Podocalyxin: a marker of blasts in acute leukemia

Keratan sulfate, an electrosensory neurosentient bioresponsive cell instructive glycosaminoglycan

The roles of keratan sulfate (KS) as a proton detection glycosaminoglycan in neurosensory processes in the central and peripheral nervous systems is reviewed. The functional properties of the KS-proteoglycans aggrecan, phosphacan, podocalyxcin as components of perineuronal nets in neurosensory processes in neuronal plasticity, cognitive learning and memory are also discussed. KS-glycoconjugate neurosensory gels used in electrolocation in elasmobranch fish species and KS substituted mucin like conjugates in some tissue contexts in mammals need to be considered in sensory signalling. Parallels are drawn between KS's roles in elasmobranch fish neurosensory processes and its roles in mammalian electro mechanical transduction of acoustic liquid displacement signals in the cochlea by the tectorial membrane and stereocilia of sensory inner and outer hair cells into neural signals for sound interpretation. The sophisticated structural and functional proteins which maintain the unique high precision physical properties of stereocilia in the detection, transmittance and interpretation of acoustic signals in the hearing process are important. The maintenance of the material properties of stereocilia are essential in sound transmission processes. Specific, emerging roles for low sulfation KS in sensory bioregulation are contrasted with the properties of high charge density KS isoforms. Some speculations are made on how the molecular and electrical properties of KS may be of potential application in futuristic nanoelectronic, memristor technology in advanced ultrafast computing devices with low energy requirements in nanomachines, nanobots or molecular switches which could be potentially useful in artificial synapse development. Application of KS in such innovative areas in bioregulation are eagerly awaited.

CD34-Structure, Functions and Relationship with Cancer Stem Cells

The CD34 protein was identified almost four decades ago as a biomarker for hematopoietic stem cell progenitors. CD34 expression of these stem cells has been exploited for therapeutic purposes in various hematological disorders. In the last few decades, studies have revealed the presence of CD34 expression on other types of cells with non-hematopoietic origins, such as interstitial cells, endothelial cells, fibrocytes, and muscle satellite cells. Furthermore, CD34 expression may also be found on a variety of cancer stem cells. Nowadays, the molecular functions of this protein have been involved in a variety of cellular functions, such as enhancing proliferation and blocking cell differentiation, enhanced lymphocyte adhesion, and cell morphogenesis. Although a complete understanding of this transmembrane protein, including its developmental origins, its stem cell connections, and other functions, is yet to be achieved. In this paper, we aimed to carry out a systematic analysis of the structure, functions, and relationship with cancer stem cells of CD34 based on the literature overview.

A pilot study of changes in urinary podocalyxin levels during normal pregnancy and labor

Introduction: Increased urinary podocalyxin, a surrogate marker of podocyte detachment, has been shown in preeclampsia and eclampsia, but there is a paucity of data of the effect of normal pregnancy on its urinary excretion. We aimed to describe these changes in this pilot study.

Methods: Urine podocalyxin levels were measured in 115 pregnant women. Of these, 12 women were in the second trimester of gestation, 57 in the third trimester and 46 women were in labor.

Results: The median [IQR] urinary podocalyxin levels were 0.81 [0.27, 3.68], 0.92 [0.44, 5.49] and 64.7 [30.5, 106.3] ng/mg creatinine in the second trimester, third trimester, and during labor, respectively (p<0.0001). Patients with hematuria during labor had higher levels of urinary podocalyxin (128.6 [79.8, 169.6] ng/mg creatinine. There was a moderate correlation between gestational age and urinary podocalyxin levels (r=0.63, p<0.0001).

Conclusion: Urinary podocalyxin levels were low in normal pregnancies and increased significantly during labor and with hematuria.

Podocalyxin Expressed in Antigen Presenting Cells Promotes Interaction With T Cells and Alters Centrosome Translocation to the Contact Site

Podocalyxin (PODXL), a cell surface sialomucin expressed in diverse types of normal and malignant cells, mediates cellular adhesion to extracellular matrix and cell-to-cell interaction. A previous study reported the expression of PODXL protein on monocytes undergoing macrophage differentiation, yet the expression of this molecule in other antigen presenting cells (APCs) and its function in the immune system still remain undetermined. In this study, we report that PODXL is expressed in human monocyte-derived immature dendritic cells at both the mRNA and protein levels. Following dendritric cells maturation using pro-inflammatory stimuli, PODXL expression level decreased substantially. Furthermore, we found that PODXL expression is positively regulated by IL-4 through MEK/ERK and JAK3/STAT6 signaling pathways. Our results revealed a polarized distribution of PODXL during the interaction of APCs with CD4⁺ T cells, partially colocalizing with F-actin. Notably, PODXL overexpression in APCs promoted their interaction with CD4⁺ T cells and CD8⁺ T cells and decreased the expression of MHC-I, MHC-II, and the costimulatory molecule CD86. In addition, PODXL reduced the translocation of CD4⁺ T-cell centrosome toward the APC-contact site. These findings suggest a regulatory role for PODXL expressed by APCs in immune responses, thus representing a potential target for therapeutic blockade in infection and cancer.

