Identification of PA2.26 antigen as a novel cell-surface mucin-type glycoprotein that induces plasma membrane extensions and increased motility in keratinocytes

Altered Cell Clusters and Upregulated Aqp1 in Connexin 50 Knockout Lens Epithelium

Purpose

To characterize the heterogeneity and cell clusters of postnatal lens epithelial cells (LECs) and to investigate the downstream targets of connexin 50 (Cx50) in the regulation of lens homeostasis and lens growth. To determine differentially expressed genes (DEGs) in the connexin 50 knockout (Cx50KO) lens epithelial cells that shed light on novel mechanism underlying the cataract and small size of the Cx50KO lenses.

Methods

Single-cell RNA sequencing (scRNA-seq) of lens epithelial cells isolated from one-month-old Cx50KO and wild-type (WT) mice were performed. Differentially expressed genes were identified, and selected DEGs were further studied by quantitative real-time PCR (RT-qPCR) analysis and Western blot analysis.

Results

The expression profiles of several thousand genes were identified by scRNA-seq data analysis. In comparison to the WT control, many DEGs were identified in the Cx50KO lens epithelial cells, including growth regulating transcriptional factors and genes encoding water channels. Significantly upregulated aquaporin 1 (Aqp1) gene expression was confirmed by RT-qPCR, and upregulated AQP1 protein expression was confirmed by Western blot analysis and immunostaining both in vivo and in vitro.

Conclusions

Lens epithelial cells exhibit an intrinsic heterogeneity of different cell clusters in regulating lens homeostasis and lens growth. Upregulated Aqp1 in Cx50KO lens epithelial cells suggests that both connexin 50 and AQP1 likely play important roles in regulating water homeostasis in lens epithelial cells.

Lack of inflammation or immune response in cyst tissue of patients with symptomatic non-hydrocephalic pineal cysts

Pineal cysts are frequently encountered as incidental findings in magnetic resonance imaging, usually devoid of symptoms, yet some patients exhibit symptomatic manifestations possibly associated with the cyst, even in the absence of hydrocephalus. The etiology of these symptoms remains contentious. This study aims to investigate the presence of lymphatic endothelial cell (LEC) markers and indications of inflammation or immune response within the pineal cysts of patients experiencing symptomatic non-hydrocephalic presentations. Eight patients who underwent surgical excision of their cysts were included in the study. Immunohistochemistry was utilized to assess the expression of LYVE-1, PDPN, and VEGFR3 as LEC markers, alongside IL-6 and CD3 for indications of inflammation or immune activity. Our analysis revealed an absence of inflammatory markers or immune response. However, a distinct expression of VEGFR3 was observed, likely localized to neurons within the pineal cyst tissue. We propose that these VEGFR3+ neurons within the pineal cyst may contribute to the headache symptoms reported by these patients. Further investigations are warranted to substantiate this hypothesis.

Prognostic Impact of Stromal Profiles Educated by Gastric Cancer

BACKGROUND

Cancer-associated fibroblasts exhibit diversity and have several subtypes. The underlying relationship between the diversity of cancer-associated fibroblasts and their effect on gastric cancer progression remains unclear. In this study, mesenchymal stem cells were differentiated into cancer-associated fibroblasts with gastric cancer cell lines; clinical specimens were used to further investigate the impact of cancer-associated fibroblast diversity on cancer progression.

METHODS

Nine gastric cancer cell lines (NUGC3, NUGC4, MKN7, MKN45, MKN74, FU97, OCUM1, NCI-N87, and KATOIII) were used to induce mesenchymal stem cell differentiation into cancer-associated fibroblasts. The cancer-associated fibroblasts were classified based on ACTA2 and PDPN expression. Cell function analysis was used to examine the impact of cancer-associated fibroblast subtypes on cancer cell phenotype. Tissue samples from 97gastric patients who underwent gastrectomy were used to examine the clinical significance of each subtype classified according to cancer-associated fibroblast expression.

RESULTS

Co-culture of mesenchymal stem cells with nine gastric cancer cell lines revealed different subtypes of ACTA2 and PDPN expression in differentiated cancer-associated fibroblasts. Cancer-associated fibroblast subtypes with high ACTA2 plus PDPN expression levels significantly increased gastric cancer cell migration, invasion, and proliferation. The cancer-associated fibroblast subtype with ACTA2 plus PDPN expression was an independent prognostic factor along with lymph node metastasis for patients who had gastric cancer and were undergoing surgery.

CONCLUSIONS

Cancer-associated fibroblasts are educated by gastric cancer cells during the development of cancer-associated fibroblast diversity. Differentiated cancer-associated fibroblasts with distinct expression patterns could affect gastric cancer progression and enable prognostic stratification for gastric cancer.

Podoplanin: A potential therapeutic target for thrombotic diseases

As a specific lymphatic marker and a key ligand of C-type lectin-like receptor 2 (CLEC-2), podoplanin (Pdpn) is involved in various physiological and pathological processes such as growth and development, respiration, blood coagulation, lymphangiogenesis, angiogenesis, and inflammation. Thrombotic diseases constitute a major cause of disability and mortality in adults, in which thrombosis and inflammation play a crucial role. Recently, increasing evidence demonstrates the distribution and function of this glycoprotein in thrombotic diseases such as atherosclerosis, ischemic stroke, venous thrombosis, ischemic-reperfusion injury (IRI) of kidney and liver, and myocardial infarction. Evidence showed that after ischemia, Pdpn can be acquired over time by a heterogeneous cell population, which may not express Pdpn in normal conditions. In this review, the research progresses in understanding the roles and mechanisms of podoplanin in thromobotic diseases are summarized. The challenges of podoplanin-targeted approaches for disease prognosis and preventions are also discussed.

The role of glycans in the mechanobiology of cancer

Although cancer is a genetic disease, physical changes such as stiffening of the extracellular matrix also commonly occur in cancer. Cancer cells sense and respond to extracellular matrix stiffening through the process of mechanotransduction. Cancer cell mechanotransduction can enhance cancer-promoting cell behaviors such as survival signaling, proliferation, and migration. Glycans, carbohydrate-based polymers, have recently emerged as important mediators and/or modulators of cancer cell mechanotransduction. Stiffer tumors are characterized by increased glycan content on cancer cells and their associated extracellular matrix. Here we review the role of cancer-associated glycans in coupled mechanical and biochemical alterations during cancer progression. We discuss the recent evidence on how increased expression of different glycans, in the form of glycoproteins and proteoglycans, contributes to both mechanical changes in tumors and corresponding cancer cell responses. We conclude with a summary of emerging tools that can be used to modify glycans for future studies in cancer mechanobiology.

Podoplanin: Its roles and functions in neurological diseases and brain cancers

Podoplanin is a small mucin-like glycoprotein involved in several physiological and pathological processes in the brain including development, angiogenesis, tumors, ischemic stroke and other neurological disorders. Podoplanin expression is upregulated in different cell types including choroid plexus epithelial cells, glial cells, as well as periphery infiltrated immune cells during brain development and neurological disorders. As a transmembrane protein, podoplanin interacts with other molecules in the same or neighboring cells. In the past, a lot of studies reported a pleiotropic role of podoplanin in the modulation of thrombosis, inflammation, lymphangiogenesis, angiogenesis, immune surveillance, epithelial mesenchymal transition, as well as extracellular matrix remodeling in periphery, which have been well summarized and discussed. Recently, mounting evidence demonstrates the distribution and function of this molecule in brain development and neurological disorders. In this review, we summarize the research progresses in understanding the roles and mechanisms of podoplanin in the development and disorders of the nervous system. The challenges of podoplanin-targeted approaches for disease prognosis and preventions are also discussed.

