Revisiting the Tenascins: Exploitable as Cancer Targets?

For their full manifestation, tumors require support from the surrounding tumor microenvironment (TME), which includes a specific extracellular matrix (ECM), vasculature, and a variety of non-malignant host cells. Together, these components form a tumor-permissive niche that significantly differs from physiological conditions. While the TME helps to promote tumor progression, its special composition also provides potential targets for anti-cancer therapy. Targeting tumor-specific ECM molecules and stromal cells or disrupting aberrant mesenchyme-cancer communications might normalize the TME and improve cancer treatment outcome. The tenascins are a family of large, multifunctional extracellular glycoproteins consisting of four members. Although each have been described to be expressed in the ECM surrounding cancer cells, tenascin-C and tenascin-W are currently the most promising candidates for exploitability and clinical use as they are highly expressed in various tumor stroma with relatively low abundance in healthy tissues. Here, we review what is known about expression of all four tenascin family members in tumors, followed by a more thorough discussion on tenascin-C and tenascin-W focusing on their oncogenic functions and their potential as diagnostic and/or targetable molecules for anti-cancer treatment purposes.

Expansion and characterization of epithelial stem cells with potential for cyclical hair regeneration

In mammals, organ induction occurs only during embryonic development except for hair follicles (HFs). However, HF-resident epithelial stem cells (HFSCs), which are responsible for repetitive HF regeneration, are not fully characterized. Here, we establish in vitro culture systems that are capable of controlling the ability of HFSCs to regenerate HFs. Based on a method that precisely controlled the number of HFs for regeneration, functional analysis revealed that CD34/CD49f/integrin β5 (Itgβ5)-triple-positive (CD34+/CD49f+/Itgβ5+) cells have multipotency and functional significance for continual hair regeneration. In native HFs, these cells reside in the uppermost area of the bulge region, which is surrounded by tenascin in mice and humans. This study unveils the subpopulation of HFSCs responsible for long-term hair cycling of HFs regenerated from bioengineered HF germ, suggesting the presence of functional heterogeneity among bulge HFSCs and the utility of our culture system to achieve HF regenerative therapy.

Tenascin-W: Discovery, Evolution, and Future Prospects

Of the four tenascins found in bony fish and tetrapods, tenascin-W is the least understood. It was first discovered in the zebrafish and later in mouse, where it was mistakenly named tenascin-N. Tenascin-W is expressed primarily in developing and mature bone, in a subset of stem cell niches, and in the stroma of many solid tumors. Phylogenetic studies show that it is the most recent tenascin to evolve, appearing first in bony fishes. Its expression in bone and the timing of its evolutionary appearance should direct future studies to its role in bone formation, in stem cell niches, and in the treatment and detection of cancer.

Increased Expression of Zyxin and Its Potential Function in Androgenetic Alopecia

Androgenetic alopecia (AGA) is the most common progressive form of hair loss, occurring in more than half of men aged > 50 years. Hair follicle (HF) miniaturization is a feature of AGA, and dermal papillae (DP) play key roles in hair growth and regeneration by regulating follicular cell activity. Previous studies have revealed that adhesion signals are important factors in AGA development. Zyxin (ZYX) is an actin-interacting protein that is essential for cell adhesion and migration. The aim of this research was to investigate the expression and potential role of ZYX in AGA. Real-time polymerase chain reaction (RT-PCR) analysis revealed that ZYX expression was elevated in the affected frontal HF of individuals with AGA compared to unaffected occipital HF. Moreover, increased ZYX expression was also observed within DP using immunofluorescence staining. Our in vivo results revealed that ZYX knockout mice showed enhanced hair growth and anagen entry compared to wild-type mice. Reducing ZYX expression in ex vivo cultured HFs by siRNA resulted in the enhanced hair shaft production, delayed hair follicle catagen entry, increased the proliferation of dermal papilla cells (DPCs), and upregulated expression of stem cell-related proteins. These results were further validated in cultured DPCs in vitro. To further reveal the mechanism by which ZYX contributes to AGA, RNA-seq analysis was conducted to identify gene signatures upon ZYX siRNA treatment in cultured hair follicles. Multiple pathways, including focal adhesion and HIF-1 signaling pathways, were found to be involved. Collectively, we discovered the elevated expression of ZYX in the affected frontal hair follicles of AGA patients and revealed the effects of ZYX downregulation on in vivo mice, ex vivo hair follicles, and in vitro DPC. These findings suggest that ZYX plays important roles in the pathogenesis of AGA and stem cell properties of DPC and may potentially be used as a therapeutic target in AGA.

