A novel tenascin type III repeat is part of a complex of tenascin mRNA alternative splices

Alternative splicing controls cell lineage-specific responses to endogenous innate immune triggers within the extracellular matrix

The identification of barely more than 20,000 human genes was amongst the most surprising outcomes of the human genome project. Alternative splicing provides an essential means of expanding the proteome, enabling a single gene to encode multiple, distinct isoforms by selective inclusion or exclusion of exons from mature mRNA. However, mis-regulation of this process is associated with most human diseases. Here, we examine the impact of post-transcriptional processing on extracellular matrix function, focusing on the complex alternative splicing patterns of tenascin-C, a molecule that can exist in as many as 500 different isoforms. We demonstrate that the pro-inflammatory activity of this endogenous innate immune trigger is controlled by inclusion or exclusion of a novel immunomodulatory site located within domains AD2AD1, identifying this as a mechanism that prevents unnecessary inflammation in healthy tissues but enables rapid immune cell mobilization and activation upon tissue damage, and defining how this goes awry in autoimmune disease.

Hedgehog signaling stimulates Tenascin C to promote invasion of pancreatic ductal adenocarcinoma cells through Annexin A2

Pancreatic adenocarcinoma (PDA) is characterized by a dense desmoplastic reaction that comprises 60-90% of the tumor, while only 10-40% of the tumor is composed of malignant epithelial cells. This desmoplastic reaction is composed of stromal fibroblast cells, extracellular matrix proteins, and immune cells. Accumulating evidence has suggested that the stromal and epithelial cell compartments interact during the pathogenesis of this disease. Therefore, it is important to identify the signaling pathways responsible for this interaction to better understand the mechanisms by which PDA invades and metastasizes. Here, we show that secreted stromal factors induce invasion of PDA cells. Specifically, hedgehog signaling from the tumor cells induces tenascin C (TnC) secretion from the stromal cells that acts back upon the tumor cells in a paracrine fashion to induce the invasion of PDA cells through its' receptor annexin A2 (AnxA2). Therefore, blocking the interaction between TnC and AnxA2 has the potential to prevent liver metastasis in PDA.

Transcriptional regulation of tenascin genes

Extracellular matrix proteins of the tenascin family resemble each other in their domain structure, and also share functions in modulating cell adhesion and cellular responses to growth factors. Despite these common features, the 4 vertebrate tenascins exhibit vastly different expression patterns. Tenascin-R is specific to the central nervous system. Tenascin-C is an “oncofetal” protein controlled by many stimuli (growth factors, cytokines, mechanical stress), but with restricted occurrence in space and time. In contrast, tenascin-X is a constituitive component of connective tissues, and its level is barely affected by external factors. Finally, the expression of tenascin-W is similar to that of tenascin-C but even more limited. In accordance with their highly regulated expression, the promoters of the tenascin-C and -W genes contain TATA boxes, whereas those of the other 2 tenascins do not. This article summarizes what is currently known about the complex transcriptional regulation of the 4 tenascin genes in development and disease.

Tenascin-C: Form versus function

Tenascin-C is a large, multimodular, extracellular matrix glycoprotein that exhibits a very restricted pattern of expression but an enormously diverse range of functions. Here, we discuss the importance of deciphering the expression pattern of, and effects mediated by, different forms of this molecule in order to fully understand tenascin-C biology. We focus on both post transcriptional and post translational events such as splicing, glycosylation, assembly into a 3D matrix and proteolytic cleavage, highlighting how these modifications are key to defining tenascin-C function.

Matrikines and the lungs

The extracellular matrix is a complex network of fibrous and nonfibrous molecules that not only provide structure to the lung but also interact with and regulate the behaviour of the cells which it surrounds. Recently it has been recognised that components of the extracellular matrix proteins are released, often through the action of endogenous proteases, and these fragments are termed matrikines. Matrikines have biological activities, independent of their role within the extracellular matrix structure, which may play important roles in the lung in health and disease pathology. Integrins are the primary cell surface receptors, characterised to date, which are used by the matrikines to exert their effects on cells. However, evidence is emerging for the need for co-factors and other receptors for the matrikines to exert their effects on cells. The potential for matrikines, and peptides derived from these extracellular matrix protein fragments, as therapeutic agents has recently been recognised. The natural role of these matrikines (including inhibitors of angiogenesis and possibly inflammation) make them ideal targets to mimic as therapies. A number of these peptides have been taken forward into clinical trials. The focus of this review will be to summarise our current understanding of the role, and potential for highly relevant actions, of matrikines in lung health and disease.

Expression of tenascin-C and its isoforms in the breast

Tenascin-C (TNC) is an extracellular matrix glycoprotein which is frequently up-regulated in a variety of pathological conditions including chronic inflammation and cancer. TNC has been implicated in the modulation of cell migration, proliferation, invasion and angiogenesis. Multiple isoforms of TNC can be generated through the alternative splicing of nine exons located in the fibronectin type III region of the molecule. The profile of isoforms expressed differs between cancers and normal breast, with the fully truncated TNC isoform being predominant in normal and benign tissues and higher molecular weight isoforms induced predominantly in cancer. The addition of extra domains within the fibronectin type III repeat domain greatly affects TNC function with multiple exon combinations available for splicing. Exons 14 and 16 are considered to be tumour-associated and have been shown to affect breast cell line invasion and growth in vitro to a greater extent than the full-length TNC isoform. This mini review will provide a summary of the literature to date regarding the expression of TNC isoforms in the breast and also discuss more recent developments in the field regarding exon AD1.

Association of invasion-promoting tenascin-C additional domains with breast cancers in young women

INTRODUCTION

Tenascin-C (TNC) is a large extracellular matrix glycoprotein that shows prominent stromal expression in many solid tumours. The profile of isoforms expressed differs between cancers and normal breast, with the two additional domains AD1 and AD2 considered to be tumour associated. The aim of the present study was to investigate expression of AD1 and AD2 in normal, benign and malignant breast tissue to determine their relationship with tumour characteristics and to perform in vitro functional assays to investigate the role of AD1 in tumour cell invasion and growth.

METHODS

Expression of AD1 and AD2 was related to hypoxanthine phosphoribosyltransferase 1 as a housekeeping gene in breast tissue using quantitative RT-PCR, and the results were related to clinicopathological features of the tumours. Constructs overexpressing an AD1-containing isoform (TNC-14/AD1/16) were transiently transfected into breast carcinoma cell lines (MCF-7, T-47 D, ZR-75-1, MDA-MB-231 and GI-101) to assess the effect in vitro on invasion and growth. Statistical analysis was performed using a nonparametric Mann-Whitney test for comparison of clinicopathological features with levels of TNC expression and using Jonckheere-Terpstra trend analysis for association of expression with tumour grade.

RESULTS

Quantitative RT-PCR detected AD1 and AD2 mRNA expression in 34.9% and 23.1% of 134 invasive breast carcinomas, respectively. AD1 mRNA was localised by in situ hybridisation to tumour epithelial cells, and more predominantly to myoepithelium around associated normal breast ducts. Although not tumour specific, AD1 and AD2 expression was significantly more frequent in carcinomas in younger women (age ≤40 years; P < 0.001) and AD1 expression was also associated with oestrogen receptor-negative and grade 3 tumours (P < 0.05). AD1 was found to be incorporated into a tumour-specific isoform, not detected in normal tissues. Overexpression of the TNC-14/AD1/16 isoform significantly enhanced tumour cell invasion (P < 0.01) and growth (P < 0.01) over base levels.