Butyrate modulates mucin secretion and bacterial adherence in LoVo cells via MAPK signaling

Short-chain fatty acids contribute to normal bowel function and prevent bacterial infections. In particular, butyrate is a promising candidate that plays an important role in regulating the functional integrity of the gastrointestinal tract by stimulating mucin secretion. We investigated whether butyrate treatment modulates mucin secretion and bacterial adherence in LoVo cells. In addition, the possible signaling pathways were also examined in connection with the upregulation of mucin secretion. The results showed that butyrate induced mucin secretion in LoVo cells, resulting in the inhibition of Escherichia coli adhesion by increasing the adherence of Lactobacillus acidophilus and Bifidobacterium longum. The gene expression analysis suggests that mitogen-activated protein kinase (MAPK) signaling pathways including Cdc42-PAK pathway appears to be involved in stimulating mucin secretion. More importantly, butyrate induced the increased actin expression and polymerization in LoVo cells, which could be attributable to the Cdc42-PAK signaling pathway, implicated in actin cytoskeleton and mucin secretion. Our results provide a molecular basis in modulating bacterial adherence and the MAPK signaling pathway for the improved homeostasis of colonic epithelial cells.

The Role of Podoplanin in the Immune System and Inflammation

Podoplanin is a small cell-surface mucin-like glycoprotein that participates in multiple physiological and pathological processes. Podoplanin exerts an important function in the immune response and is upregulated in fibroblasts, macrophages, T helper cells, and epithelial cells during inflammation. Herein, we summarize the latest knowledge on the functional expression of podoplanin in the immune system and review the contribution of podoplanin to several inflammatory diseases. Furthermore, we discuss podoplanin as a novel therapeutic target for various inflammatory diseases.

Roles of Podoplanin in Malignant Progression of Tumor

Podoplanin (PDPN) is a cell-surface mucin-like glycoprotein that plays a critical role in tumor development and normal development of the lung, kidney, and lymphatic vascular systems. PDPN is overexpressed in several tumors and is involved in their malignancy. PDPN induces platelet aggregation through binding to platelet receptor C-type lectin-like receptor 2. Furthermore, PDPN modulates signal transductions that regulate cell proliferation, differentiation, migration, invasion, epithelial-to-mesenchymal transition, and stemness, all of which are crucial for the malignant progression of tumor. In the tumor microenvironment (TME), PDPN expression is upregulated in the tumor stroma, including cancer-associated fibroblasts (CAFs) and immune cells. CAFs play significant roles in the extracellular matrix remodeling and the development of immunosuppressive TME. Additionally, PDPN functions as a co-inhibitory molecule on T cells, indicating its involvement with immune evasion. In this review, we describe the mechanistic basis and diverse roles of PDPN in the malignant progression of tumors and discuss the possibility of the clinical application of PDPN-targeted cancer therapy, including cancer-specific monoclonal antibodies, and chimeric antigen receptor T technologies.

The Role of Podoplanin in Skin Diseases

Podoplanin is a sialomucin-like type I transmembrane receptor glycoprotein that is expressed specifically in lymphatic vessels, sebaceous glands, and hair follicles in normal skin. However, under pathological conditions podoplanin expression is upregulated in various cells, such as keratinocytes, fibroblasts, tumor cells, and inflammatory cells, and plays pivotal roles in different diseases. In psoriasis, podoplanin expression is induced in basal keratinocytes via the JAK-STAT pathway and contributes toward epidermal hyperproliferation. Podoplanin expression on keratinocytes can also promote IL-17 secretion from lymphocytes, promoting chronic inflammation. During wound healing, the podoplanin/CLEC-2 interaction between keratinocytes and platelets regulates re-epithelialization at the wound edge. In skin cancers, podoplanin expresses on tumor cells and promotes their migration and epithelial-mesenchymal transition, thereby accelerating invasion and metastasis. Podoplanin is also expressed in normal peritumoral cells, such as cancer-associated fibroblasts in melanoma and keratinocytes in extramammary Paget's disease, which promote tumor progression and predict aggressive behavior and poor prognosis. This review provides an overview of our current understanding of the mechanisms via which podoplanin mediates these pathological skin conditions.

Glycocalyx Curving the Membrane: Forces Emerging from the Cell Exterior

Morphological transitions are typically attributed to the actions of proteins and lipids. Largely overlooked in membrane shape regulation is the glycocalyx, a pericellular membrane coat that resides on all cells in the human body. Comprised of complex sugar polymers known as glycans as well as glycosylated lipids and proteins, the glycocalyx is ideally positioned to impart forces on the plasma membrane. Large, unstructured polysaccharides and glycoproteins in the glycocalyx can generate crowding pressures strong enough to induce membrane curvature. Stress may also originate from glycan chains that convey curvature preference on asymmetrically distributed lipids, which are exploited by binding factors and infectious agents to induce morphological changes. Through such forces, the glycocalyx can have profound effects on the biogenesis of functional cell surface structures as well as the secretion of extracellular vesicles. In this review, we discuss recent evidence and examples of these mechanisms in normal health and disease.

Podoplanin is required for tumor cell invasion in cutaneous squamous cell carcinoma

The invasiveness of late-stage cutaneous squamous cell carcinoma (cSCC) is associated with poor patients' prognosis and linked to strong upregulation of the glycoprotein Podoplanin (PDPN) in cancer cells. However, the function of PDPN in these processes in cSCC carcinogenesis has not been characterized in detail yet. Employing a CRISPR/Cas9-based loss-of-function approach on murine cSCC cells, we show that the loss of Pdpn results in decreased migration and invasion in vitro. Complementing these in vitro studies, labelled murine control and Pdpn knockout cells were injected orthotopically into the dermis of nude mice to recapitulate the formation of human cSCC displaying a well-differentiated morphology with a PDPN-positive reaction in fibroblasts in the tumor stroma. Smaller tumors were observed upon Pdpn loss, which is associated with reduced tumor cell infiltration into the stroma. Utilizing Pdpn mutants in functional experiments in vitro, we provide evidence that both the intra- and extracellular domains are essential for cancer cell invasion. These findings underline the critical role of PDPN in cSCC progression and highlight potential therapeutic strategies targeting PDPN-dependent cancer cell invasion, especially in late-stage cSCC patients.

Podoplanin, a Potential Therapeutic Target for Nasopharyngeal Carcinoma

Introduction

The role of podoplanin (PDPN) in nasopharyngeal carcinoma (NPC) is still unknown. The aims of this study were to investigate the expression and role of PDPN in NPC cells.

Materials and Methods

Immunofluorescence staining and functional tests were used to determine the effects of PDPN knockdown by siRNA in TW01 NPC cells. Microarray analysis was conducted to identify genes regulated by PDPN. The molecular mechanism of PDPN on NPC cells was further determined by Ingenuity Pathways Analysis (IPA).