Podocalyxin in Normal Tissue and Epithelial Cancer

Podocalyxin (PODXL), a glycosylated cell surface sialomucin of the CD34 family, is normally expressed in kidney podocytes, vascular endothelial cells, hematopoietic progenitors, mesothelium, as well as a subset of neurons. In the kidney, PODXL functions primarily as an antiadhesive molecule in podocyte epithelial cells, regulating adhesion and cell morphology, and playing an essential role in the development and function of the organ. Outside the kidney, PODXL plays subtle roles in tissue remodelling and development. Furthermore, many cancers, especially those that originated from the epithelium, have been reported to overexpress PODXL. Collective evidence suggests that PODXL overexpression is linked to poor prognosis, more aggressive tumour progression, unfavourable treatment outcomes, and possibly chemoresistance. This review summarises our current knowledge of PODXL in normal tissue function and epithelial cancer, with a particular focus on its underlying roles in cancer metastasis, likely involvement in chemoresistance, and potential use as a diagnostic and prognostic biomarker.

Emerging Role of Podocalyxin in the Progression of Mature B-Cell Non-Hodgkin Lymphoma

Mature B-cell non-Hodgkin lymphoma (B-NHL) constitutes a group of heterogeneous malignant lymphoproliferative diseases ranging from indolent to highly aggressive forms. Although the survival after chemo-immunotherapy treatment of mature B-NHL has increased over the last years, many patients relapse or remain refractory due to drug resistance, presenting an unfavorable prognosis. Hence, there is an urgent need to identify new prognostic markers and therapeutic targets. Podocalyxin (PODXL), a sialomucin overexpressed in a variety of tumor cell types and associated with their aggressiveness, has been implicated in multiple aspects of cancer progression, although its participation in hematological malignancies remains unexplored. New evidence points to a role for PODXL in mature B-NHL cell proliferation, survival, migration, drug resistance, and metabolic reprogramming, as well as enhanced levels of PODXL in mature B-NHL. Here, we review the current knowledge on the contribution of PODXL to tumorigenesis, highlighting and discussing its role in mature B-NHL progression.

Keratan sulfate, a complex glycosaminoglycan with unique functional capability

From an evolutionary perspective keratan sulfate (KS) is the newest glycosaminoglycan (GAG) but the least understood. KS is a sophisticated molecule with a diverse structure, and unique functional roles continue to be uncovered for this GAG. The cornea is the richest tissue source of KS in the human body but the central and peripheral nervous systems also contain significant levels of KS and a diverse range of KS-proteoglycans with essential functional roles. KS also displays important cell regulatory properties in epithelial and mesenchymal tissues and in bone and in tumor development of diagnostic and prognostic utility. Corneal KS-I displays variable degrees of sulfation along the KS chain ranging from non-sulfated polylactosamine, mono-sulfated and disulfated disaccharide regions. Skeletal KS-II is almost completely sulfated consisting of disulfated disaccharides interrupted by occasional mono-sulfated N-acetyllactosamine residues. KS-III also contains highly sulfated KS disaccharides but differs from KS-I and KS-II through 2-O-mannose linkage to serine or threonine core protein residues on proteoglycans such as phosphacan and abakan in brain tissue. Historically, the major emphasis on the biology of KS has focused on its sulfated regions for good reason. The sulfation motifs on KS convey important molecular recognition information and direct cell behavior through a number of interactive proteins. Emerging evidence also suggest functional roles for the poly-N-acetyllactosamine regions of KS requiring further investigation. Thus further research is warranted to better understand the complexities of KS.

Cancer stem cell surface markers on normal stem cells

The cancer stem cell (CSC) hypothesis has captured the attention of many scientists. It is believed that elimination of CSCs could possibly eradicate the whole cancer. CSC surface markers provide molecular targeted therapies for various cancers, using therapeutic antibodies specific for the CSC surface markers. Various CSC surface markers have been identified and published. Interestingly, most of the markers used to identify CSCs are derived from surface markers present on human embryonic stem cells (hESCs) or adult stem cells. In this review, we classify the currently known 40 CSC surface markers into 3 different categories, in terms of their expression in hESCs, adult stem cells, and normal tissue cells. Approximately 73% of current CSC surface markers appear to be present on embryonic or adult stem cells, and they are rarely expressed on normal tissue cells. The remaining CSC surface markers are considerably expressed even in normal tissue cells, and some of them have been extensively validated as CSC surface markers by various research groups. We discuss the significance of the categorized CSC surface markers, and provide insight into why surface markers on hESCs are an attractive source to find novel surface markers on CSCs.