CONCLUSIONS

Together these data suggest a highly significant association between AD-containing TNC isoforms and breast cancers in younger women (age ≤40 years), which may have important functional significance in vivo.

Transcriptional regulation of the endogenous danger signal tenascin-C: a novel autocrine loop in inflammation

Inappropriate expression of proinflammatory mediators underpins the pathogenesis of autoimmune disease and tumor metastasis. The extracellular matrix glycoprotein tenascin-C is an endogenous activator of innate immunity that promotes the synthesis of inflammatory cytokines via activation of TLR4. Little tenascin-C is observed in most healthy adult tissues, but expression is specifically upregulated at sites of inflammation. Moreover, high levels of tenascin-C are associated with chronic inflammation and found in the tumor stroma. In this study, we show that the expression of tenascin-C is induced in immune myeloid cells activated by a variety of inflammatory stimuli, including specific TLR ligands. Its synthesis is transcriptionally regulated and requires the specific activation of AKT/PI3K and NF-kappaB signaling pathways. Using a bioinformatic approach, we identified a large number of conserved noncoding regions throughout the tenascin-C genomic locus that may contribute to its transcriptional regulation during inflammation. We also demonstrate that tenascin-C expression is transient during acute inflammation. In contrast, persistently high levels of expression occur in the inflamed synovium of joints from rheumatoid arthritis patients. Thus, misregulated expression of this endogenous danger signal may promote an autocrine loop of inflammation and contribute to the persistence of inflammation in autoimmune diseases or to tumor egress and invasion during metastasis.

The role of tenascin-C in tissue injury and tumorigenesis

The extracellular matrix molecule tenascin-C is highly expressed during embryonic development, tissue repair and in pathological situations such as chronic inflammation and cancer. Tenascin-C interacts with several other extracellular matrix molecules and cell-surface receptors, thus affecting tissue architecture, tissue resilience and cell responses. Tenascin-C modulates cell migration, proliferation and cellular signaling through induction of pro-inflammatory cytokines and oncogenic signaling molecules amongst other mechanisms. Given the causal role of inflammation in cancer progression, common mechanisms might be controlled by tenascin-C during both events. Drugs targeting the expression or function of tenascin-C or the tenascin-C protein itself are currently being developed and some drugs have already reached advanced clinical trials. This generates hope that increased knowledge about tenascin-C will further improve management of diseases with high tenascin-C expression such as chronic inflammation, heart failure, artheriosclerosis and cancer.

The role of tenascin-C in tissue injury and tumorigenesis

The extracellular matrix molecule tenascin-C is highly expressed during embryonic development, tissue repair and in pathological situations such as chronic inflammation and cancer. Tenascin-C interacts with several other extracellular matrix molecules and cell-surface receptors, thus affecting tissue architecture, tissue resilience and cell responses. Tenascin-C modulates cell migration, proliferation and cellular signaling through induction of pro-inflammatory cytokines and oncogenic signaling molecules amongst other mechanisms. Given the causal role of inflammation in cancer progression, common mechanisms might be controlled by tenascin-C during both events. Drugs targeting the expression or function of tenascin-C or the tenascin-C protein itself are currently being developed and some drugs have already reached advanced clinical trials. This generates hope that increased knowledge about tenascin-C will further improve management of diseases with high tenascin-C expression such as chronic inflammation, heart failure, artheriosclerosis and cancer.

Tenascin-C patterns and splice variants in actinic keratosis and cutaneous squamous cell carcinoma

BACKGROUND

Tenascin-C (Tn-C) is an extracellular matrix protein with multiple functions that is present at low levels in normal tissues, but which is highly present in various tumours. The mRNA expression and protein level of Tn-C including its various isoforms have not been investigated comprehensively so far in cutaneous squamous cell carcinoma (SCC) and the precursor lesion actinic keratosis (AK).

OBJECTIVES

To assess the dysregulated expression and splice variants of Tn-C in cutaneous squamous cell dysplasia and carcinoma.

METHODS

Biopsies from 66 patients (or representative subsets) that comprised 25 specimens from normal skin, 19 AK and 22 cutaneous SCC were analysed for Tn-C splice variants using splice-specific primers. The amount of Tn-C mRNA was investigated by quantitative real-time reverse transcription-polymerase chain reaction. In addition, the presence of Tn-C protein was analysed in sections of paraffin-embedded tissues using immunohistochemistry.

RESULTS

The large Tn-C splice variant was present in only 5% of normal skin samples, in comparison with 63% of AK (P < 0.001) and 88% of SCC (P < 0.001). Tn-C mRNA expression was significantly increased in AK and SCC compared with normal skin (P < 0.001). The corresponding proteins were rarely detected in cells of the vascular epithelial layers and perifollicular layers of some normal skin specimens, and their spatial localization expanded into the papillary dermis of AK. The largest amount and the widest distribution were found in samples of SCC, in which Tn-C was located in the basal cells at the tumour invasion front and additionally in the papillary dermis and reticular dermis.

CONCLUSIONS

Tn-C is present in the dermis, its expression is increased during skin cancer development, and the large splice variant is characteristic for AK and SCC, which may prove useful for diagnostic approaches in cutaneous SCC.

Differential expression of tenascin-C splicing domains in urothelial carcinomas of the urinary bladder

PURPOSE

Through alternative splicing of the extracellular matrix protein tenascin-C (Tn-C) primary transcript nine type III homology repeats can be independently included or omitted. Large, low spliced Tn-C variants (Tn-C(L)) are preferentially expressed during tissue remodelling processes like tumour invasion to modulate cell migration. The study was aimed to evaluate the differential expression of Tn-C splicing domains in urinary bladder carcinoma with respect to the invasive behaviour.

METHODS

The deposition and synthesis of the Tn-C splicing domains A1-D was analysed in 34 urinary bladder carcinomas by semiquantitative immunohistochemistry using domain specific antibodies and by RT-PCR. Results were correlated to tumour stage and grade.

RESULTS

There is a significant increase of Tn-C(L) with higher tumour stage and grade. Immunohistochemistry revealed a more restricted distribution pattern of A1, B, and/or D domain containing Tn-C variants to invasive tumours, tumour vessels, and to destructed muscle. The mRNA expression patterns of the domains A1-A3 are similar among the different carcinomas. Stronger differences exist in the region from the B to D domain. In general, the domains AD1/C are rarely expressed. AD1 domain expression seems to be connected with compact invasion pattern.

CONCLUSION

In urinary bladder carcinoma a differential expression of Tn-C splicing variants exists in dependence of tumour type, vascularization, and invasive behaviour. Therefore, the detection of different Tn-C splicing domains could be useful for assessment of muscle invasion, tumour surveillance, as well as target structures for antibody based tumour detection and therapy.