Results

PDPN was expressed in most TW01 NPC cells. PDPN knockdown by siRNA decreased NPC cell proliferation, migration, and invasion. The microarray data showed 63 upregulated genes and 12 downregulated genes following PDPN knockdown. The top 5 most upregulated genes analyzed by IPA were IFI27, IFI44L, IFI6, OAS1, and TRIM22, and the most relevant pathway was the interferon signaling pathway.

Conclusions

To the best of our knowledge, this is the first report to show that knocking down PDPN leads to suppression of NPC cell proliferation, migration, and invasion. Our results suggest that PDPN may serve as a potential chemotherapeutic target for NPC treatment in the future.

Podoplanin regulates the migration of mesenchymal stromal cells and their interaction with platelets

Mesenchymal stromal cells (MSCs) upregulate podoplanin at sites of infection, chronic inflammation and cancer. Here, we investigated the functional consequences of podoplanin expression on the migratory potential of MSCs and their interactions with circulating platelets. Expression of podoplanin significantly enhanced the migration of MSCs compared to MSCs lacking podoplanin. Rac-1 inhibition altered the membrane localisation of podoplanin and in turn significantly reduced MSC migration. Blocking Rac-1 activity had no effect on the migration of MSCs lacking podoplanin, indicating that it was responsible for regulation of migration through podoplanin. When podoplanin-expressing MSCs were seeded on the basal surface of a porous filter, they were able to capture platelets perfused over the uncoated apical surface and induce platelet aggregation. Similar microthrombi were observed when endothelial cells (ECs) were co-cultured on the apical surface. Confocal imaging shows podoplanin-expressing MSCs extending processes into the EC layer, and these processes could interact with circulating platelets. In both models, platelet aggregation induced by podoplanin-expressing MSCs was inhibited by treatment with recombinant soluble C-type lectin-like receptor 2 (CLEC-2; encoded by the gene Clec1b). Thus, podoplanin may enhance the migratory capacity of tissue-resident MSCs and enable novel interactions with cells expressing CLEC-2.

Summary: Podoplanin enhances the migration of mesenchymal stromal cells in a Rac-1-dependent manner, enabling direct interactions of subendothelial stroma with circulating platelets.

Podoplanin in Inflammation and Cancer

Podoplanin is a small cell-surface mucin-like glycoprotein that plays a crucial role in the development of the alveoli, heart, and lymphatic vascular system. Emerging evidence indicates that it is also involved in the control of mammary stem-cell activity and biogenesis of platelets in the bone marrow, and exerts an important function in the immune response. Podoplanin expression is upregulated in different cell types, including fibroblasts, macrophages, T helper cells, and epithelial cells, during inflammation and cancer, where it plays important roles. Podoplanin is implicated in chronic inflammatory diseases, such as psoriasis, multiple sclerosis, and rheumatoid arthritis, promotes inflammation-driven and cancer-associated thrombosis, and stimulates cancer cell invasion and metastasis through a variety of strategies. To accomplish its biological functions, podoplanin must interact with other proteins located in the same cell or in neighbor cells. The binding of podoplanin to its ligands leads to modulation of signaling pathways that regulate proliferation, contractility, migration, epithelial⁻mesenchymal transition, and remodeling of the extracellular matrix. In this review, we describe the diverse roles of podoplanin in inflammation and cancer, depict the protein ligands of podoplanin identified so far, and discuss the mechanistic basis for the involvement of podoplanin in all these processes.

Podoplanin (PDPN) affects the invasiveness of thyroid carcinoma cells by inducing ezrin, radixin and moesin (E/R/M) phosphorylation in association with matrix metalloproteinases

Background

Podoplanin (PDPN) is a mucin-type transmembrane glycoprotein specific to the lymphatic system. PDPN expression has been found in various human tumors and is considered to be a marker of cancer. We had previously shown that PDPN expression contributes to carcinogenesis in the TPC1 papillary thyroid cancer-derived cell line by enhancing cell migration and invasiveness. The aim of this study was to determine the effect of PDPN down-regulation in another thyroid cancer-derived cell line: BcPAP.

Methods

In order to determine the effects of PDPN on malignant features of BcPAP cells (harboring the BRAFV600E mutated allele) and TPC1 cells (carrying the RET/PTC1 rearrangement), we silenced PDPN in these cells using small interfering RNA (siRNA). The efficacy of PDPN silencing was confirmed by qRT-PCR and Western blotting. Then, we tested the motility and invasiveness of these cells (using scratch test and Transwell assay), their growth capacities F(cell cycle analysis, viability, clonogenic activity) and apoptosis assays), adhesion-independent colony-formation capacities, as well as the effect of PDPN silencing on MMPs expression and activity (zymography).

Results

We found that PDPN-induced cell phenotype depended on the genetic background of thyroid tumor cells. PDPN down-regulation in BcPAP cells was negatively correlated with the migration and invasion, in contrast to TPC1 cells in which PDPN depletion resulted in enhanced migration and invasiveness. Moreover, our results suggest that in BcPAP cells, PDPN may be involved in the epithelial-mesenchymal transition (EMT) through regulating the expression of the ezrin, radixin and moesin (E/R/M) proteins, MMPs 9 and MMP2, remodeling of actin cytoskeleton and cellular protrusions. We also demonstrated that PDPN expression is associated with the MAPK signaling pathway. The inhibition of the MAPK pathway resulted in a decreased PDPN expression, increased E/R/M phosphorylation and reduced cell migration. Additionally, PDPN depleted BcPAP cells treated with inhibitors of MEK1/2 kinases (U0126) or of the BRAF V600E protein (PLX4720) had reduced motility, similar to that previously observed in TPC1 cells after PDPN knock-down.

Conclusions

Altogether, our data suggest that PDPN may play an important role in the control of invasion and migration of papillary thyroid carcinoma cells in association with the E/R/M, MMPs and MAPK kinases.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-5239-z) contains supplementary material, which is available to authorized users.

Podoplanin: An emerging cancer biomarker and therapeutic target

Podoplanin (PDPN) is a transmembrane receptor glycoprotein that is upregulated on transformed cells, cancer associated fibroblasts and inflammatory macrophages that contribute to cancer progression. In particular, PDPN increases tumor cell clonal capacity, epithelial mesenchymal transition, migration, invasion, metastasis and inflammation. Antibodies, CAR-T cells, biologics and synthetic compounds that target PDPN can inhibit cancer progression and septic inflammation in preclinical models. This review describes recent advances in how PDPN may be used as a biomarker and therapeutic target for many types of cancer, including glioma, squamous cell carcinoma, mesothelioma and melanoma.

Expression and Dynamics of Podoplanin in Cultured Osteoblasts with Mechanostress and Mineralization Stimulus

This study investigates the significance of the expression and dynamics of podoplanin in mechanostress and mineralization in cultured murine osteoblasts. Podoplanin increased in osteoblasts subjected to straining in non-mineralization medium, suggesting that the mechanostress alone is a podoplanin induction factor. In osteoblasts subjected to vertical elongation straining in the mineralization medium, the mRNA amounts of podoplanin, osteopontin, and osteocalcin were significantly larger than those in cells not subjected to straining, suggesting that mechanostress is the cause of a synergistic effect in the expression of these proteins. In osteoblasts in the mineralization medium, significant increases in osteocalcin mRNA occurred earlier in cells subjected to straining than in the cells not subjected to straining, suggesting that the mechanostress is a critical factor to enhance the expression of osteocalcin. Western blot and ELISA analysis showed increased podoplanin production in osteoblasts with longer durations of straining. There was significantly less mineralization product in osteoblasts with antibodies for podoplanin, osteopontin, and osteocalcin. There was also less osteopontin and osteocalcin produced in osteoblasts with anti-podoplanin. These findings suggest that mechanostress induces the production of podoplanin in osteoblasts and that podoplanin may play a role in mineralization in cooperation with bone-associated proteins.