Podocalyxin promotes proliferation and survival in mature B-cell non-Hodgkin lymphoma cells

Podocalyxin (PCLP1) is a CD34-related sialomucin expressed by some normal cells and a variety of malignant tumors, including leukemia, and associated with the most aggressive cancers and poor clinical outcome. PCLP1 increases breast tumor growth, migration and invasion; however, its role in hematologic malignancies still remains undetermined. The purpose of this study was to investigate the expression and function of PCLP1 in mature B-cell lymphoma cells. We found that overexpression of PCLP1 significantly increases proliferation, cell-to-cell interaction, clonogenicity, and migration of B-cell lymphoma cells. Furthermore, PCLP1 overexpression results in higher resistance to death induced by dexamethasone, reactive oxygen species and type II anti-CD20 monoclonal antibody obinutuzumab. Strikingly, enforced expression of PCLP1 enhances lipid droplet formation as well as pentose phosphate pathway and glutamine dependence, indicative of metabolic reprogramming necessary to support the abnormal proliferation rate of tumor cells. Flow cytometry analysis revealed augmented levels of PCLP1 in malignant cells from some patients with mature B-cell lymphoma compared to their normal B-cell counterparts. In summary, our results demonstrate that PCLP1 contributes to proliferation and survival of mature B-cell lymphoma cells, suggesting that PCLP1 may promote lymphomagenesis and represents a therapeutic target for the treatment of B-cell lymphomas.

Glycosphingolipid dynamics in human embryonic stem cell and cancer: their characterization and biomedical implications

Glycosphingolipids (GSLs) are composed of complex glycans linked to sphingosines and various fatty acid chains. Antibodies against several GSLs designated as stage-specific embryonic antigens (SSEAs), have been widely used to characterize differentiation of embryonic stem (ES) cells. In view of the cross-reactivities of these antibodies with multiple glycans, a few laboratories have employed advanced mass spectrometry (MS) technologies to define the dynamic changes of surface GSLs upon ES differentiation. However, the amphiphilic nature and heterogeneity of GSLs make them difficult to decipher. In our studies, systematic survey of GSL expression profiles in human ES cells and differentiated derivatives was conducted, primarily with matrix-assisted laser desorption/ionization MS (MALDI-MS) and MS/MS analyses. In addition to the well-known ES-specific markers, SSEA-3 and SSEA-4, several previously undisclosed globo- and lacto-series GSLs, including Gb4Cer, Lc4Cer, fucosyl Lc4Cer, Globo H, and disialyl Gb5Cer were identified in the undifferentiated human ES and induced pluripotent stem cells. Furthermore, during differentiation to embryoid body outgrowth, the core structures of GSLs switched from globo- and lacto- to ganglio-series. Lineage-specific differentiation was also marked by alterations of specific GSLs. During differentiation into neural progenitors, core structures shifted to primarily ganglio-series dominated by GD3. GSL patterns shifted to prominent expression of Gb4Cer with little SSEA-3 and- 4 or GD3 during endodermal differentiation. Several issues relevant to MS analysis and novel GSLs in ES cells were discussed. Finally, unique GSL signatures in ES and cancer cells are exploited in glycan-targeted anti-cancer immunotherapy and their mechanistic investigations were discussed using anti-GD2 mAb and Globo H as examples.

The cell surface mucin podocalyxin regulates collective breast tumor budding

Background

Overexpression of the transmembrane sialomucin podocalyxin, which is known to play a role in lumen formation during polarized epithelial morphogenesis, is an independent indicator of poor prognosis in a number of epithelial cancers, including those that arise in the breast. Therefore, we set out to determine if podocalyxin plays a functional role in breast tumor progression.

Methods

MCF-7 breast cancer cells, which express little endogenous podocalyxin, were stably transfected with wild type podocalyxin for forced overexpression. 4T1 mammary tumor cells, which express considerable endogenous podocalyxin, were retrovirally transduced with a short hairpin ribonucleic acid (shRNA) targeting podocalyxin for stable knockdown. In vitro, the effects of podocalyxin on collective cellular migration and invasion were assessed in two-dimensional monolayer and three-dimensional basement membrane/collagen gel culture, respectively. In vivo, local invasion was assessed after orthotopic transplantation in immunocompromised mice.

Results

Forced overexpression of podocalyxin caused cohesive clusters of epithelial MCF-7 breast tumor cells to bud off from the primary tumor and collectively invade the stroma of the mouse mammary gland in vivo. This budding was not associated with any obvious changes in histoarchitecture, matrix deposition or proliferation in the primary tumour. In vitro, podocalyxin overexpression induced a collective migration of MCF-7 tumor cells in two-dimensional (2-D) monolayer culture that was dependent on the activity of the actin scaffolding protein ezrin, a cytoplasmic binding partner of podocalyxin. In three-dimensional (3-D) culture, podocalyxin overexpression induced a collective budding and invasion that was dependent on actomyosin contractility. Interestingly, the collectively invasive cell aggregates often contained expanded microlumens that were also observed in vivo. Conversely, when endogenous podocalyxin was removed from highly metastatic, but cohesive, 4T1 mammary tumor cells there was a decrease in collective invasion in three-dimensional culture.

Conclusions

Podocalyxin is a tumor cell-intrinsic regulator of experimental collective tumor cell invasion and tumor budding.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0670-4) contains supplementary material, which is available to authorized users.

Co-Expression of Ezrin-CLIC5-Podocalyxin Is Associated with Migration and Invasiveness in Hepatocellular Carcinoma

Background and Aim

Prognostic markers are important for predicting the progression and staging of hepatocellular carcinoma (HCC). Ezrin (EZR) and Podocalyxin (PODXL) are proteins associated with invasion, migration and poor prognosis in various types of cancer. Recently, it has been observed that chloride intracellular channel 5 (CLIC5) forms a complex with EZR and PODXL and that it is required for podocyte structure and function. In this study, we evaluated the overexpression of EZR, PODXL and CLIC5 in HCC.