Tenascin-C regulates proliferation and migration of cultured astrocytes in a scratch wound assay

Tenascin-C (TNC), an extracellular matrix glycoprotein, is involved in tissue morphogenesis like embryogenesis, wound healing or tumorigenesis. Astrocytes are known to play major roles in wound healing in the CNS. To elucidate the roles of TNC in wound closure by astrocytes, we have examined the morphological changes of cultured astrocytes in a scratch wound assay and measured the content of soluble TNC released into the medium. We have also localized the expression of TNC mRNA, TNC, glial fibrillary acidic protein (GFAP), vimentin and integrin beta1. After wounding, glial cells rapidly released the largest TNC isoform and proliferated in the border zones. Subsequently, they became polarized with unidirectional processes and finally migrated toward the denuded area. The proliferating border zone cells and pre-migratory cells intensely expressed TNC mRNA, TNC-, vimentin-, GFAP- and integrin beta1-like immunoreactivity, while the migratory cells showed generally reduced expression except the front. Exogenous TNC enhanced cell proliferation and migration, while functional blocking with anti-TNC or anti-integrin beta1 antibody reduced both of them. These results suggest that mechanical injury induces boundary astrocytes to produce and release TNC that promotes cell proliferation and migration via integrin beta1 in an autocrine/paracrine fashion.

Secretion of tenascin-C by cultured astrocytes: regulation of cell proliferation and process elongation

Tenascin-C (TNC), an extracellular matrix glycoprotein, is involved in tissue morphogenesis like embryogenesis, wound healing or tumorigenesis. Quiescent astroglia in long-term primary cultures are known to show rapid morphological changes after subculture and serum deprivation/re-addition (SSDR). To elucidate roles of TNC in the morphogenetic processes of cultured astrocytes, we have revealed morphological changes in association with soluble TNC contents in the medium and expression of TNC mRNA, TNC, glial fibrillary acidic protein (GFAP) and integrin beta1, one of its cell surface receptors, in glial cells after SSDR. Soluble TNC in the medium rapidly increased in amount at 4 h when GFAP-positive cells expressed TNC mRNA, TNC and integrin beta1. Cellular proliferation and growth occurred in colonies expressing TNC mRNA, TNC and integrin beta1 during the first 24 h. During the next 24 h, process elongation and cell migration occurred in association with increased GFAP expression and re-elevation of soluble TNC in the medium. Cell bodies became flat and larger with increased GFAP and reduced TNC expression at 72 h, while cultures became confluent with reduced GFAP and TNC expression at 96 h after SSDR. Functional blocking with anti-TNC antibody reduced cell proliferation and induced morphological change from a process-bearing slender shape to a flat and wide shape presumably due to increased cell adhesion. These findings strongly support the idea that endogenous TNC produced and released by astrocytes in response to serum stimulation induces their proliferation and process elongation through a paracrine/autocrine mechanism.

Tenascins: regulation and putative functions during pathological stress

In this review, we discuss the structure and function of the extracellular matrix protein family of tenascins with emphasis on their involvement in human pathologies. The article is divided into the following sections:

INTRODUCTION

the tenascin family of extracellular matrix proteins; Structural roles: tenascin-X deficiency and Ehlers-Danlos syndrome; Tenascins as modulators of cell adhesion, migration, and growth; Role of tenascin-C in inflammation; Regulation of tenascins by mechanical stress: implications for wound healing and regeneration; Association of tenascin-C with cancer: antibodies as diagnostic and therapeutic tools; Conclusion and perspectives.

Clinical impact and functional aspects of tenascin-C expression during glioma progression

The extracellular matrix protein tenascin-C is expressed in processes like embryogenesis and wound healing and in neoplasia. Tenascin-C expression in gliomas has been described previously; however, the relation to clinical data remains inconsistent. Generally, analysis of tenascin-C function is difficult due to different alternatively spliced isoforms. Our studies focus on changes in tenascin-C expression in human gliomas, correlating these changes with tumor progression and elucidating the functional role of the glioma cell-specific tenascin-C isoform pool. Eighty-six glioma tissues of different World Health Organization (WHO) grades were analyzed immunohistochemically for tenascin-C expression. The influence of the specific tenascin-C isoforms produced by glioblastoma cells on proliferation and migration was examined in vitro using blocking antibodies recognizing all isoforms. In general, tenascin-C expression increased with tumor malignancy. Perivascular staining of tenascin-C around tumor-supplying blood vessels was observed in all glioblastoma tissues, whereas in WHO II and III gliomas, perivascular tenascin-C staining appeared less frequently. The appearance of perivascular tenascin-C correlated significantly with a shorter disease-free time. Analysis of proliferation and migration in the presence of blocking antibodies revealed an inhibition of proliferation by around 30% in all 3 glioblastoma cell cultures, as well as a decrease in migration of 30.6-46.7%. Thus we conclude that the endogenous pool of tenascin-C isoforms in gliomas supports both tumor cell proliferation and tumor cell migration. In addition, our data on the perivascular staining of tenascin-C in WHO II and III gliomas and its correlation with a shorter disease-free time suggest that tenascin-C may be a new and potent prognostic marker for an earlier tumor recurrence.

The structure and function of tenascins in the nervous system

The tenascins are a family of large extracellular matrix glycoproteins that comprise five known members. Three of these, tenascin-C (TN-C) tenascin-R (TN-R) and tenascin-Y (TN-Y) are expressed in specific patterns during nervous system development and are down-regulated after maturation. The expression of TN-C, the best studied member of the family, persists in restricted areas of the nervous system that exhibit neuronal plasticity and is reexpressed after lesion. Numerous studies in vitro suggest specific roles for tenascins in the nervous system involving precursor cell migration, axon growth and guidance. TN-C has been shown to occur in a large number of isoform variants generated by combinatorial variation of alternatively spliced fibronectin type III (FNIII) repeats. This finding indicates that TN-C might specify neural microenvironments, a hypothesis supported by recent analysis of TN-C knockout animals, which has begun to reveal subtle nervous system dysfunctions.

Tenascin-C in development and disease: gene regulation and cell function

Tenascin-C (TN-C) is a modular and multifunctional extracellular matrix (ECM) glycoprotein that is exquisitely regulated during embryonic development and in adult tissue remodeling. TN-C gene transcription is controlled by intracellular signals that are generated by multiple soluble factors, integrins and mechanical forces. These external cues are interpreted by particular DNA control elements that interact with different classes of transcription factors to activate or repress TN-C expression in a cell type- and differentiation-dependent fashion. Among the transcriptional regulators of the TN-C gene that have been identified, the homeobox family of proteins has emerged as a major player. Downstream from TN-C, intracellular signals that are relayed via specific cell surface receptors often impart contrary cellular functions, even within the same cell type. A key to understanding this behavior may lie in the dual ability of TN-C-enriched extracellular matrices to generate intracellular signals, and to define unique cellular morphologies that modulate these signal transduction pathways. Thus, despite the contention that TN-C null mice appear to develop and act normally, TN-C biology continues to provide a wealth of information regarding the complex nature of the ECM in development and disease.