Podoplanin emerges as a functionally relevant oral cancer biomarker and therapeutic target

Oral cancer has become one of the most aggressive types of cancer, killing 140,000 people worldwide every year. Current treatments for oral cancer include surgery and radiation therapies. These procedures can be very effective; however, they can also drastically decrease the quality of life for survivors. New chemotherapeutic treatments are needed to more effectively combat oral cancer. The transmembrane receptor podoplanin (PDPN) has emerged as a functionally relevant oral cancer biomarker and chemotherapeutic target. PDPN expression promotes tumor cell migration leading to oral cancer invasion and metastasis. Here, we describe the role of PDPN in oral squamous cell carcinoma progression, and how it may be exploited to prevent and treat oral cancer.

Inflammatory Cytokines Induce Podoplanin Expression at the Tumor Invasive Front

Tumor invasion is a critical first step in the organismic dissemination of cancer cells and the formation of metastasis in distant organs, the most important prognostic factor and the actual cause of death in most of the cancer patients. We report herein that the cell surface protein podoplanin (PDPN), a potent inducer of cancer cell invasion, is conspicuously expressed by the invasive front of squamous cell carcinomas (SCCs) of the cervix in patients and in the transgenic human papillomavirus/estrogen mouse model of cervical cancer. Laser capture microscopy combined with gene expression profiling reveals that the expression of interferon-responsive genes is up-regulated in PDPN-expressing cells at the tumor invasive front, which are exposed to CD45-positive inflammatory cells. Indeed, PDPN expression can be induced in cultured SCC cell lines by single or combined treatments with interferon-γ, transforming growth factor-β, and/or tumor necrosis factor-α. Notably, shRNA-mediated ablation of either PDPN or STAT1 in A431 SCC cells repressed cancer cell invasion on s.c. transplantation into immunodeficient mice. The results highlight the induction of tumor cell invasion by the inflammatory cytokine-stimulated expression of PDPN in the outermost cell layers of cervical SCC.

Notch expressed by osteocytes plays a critical role in mineralisation

Notch is actively involved in various life processes including osteogenesis; however, the role of Notch signalling in the terminal mineralisation of bone is largely unknown. In this study, it was noted that Hey1, a downstream target of Notch signalling was highly expressed in mature osteocytes compared to osteoblasts, indicating a potential role of Notch in osteocytes. Using a recently developed thermosensitive cell line (IDG-SW3), we demonstrated that dentin matrix acidic phosphoprotein 1 (DMP1) expression was inhibited and mineralisation process was significantly altered when Notch pathway was inactivated via administration of N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), an inhibitor of Notch. Dysregulation of Notch in osteocyte differentiation can result in spontaneous deposition of calcium phosphate on collagen fibrils, disturbed transportation of intracellular mineral vesicles, alteration of mineral crystal structure, decreased bonding force between minerals and organic matrix, and suppression of dendrite development coupled with decreased expression of E11. In conclusion, the evidence presented here suggests that Notch plays a critical role in osteocyte differentiation and biomineralisation process.

KEY MESSAGES

Notch plays a regulatory role in osteocyte phenotype. Notch modulates the mineralisation mediated by osteocytes. Notch activity influences the ultrastructural properties of bone mineralisation.

FGF-2 promotes osteocyte differentiation through increased E11/podoplanin expression

E11/podoplanin is critical in the early stages of osteoblast‐to‐osteocyte transitions (osteocytogenesis), however, the upstream events which regulate E11 expression are unknown. The aim of this study was to examine the effects of FGF‐2 on E11‐mediated osteocytogenesis and to reveal the nature of the underlying signaling pathways regulating this process. Exposure of MC3T3 osteoblast‐like cells and murine primary osteoblasts to FGF‐2 (10 ng/ml) increased E11 mRNA and protein expression (p < 0.05) after 4, 6, and 24 hr. FGF‐2 induced changes in E11 expression were also accompanied by significant (p < 0.01) increases in Phex and Dmp1 (osteocyte markers) expression and decreases in Col1a1, Postn, Bglap, and Alpl (osteoblast markers) expression. Immunofluorescent microscopy revealed that FGF‐2 stimulated E11 expression, facilitated the translocation of E11 toward the cell membrane, and subsequently promoted the formation of osteocyte‐like dendrites in MC3T3 and primary osteoblasts. siRNA knock down of E11 expression achieved >70% reduction of basal E11 mRNA expression (p < 0.05) and effectively abrogated FGF‐2‐related changes in E11 expression and dendrite formation. FGF‐2 strongly activated the ERK signaling pathway in osteoblast‐like cells but inhibition of this pathway did not block the ability of FGF‐2 to enhance E11 expression or to promote acquisition of the osteocyte phenotype. The results of this study highlight a novel mechanism by which FGF‐2 can regulate osteoblast differentiation and osteocyte formation. Specifically, the data suggests that FGF‐2 promotes osteocytogenesis through increased E11 expression and further studies will identify if this regulatory pathway is essential for bone development and maintenance in health and disease.

Podoplanin is a component of extracellular vesicles that reprograms cell-derived exosomal proteins and modulates lymphatic vessel formation

Podoplanin (PDPN) is a transmembrane glycoprotein that plays crucial roles in embryonic development, the immune response, and malignant progression. Here, we report that cells ectopically or endogenously expressing PDPN release extracellular vesicles (EVs) that contain PDPN mRNA and protein. PDPN incorporates into membrane shed microvesicles (MVs) and endosomal-derived exosomes (EXOs), where it was found to colocalize with the canonical EV marker CD63 by immunoelectron microscopy. We have previously found that expression of PDPN in MDCK cells induces an epithelial-mesenchymal transition (EMT). Proteomic profiling of MDCK-PDPN cells compared to control cells shows that PDPN-induced EMT is associated with upregulation of oncogenic proteins and diminished expression of tumor suppressors. Proteomic analysis of exosomes reveals that MDCK-PDPN EXOs were enriched in protein cargos involved in cell adhesion, cytoskeletal remodeling, signal transduction and, importantly, intracellular trafficking and EV biogenesis. Indeed, expression of PDPN in MDCK cells stimulated both EXO and MV production, while knockdown of endogenous PDPN in human HN5 squamous carcinoma cells reduced EXO production and inhibited tumorigenesis. EXOs released from MDCK-PDPN and control cells both stimulated in vitro angiogenesis, but only EXOs containing PDPN were shown to promote lymphatic vessel formation. This effect was mediated by PDPN on the surface of EXOs, as demonstrated by a neutralizing specific monoclonal antibody. These results contribute to our understanding of PDPN-induced EMT in association to tumor progression, and suggest an important role for PDPN in EV biogenesis and/or release and for PDPN-EXOs in modulating lymphangiogenesis.