Methods

The modified resistant hepatocyte model (MRHR), human biopsies and HCC cell lines (HepG2, Huh7 and SNU387) were used in this study. Gene and protein expression levels were evaluated in the MRHR by qRT-PCR, Western blot and immunohistochemistry analyses, and protein expression in the human biopsies was evaluated by immunohistochemistry. Protein expression in the HCC cell lines was evaluated by immunofluorescence and Western blot, also the migration and invasive abilities of Huh7 cells were evaluated using shRNA-mediated inhibition.

Results

Our results indicated that these genes and proteins were overexpressed in HCC. Moreover, when the expression of CLIC5 and PODXL was inhibited in Huh7 cells, we observed decreased migration and invasion.

Conclusion

This study suggested that EZR, CLIC5 and PODXL could be biological markers to predict the prognosis of HCC and that these proteins participate in migration and invasion processes.

Podocalyxin Is a Marker of Poor Prognosis in Pancreatic Ductal Adenocarcinoma

Aim of the Study

Podocalyxin-like 1 is a transmembrane glyco-protein whose overexpression associates in many cancers with poor prognosis and unfavorable clinicopathological characteristics. Until now, its prognostic value has never been studied in pancreatic ductal adenocarcinoma (PDAC). The aim of this study was to investigate podocalyxin expression in PDAC by a novel monoclonal antibody and a commercially available polyclonal antibody.

Patients and Materials

With tissue microarrays and immuno-histochemistry, podocalyxin expression evaluation involved 168 PDAC patients. The associa-tions of the podocalyxin tumor expression with clinicopathological variables were explored by Fisher’s exact test and the linear-by-linear test. Survival analyses were by Kaplan-Meier anal-ysis and the Cox proportional hazard model.

Results

The polyclonal antibody revealed membranous podocalyxin expression in 73 (44.0%) specimens and the monoclonal antibody was highly expressed in 36 (21.8%) cases. Membranous expression by the polyclonal antibody was associated with T classification (p=0.045) and perineural invasion (p=0.005), and high expression by the mono-clonal antibody with poor differentiation (p=0.033). High podocalyxin expression associated significantly with higher risk of death from PDAC by both the polyclonal antibody (hazard ratio (HR) = 1.62; 95% confidence interval (CI) 1.12-2.33; p=0.01) and the monoclonal antibody (HR = 2.10, 95% CI 1.38-3.20; p<0.001). The results remained significant in multivariate analysis, adjusted for age, gender, stage, lymph node ratio (≥/< 20%), and perivascular invasion (respectively as HR = 2.03; 95% CI 1.32-3.13, p=0.001; and as HR = 2.36; 95% CI 1.47-3.80, p<0.001).

Conclusion

We found podocalyxin to be an independent factor for poor prognosis in PDAC. To our knowledge, this is the first such report of its prognostic value.

Bmi1 essentially mediates podocalyxin-enhanced Cisplatin chemoresistance in oral tongue squamous cell carcinoma

Oral tongue squamous cell carcinoma (OTSCC) is one of the most common head and neck cancers. Innate or acquired resistance to cisplatin, a standard chemotherapy agent for OTSCC, is common in patients with OTSCC. Understanding the molecular basis for cisplatin chemoresistance in OTSCC cells may serve as a basis for identification of novel therapeutic targets. Podocalyxin (PODXL) has been found critical for malignant progression in a variety of cancers. Bmi1 has recently been found to induce cell apoptosis and cisplatin chemosensitivity in OTSCC cells. In this study, we explored the interaction between PODXL and Bmi1 in OTSCC cells, and assessed its impact on OTSCC cell chemoresistance to cisplatin. PODXL and/or Bmi1 were stably overexpressed or knocked down in SCC-4 and Tca8113 human OTSCC cells. Overexpression of PODXL in both cell lines markedly elevated the expression level of Bmi1 and the half maximal inhibitory concentration (IC50) of cisplain and reduced cisplatin-induced cell apoptosis, which was abolished by knockdown of Bmi1 or a selective focal adhesion kinase (FAK) inhibitor. On the other hand, knockdown of PODXL significantly decreased the Bmi1 expression level and cisplatin IC50 and increased cisplatin-induced cell apoptosis, which was completely reversed by overexpression of Bmi1. While overexpression and knockdown of PODXL respectively increased and decreased the FAK activity, Bmi1 showed no significant effect on the FAK activity in OTSCC cells. In addition, overexpression of PODXL markedly elevated the stability of Bmi1 mRNA, which was abolished by a selective FAK inhibitor. In conclusion, this study provides the first evidence that PODXL up-regulates the expression level of Bmi1 in OTSCC cells by increasing the stability of Bmi1 mRNA through a FAK-dependent mechanism; this effect leads to enhanced cisplatin chemoresistance in OTSCC cells. This study adds new insights into the molecular mechanisms underlying OTSCC chemoresistance.

Podocalyxin enhances breast tumor growth and metastasis and is a target for monoclonal antibody therapy

Introduction

Podocalyxin (gene name PODXL) is a CD34-related sialomucin implicated in the regulation of cell adhesion, migration and polarity. Upregulated expression of podocalyxin is linked to poor patient survival in epithelial cancers. However, it is not known if podocalyxin has a functional role in tumor progression.