Tenascin-C deficiency impairs alveolarization and microvascular maturation during postnatal lung development

After the airways have been formed by branching morphogenesis the gas exchange area of the developing lung is enlarged by the formation of new alveolar septa (alveolarization). The septa themselves mature by a reduction of their double-layered capillary networks to single-layered ones (microvascular maturation). Alveolarization in mice is subdivided into a first phase (postnatal days 4-21, classical alveolarization), where new septa are lifted off from immature preexisting septa, and a second phase (day 14 to adulthood, continued alveolarization), where new septa are formed from mature septa. Tenascin-C (TNC) is a multidomain extracellular matrix protein contributing to organogenesis and tumorigenesis. It is highly expressed during classical alveolarization, but afterward its expression is markedly reduced. To study the effect of TNC deficiency on postnatal lung development, the formation and maturation of the alveolar septa were followed stereologically. Furthermore, the number of proliferating (Ki-67-positive) and TUNEL-positive cells was estimated. In TNC-deficient mice for both phases of alveolarization a delay and catch-up were observed. Cell proliferation was increased at days 4 and 6; at day 7, thick septa with an accumulation of capillaries and cells were observed; and the number of TUNEL-positive cells (dying cells or DNA repair) was increased at day 10. Whereas at days 15 and 21 premature microvascular maturation was detected, the microvasculature was less mature at day 60 compared with wild type. No differences were observed in adulthood. We conclude that TNC contributes to the formation of new septa, to microvascular maturation, and to cell proliferation and migration during postnatal lung development.NEW & NOTEWORTHY Previously, we showed that the extracellular matrix protein tenascin-C takes part in prenatal lung development by controlling branching morphogenesis. Now we report that tenascin-C is also important during postnatal lung development, because tenascin-C deficiency delays the formation and maturation of the alveolar septa during not only classical but also continued alveolarization. Adult lungs are indistinguishable from wild type because of a catch-up formation of new septa.

The Expression and Possible Functions of Tenascin-W During Development and Disease

Tenascins are a family of multifunctional glycoproteins found in the extracellular matrix of chordates. Two of the tenascins, tenascin-C and tenascin-W, form hexabrachions. In this review, we describe the discovery and domain architecture of tenascin-W, its evolution and patterns of expression during embryogenesis and in tumors, and its effects on cells in culture. In avian and mammalian embryos tenascin-W is primarily expressed at sites of osteogenesis, and in the adult tenascin-W is abundant in certain stem cell niches. In primary cultures of osteoblasts tenascin-W promotes cell migration, the formation of mineralized foci and increases alkaline phosphatase activity. Tenascin-W is also prominent in many solid tumors, yet it is missing from the extracellular matrix of most adult tissues. This makes it a potential candidate for use as a marker of tumor stroma and a target for anti-cancer therapies.

Cancer Stem Cells: Emergent Nature of Tumor Emergency

A functional analysis of 167 genes overexpressed in Krebs-2 tumor initiating cells was performed. In the first part of the study, the genes were analyzed for their belonging to one or more of the three groups, which represent the three major phenotypic manifestation of malignancy of cancer cells, namely (1) proliferative self-sufficiency, (2) invasive growth and metastasis, and (3) multiple drug resistance. 96 genes out of 167 were identified as possible contributors to at least one of these fundamental properties. It was also found that substantial part of these genes are also known as genes responsible for formation and/or maintenance of the stemness of normal pluri-/multipotent stem cells. These results suggest that the malignancy is simply the ability to maintain the stem cell specific genes expression profile, and, as a consequence, the stemness itself regardless of the controlling effect of stem niches. In the second part of the study, three stress factors combined into the single concept of "generalized cellular stress," which are assumed to activate the expression of these genes, were defined. In addition, possible mechanisms for such activation were identified. The data obtained suggest the existence of a mechanism for the de novo formation of a pluripotent/stem phenotype in the subpopulation of "committed" tumor cells.

Extracellular Matrix as a Regulator of Epidermal Stem Cell Fate

Epidermal stem cells reside within the specific anatomic location, called niche, which is a microenvironment that interacts with stem cells to regulate their fate. Regulation of many important processes, including maintenance of stem cell quiescence, self-renewal, and homeostasis, as well as the regulation of division and differentiation, are common functions of the stem cell niche. As it was shown in multiple studies, extracellular matrix (ECM) contributes a lot to stem cell niches in various tissues, including that of skin. In epidermis, ECM is represented, primarily, by a highly specialized ECM structure, basement membrane (BM), which separates the epidermal and dermal compartments. Epidermal stem cells contact with BM, but when they lose the contact and migrate to the overlying layers, they undergo terminal differentiation. When considering all of these factors, ECM is of fundamental importance in regulating epidermal stem cells maintenance, proper mobilization, and differentiation. Here, we summarize the remarkable progress that has recently been made in the research of ECM role in regulating epidermal stem cell fate, paying special attention to the hair follicle stem cell niche. We show that the destruction of ECM components impairs epidermal stem cell morphogenesis and homeostasis. A deep understanding of ECM molecular structure as well as the development of in vitro system for stem cell maintaining by ECM proteins may bring us to developing new approaches for regenerative medicine.