Podoplanin increases the migration of human fibroblasts and affects the endothelial cell network formation: A possible role for cancer-associated fibroblasts in breast cancer progression

In our previous studies we showed that in breast cancer podoplanin-positive cancer-associated fibroblasts correlated positively with tumor size, grade of malignancy, lymph node metastasis, lymphovascular invasion and poor patients’ outcome. Therefore, the present study was undertaken to assess if podoplanin expressed by fibroblasts can affect malignancy-associated properties of breast cancer cells. Human fibroblastic cell lines (MSU1.1 and Hs 578Bst) overexpressing podoplanin and control fibroblasts were co-cultured with breast cancer MDA-MB-231 and MCF7 cells and the impact of podoplanin expressed by fibroblasts on migration and invasiveness of breast cancer cells were studied in vitro. Migratory and invasive properties of breast cancer cells were not affected by the presence of podoplanin on the surface of fibroblasts. However, ectopic expression of podoplanin highly increases the migration of MSU1.1 and Hs 578Bst fibroblasts. The present study also revealed for the first time, that podoplanin expression affects the formation of pseudo tubes by endothelial cells. When human HSkMEC cells were co-cultured with podoplanin-rich fibroblasts the endothelial cell capillary-like network was characterized by significantly lower numbers of nodes and meshes than in co-cultures of endothelial cells with podoplanin-negative fibroblasts. The question remains as to how our experimental data can be correlated with previous clinical data showing an association between the presence of podoplanin-positive cancer-associated fibroblasts and progression of breast cancer. Therefore, we propose that expression of podoplanin by fibroblasts facilitates their movement into the tumor stroma, which creates a favorable microenvironment for tumor progression by increasing the number of cancer-associated fibroblasts, which produce numerous factors affecting proliferation, survival and invasion of cancer cells. In accordance with this, the present study revealed for the first time, that such podoplanin-mediated effects can affect tube formation by endothelial cells and participate in their pathological properties in the tumor context. Our experimental data were supported by clinical studies. First, when IDC and DCIS were analyzed by immunohistochemistry according to the presence of podoplanin-expressing cells, the numbers of cancer-associated fibroblasts with high expression of this glycoprotein were significantly higher in IDC than in DCIS cases. Second, using immunofluorescence, the co-localization of PDPN-positive CAFs with blood vessels stained with antibody directed against CD34 was observed in tumor stroma of IDC samples.

Podoplanin is a negative regulator of Th17 inflammation

Recent data indicate that there are different subpopulations of Th17 cells that can express a regulatory as opposed to an inflammatory gene signature. The transmembrane glycoprotein PDPN is critical in the development of multiple organs including the lymphatic system and has been described on T cells in mouse models of autoimmune Th17 inflammation. Here, we demonstrate that unlike in mice, PDPN+ T cells induced under classic Th17-polarizing conditions express transcription factors associated with Th17 cells but do not produce IL-17. Moreover, these cells express a transcriptional profile enriched for immunosuppressive and regulatory pathways and express a distinct cytokine profile compared with potentially pathogenic PDPN- Th17 cells. Ligation of PDPN by its ligand CLEC-2 ameliorates the Th17 inflammatory response. IL-17 secretion is restored with shRNA gene silencing of PDPN. Furthermore, PDPN expression is reduced via an Sgk1-mediated pathway under proinflammatory, high sodium chloride conditions. Finally, CD3+PDPN+ T cells are devoid of IL-17 in skin biopsies from patients with candidiasis, a prototypical Th17-driven skin disease. Thus, our data support the hypothesis that PDPN may serve as a marker of a nonpathogenic Th17 cell subset and may also functionally regulate pathogenic Th17 inflammation.

The optimum marker for the detection of lymphatic vessels

Podoplanin, lymphatic vessel endothelial hyaluronic acid receptor-1, prospero-related homeobox-1 and vascular endothelial growth factor receptor 3 have been demonstrated to have crucial roles in the development of the lymphatic system and lymphangiogenesis process by combining with their corresponding receptors. Thus, the four markers have been widely used in labelling lymphatic vessels for the detection of lymphangiogenesis and lymphatic vessel invasion. Numerous authors have aimed to identify the roles of these four markers in the lymphatic system and the mechanisms have been partly clarified at the molecular level. The aim of the present review was to comprehensively clarify the characteristics and latent action modes of the four markers in order to determine which is the best one for the detection of lymphangiogenesis and lymphatic vessel invasion.

Ezrin directly interacts with AQP2 and promotes its endocytosis

The water channel aquaporin-2 (AQP2) is a major regulator of water homeostasis in response to vasopressin (VP). Dynamic trafficking of AQP2 relies on its close interaction with trafficking machinery proteins and the actin cytoskeleton. Here, we report the identification of ezrin, an actin-binding protein from the ezrin/radixin/moesin (ERM) family as an AQP2-interacting protein. Ezrin was first detected in a co-immunoprecipitation (co-IP) complex using an anti-AQP2 antibody in a proteomic analysis. Immunofluorescence staining revealed the co-expression of ezrin and AQP2 in collecting duct principal cells, and VP treatment caused redistribution of both proteins to the apical membrane. The ezrin-AQP2 interaction was confirmed by co-IP experiments with an anti-ezrin antibody, and by pulldown assays using purified full-length and FERM domain-containing recombinant ezrin. By using purified recombinant proteins, we showed that ezrin directly interacts with AQP2 C-terminus through its N-terminal FERM domain. Knocking down ezrin expression with shRNA resulted in increased membrane accumulation of AQP2 and reduced AQP2 endocytosis. Therefore, through direct interaction with AQP2, ezrin facilitates AQP2 endocytosis, thus linking the dynamic actin cytoskeleton network with AQP2 trafficking.

Modulation of VEGF-induced migration and network formation by lymphatic endothelial cells: Roles of platelets and podoplanin

Lymphatic endothelial cells (LEC) express the transmembrane receptor podoplanin whose only known endogenous ligand CLEC-2 is found on platelets. Both podoplanin and CLEC-2 are required for normal lymphangiogenesis as mice lacking either protein develop a blood-lymphatic mixing phenotype. We investigated the roles of podoplanin and its interaction with platelets in migration and tube formation by LEC. Addition of platelets or antibody-mediated crosslinking of podoplanin inhibited LEC migration induced by vascular endothelial growth factors (VEGF-A or VEGF-C), but did not modify basal migration or the response to basic fibroblast growth factor or epidermal growth factor. In addition, platelets and podoplanin crosslinking disrupted networks of LEC formed in co-culture with fibroblasts. Depletion of podoplanin in LEC using siRNA negated the pro-migratory effect of VEGF-A and VEGF-C. Inhibition of RhoA or Rho-kinase reduced LEC migration induced by VEGF-C, but had no further effect after crosslinking of podoplanin, suggesting that podoplanin is required for signaling downstream of VEGF-receptors but upstream of RhoA. Together, these data reveal for the first time that podoplanin is an intrinsic specific regulator of VEGF-mediated migration and network formation in LEC and identify crosslinking of podoplanin by platelets or antibodies as mechanisms to modulate this pathway.