Methods

We silenced podocalyxin expression in the aggressive basal-like human (MDA-MB-231) and mouse (4T1) breast cancer cell lines and also overexpressed podocalyxin in the more benign human breast cancer cell line, MCF7. We evaluated how podocalyxin affects tumorsphere formation in vitro and compared the ability of podocalyxin-deficient and podocalyxin-replete cell lines to form tumors and metastasize using xenogenic or syngeneic transplant models in mice. Finally, in an effort to develop therapeutic treatments for systemic cancers, we generated a series of antihuman podocalyxin antibodies and screened these for their ability to inhibit tumor progression in xenografted mice.

Results

Although deletion of podocalyxin does not alter gross cell morphology and growth under standard (adherent) culture conditions, expression of PODXL is required for efficient formation of tumorspheres in vitro. Correspondingly, silencing podocalyxin resulted in attenuated primary tumor growth and invasiveness in mice and severely impaired the formation of distant metastases. Likewise, in competitive tumor engraftment assays where we injected a 50:50 mixture of control and shPODXL (short-hairpin RNA targeting PODXL)-expressing cells, we found that podocalyxin-deficient cells exhibited a striking decrease in the ability to form clonal tumors in the lung, liver and bone marrow. Finally, to validate podocalyxin as a viable target for immunotherapy, we screened a series of novel antihuman podocalyxin antibodies for their ability to inhibit tumor progression in vivo. One of these antibodies, PODOC1, potently blocked tumor growth and metastasis.

Conclusions

We show that podocalyxin plays a key role in the formation of primary tumors and distant tumor metastasis. In addition, we validate podocalyxin as potential target for monoclonal antibody therapy to inhibit primary tumor growth and systemic dissemination.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-015-0562-7) contains supplementary material, which is available to authorized users.

Preparation of Proper Immunogen by Cloning and Stable Expression of cDNA coding for Human Hematopoietic Stem Cell Marker CD34 in NIH-3T3 Mouse Fibroblast Cell Line

PURPOSE

Transmembrane CD34 glycoprotein is the most important marker for identification, isolation and enumeration of hematopoietic stem cells (HSCs). We aimed in this study to clone the cDNA coding for human CD34 from KG1a cell line and stably express in mouse fibroblast cell line NIH-3T3. Such artificial cell line could be useful as proper immunogen for production of mouse monoclonal antibodies.

METHODS

CD34 cDNA was cloned from KG1a cell line after total RNA extraction and cDNA synthesis. Pfu DNA polymerase-amplified specific band was ligated to pGEMT-easy TA-cloning vector and sub-cloned in pCMV6-Neo expression vector. After transfection of NIH-3T3 cells using 3 μg of recombinant construct and 6 μl of JetPEI transfection reagent, stable expression was obtained by selection of cells by G418 antibiotic and confirmed by surface flow cytometry.

RESULTS

1158 bp specific band was aligned completely to reference sequence in NCBI database corresponding to long isoform of human CD34. Transient and stable expression of human CD34 on transfected NIH-3T3 mouse fibroblast cells was achieved (25% and 95%, respectively) as shown by flow cytometry.

CONCLUSION

Cloning and stable expression of human CD34 cDNA was successfully performed and validated by standard flow cytometric analysis. Due to murine origin of NIH-3T3 cell line, CD34-expressing NIH-3T3 cells could be useful as immunogen in production of diagnostic monoclonal antibodies against human CD34. This approach could bypass the need for purification of recombinant proteins produced in eukaryotic expression systems.

Podocalyxin promotes glioblastoma multiforme cell invasion and proliferation by inhibiting angiotensin-(1-7)/Mas signaling

Podocalyxin (PODX) reportedly enhances invasion in many human cancers including glioblastoma multiforme (GBM). Recent studies have shown that the local renin-angiotensin system (RAS) in tumor environment contributes significantly to tumor progression. As a counter-regulatory axis in RAS, angiotensin (Ang)-(1-7)/Mas signaling has been shown to inhibit the growth and invasiveness of several human cancers including GBM. In the present study, we examined the crosstalk between PODX and Ang-(1-7)/Mas signaling in GBM cells, and assessed its impact on GBM cell invasion and proliferation. A strong negative correlation between the expression of PODX and Mas in GBM tumor tissues from 10 consecutive patients (r=-0.768, p<0.01) was observed. The stable overexpression of PODX in LN-229 and U-118 MG human GBM cells decreased the expression of Mas at the mRNA and protein levels, which led to decreased density of Ang-(1-7)-binding Mas on the cell membrane. This effect was completely abolished by selective phosphatidylinositol 3-kinase (PI3K) inhibitor BKM120. By contrast, the stable knockdown of PODX in LN-229 and U-118 MG cells increased the expression of Mas and the density of Ang-(1-7)-binding Mas on the cell membrane. Overexpression and knockdown of PODX respectively reversed and enhanced the inhibitory effects of Ang-(1-7) on the expression/activity of matrix metalloproteinase-9 and cell invasion and proliferation in GBM cells. Although the overexpression of Mas showed no significant effect on the promoting effect of PODX on GBM cell invasion and proliferation in the absence of Ang-(1-7), it completely eliminated the effect of PODX in the presence of Ang-(1-7). In conclusion, to the best of our knowledge, the present study provided the first evidence that PODX inhibits Ang-(1-7)/Mas signaling by downregulating the expression of Mas through a PI3K-dependent mechanism in GBM cells. This effect led to enhanced GBM cell invasion and proliferation. The results of this study add new insight into the biological functions of PODX and the molecular mechanisms underlying GBM progression.