The tenascin family of ECM glycoproteins: structure, function, and regulation during embryonic development and tissue remodeling

The determination of animal form depends on the coordination of events that lead to the morphological patterning of cells. This epigenetic view of development suggests that embryonic structures arise as a consequence of environmental influences acting on the properties of cells, rather than an unfolding of a completely genetically specified and preexisting invisible pattern. Specialized cells of developing multicellular organisms are surrounded by a complex extracellular matrix (ECM), comprised largely of different collagens, proteoglycans, and glycoproteins. This ECM is a substrate for tissue morphogenesis, lends support and flexibility to mature tissues, and acts as an epigenetic informational entity in the sense that it transduces and integrates intracellular signals via distinct cell surface receptors. Consequently, ECM-receptor interactions have a profound influence on major cellular programs including growth, differentiation, migration, and survival. In contrast to many other ECM proteins, the tenascin (TN) family of glycoproteins (TN-C, TN-R, TN-W, TN-X, and TN-Y) display highly restricted and dynamic patterns of expression in the embryo, particularly during neural development, skeletogenesis, and vasculogenesis. These molecules are reexpressed in the adult during normal processes such as wound healing, nerve regeneration, and tissue involution, and in pathological states including vascular disease, tumorigenesis, and metastasis. In concert with a multitude of associated ECM proteins and cell surface receptors that include members of the integrin family, TN proteins impart contrary cellular functions, depending on their mode of presentation (i.e., soluble or substrate-bound) and the cell types and differentiation states of the target tissues. Expression of tenascins is regulated by a variety of growth factors, cytokines, vasoactive peptides, ECM proteins, and biomechanical factors. The signals generated by these factors converge on particular combinations of cis-regulatory elements within the recently identified TN gene promoters via specific transcriptional activators or repressors. Additional complexity in regulating TN gene expression is achieved through alternative splicing, resulting in variants of TN polypeptides that exhibit different combinations of functional protein domains. In this review, we discuss some of the recent advances in TN biology that provide insights into the complex way in which the ECM is regulated and how it functions to regulate tissue morphogenesis and gene expression.

Tenascin expression patterns and cells of monocyte lineage: relationship in human gliomas

Stromal extracellular matrix (ECM) components are thought to play an important role in regulating invasion of human gliomas. Macrophages and microglial cells may heavily influence the integrity of the extracellular compartment of gliomas, and the affected ECM may play a key role in regulating migratory activity of both tumor cells and macrophages/microglia. The aim of this investigation was to study immunohistochemically the expression patterns of four ECM components: fibronectin, laminin, collagen IV, and tenascin (TN) in human gliomas, with special attention to TN. Our main goal was to study the possible correlation between TN expression and macrophagic/microglial infiltration in gliomas. Altogether, 90 gliomas were studied. Tumors included 46 glioblastomas, 19 anaplastic gliomas, 22 low grade gliomas, and 3 pilocytic astrocytomas. Vascular TN prevailed in perinecrotic areas of glioblastomas, whereas interstitial TN was more often expressed distant from necrosis and in the ECM of anaplastic and low grade gliomas. Double staining with CD68 and anti-TN antibodies showed that macrophagic/microglial density was significantly higher in TN-positive areas of most of the glioblastomas and anaplastic gliomas, whereas microglial percentage from total number of CD68-positive cells was in most of the cases significantly higher in TN-negative areas. In addition, we saw a morphologically spatial correlation between higher densities of macrophagic/microglial infiltration and TN expression in perinecrotic areas in glioblastomas. Attachment of macrophages to TN-positive basement membrane zones of newly formed stromal blood vessels was evident. On the basis of our results, we conclude that TN may play a crucial role in regulating trafficking of cells of monocyte lineage in human gliomas.

Synthesis and protein distribution of the unspliced large tenascin-C isoform in oral squamous cell carcinoma

The inclusion or omission of the alternatively spliced region in the tenascin-C (Tn-C) mRNA gives rise to the large (Tn-C(L)) or small (Tn-C(S)) variant, respectively. Tn-C(L) is thought to be a typical component of provisional extracellular matrices (ECMs) and is expressed during tumour stroma remodelling. Tn-C(L) synthesis has been studied using RNA/RNA in situ hybridization, and Tn-C(L) protein distribution, using immunohistochemistry (clone BC-2), in 18 oral squamous cell carcinomas (OSCCs) of different grades of malignancy. While the Tn-C(L) protein was demonstrated within the whole stromal compartment regardless of grade of malignancy, the majority of the Tn-C(L) mRNA signal-bearing cells were carcinoma cells. Only a few stromal myofibroblasts were able to synthesize Tn-C(L), as revealed by alpha-smooth muscle actin double staining. In well-differentiated carcinomas (G1), the Tn-C(L) synthesizing carcinoma cells were localized as a single positive cell layer in the tumour stroma interface, particularly in invasive areas. A higher grade of malignancy (G2/G3) is associated with a significantly increased number of Tn-C(L) synthesizing carcinoma cells randomly distributed within the invading tumour areas. Double-staining experiments (Tn-C(L) mRNA ISH/BC-2 immunohistochemistry) indicate that these cells are capable of organizing and depositing a three-dimensional Tn-C(L) matrix. Even though an instructive and/or inductive role of the carcinoma cells in tumour stroma formation cannot be excluded, these results demonstrate that carcinoma cells can directly produce the ECM components of tumour stroma.

Tenascin is expressed in the mesenchyme of the embryonic lung and down-regulated by dexamethasone in early organogenesis

Tenascin (TN) is a hexameric extracellular matrix glycoprotein that is temporally and spatially restricted during lung development. This study examines the expression and regulation of TN in early lung organogenesis. Two TN isoforms were detected in total RNA isolated from embryonic day 14 rat lung tissues by reverse transcriptase polymerase chain reaction. The localization of TN in embryonic day 14 rat lung tissues was investigated by using in situ hybridization performed with an antisense RNA probe. TN mRNA was expressed exclusively by the mesenchyme but not by the epithelium of embryonic rat lungs. The intense expression of TN was observed in the mesenchyme that immediately surrounds the growing epithelial cells of the developing bronchi. The effect of the synthetic glucocorticoid hormone dexamethasone on the regulation of TN expression was examined by in vitro lung explant culture. Two TN polypeptides, the larger (M(r) 230 kDa, TN230) polypeptide and the smaller (M(r) 180 kDa, TN180) isoform, were detected in embryonic day 21 rat lungs by immunoblot analysis with anti-TN antibody. Dexamethasone inhibited both TN230 and TN180 biosynthesis. The study demonstrates the expression of TN at the early stage of lung organogenesis and presents evidence of hormonal regulation of TN in lung development, suggesting a potential role of TN in the communication between the epithelial and mesenchymal cells during lung branching morphogenesis.