Hypomorphic conditional deletion of E11/Podoplanin reveals a role in osteocyte dendrite elongation

The transmembrane glycoprotein E11/Podoplanin (Pdpn) has been implicated in the initial stages of osteocyte differentiation. However, its precise function and regulatory mechanisms are still unknown. Due to the known embryonic lethality induced by global Pdpn deletion, we have herein explored the effect of bone‐specific Pdpn knockdown on osteocyte form and function in the post‐natal mouse. Extensive skeletal phenotyping of male and female 6‐week‐old Oc‐cre;Pdpn^flox/flox (cKO) mice and their Pdpn^flox/flox controls (fl/fl) has revealed that Pdpn deletion significantly compromises tibial cortical bone microarchitecture in both sexes, albeit to different extents (p < 0.05). Consistent with this, we observed an increase in stiffness in female cKO mice in comparison to fl/fl mice (p < 0.01). Moreover, analysis of the osteocyte phenotype by phalloidin staining revealed a significant decrease in the dendrite volume (p < 0.001) and length (p < 0.001) in cKO mice in which deletion of Pdpn also modifies the bone anabolic loading response (p < 0.05) in comparison to age‐matched fl/fl mice. Together, these data confirm a regulatory role for Pdpn in osteocyte dendrite formation and as such, in the control of osteocyte function. As the osteocyte dendritic network is known to play vital roles in regulating bone modeling/remodeling, this highlights an essential role for Pdpn in bone homeostasis.

Morphological study of tooth development in podoplanin-deficient mice

Podoplanin is a mucin-type highly O-glycosylated glycoprotein identified in several somatyic cells: podocytes, alveolar epithelial cells, lymphatic endothelial cells, lymph node stromal fibroblastic reticular cells, osteocytes, odontoblasts, mesothelial cells, glia cells, and others. It has been reported that podoplanin-RhoA interaction induces cytoskeleton relaxation and cell process stretching in fibroblastic cells and osteocytes, and that podoplanin plays a critical role in type I alveolar cell differentiation. It appears that podoplanin plays a number of different roles in contributing to cell functioning and growth by signaling. However, little is known about the functions of podoplanin in the somatic cells of the adult organism because an absence of podoplanin is lethal at birth by the respiratory failure. In this report, we investigated the tooth germ development in podoplanin-knockout mice, and the dentin formation in podoplanin-conditional knockout mice having neural crest-derived cells with deficiency in podoplanin by the Wnt1 promoter and enhancer-driven Cre recombinase: Wnt1-Cre;Pdpn^Δ/Δmice. In the Wnt1-Cre;Pdpn^Δ/Δmice, the tooth and alveolar bone showed no morphological abnormalities and grow normally, indicating that podoplanin is not critical in the development of the tooth and bone.

Epithelial deletion of podoplanin is dispensable for re-epithelialization of skin wounds

The mucin-like transmembrane protein podoplanin (PDPN) is prominently represented in tumor-associated gene expression signatures of numerous types of cancer including squamous cell carcinoma, and gain-of-function and knockdown approaches in tissue culture strongly suggested an important role of PDPN in cell proliferation, migration and adhesion. PDPN is absent during epidermal homeostasis but is highly expressed in basal keratinocytes during cutaneous wound healing. Enhanced motility of immortalized keratinocytes upon ectopic PDPN overexpression argues for wound healing defects upon podoplanin deficiency in keratinocytes; however, in vivo data that unequivocally define the impact of PDPN by functional studies in a physiologically relevant system are still missing. Here, we have applied an in vivo loss-of-function approach by generating a novel transgenic mouse line with keratinocyte-specific podoplanin deficiency. Performing cutaneous full-thickness excisional wounds to examine re-epithelialization capacity, unexpectedly, no defects were observed in wound healing properties of mutant mice. Similarly, PDPN-deficient primary keratinocytes showed no impairment in migration, adhesion or proliferation. Thus, PDPN function is not rate-limiting for re-epithelialization but may be functionally compensated by an as yet unknown protein. Our data also call for in vivo functional studies on PDPN in settings of skin tumor development and progression to clarify PDPN's role in skin pathology.

Podoplanin-mediated TGF-β-induced epithelial-mesenchymal transition and its correlation with bHLH transcription factor DEC in TE-11 cells

Podoplanin is reported involved in the collective cell invasion, another tumor invasion style which is distinct from the single cell invasion, so-called epithelial-mesenchymal transition (EMT). In this study, we investigated the correlation between podoplanin and EMT-related markers in esophageal squamous cell carcinoma (ESCC), and evaluated its linkage with the basic helix-loop-helix (bHLH) transcription factor differentiated embryonic chondrocyte (DEC) 1 and DEC2. Three ESCC cell lines and human squamous cell carcinoma A431 cells were subjected to western blot analyses for podoplanin and EMT markers, as well as the expression of DEC1 and DEC2. By RT-qPCR and western blotting, we found that TGF-β increased the expression of podoplanin and mensenchymal markers (e.g., N-cadherin and vimentin), while decreased the expression of epithelial markers (e.g., Claudin-4 and E-cadherin), accompanied by Smad2 phosphorylation and slug activation. Moreover, TGF-β has different effects on the expression of DEC1 and DEC2, that is, it upregulates DEC1, but downregulates DEC2. Capability of cell proliferation, invasion and migration were further analyzed using CCK-8 assay, Matrigel-invasion assay, and the wound-healing assay, respectively. The proliferation, invasion and migration ability were significantly lost in podoplanin-knockdown cells when compared with the scrambled siRNA group. In addition to these changes, the expression of Claudin-4, but not that of Claudin-1 or E-cadherin, was induced by the siRNA against podoplanin. On the contrary, overexpression of DEC1 and DEC2 exhibits opposite effects on podoplanin, but only slight effect on Claudin-4 was detected. These data indicated that podoplanin is significantly associated with EMT of TE-11 cells, and may be directly or indirectly regulated by bHLH transcription factors DEC1 and DEC2.

E11/Podoplanin Protein Stabilization Through Inhibition of the Proteasome Promotes Osteocyte Differentiation in Murine in Vitro Models

The transmembrane glycoprotein E11 is considered critical in early osteoblast-osteocyte transitions (osteocytogenesis), however its function and regulatory mechanisms are still unknown. Using the late osteoblast MLO-A5 cell line we reveal increased E11 protein/mRNA expression (P < 0.001) concomitant with extensive osteocyte dendrite formation and matrix mineralization (P < 0.001). Transfection with E11 significantly increased mRNA levels (P < 0.001), but immunoblotting failed to detect any correlative increases in E11 protein levels, suggestive of post-translational degradation. We found that exogenous treatment of MLO-A5 and osteocytic IDG-SW3 cells with 10 μM ALLN (calpain and proteasome inhibitor) stabilized E11 protein levels and induced a profound increase in osteocytic dendrite formation (P < 0.001). Treatment with other calpain inhibitors failed to promote similar osteocytogenic changes, suggesting that these effects of ALLN rely upon its proteasome inhibitor actions. Accordingly we found that proteasome-selective inhibitors (MG132/lactacystin/ Bortezomib/Withaferin-A) produced similar dose-dependent increases in E11 protein levels in MLO-A5 and primary osteoblast cells. This proteasomal targeting was confirmed by immunoprecipitation of ubiquitinylated proteins, which included E11, and by increased levels of ubiquitinylated E11 protein upon addition of the proteasome inhibitors MG132/Bortezomib. Activation of RhoA, the small GTPase, was found to be increased concomitant with the peak in E11 levels and its downstream signaling was also observed to promote MLO-A5 cell dendrite formation. Our data indicate that a mechanism reliant upon blockade of proteasome-mediated E11 destabilization contributes to osteocytogenesis and that this may involve downstream targeting of RhoA. This work adds to our mechanistic understanding of the factors regulating bone homeostasis, which may lead to future therapeutic approaches.