Involvement of platelet-tumor cell interaction in immune evasion. Potential role of podocalyxin-like protein 1

Besides their essential role in hemostasis and thrombosis, platelets are involved in the onset of cancer metastasis by interacting with tumor cells. Platelets release secretory factors that promote tumor growth, angiogenesis, and metastasis. Furthermore, the formation of platelet-tumor cell aggregates in the bloodstream provides cancer cells with an immune escape mechanism by protecting circulating malignant cells from immune-mediated lysis by natural killer (NK) cells. Platelet-tumor cell interaction is accomplished by specific adhesion molecules, including integrins, selectins, and their ligands. Podocalyxin-like protein 1 (PCLP1) is a selectin-ligand protein in which overexpression has been associated with several aggressive cancers. PCLP1 expression enhances cell adherence to platelets in an integrin-dependent process and through the interaction with P-selectin expressed on activated platelets. However, the involvement of PCLP1-induced tumor-platelet interaction in tumor immune evasion still remains unexplored. The identification of selectin ligands involved in the interaction of platelets with tumor cells may provide help for the development of effective therapies to restrain cancer cell dissemination. This article summarizes the current knowledge on molecules that participate in platelet-tumor cell interaction as well as discusses the potential role of PCLP1 as a molecule implicated in tumor immune evasion.

Cancer stem cells: progress and challenges in lung cancer

The identification of a subpopulation of tumor cells with stem cell-like characteristics first in hematological malignancies and later in solid tumors has emerged into a novel field of cancer research. It has been proposed that this aberrant population of cells now called "cancer stem cells" (CSCs) drives tumor initiation, progression, metastasis, recurrence, and drug resistance. CSCs have been shown to have the capacity of self-renewal and multipotency. Adopting strategies from the field of stem cell research has aided in identification, localization, and targeting of CSCs in many tumors. Despite the huge progress in other solid tumors such as brain, breast, and colon cancers no substantial advancements have been made in lung cancer. This is most likely due to the current rudimentary understanding of lung stem cell hierarchy and heterogeneous nature of lung disease. In this review, we will discuss the most recent findings related to identification of normal lung stem cells and CSCs, pathways involved in regulating the development of CSCs, and the importance of the stem cell niche in development and maintenance of CSCs. Additionally, we will examine the development and feasibility of novel CSC-targeted therapeutic strategies aimed at eradicating lung CSCs.

Expression of caveolin-1 and podocalyxin in rat lungs challenged with 2-kDa macrophage-activating lipopeptide and Flt3L

Caveolin-1 is one of the important regulators of vascular permeability in inflamed lungs. Podocalyxin is a CD34 protein expressed on vascular endothelium and has a role in podocyte development in the kidney. Few data are available on the expression of caveolin-1 and podocalyxin in lungs challenged with Toll-like receptor 2 (TLR2) agonists such as mycoplasma-derived macrophage activating lipopeptide or with immune modulators such as Fms-like tyrosine kinase receptor-3 ligand (Flt3L), which expands dendritic cell populations in the lung. Because of the significance of pathogen-derived molecules that act through TLR2 and of the role of immune modulators in lung physiology, we examine the immunohistochemical expression of caveolin-1 and podocalyxin in lungs from rats challenged with a 2-kDa macrophage-activating lipopeptide (MALP-2) and Flt3L. Normal rat lungs expressed caveolin-1 in alveolar septa, vascular endothelium and airway epithelium, especially along the lateral borders of epithelial cells but not in alveolar macrophages. MALP-2 and Flt3L decreased and increased, respectively, the expression of caveolin-1. Caveolin-1 expression seemed to increase in microvessels in bronchiole-associated lymphoid tissue (BALT) in Flt3L-challenged lungs but not in normal or MALP-2-treated lungs. Podocalyxin was absent in the epithelium and alveolar macrophages but was present in the vasculature of control, Flt3L- and MALP-2-treated rats. Compared with control and MALP-2-treated rats, Flt3L-treated lungs showed greater expression of podocalyxin in BALT vasculature and at the interface of monocytes and the endothelium. These immunohistochemical data describing the altered expression of caveolin-1 and podocalyxin in lungs treated with MALP-2 or Flt3L encourage further mechanistic studies on the role of podocalyxin and caveolin-1 in lung inflammation.