Evidence for combinatorial variability of tenascin-C isoforms and developmental regulation in the mouse central nervous system

The extracellular matrix glycoprotein tenascin-C (TN-C) displays a restricted and developmentally regulated distribution in the mouse central nervous system. Defined modules of the molecule have been shown to mediate specific functions, such as neuron migration, neurite outgrowth, cell adhesion, and cell proliferation. The smallest TN-C form contains a stretch of eight fibronectin type III (FNIII) domains, which are common to all TN-C isoforms. Unrestricted and independent alternative splicing of six consecutive FNIII cassettes between the fifth and sixth constitutive FNIII domain bears the potential to generate 64 different combinations that might code for TN-C proteins with subtly different functions. To explore TN-C isoform variability in mouse brain, the alternatively spliced region of TN-C mRNAs was examined by the reverse transcription-polymerase chain reaction technique. Polymerase chain reaction products of uniform size were subcloned and analyzed using domain-specific probes to reveal the expression of particular combinations of alternatively spliced FNIII domains. 27 TN-C isoforms were identified to be expressed in mouse central nervous system, of which 22 are novel. Furthermore, during development, specific TN-C isoforms were found to occur in distinct relative frequencies, as demonstrated for isoforms containing two alternatively spliced FNIII domains. We conclude that TN-C is expressed in a complex and regulated pattern in mouse central nervous system. These findings highlight the potential role of TN-C in mediating specific neuron glia interactions.

Identification of a glioblastoma-associated tenascin-C isoform by a high affinity recombinant antibody

Tenascin-C exists in several polymorphic isoforms due to alternative splicing of nine fibronectin-like type III repeats. Large Tenascin-C isoforms are present in almost all normal adult tissues but are upregulated in fetal, regenerating, and neoplastic tissues. Here, we report a human antibody fragment, TN11, derived from a phage library with high affinity for the spliced repeat C and demonstrate that this repeat is undetectable in normal adult tissues, barely detectable or undetectable in breast, lung and gastric carcinomas, meningioma, and low grade astrocytoma, but extremely abundant in high grade astrocytoma (grade III and glioblastoma), especially around vascular structures and proliferating cells. The antibody appears to have potential for development of a therapeutic agent for patients with high grade astrocytoma.

Tenascin-cytotactin (TN-C) variants in pseudophakic/aphakic bullous keratopathy corneas

PURPOSE

To examine pseudophakic/aphakic bullous keratopathy (PBK/ABK) human corneas for patterns of expression of tenascincytotactin (TN-C) variants known to mediate specific cellular functions, viz. anti-adhesion (high molecular mass (M(r))) and adhesion (low/intermediate M(r)).

METHODS

PBK/ABK corneas were selected to encompass only those with bullae and without inflammation, scarring or neovascularisation. Serial sections from these and normal corneas were labelled with antibodies BC-4 (recognising all TN-C variants) and BC-2 (specific for the high M(r) TN-C variant). Bound antibody was revealed with an avidin-biotin peroxidase technique. In a given pair of corneal sections, positivity with BC-4 but not BC-2 indicates localisation of low/ intermediate M(r) TN-C variants and absence of the high M(r) TN-C variant. BC-2 identifies the high M(r) variant.

RESULTS

There was no immunostaining with either BC-2 or BC-4 in normal corneas except at the corneoscleral interface, where both BC-2 and BC-4 were immunolocalised. In PBK/ABK corneas, BC-2 staining was seen in 5 of 13 corneas and was restricted mainly to epithelial basement membrane (BM) overlying bullae. BC-2 did not label the stroma. BC-4 immunostaining was present in all PBK/ABK corneas and was localised in epithelial BM, both epithelial and stromal borders of bullae, pannus, endothelial BM and in oedematous stromal regions.

CONCLUSIONS

TN-C variants are differentially expressed in PBK/ABK corneas. The high M(r) variant is restricted mainly to epithelial BM overlying bullae, while low/intermediate M(r) variants occur in epithelial BM, both epithelial and stromal borders of bullae, and in pannus. Given the in vitro functions of TN-C, a role for promoting epithelial dehiscence and reattachment to the substratum in PBK/ABK corneas by high and low/intermediate M(r) variants respectively is likely.

Regulation of tenascin-C expression in bone cells by transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) stimulates new bone formation when administered locally in vivo. The extracellular matrix protein tenascin-C, which is secreted by osteoblasts but absent from mineralized bone matrix, supports differentiation of cultured osteoblast-like cells. The current study was undertaken to determine whether expression patterns of tenascin-C in TGF-beta-treated bone cells are in agreement with a role for this protein as a mediator of TGF-beta-stimulated new bone formation. Expression of tenascin-C was investigated by immunohistochemistry in calvarial bones of mice to which TGF-beta had been locally administered. Three days after initiation of daily TGF-beta treatment, strong staining for tenascin-C was seen in regions where periosteal osteoprogenitor cells were undergoing proliferation in response to TGF-beta; by comparison, staining of periosteal surfaces of control bones was weak and discontinuous. Seven days after initiation of a course of five daily injections of TGF-beta, tenascin-C staining was still enhanced in treated bones. The ability of TGF-beta to regulate expression of tenascin-C in osteoblast-like cells in vitro was investigated using an osteosarcoma-derived cell line (ROS 17/2.8). TGF-beta caused a small but significant increase in secretion of tenascin-C into the medium, as determined by a solid phase dot immunoassay quantitated by densitometry. Western and northern blot analysis indicated that TGF-beta did not influence the pattern of expression of tenascin-C splice variants. These results indicate that TGF-beta stimulates osteoblastic tenascin-C expression and suggest that tenascin-C may act as a mediator of TGF-beta-induced new bone formation.

Expression of tenascin-C by human endometrial adenocarcinoma and stroma cells: heterogeneity of splice variants and induction by TGF- b

Localization of tenascin-C in vivo and cell culture experiments in vitro have provided evidence for stromal production of tenascin-C in malignant tumors of a variety of organs. Here we raised the question of whether the mesenchymal stroma in the case of endometrial adenocarcinoma is the unique source of tenascin-C. Therefore, the expression of tenascin-C mRNA by human endometrial adenocarcinoma cells and endometrial stroma cells was investigated. Several preparations of endometrial stroma cells produced tenascin-C mRNA. Using a serum-free defined cell culture medium, production of tenascin-C mRNA could be increased by adding either serum or 20 ng TGF- beta /mL to the cell culture medium. Reverse transcriptase polymerase chain reaction analysis revealed that five out of six endometrial adenocarcinoma cell lines produced tenascin-C mRNA. Northern blot experiments and ribonuclease protection assays provided evidence that the number of copies of tenascin-C mRNA was small. Analysis of expressed splice variants by reverse transcriptase polymerase chain reaction analysis revealed the abundance of one major splice variant that lacked all potential alternatively spliced fibronectin type-III-like repeats. Regarding larger splice variants, all fragment sizes that could theoretically originate from seven alternatively spliced fibronectin type-III-like repeats were observed. Evaluating relative signal intensities, the splice variants containing a single fibronectin type-III-like repeat and the variant possessing all but one alternatively spliced repeats were most frequent. In summary, evidence is provided that tenascin-C can originate from both tissue compartments of the human endometrium stroma and (tumor) epithelium. Splice variant analysis revealed a high number of splice variants and a relative high proportion of variants that have so far been regarded as minor constituents of expressed tenascin-C. Key words: gene expression, splice variant analysis, extracellular matrix, endometrial cancer, growth factors.