Expression of the invertebrate sea urchin P16 protein into mammalian MC3T3 osteoblasts transforms and reprograms them into "osteocyte-like" cells

P16 is an acidic phosphoprotein important in both sea urchin embryonic spicule development and transient mineralization during embryogenesis, syncytium formation, and mineralization in mature urchin tooth. Anti-P16 has been used to localize P16 to the syncytial membranes and the calcite mineral. Specific amino acid sequence motifs in P16 are similar to sequences in DSPP, a protein common to all vertebrate teeth, and crucial for their mineralization. Here, we examine the effect of P16 on vertebrate fibroblastic NIH3T3 cells and osteoblastic MC3T3 cells. Transfection of NIH3T3 cells with P16 cDNA resulted in profound changes in the morphology of the cells. In culture, the transfected cells sent out long processes that contacted processes from neighboring cells forming networks or syncytia. There was a similar change in morphology in cultured osteoblastic MC3T3 cells. In addition, the MC3T3 developed numerous dendrites as found in osteocytes. Importantly, there was also a change in the expression of the osteoblast and osteocyte specific genes. MC3T3 cells transfected with P16 showed an 18-fold increase in expression of the osteocyte specific Dentin matrix protein (DMP1) gene, accompanied by decreased expression of osteoblast specific genes: Bone sialoprotein (BSP), osteocalcin (OCN), and β-catenin decreased by 70%, 64%, and 68 %, respectively. Thus, invertebrate urchin P16 with no previously known analog in vertebrates was able to induce changes in both cell morphology and gene expression, converting vertebrate-derived osteoblast-like precursor cells to an "osteocyte-like" phenotype, an important process in bone biology. The mechanisms involved are presently under study.

Alteration in the podoplanin-ezrin-cytoskeleton linkage is an important initiation event of the podocyte injury in puromycin aminonucleoside nephropathy, a mimic of minimal change nephrotic syndrome

Podoplanin was identified as a protein associated with the transformation of arborized foot processes of glomerular epithelial cells (podocytes) to flat feet. However, the function of podoplanin in the podocyte is not yet fully clarified. In this study, we analyzed the molecular nature of podoplanin, and its expression in rat nephrotic models and patients with minimal change nephrotic syndrome (MCNS). We demonstrated here that podoplanin has two forms: one contains abundant sialic acid and the other a lesser amount of sialic acid. Podoplanin bound ezrin to interact with the cytoskeleton. The silencing of podoplanin in cultured podocytes caused a change in the cell shape and the distribution of ezrin and actin. The expression of podoplanin was clearly reduced before the onset of proteinuria in puromycin aminonucleoside (PAN) nephropathy, a mimic of MCNS, and the decrease in the expression of podoplanin became more evident at the proteinuric stage. Podoplanin was detected in normal urine samples, and the amount of urinary podoplanin markedly increased on day 1 of PAN nephropathy. Urinary ezrin was also detected. The amount of the phosphorylated ezrin was reduced, while the amount of the podoplanin-interacting ezrin increased. The podoplanin expression was reduced in a patient with active-phase MCNS. It is conceivable that the alteration of the podoplanin-ezrin-cytoskeleton linkage is an important event of the podocyte injury in MCNS.

Podoplanin and CLEC-2 drive cerebrovascular patterning and integrity during development

Mice with a constitutive or platelet-specific deletion of the C-type-lectin-like receptor (CLEC-2) exhibit hemorrhaging in the brain at mid-gestation. We sought to investigate the basis of this defect, hypothesizing that it is mediated by the loss of CLEC-2 activation by its endogenous ligand, podoplanin, which is expressed on the developing neural tube. To induce deletion of podoplanin at the 2-cell stage, we generated a podoplanin(fl/fl) mouse crossed to a PGK-Cre mouse. Using 3-dimensional light-sheet microscopy, we observed cerebral vessels were tortuous and aberrantly patterned at embryonic (E) day 10.5 in podoplanin- and CLEC-2-deficient mice, preceding the formation of large hemorrhages throughout the fore-, mid-, and hindbrain by E11.5. Immunofluorescence and electron microscopy revealed defective pericyte recruitment and misconnections between the endothelium of developing blood vessels and surrounding pericytes and neuro-epithelial cells. Nestin-Cre-driven deletion of podoplanin on neural progenitors also caused widespread cerebral hemorrhaging. Hemorrhaging was also seen in the ventricles of embryos deficient in the platelet integrin subunit glycoprotein IIb or in embryos in which platelet α-granule and dense granule secretion is abolished. We propose a novel role for podoplanin on the neuro-epithelium, which interacts with CLEC-2 on platelets, mediating platelet adhesion, aggregation, and secretion to guide the maturation and integrity of the developing vasculature and prevent hemorrhage.

New insights into the role of podoplanin in epithelial-mesenchymal transition

Podoplanin is a small mucin-like transmembrane protein expressed in several adult tissues and with an important role during embryogenesis. It is needed for the proper development of kidneys and lungs as well as accurate formation of the lymphatic vascular system. In addition, it is involved in the physiology of the immune system. A wide variety of tumors express podoplanin, both in the malignant cells and in the stroma. Although there are exceptions, the presence of podoplanin results in poor prognosis. The main consequence of forced podoplanin expression in established and tumor-derived cell lines is an increase in cell migration and, eventually, the triggering of an epithelial-mesenchymal transition, whereby cells acquire a fibroblastoid phenotype and increased motility. We will examine the current status of the role of podoplanin in the induction of epithelial-mesenchymal transition as well as the different interactions that lead to this program.

Mutation of threonine 34 in mouse podoplanin-Fc reduces CLEC-2 binding and toxicity in vivo while retaining antilymphangiogenic activity

The lymphatic system plays an important role in cancer metastasis and inhibition of lymphangiogenesis could be valuable in fighting cancer dissemination. Podoplanin (Pdpn) is a small, transmembrane glycoprotein expressed on the surface of lymphatic endothelial cells (LEC). During mouse development, binding of Pdpn to the C-type lectin-like receptor 2 (CLEC-2) on platelets is critical for the separation of the lymphatic and blood vascular systems. Competitive inhibition of Pdpn functions with a soluble form of the protein, Pdpn-Fc, leads to reduced lymphangiogenesis in vitro and in vivo. However, the transgenic overexpression of human Pdpn-Fc in mouse skin causes disseminated intravascular coagulation due to platelet activation via CLEC-2. In the present study, we produced and characterized a mutant form of mouse Pdpn-Fc, in which threonine 34, which is considered essential for CLEC-2 binding, was mutated to alanine (PdpnT34A-Fc). Indeed, PdpnT34A-Fc displayed a 30-fold reduced binding affinity for CLEC-2 compared with Pdpn-Fc. This also translated into fewer side effects due to platelet activation in vivo. Mice showed less prolonged bleeding time and fewer embolized vessels in the liver, when PdpnT34A-Fc was injected intravenously. However, PdpnT34A-Fc was still as active as wild-type Pdpn-Fc in inhibiting lymphangiogenesis in vitro and also inhibited lymphangiogenesis in vivo. These data suggest that the function of Pdpn in lymphangiogenesis does not depend on threonine 34 in the CLEC-2 binding domain and that PdpnT34A-Fc might be an improved inhibitor of lymphangiogenesis with fewer toxic side effects.