Podocalyxin-like protein is expressed in glioblastoma multiforme stem-like cells and is associated with poor outcome

Glioblastoma multiforme (GBM) is the most common primary malignant adult brain tumor and is associated with poor survival. Recently, stem-like cell populations have been identified in numerous malignancies including GBM. To identify genes whose expression is changed with differentiation, we compared transcript profiles from a GBM oncosphere line before and after differentiation. Bioinformatic analysis of the gene expression profiles identified podocalyxin-like protein (PODXL), a protein highly expressed in human embryonic stem cells, as a potential marker of undifferentiated GBM stem-like cells. The loss of PODXL expression upon differentiation of GBM stem-like cell lines was confirmed by quantitative real-time PCR and flow cytometry. Analytical flow cytometry of numerous GBM oncosphere lines demonstrated PODXL expression in all lines examined. Knockdown studies and flow cytometric cell sorting experiments demonstrated that PODXL is involved in GBM stem-like cell proliferation and oncosphere formation. Compared to PODXL-negative cells, PODXL-positive cells had increased expression of the progenitor/stem cell markers Musashi1, SOX2, and BMI1. Finally, PODXL expression directly correlated with increasing glioma grade and was a marker for poor outcome in patients with GBM. In summary, we have demonstrated that PODXL is expressed in GBM stem-like cells and is involved in cell proliferation and oncosphere formation. Moreover, high PODXL expression correlates with increasing glioma grade and decreased overall survival in patients with GBM.

Elevated expression of podocalyxin is associated with lymphatic invasion, basal-like phenotype, and clinical outcome in axillary lymph node-negative breast cancer

Lymphatic invasion (LVI) is associated with disease recurrence in axillary node-negative (ANN) breast cancer. Using gene expression profiling of 105 ANN tumors, we found that podocalyxin (PODXL) was more highly expressed in tumors with LVI (LVI+) than in those without LVI (LVI-). Differences in PODXL expression were validated using real-time polymerase chain reaction as well as by immunohistochemistry in an independent set of 652 tumors on tissue microarrays. Disease-free survival (DFS) analyses were conducted for association of high PODXL protein expression with risk of distant recurrence overall and within breast cancer subtypes using both Cox and cure-rate models. High PODXL expression was associated with poor prognosis features including large tumor size, high histological grade, estrogen and progesterone receptor negativity, and with clinical alterations characteristic of the basal-like breast cancer phenotype. Surprisingly, despite having other poor prognosis characteristics, women with high PODXL expressing tumors had better long-term DFS in multivariate analysis with traditional clinicopathologic factors including LVI and HER2 status (P = 0.001). PODXL has the potential to be a useful biomarker for identifying good prognosis patients in characteristically poor prognosis breast cancer groups and may impact treatment of women with this disease.

Immunohistochemical evaluation of podocalyxin expression in glomerulopathies associated with nephrotic syndrome

It is now well established that morphological change of podocytes is closely correlated to the development of proteinuria. The aim of this study was to investigate the role of podocalyxin, a major podocyte protein, in the pathogenesis of glomerulopathies primarily associated with the nephrotic syndrome. Immunohistochemical expression of podocalyxin has been evaluated in 51 renal samples, including healthy controls, patients with podocytopathies (minimal change disease [MCD], focal segmental glomerulosclerosis [FSGS]) and membranous glomerulopathy (MG). A computerized image analysis program has been used. Statistical analysis was performed using analysis of variance and Bonferroni tests. Immunohistochemical expression of podocalyxin has been observed within the podocytes of healthy controls. In MCD, podocalyxin expression was globally reduced despite the normal appearance of the glomeruli. In FSGS, podocalyxin loss was observed in both the segmental sclerotic and the nonsclerotic areas being significantly more prominent in the former. Reduction of podocalyxin in MG was demonstrated for the first time immunohistochemically. The percentage of the stained area was statistical significantly higher in the controls than in each pathologic group. However, among pathologic groups (FSGS, MCD, MG), there was no statistically significant difference. This is one of the few studies investigating podocalyxin immunohistochemical expression in glomerulopathies associated with nephrotic syndrome. The observed reduction in podocalyxin expression suggests that it constitutes a target molecule in nephrotic syndrome pathogenesis regardless of the underlying cause.

Podocalyxin EBP50 ezrin molecular complex enhances the metastatic potential of renal cell carcinoma through recruiting Rac1 guanine nucleotide exchange factor ARHGEF7

Podocalyxin was initially identified in glomerular podocytes to critically maintain the structural and functional integrity of the glomerular ultrafiltrative apparatus. Lately, it has emerged as a malignant marker in tumors arising from a variety of tissue origins. By immunohistochemistry, we identified that 9.6% of renal cell carcinoma patients overexpress this protein. This subset of patients had significantly shorter disease-specific and overall survivals, and, importantly, we established podocalyxin overexpression as an independent prognostic factor for latent distant metastasis with multivariate analysis. Podocalyxin down-regulation by small interfering RNA led to defective migration in model renal tubular cells, which was corrected by re-expression of podocalyxin. The activity of the small GTPase Rac1, a well-characterized modulator of cell migration, was diminished by podocalyxin knock-down. Conversely, podocalyxin overexpression in human embryonic kidney cells up-regulated Rac1 activity, which depended on a complex formed by podocalyxin, ERM-binding phosphoprotein 50, ezrin, and ARHGEF7, a Rac1 activator. Therefore, podocalyxin can serve as a biomarker to identify renal cell carcinoma patients with higher metastatic potential for more aggressive intervention at earlier clinical stages.