The expression of tenascin-C with the AD1 variable repeat in embryonic tissues, cell lines and tumors in various vertebrate species

Tenascin-C is a modular glycoprotein composed of domains of amino acid repeats. All forms of tenascin-C have eight constant fibronectin type III repeats, but additional fibronectin type III repeats can be spliced into a variable domain found between the fifth and sixth constant repeats. Four extra repeats, named A, B, C and D, have been examined previously. Here, we have used in situ hybridization to determine the tissue origins of the novel AD1 and AD2 repeats. In the embryonic-day-10 chicken embryo, transcripts encoding the AD2 repeat are limited to the tips of lung bronchioles and the base of feather buds. In contrast the AD1 hybridization signal was widespread. Quantitative in situ hybridization reveals AD1-containing transcripts represent up to 85% of the total tenascin-C mRNA in some tissues (developing bone), and are undetectable in others (e.g. radial glia). Avian and human tumor cell lines were examined for the expression of the AD1 repeat using the reverse transcriptase polymerase chain reaction (RT-PCR). Transcripts encoding six different tenascin-C splice variants incorporating the AD1 repeat were found in the fibrosarcoma cell line, QT6. Many human tumor cells, including malignant melanoma and ductal breast carcinoma, were positive for AD1 tenascin-C expression. In addition, we found evidence of AD1 tenascin-C expression in samples of excised human tumors. Our results show that a novel variant may be a major part of the tenascin-C of the embryonic extracellular matrix, and may also be found in the stroma surrounding some human tumors.

Cell-adhesive responses to tenascin-C splice variants involve formation of fascin microspikes

Tenascin-C is an adhesion-modulating matrix glycoprotein that has multiple effects on cell behavior. Tenascin-C transcripts are expressed in motile cells and at sites of tissue modeling during development, and alternative splicing generates variants that encode different numbers of fibronectin type III repeats. We have examined the in vivo expression and cell adhesive properties of two full-length recombinant tenascin-C proteins: TN-190, which contains the eight constant fibronectin type III repeats, and TN-ADC, which contains the additional AD2, AD1, and C repeats. In situ hybridization with probes specific for the AD2, AD1, and C repeats shows that these splice variants are expressed at sites of active tissue modeling and fibronectin expression in the developing avian feather bud and sternum. Transcripts incorporating the AD2, AD1, and C repeats are present in embryonic day 10 wing bud but not in embryonic day 10 lung. By using a panel of nine cell lines in attachment assays, we have found that C2C12, G8, and S27 myoblastic cells undergo concentration-dependent adhesion to both variants, organize actin microspikes that contain the actin-bundling protein fascin, and do not assemble focal contacts. On a molar basis, TN-ADC is more active than TN-190 in promoting cell attachment and irregular cell spreading. The addition of either TN-190 or TN-ADC in solution to C2C12, COS-7, or MG-63 cells adherent on fibronectin decreases cell attachment and results in decreased organization of actin microfilament bundles, with formation of cortical membrane ruffles and retention of residual points of substratum contact that contain filamentous actin and fascin. These data establish a biochemical similarity in the processes of cell adhesion to tenascin-C and thrombospondin-1, also an "antiadhesive" matrix component, and also demonstrate that both the adhesive and adhesion-modulating properties of tenascin-C involve similar biochemical events in the cortical cytoskeleton. In addition to these generic properties, TN-ADC is less active in adhesion modulation than TN-190. The coordinated expression of different tenascin-C transcripts during development may, therefore, provide appropriate microenvironments for regulated changes in cell shape, adhesion, and movement.

Human tenascin-C: identification of a novel type III repeat in oral cancer and of novel splice variants in normal, malignant and reactive oral mucosae

Tenascin-C is a mosaic, linear glycoprotein that is up-regulated during many normal and pathological processes involving either cell migration or tissue morphogenesis, such as invasion of malignant cells and wound healing. Human tenascin-C contains 8 consecutive type III fibronectin (TNCfn) domains that are involved in alternative splicing and potentially generate a large number of isoforms that code for tenascin-C proteins with subtly different functions. Human tenascin-C splice variants were investigated by RT-PCR in a range of normal and pathological oral mucosal tissues. A novel, 9th human TNCfn domain involved in alternative splicing was identified. It shares 70% nucleic acid and 55% protein sequence homology with chicken TNCfn-ad2. As in avians, this novel repeat was located between TNCfn-B and TNCfn-ad1 and accordingly was designated human TNCfn-ad2. Human TNCfn-ad2 was detected in only 2 of 10 oral cancers. However, TNCfn-ad2 was absent from 40 normal, reactive, pre-malignant and other oral mucosal specimens investigated. Previous studies have described 8 splice variant transcripts for human tenascin-C. By systematic investigation we identified further novel splice variants for human tenascin-C. Furthermore, our results indicate that many potential splice variants probably do not exist in the tissues investigated. Thus, we have demonstrated that human tenascin-C transcripts generate a complex but selected repertoire of different alternative splice products.

Expression of the extracellular matrix protein tenascin in malignant and benign ovarian tumours

The extracellular matrix protein tenascin (TN) is overexpressed in a number of solid tumours. Thi however, is the first study to examine TN expression in ovarian tumours. TN protein was examined in froze sections of 50 human ovarian tumours by immunohistochemistry. Malignant and borderline tumours showed significantly greater incidence and intensity of stromal staining than benign tumours (P < 0.0001 and P = 0.038 respectively). Seven omental metastases were also examined and showed a strikingly similar protein distribution to their primary tumour counterparts. The expression pattern of different RNA isoforms, created by alternative splicing of the primary transcript, was identified using reverse transcription-polymerase chain reactions (RT-PCR). The smallest TN RNA splice variant (284 bp) was found in all tumours examined, while the appearance of larger molecular weight transcripts (approximately 490 and 556 bp), as major forms, was predominantly limited to malignant tumours, with 9/12 malignant tumours showing this pattern compared with 1/6 benign tumours. These data suggest that malignant ovarian tumours have increased expression of TN compared with benign tumours and this may be associated with induction of specific isoforms.

Tenascin-C mRNA and tenascin-C protein immunoreactivity increase in astrocytes after activation by bFGF

Tenascin-C is an extracellular matrix glycoprotein with trophic and repulsive properties, involved in migratory processes in CNS. Previous reports demonstrated that this molecule is produced and secreted by astrocytes. Preliminary data on fibroblasts and astrocytes have suggested that bFGF may modulate tenascin-C expression. bFGF is a mitogenic growth factor, involved in cell differentiation and neovascularization. In the present study, we examined whether bFGF modulates the expression of tenascin-C in hippocampal astrocytes from newborn rats. Our results suggest that bFGF increases the production of tenascin-C by cultured hippocampal astrocytes. We found that both tenascin-C mRNA and protein immunoreactivity were increased after bFGF treatment. Our results also demonstrated that tenascin-C polypeptides were secreted into the extracellular medium. In agreement with previous studies, we suggest that secreted tenascin-C is mainly the high molecular weight form. In addition, our results suggest that a cleavage of the high molecular weight form. In addition, our results suggest that a cleavage of the high molecular weight form may occur in the extracellular medium causing production of proteolytic fragments, that may modify the biological properties of tenascin-C. The present results may be relevant to the understanding of lesion scarring and regeneration process.