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 in metastasis: A view from the invasive front

The extracellular matrix protein tenascin C (TNC) is a large glycoprotein expressed in connective tissues and stem cell niches. TNC over-expression is repeatedly observed in cancer, often at the invasive tumor front, and is associated with poor clinical outcome in several malignancies. The link between TNC expression and poor survival in cancer patients suggests a role for TNC in metastatic progression, which is responsible for the majority of cancer related deaths. Indeed, functional studies using mouse models are revealing new roles of TNC in cancer progression and underscore its important contribution to the development of metastasis. TNC has a pleiotropic role in advancing metastasis by promoting migratory and invasive cell behavior, angiogenesis and cancer cell viability under stress. TNC is an essential component of the metastatic niche and modulates stem cell signaling within the niche. This may be crucial for the fitness of disseminated cancer cells confronted with a foreign environment in secondary organs, that can exert a strong selective pressure on invading cells. TNC is a compelling example of how an extracellular matrix protein can provide a molecular context that is imperative to cancer cell fitness in metastasis.

Cancer Microenvironment: What Can We Learn from the Stem Cell Niche

Epidermal stem cells (ESCs) are crucial for maintenance and self- renewal of skin epithelium and also for regular hair cycling. Their role in wound healing is also indispensable. ESCs reside in a defined outer root sheath portion of hair follicle—also known as the bulge region. ECS are also found between basal cells of the interfollicular epidermis or mucous membranes. The non-epithelial elements such as mesenchymal stem cell-like elements of dermis or surrounding adipose tissue can also contribute to this niche formation. Cancer stem cells (CSCs) participate in formation of common epithelial malignant diseases such as basal cell or squamous cell carcinoma. In this review article, we focus on the role of cancer microenvironment with emphasis on the effect of cancer-associated fibroblasts (CAFs). This model reflects various biological aspects of interaction between cancer cell and CAFs with multiple parallels to interaction of normal epidermal stem cells and their niche. The complexity of intercellular interactions within tumor stroma is depicted on example of malignant melanoma, where keratinocytes also contribute the microenvironmental landscape during early phase of tumor progression. Interactions seen in normal bulge region can therefore be an important source of information for proper understanding to melanoma. The therapeutic consequences of targeting of microenvironment in anticancer therapy and for improved wound healing are included to article.

AngioMatrix, a signature of the tumor angiogenic switch-specific matrisome, correlates with poor prognosis for glioma and colorectal cancer patients

Angiogenesis represents a rate-limiting step during tumor progression. Targeting angiogenesis is already applied in cancer treatment, yet limits of anti-angiogenic therapies have emerged, notably because tumors adapt and recur after treatment. Therefore, there is a strong need to better understand the molecular and cellular mechanisms underlying tumor angiogenesis. Using the RIP1-Tag2 transgenic murine model, we identified 298 genes that are deregulated during the angiogenic switch, revealing an ingression/expansion of specific stromal cell types including endothelial cells and pericytes, but also macrophages and perivascular mesenchymal cells. Canonical TGF-β signaling is up-regulated during the angiogenic switch, especially in tumor-associated macrophages and fibroblasts. The matrisome, comprising extracellular matrix (ECM) and ECM-associated molecules, is significantly enriched, which allowed us to define the AngioMatrix signature as the 110 matrisomal genes induced during the RIP1-Tag2 angiogenic switch. Several AngioMatrix molecules were validated at expression level. Ablation of tenascin-C, one of the most highly induced ECM molecules during the switch, resulted in reduced angiogenesis confirming its important role. In human glioma and colorectal samples, the AngioMatrix signature correlates with the expression of endothelial cell markers, is increased with tumor progression and finally correlates with poor prognosis demonstrating its diagnostic and therapeutic potential.

