negative regulator of matrix mineralization likely by modulating the process of osteoblast differentiation.

ALG-2: a Ca2+ -binding modulator protein involved in cell proliferation and in cell death

During the development of an organism, cell proliferation, differentiation and cell death are tightly balanced, and are controlled by a number of different regulators. Alterations in this balance are often observed in a variety of human diseases. The role of Ca(2+) as one of the key regulators of the cell is discussed with respect to a recently discovered Ca(2+)-binding protein, ALG-2, which is highly upregulated in cancerous tissues of different origins. The role of ALG-2 as a possible clinical marker and, molecularly, as a possible modulator at the interface between cell proliferation and cell death is discussed.

A role for CCN3 (NOV) in calcium signalling

AIMS

In animals and humans increased expression of CCN3 (NOV) is detected in tissues where calcium is a key regulator, such as the adrenal gland, central nervous system, bone and cartilage, heart muscle, and kidney. Because the multimodular structure of the CCN proteins strongly suggests that these cell growth regulators are metalloproteins, this study investigated the possible role of CCN3 in ion flux and transport during development, control of cell proliferation, differentiation, and pathobiology.

METHODS

The isolation of CCN3 partners was performed by means of the two hybrid system. Yeasts were cotransfected with an HL60 cDNA library fused to the transactivation domain of the GAL4 transcription factor, and with a plasmid expressing CCN3 fused to the DNA binding domain of GAL4. Screening of the recombinant clones selected on the basis of leucine, histidine, and tryptophan prototrophy was performed with a beta-galactosidase assay. After the interaction between CCN3 and its putative partners was checked with a GST (glutathione S-transferase) pull down assay, the positive clones were identified by cloning. To establish whether the CCN3 protein affected calcium ion flux, a dynamic imaging microscopy system was used, which allowed the fluorometric measurement of the intracellular calcium concentration. The proteins used in the assays were GST fused with either CCN3 or CCN2 (CTGF) and GST alone as a control.

RESULTS

The two hybrid system identified the S100A4 (mts1) calcium binding protein as a partner of CCN3 and the use of the GST fusion proteins showed that the addition of CCN3 and CCN2 to G59 glioblastoma and SK-N-SH neuroblastoma cells caused a pronounced but transient increase of intracellular calcium, originating from both the entry of extracellular calcium and the mobilisation of intracellular stores.

CONCLUSIONS

The interaction of CCN3 with S100A4 may account, in part, for the association of CCN3 with carcinogenesis and its pattern of expression in normal conditions. The increased intracellular calcium concentrations induced by CCN3 and CCN2 both involve different processes, among which voltage independent calcium channels might be of considerable importance in regulating the calcium flux associated with cell growth control, motility, and spreading. These observations assign for the first time a biological function to the CCN3 protein and point out a broader role for the CCN proteins in calcium ion signalling.

Methionine aminopeptidase 2 is a new target for the metastasis-associated protein, S100A4

S100A4 is an EF-hand type calcium-binding protein that regulates tumor metastasis and a variety of cellular processes via interaction with different target proteins. Here we report that S100A4 physically interacts with methionine aminopeptidase 2 (MetAP2), the primary target for potent angiogenesis inhibitors, fumagillin and ovalicin. Using a yeast two-hybrid screen, S100A4 was found to interact with the N-terminal half of MetAP2. In vitro pull-down assays showed that S100A4 associates with MetAP2 in a calcium-dependent manner. In addition, the binding site of S100A4 was found located within the region between amino acid residues 170 and 229 of MetAP2. In vivo interaction of S100A4 with MetAP2 was verified by co-immunoprecipitation analysis. Immunofluorescent staining revealed that S100A4 and MetAP2 were co-localized in both quiescent and basic fibroblast growth factor-treated murine endothelial MSS31 cells, in the latter of which a significant change of intracellular distribution of both proteins was observed. Although the binding of S100A4 did not affect the in vitro methionine aminopeptidase activity of MetAP2, the cytochemical observation suggests a possible involvement of S100A4 in the regulation of MetAP2 activity through changing its localization, thereby modulating the N-terminal methionine processing of nascent substrates. These results may offer an essential clue for understanding the functional role of S100A4 in regulating endothelial cell growth and tumor metastasis.

Liprin beta 1, a member of the family of LAR transmembrane tyrosine phosphatase-interacting proteins, is a new target for the metastasis-associated protein S100A4 (Mts1)

Metastasis-associated protein S100A4 (Mts1) induces invasiveness of primary tumors and promotes metastasis. S100A4 belongs to the family of small calcium-binding S100 proteins that are involved in different cellular processes as transducers of calcium signal. S100A4 modulates properties of tumor cells via interaction with its intracellular targets, heavy chain of non-muscle myosin and p53. Here we report identification of a new molecular target of the S100A4 protein, liprin beta1. Liprin beta1 belongs to the family of leukocyte common antigen-related (LAR) transmembrane tyrosine phosphatase-interacting proteins that may regulate LAR protein properties via interaction with another member of the family, liprin alpha1. We showed by the immunoprecipitation analysis that S100A4 interacts specifically with liprin beta1 in vivo. Immunofluorescence staining demonstrated the co-localization of S100A4 and liprin beta1 in the cytoplasm and particularly at the protrusion sites of the plasma membrane. We mapped the S100A4 binding site at the C terminus of the liprin beta1 molecule between amino acid residues 938 and 1005. The S100A4-binding region contains two putative phosphorylation sites by protein kinase C and protein kinase CK2. S100A4-liprin beta1 interaction resulted in the inhibition of liprin beta1 phosphorylation by both kinases in vitro.