Tenascin-C and human tendon degeneration

We investigated the distribution of tenascin in supraspinatus tendons to determine whether an alteration in tenascin expression was associated with human tendon degeneration. Tenascin was present in all of the tendons studied, although with two distinct patterns of expression. First, tenascin was associated with organized, fibrous regions of the tendon matrix that were typical of the normal tendon structure. This distribution is consistent with a role for tenascin in collagen fibril organization, perhaps maintaining the interface between fibrils and adjacent structures. Second, although tenascin was generally absent from poorly organized matrix in degenerate tendons, it was strongly associated with some rounded cells in disorganized fibrocartilaginous regions that were more abundant in pathological specimens. Tenascin was also found around infiltrating blood vessels, with more intense staining associated with a mononuclear cell infiltrate. Western blotting of tendon extracts showed differences in tenascin isoform expression, with only the small (200-kd) tenascin isoform found in normal tendons. Degenerate tendons also expressed the 300-kd isoform, consistent with a role for the larger tenascin isoform in tendon disease, potentially stimulating tenocyte proliferation, cell rounding, and fibrocartilaginous change. Proteolytic fragments of tenascin were detected but only in ruptured tendons, an indication of matrix remodeling in degenerate tendons, with fragment sizes consistent with the activity of matrix metalloproteinase enzymes.

Contrasting migratory response of astrocytoma cells to tenascin mediated by different integrins

Tenascin, an extracellular matrix protein, is expressed in human gliomas in vitro and in vivo. The distribution of tenascin at the invasive edge of these tumors, even surrounding solitary invading cells, suggests a role for this protein as a regulator of glioma cell migration. We tested whether purified tenascin, passively deposited on surfaces, influenced the adhesion or migration of a human gliomaderived cell line, SF-767. Adhesion of glioma cells to tenascin increased in a dose-dependent fashion up to a coating concentration of 10 micrograms/ml. Higher coating concentrations resulted in progressively fewer cells attaching. Cell adhesion could be blocked to basal levels using anti-beta 1 integrin antibodies. In contrast, when anti-alpha v antibodies were added to the medium of cells on tenascin, cell adhesion was enhanced slightly. Using a microliter scale migration assay, we found that cell motility on tenascin was dose dependently stimulated at coating concentrations of 1 and 3 micrograms/ml, but migration was inhibited below levels of non-specific motility when tested at coating concentrations of 30 and 100 micrograms/ml. Migration on permissive concentrations of tenascin could be reversibly inhibited with anti-beta 1, while treatment with anti-alpha v antibodies increased migration rates. We conclude that SF-767 glioma cells express two separate integrin receptors that mediate contrasting adhesive and migratory responses to tenascin.

Extracellular pH controls pre-mRNA alternative splicing of tenascin-C in normal, but not in malignantly transformed, cells

In cultured normal human fibroblasts, 2 main tenascin-C (TN-C) isoforms are generated by alternative splicing of the single TN-C primary transcript, 8 type III repeats being included or omitted in the mRNA. In these cultured cells, small pH variations of the culture medium (from 7.2 to 6.8) strikingly modify the alternative splicing pattern of the TN-C primary transcript. We report that malignantly transformed cells do not respond to extracellular pH variations as normal cells do. Indeed, malignantly transformed cells kept in culture media at pH values from 6.6 to 7.6 show no variations in the splicing pattern of the TN-C primary transcript and accumulate almost exclusively the large TN-C mRNA. These observations may explain the preferential accumulation in vivo of the large TN-C isoform in the extracellular matrix of different types of neoplasia.

Tenascin mediates human glioma cell migration and modulates cell migration on fibronectin

The role of tenascin in mediating tumor cell migration was studied using two cell migration models. In migration/invasion Transwell assays U251.3 glioma cells rapidly migrated through the 8 mu m pore size membranes onto tenascin- and fibronectin-coated surfaces. In this assay the number of cells migrating onto tenascin was 52.2 +/- 9.6% greater than on fibronectin within 4 hours. To assess cell migration rates and cell morphology, U251.3 migration was examined in a two-dimension spheroid outgrowth assay. The radial distance migrated by U251.3 cells from tumor spheroids was found to be 53.8 +/- 4.9% greater on tenascin than on fibronectin. Cells migrating on tenascin display a very motile appearance, while cells migrating on fibronectin spread and maintain close intercellular contacts. Cell migration in the presence of integrin blocking antibodies demonstrated that migration on tenascin and fibronectin is mediated by distinct integrins, alpha2beta1 and alphavbeta5/alphavbeta3, respectively. Since tenascin is coexpressed in malignant tumor matrices with fibronectin, we assessed the effects of tenascin on U251.3 cell migration mediated by fibronectin. Tenascin was found to provide a positive effect on fibronectin-mediated migration by altering cell morphology and enhancing cell motility. These effects of tenascin on fibronectin-mediated cell migration were inhibited by blocking beta1 and alpha2beta1 integrins. The results suggest that tenascin may play a significant role in promoting tumor cell migration and invasiveness by modulating cell responses to normal matrix components.

Distinct effects of recombinant tenascin-C domains on neuronal cell adhesion, growth cone guidance, and neuronal polarity

Using a set of recombinantly expressed proteins, distinct domains of the mouse extracellular matrix glycoprotein tenascin-C, hereafter called tenascin, have been identified to confer adhesion, anti-adhesion, and changes in morphology of neuronal cells. In short-term adhesion assays (1 hr), cerebellar and hippocampal neurons adhered to several domains, encompassing the fibronectin type III-like (FN III) repeats 1-2 and 6-8, as well as to the alternatively spliced FN III repeats and to tenascin itself. Although no short-term adhesion to the EGF repeats containing fragment could be detected under the conditions used, it was anti-adhesive for neuronal cell bodies and repellent for growth cone advance and neuritogenesis. FN III repeats 3-5 were repellent only for growth cones but not for neuronal cell bodies. Neurite outgrowth promoting activities at early stages and induction of a polarized neuronal morphology at later stages of differentiation were associated with the EGF repeats and the FN III repeats 6-8. These observations suggest differential effects of particular domains of the tenascin molecule on distinct cellular compartments, i.e., cell body, axon and dendrite, and existence of multiple neuronal receptors with distinct intracellular signaling features.

Distinct sites on tenascin-C mediate repellent or adhesive interactions with different neuronal cell types

In this study we have determined the binding specificities of four different neuronal cell types to tenascin-C (TN-C) and laminin using a cell adhesion assay. TN-C was repulsive for small cerebellar neurons and PC12 phaeochromocytoma cells, since after short-term adhesion to the substrate-bound molecule with a maximum of cell binding at 45 min, the cells detached from the substrate and after 22 h only about 25% of the originally adherent cells were still bound. For N2A neuroblastoma cells and retinal cells TN-C was an adhesive substrate, since the number of adherent cells did not decrease after the initial attachment period. All four cell types adhered well to laminin at all time points studied. For short-term adhesion of small cerebellar neurons and PC12 cells two binding sites were identified on TN-C, one being localized within the epidermal growth factor-like repeats three to five and the second within fibronectin type III-like repeats three and four. One binding site for N2A and retinal cells was localized within fibronectin type III-like repeat seven. Binding of small cerebellar neurons to TN-C was dependent on Ca2+, but not on Mg2+ and was inhibitable by polyclonal antibodies to beta 1 integrin. Short-term adhesion of small cerebellar neurons was also inhibitable with a mixture of recombinant fragments of TN-C encompassing the whole molecule, although the specific inhibitory activity of this mixture was ten-fold lower on a molar basis when compared to the native molecule. Our observations indicate that different neuronal cell types use distinct binding sites on TN-C for repellent or adhesive interactions and that beta 1 integrin is involved in the recognition event leading to repulsion of small cerebellar neurons.