Podoplanin mediates ECM degradation by squamous carcinoma cells through control of invadopodia stability

Invadopodia are actin-rich cell membrane projections used by invasive cells to penetrate the basement membrane. Control of invadopodia stability is critical for efficient degradation of the extracellular matrix (ECM); however, the underlying molecular mechanisms remain poorly understood. Here, we uncover a new role for podoplanin, a transmembrane glycoprotein closely associated with malignant progression of squamous cell carcinomas (SCCs), in the regulation of invadopodia-mediated matrix degradation. Podoplanin downregulation in SCC cells impairs invadopodia stability, thereby reducing the efficiency of ECM degradation. We report podoplanin as a novel component of invadopodia-associated adhesion rings, where it clusters prior to matrix degradation. Early podoplanin recruitment to invadopodia is dependent on lipid rafts, whereas ezrin/moesin proteins mediate podoplanin ring assembly. Finally, we demonstrate that podoplanin regulates invadopodia maturation by acting upstream of the ROCK-LIMK-Cofilin pathway through the control of RhoC GTPase activity. Thus, podoplanin has a key role in the regulation of invadopodia function in SCC cells, controlling the initial steps of cancer cell invasion.

Podoplanin: a novel regulator of tumor invasion and metastasis

Podoplanin, a small mucin-type sialoglycoprotein, was recently shown to be involved in tumor progression. Podoplanin is overexpressed in cancer cells of various human malignancies, and recently, it is also detected in intratumoral stromal cells. We now appreciate that podoplanin plays a dual role in cancer: it can not only suppress tumor growth but also promote tumor progression. Researchers have identified several potential pathways invoked by podoplanin, which participate in the epithelial-to-mesenchymal transition, collective-cell migration, platelet activation and aggregation, and lymphangiogenesis, and thus regulate the tumor invasion and metastasis. Here, we discuss the current experimental and human clinical data on podoplanin to validate the multiple context-dependent functions in different microenvironments and to delineate the diverse regulatory mechanisms.

Small Rho GTPases in the control of cell shape and mobility

Rho GTPases are a class of evolutionarily conserved proteins comprising 20 members, which are predominantly known for their role in regulating the actin cytoskeleton. They are primarily regulated by binding of GTP/GDP, which is again controlled by regulators like GEFs, GAPs, and RhoGDIs. Rho GTPases are thus far well known for their role in the regulation of actin cytoskeleton and migration. Here we present an overview on the role of Rho GTPases in regulating cell shape and plasticity of cell migration. Finally, we discuss the emerging roles of ubiquitination and sumoylation in regulating Rho GTPases and cell migration.

Stromal transforming growth factor-beta 1 is crucial for reinforcing the invasive potential of low invasive cancer

OBJECTIVE

Tumour cells alter the characteristics of the adjacent stroma to create a supportive microenvironment during cancer progression. In vitro and in vivo experiments were carried out to verify the role of stromal TGF-β1 in reinforcing of the invasive potential in low invasive cancer.

MATERIALS AND METHODS

Isolated NF or CAF was co-cultured with low invasive HSC-2 cells to evaluate whether stromal TGF-β1 induced PDPN expression by Transwell invasion and influenced tumour growth in orthotopic xenografts.

RESULTS

Stimulation by TGF-β1 promoted PDPN expression and Transwell invasion through SMAD signalling as well as activation of Src, P38 mitogen activated protein kinase and extracellular regulated kinase 1/2. PDPN induction was TβRII-dependent. Tumour growth of HSC-2 OSCC in a mouse xenograft was intensified in the tumour CAF microenvironment.

CONCLUSIONS

Stromal TGF-β1 signalling promoted PDPN expression in cancer cells, thereby enhancing tumour growth and leading to a more invasive phenotype.

Distribution of podoplanin-expressing cells in the mouse nervous systems

Podoplanin is a mucin-type glycoprotein which was first identified in podocytes. Recently, podoplanin has been successively reported as a marker for brain and peripheral nerve tumors, however, the distribution of podoplanin-expressing cells in normal nerves has not been fully investigated. This study aims to examine the podoplanin-expressing cell distribution in the mouse head and nervous systems. An immunohistochemical study showed that the podoplanin-positive areas in the mouse peripheral nerve and spinal cord are perineurial fibroblasts, satellite cells in the dorsal root ganglion, glia cells in the ventral and dorsal horns, and schwann cells in the ventral and dorsal roots; in the cranial meninges the dura mater, arachnoid, and pia mater; in the eye the optic nerve, retinal pigment epithelium, chorioidea, sclera, iris, lens epithelium, corneal epithelium, and conjunctival epithelium. In the mouse brain choroid plexus and ependyma were podoplanin-positive, and there were podoplanin-expressing brain parenchymal cells in the nuclei and cortex. The podoplanin-expressing cells were astrocyte marker GFAP-positive and there were no differences in the double positive cell distribution of several portions in the brain parenchyma except for the fornix. The results suggest that podoplanin may play a common role in nervous system support cells and eye constituents.

Podoplanin expression in cancer-associated fibroblasts enhances tumor progression of invasive ductal carcinoma of the pancreas

Background

Interactions between cancer cells and surrounding cancer-associated fibroblasts (CAFs) play an important role in cancer progression. Invasive ductal carcinoma (IDC) of the pancreas is characterized by abundant fibrous connective tissue called desmoplasia. Podoplanin (PDPN) is a lymphatic vessel marker (D2-40), and expression of PDPN by stromal CAFs has been reported to be a prognostic indicator in various types of cancer.

Methods

Expression of PDPN in pancreatic IDCs was assessed by immunohistochemical examination in 105 patients who underwent pancreatic resection. Primary CAFs were established from pancreatic cancer tissue obtained by surgery. Quantitative reverse transcription-polymerase chain reaction and flow cytometric analysis were performed to investigate PDPN expression in CAFs. We sorted CAFs according to PDPN expression, and analyzed the functional differences between PDPN+ CAFs and PDPN– CAFs using indirect co-culture with pancreatic cancer cell lines. We also investigated the culture conditions to regulate PDPN expression in CAFs.

Results

PDPN expression in stromal fibroblasts was associated with lymphatic vessel invasion (P = 0.0461), vascular invasion (P = 0.0101), tumor size ≥3 cm (P = 0.0038), histological grade (P = 0.0344), Union for International Cancer Control classification T stage (P = 0.029), and shorter survival time (P < 0.0001). Primary CAFs showed heterogeneous PDPN expression in vitro. Moreover, migration and invasion of pancreatic cancer cell lines (PANC-1 and SUIT-2) were associated with PDPN expression in CAFs (P < 0.01) and expression of CD10, matrix metalloproteinase (MMP) 2, and MMP3. In cultured CAFs, PDPN positivity changed over time under several conditions including co-culture with cancer cells, different culture media, and addition of growth factor.

Conclusions

PDPN-expressing CAFs enhance the progression of pancreatic IDC, and a high ratio of PDPN-expressing CAFs is an independent predictor of poor outcome. Understanding the regulation of the tumor microenvironment is an important step towards developing new therapeutic strategies.