Molecular mechanisms of renal allograft fibrosis

BACKGROUND

Chronic graft nephropathy (CGN) remains the leading cause of renal allograft loss after the first year following transplantation. Histologically it is characterized by glomerulosclerosis, intimal hyperplasia and interstitial fibrosis. The pathogenesis is unclear, but is likely to involve both immunological and non-immunological factors. Despite improvements in short-term graft survival rates, new immunosuppressive regimens have made no impact on CGN.

METHODS

A review of the current literature on renal transplantation, novel immunosuppression regimens and advances in the molecular pathogenesis of renal allograft fibrosis was performed.

RESULTS AND CONCLUSION

Recent advances in understanding of the underlying molecular mechanisms involved suggest autocrine secretion of cytokines and growth factors, especially transforming growth factor beta, are associated with a change in fibroblast phenotype leading to the deposition of extracellular matrix. Repeated insults trigger upregulation of the tissue inhibitors of matrix metalloproteinases, favouring accumulation of extracellular matrix. To date, no drug has proved effective in inhibiting or reducing allograft fibrosis. The deleterious consequences of chronic immunosuppression on the development of such fibrosis are now recognized; newer immunosuppressive drugs, including rapamycin and mycophenolate mofetil, reduce profibrotic gene expression in both experimental and clinical settings, and offer potential strategies for prolonging allograft survival.

Characterization of Sp1, AP-1, CBF and KRC binding sites and minisatellite DNA as functional elements of the metastasis-associated mts1/S100A4 gene intronic enhancer

The mts1/S100A4 gene encodes a small acidic calcium-binding protein that is expressed in a cell-specific manner in development, tumorigenesis and certain tissues of adult mice. A composite enhancer that is active in murine mammary adenocarcinoma cells was previously identified in the first intron of the mts1/S100A4 gene. Here we present a detailed analysis of the structure and function of this enhancer in the Mts1/S100A4-expressing CSML100 and non-expressing CSML0 mouse adenocarcinoma cell lines. In CSML100 cells the enhancer activity is composed of at least six cis-elements interacting with Sp1 and AP-1 family members and CBF/AML/PEBP2 and KRC transcription factors. In addition, a minisatellite-like DNA sequence significantly contributes to the enhancer activity via interaction with abundant proteins, which likely have been described previously under the name minisatellite-binding proteins. Extensive mutational analysis of the mts1/S100A4 enhancer revealed a cooperative function of KRC and the factors binding minisatellite DNA. This is the first example of an enhancer where two nuclear factors earlier implicated in different recombination processes cooperate to activate transcription. In Mts1/S100A4-negative CSML0 cells the strength of the enhancer was 7- to 12.5-fold lower compared to that in CSML100 cells, when referred to the activities of three viral promoters. In CSML0 cells the enhancer could be activated by exogenous AP-1 and CBF transcription factors.

The metastasis-associated Mts1(S100A4) protein could act as an angiogenic factor

The involvement of Mts1(S100A4), a small Ca(2+)-binding protein in tumor progression and metastasis had been demonstrated. However, the mechanism by which mts1(S100A4) promoted metastasis had not been identified. Here we demonstrated that Mts1(S100A4) had significant stimulatory effect on the angiogenesis. We detected high incidence of hemangiomas--benign tumors of vascular origin in aged transgenic mice ubiquitously expressing the mts1(S100A4) gene. Furthermore, the serum level of the Mts1(S100A4) protein increased with ageing. Tumors developed in Mts1-transgenic mice revealed an enhanced vascular density. We showed that an oligomeric, but not a dimeric form of the Mts1(S100A4) protein was capable of enhancing the endothelial cell motility in vitro and stimulate the corneal neovascularization in vivo. An oligomeric fraction of the protein was detected in the conditioned media as well as in human serum. The data obtained allowed us to conclude that mts1(S100A4) might induce tumor progression via stimulation of angiogenesis.

Expression of metastasis-associated mts1 gene is co-induced with membrane type-1 matrix metalloproteinase (MT1-MMP) during oncogenic transformation and tubular formation of Madin Darby canine kidney (MDCK) epithelial cells

Madin-Darby canine kidney (MDCK) epithelial cells form branching tubules in three-dimensional collagen gel in the presence of hepatocyte growth factor (HGF). Membrane type-1 matrix metalloproteinase (MT1-MMP), expression of which was induced by collagen-gel culture, was demonstrated to play an essential role in tubular formation (Y. Kadono et al. Biochem Biophys Res Commun 1988; 251: 681-7 [13]). Oncogenic transformation of MDCK cells by erbB2 and v-src induced expression of MT1-MMP, loss of cell-cell adhesion and scattered invasion into collagen gel, mRNA differential display and Northern hybridization identified metastasis-associated mts1 as one of the genes co-induced with MT1-MMP by oncogenic transformation or collagen-gel culture of MDCK cells. Expression of antisense RNA to mts1 in MDCK cells interfered with the extension of tubules into the collagen gel, however, it did not affect the morphological changes induced by HGF in culture on plastic dishes. ErbB2-transformant transfected with mts1 antisense construct, which showed unaltered morphology in culture on plastic dishes, did not scatter into collagen gel but formed aggregates. These results suggested that Mts1 contributes not only to tumor invasion but also to kidney tubulogenesis in cooperation with MT1-MMP. The coordinated action of MT1-MMP and Mts1, which is responsible for the highly invasive properties of mesenchymal cells, may be involved in epithelial tubulogenesis and invasion of malignant carcinoma cells.