Tenascins, a growing family of extracellular matrix proteins

The tenascins are a family of large multimeric extracellular matrix proteins consisting of repeated structural modules including heptad repeats, epidermal growth factor (EGF)-like repeats, fibronectin type III repeats, and a globular domain shared with the fibrinogens. The tenascins are believed to be involved in the morphogenesis of many organs and tissues. To date three members of the tenascin family have been described, tenascin-C, tenascin-R, and tenascin-X. Tenascin-R seems to be specific for the central and peripheral nervous system, tenascin-X is most prominent in skeletal and heart muscle, while tenascin-C is present in a large number of developing tissues including the nervous system, but is absent in skeletal and heart muscles. Tenascin-C was the original tenascin discovered, partly because of its overexpression in tumors. Inferring from cell biological studies, it has been proposed that tenascin-C is an adhesion-modulating protein.

Expression of tenascin in odontogenic tumours

We investigated the expression of tenascin in a series of odontogenic tumours (n = 63) of epithelial and epithelial-ectomesenchymal origin by using immunohistochemical methods. A heterogeneity of expression of tenascin was observed in odontogenic tumours. The heterogeneity was most prominent in odontogenic tumours not forming calcified tissues. In these ameloblastomas and adenomatoid odontogenic tumours, tenascin was mainly localised at the epithelial tumour cell-mesenchymal tissue interface. In the calcifying epithelial odontogenic tumour, ameloblastic fibroma and odontoma, a widespread stromal immunoreactivity was observed which was, however, unreactive in the calcified masses. The stellate reticulum-like cells and granular cells of ameloblastoma also showed a positive immunoreactivity for tenascin. The results of the present study suggest that expression of tenascin in the stromal tissue of odontogenic tumours differs according to the potential of forming calcified masses by the tumour cells irrespective of tumour cell morphology.

Dermo-epidermal separation is associated with induced tenascin expression in human skin

Tenascin, a large glycoprotein of the extracellular matrix, shows a site-restricted distribution during embryogenesis, and can be found in adults in a variety of pathological conditions. In normal skin, tenascin is expressed at low levels, but it is upregulated in skin tumours, in a number of skin diseases with epidermal hyperproliferation and during wound healing. Several tenascin variants have been described, and these arise by alternative splicing. Using a monoclonal antibody recognizing all tenascin variants, and polyclonal antibodies specific for the large tenascin variants, we have investigated tenascin expression in bullous diseases such as epidermolysis bullosa, pemphigus, bullous pemphigoid and pemphigoid gestationis. By immunohistochemistry, we have found increased tenascin staining in all patient skin samples, with a more pronounced tenascin expression in samples of autoimmune bullous diseases. The large tenascin variants seem to be major forms of tenascin occurring in healthy skin. In patients with blistering diseases, however, these large variants appear to represent a subpopulation of the induced tenascin accumulation. These findings suggest different functions for the tenascin variants in normal and diseased skin.

Characterization of two splice variants of metastasis-associated human mts1 gene

The mts1 gene is one of the genes specifically expressed in mouse metastatic tumors and tumor cell lines. In this paper, we present data on cloning and sequencing of two variants of human mts1 cDNAs (hu-mts1 and hu-mts1 (var)), as well as of the corresponding region in the human genome. Comparison of the genomic sequence with the sequence of the mts1 cDNAs demonstrates presence of two alternatively spliced variants of the mts1 in the human osteosarcoma cell line (OHS). The alternative splicing occurs within the 5'-untranslated region (UTR) of human mts1 pre-mRNA. Both splice variants, hu-mts1 and hu-mts1 (var), retain similar stability in the cells, contain one open reading frame coding for the MTS1 protein and differ only slightly in their translational capacity. The splice variants demonstrate dramatic variations in the level of expression in different human tissues and in human tumor cell lines. Although we have not revealed substantial differences in the mode of action of the two splice variants in the cells, the observed tissue specificity of expression supports the notion that it plays an important role in determining the activity of mts1 in different tissues.

The alternative splicing pattern of the tenascin-C pre-mRNA is controlled by the extracellular pH

Alternative splicing of primary transcripts is an ubiquitous and reversible mechanism for the generation of multiple protein isoforms from single genes. Here we report that in cultured normal human fibroblasts, small pH variations of the culture medium (from 7.2 to 6.9) strikingly modify the alternative splicing pattern of the tenascin-C primary transcript. Since such extracellular pH variations occur in many normal and pathological conditions, microenvironmental pH may be an important element for the regulation of RNA alternative splicing in vivo.

Immunoreactive tenascin in tumours of salivary glands: evidence for enhanced expression in tumour stroma and production by tumour cells

Tenascin, a large molecular weight extracellular glycoprotein expressed at the epithelial-mesenchymal interface during morphogenesis in embryo, wound healing and in the stroma of various benign and malignant tumours was evaluated in a series of primary epithelial tumours of salivary glands using a monoclonal antibody. Normal salivary glands (n = 5) had linear delicate band-like immunoreactive tenascin in relatively large excretory or intralobular ducts. Pleomorphic adenomas (n = 40) had heterogeneity of expression in modified myoepithelial cell-associated myxoid, hyaline and chondroid areas. Warthin's tumours (n = 10) had a linear immunoreactivity profile of tenascin just adjacent to the basal cells of the epithelial tumour component. A heterogeneity of expression with intense to low or negative stromal immunoreactivity was observed in adenoid cystic carcinomas (n = 8), mucoepidermoid carcinomas (n = 8), epithelial-myoepithelial carcinomas (n = 4), polymorphous low-grade carcinomas (n = 3), papillary cystadenocarcinomas (n = 15) and undifferentiated carcinomas (n = 3). In addition, small cystic spaces or lumens of epithelial-lined tubulo-ductal structures in numerous salivary tumours had positive immunoreactivity for tenascin, suggesting its production by the epithelial tumour component. An enhanced expression of tenascin in salivary tumours suggests a role of this protein in the stromal remodelling and tumour growth.

Tenascin: does it play a role in epidermal morphogenesis and homeostasis?

Tenascin is a large glycoprotein of the extracellular matrix. Its complex multidomain structure, along with its unique distribution during embryogenesis, inflammation, wound healing, and tumorigenesis suggest this protein may play a significant role in regulating cell proliferation, migration, and differentiation. In this review I will summarize the structural features of tenascin and its localization in skin and discuss some of the potential roles of tenascin in the regulation of keratinocyte biology.