Expression of Wnt/β-catenin signaling, stem-cell markers and proliferating cell markers in rat whisker hair follicles

The rat whisker hair follicle (HF) is a model for studying the reconstruction of the HF or dermal papilla (DP), and involves the Wnt/β-catenin signaling pathway, which is a key pathway in HF development and HF cycling after birth. It has been reported that Wnt/catenin signaling plays an indispensable role in human or rat pelages development and postnatal growth. However, the distribution of some Wnt/β-catenin signaling pathway factors and their relationship with the epithelial stem cell markers in whisker follicles has not been characterized. In this study, we investigated the immunolocalization of Wnt/catenin signaling pathway members, including Wnt10b, Wnt10a, Wnt5a, β-catenin, and downstream lymphoid enhancer-binding factor 1 (LEF1) and transcription factor 3 (TCF3), as well as, HF stem-cell markers CD34, CK15 and proliferating cell nuclear antigen (PCNA) protein, in rat anagen phase whisker follicles. β-catenin, Wnt5a, Wnt10b, Wnt10a, LEF1, and TCF3 were expressed in the outer root sheath (ORS), inner root sheath, matrix and hair shaft of anagen follicles. β-catenin, Wnt10b, LEF1, and TCF3 were highly expressed and Wnt5a and Wnt10a weakly expressed in DP and dermal sheath (DS) regions. The expression of α-smooth muscle actin was strong in the lower DS and it was also detected in some DP cells. CD34, CK15 and PCNA were all expressed in the ORS; and CD34 and PCNA were also detected in the matrix, however CD34 was extensively expressed in DP and DS regions. Our studies located the position of Wnts, downstream LEF1 and TCF3 and stem cell marker proteins, which provide new information in understanding the role of the Wnt singaling pathway in whisker follicles' growth.

Therapeutic potential of gingival fibroblasts for cutaneous radiation syndrome: comparison to bone marrow-mesenchymal stem cell grafts

Mesenchymal stem cell (MSC) therapy has recently been investigated as a potential treatment for cutaneous radiation burns. We tested the hypothesis that injection of local gingival fibroblasts (GFs) would promote healing of radiation burn lesions and compared results with those for MSC transplantation. Human clinical- grade GFs or bone marrow-derived MSCs were intradermally injected into mice 21 days after local leg irradiation. Immunostaining and real-time PCR analysis were used to assess the effects of each treatment on extracellular matrix remodeling and inflammation in skin on days 28 and 50 postirradiation. GFs induced the early development of thick, fully regenerated epidermis, skin appendages, and hair follicles, earlier than MSCs did. The acceleration of wound healing by GFs involved rearrangement of the deposited collagen, modification of the Col/MMP/TIMP balance, and modulation of the expression and localization of tenascin-C and of the expression of growth factors (VEGF, EGF, and FGF7). As MSC treatment did, GF injection decreased the irradiation-induced inflammatory response and switched the differentiation of macrophages toward an M2-like phenotype, characterized by CD163(+) macrophage infiltration and strong expression of arginase-1. These findings indicate that GFs are an attractive target for regenerative medicine, for easier to collect, can grow in culture, and promote cutaneous wound healing in irradiation burn lesions.

Tenascin-C is required for normal Wnt/β-catenin signaling in the whisker follicle stem cell niche

Whisker follicles have multiple stem cell niches, including epidermal stem cells in the bulge as well as neural crest-derived stem cells and mast cell progenitors in the trabecular region. The neural crest-derived stem cells are a pool of melanocyte precursors. Previously, we found that the extracellular matrix glycoproteins tenascin-C and tenascin-W are expressed near CD34-positive cells in the trabecular stem cell niche of mouse whisker follicles. Here, we analyzed whiskers from tenascin-C knockout mice and found intrafollicular adipocytes and supernumerary mast cells. As Wnt/β-catenin signaling promotes melanogenesis and suppresses the differentiation of adipocytes and mast cells, we analyzed β-catenin subcellular localization in the trabecular niche. We found cytoplasmic and nuclear β-catenin in wild-type mice reflecting active Wnt/β-catenin signaling, whereas β-catenin in tenascin-C knockout mice was mostly cell membrane-associated and thus transcriptionally inactive. Furthermore, cells expressing the Wnt/β-catenin target gene cyclin D1 were enriched in the CD34-positive niches of wild-type compared to tenascin-C knockout mice. We then tested the effects of tenascins on this signaling pathway. We found that tenascin-C and tenascin-W can be co-precipitated with Wnt3a. In vitro, substrate bound tenascins promoted β-catenin-mediated transcription in the presence of Wnt3a, presumably due to the sequestration and concentration of Wnt3a near the cell surface. We conclude that the presence of tenascin-C in whiskers assures active Wnt/β-catenin signaling in the niche thereby maintaining the stem cell pool and suppressing aberrant differentiation, while in the knockout mice with reduced Wnt/β-catenin signaling, stem cells from the trabecular niche can differentiate into ectopic adipocytes and mast cells.