The role of podocalyxin in health and disease

Podocalyxin, a sialomucin most closely related to CD34 and endoglycan, is expressed by kidney podocytes, hematopoietic progenitors, vascular endothelia, and a subset of neurons; aberrant expression has recently been implicated in a range of cancers. Through interactions with several intracellular proteins and at least one extracellular ligand, podocalyxin regulates both adhesion and cell morphology. In the developing kidney, podocalyxin plays an essential role in the formation and maintenance of podocyte foot processes, and its absence results in perinatal lethality. Podocalyxin expression in the hematopoietic system correlates with cell migration and the seeding of new hematopoietic tissues. In addition, it is abnormally expressed in subsets of breast, prostate, liver, pancreatic, and kidney cancer as well as leukemia. Strikingly, it is often associated with the most aggressive cases, and it is likely involved in metastasis. Thus, a thorough investigation of the normal activities of podocalyxin may facilitate the development of new cancer treatment strategies.

Novel functions of the CD34 family

For almost 30 years, the cell-surface protein CD34 has been widely used as a marker to assist in the identification and Summary isolation of hematopoietic stem cells (HSCs) and progenitors in preparation for bone-marrow transplantation. In addition, it has increasingly been used as a marker to help identify other tissue-specific stem cells, including muscle satellite cells and epidermal precursors. Despite its utility as a stem-cell marker, however, the function of CD34 has remained remarkably elusive. This is probably because: (1) it is subject to a range of tissue-specific post-transcriptional and post-translational modifications that are expected to alter its function dramatically; (2) the simple interpretation of CD34 gain- and loss-of-function experiments has been confounded by the overlapping expression of the two recently discovered CD34-related proteins podocalyxin and endoglycan; and (3) there has been a glaring lack of robust in vitro and in vivo functional assays that permit the structural and functional analysis of CD34 and its relatives. Here, we provide a brief review of the domain structure, genomic organization, and tissue distribution of the CD34 family. We also describe recent insights from gain- and loss-of-function experiments and improved assays, which are elucidating a fascinating role for these molecules in cell morphogenesis and migration.

CNTO 530 functions as a potent EPO mimetic via unique sustained effects on bone marrow proerythroblast pools

Anemia as associated with numerous clinical conditions can be debilitating, but frequently can be treated via administration of epoetin-alfa, darbepoietin-alfa, or methoxy-PEG epoetin-beta. Despite the complexity of EPO-EPO receptor interactions, the development of interesting EPO mimetic peptides (EMPs) also has been possible. CNTO 530 is one such novel MIMETIBODY Fc-domain dimeric EMP fusion protein. In a mouse model, single-dose CNTO 530 (unlike epoetin-alfa or darbepoietin-alfa) bolstered red cell production for up to 1 month. In 5-fluorouracil and carboplatin-paclitaxel models, CNTO 530 also protected against anemia with unique efficiency. These actions were not fully accounted for by half-life estimates, and CNTO 530 signaling events therefore were studied. Within primary bone marrow erythroblasts, kinetics of STAT5, ERK, and AKT activation were similar for CNTO 530 and epoetin-alfa. p70S6K activation by CNTO 530, however, was selectively sustained. In vivo, CNTO 530 uniquely stimulated the enhanced formation of PODXL(high)CD71(high) (pro)erythroblasts at frequencies multifold above epoetin-alfa or darbepoietin-alfa. CNTO 530 moreover supported the sustained expansion of a bone marrow-resident Kit(neg)CD71(high)Ter119(neg) progenitor pool. Based on these distinct erythropoietic and EPOR signaling properties, CNTO 530 holds excellent promise as a new EPO mimetic.

Ubiquitous yet distinct expression of podocalyxin on vascular surfaces in normal and tumor tissues in the rat

BACKGROUND/AIMS

The vasculature has become an important target in the development of therapies for increasing numbers of human diseases, yet there are few reliable markers available to identify the endothelium in rodent models. We have characterized the expression, subcellular localization and accessibility of the rat pan-endothelial marker podocalyxin (podxl) using a newly developed monoclonal antibody (mAb), G278.

METHODS

podxl expression and accessibility to binding by G278 were determined in the rat by a variety of experimental approaches.

RESULTS

mAb G278 reliably immunostained blood vessels of all types and of every size in fresh-frozen, fixed-frozen and paraffin-embedded sections of all tissues, but did not stain lymphatic vessels. Western blotting, in vivo imaging and biodistribution analyses demonstrated that the highest levels of endothelial podxl were found in the lung and heart. We also determined that podxl is not enriched in caveolae and that its expression can be modulated in the tumor microenvironment.

CONCLUSION

Our study shows that podxl is a better identifier of rat endothelia than are some of the more commonly used markers and that mAb G278 is a robust antibody for use not only in identifying rat blood vessels but also as a tool to elucidate podxl function.

Podocalyxin-like protein is an E-/L-selectin ligand on colon carcinoma cells: comparative biochemical properties of selectin ligands in host and tumor cells

Selectins facilitate metastasis and tumor cell arrest in the microvasculature by mediating binding of selectin-expressing host cells to ligands on tumor cells. We recently identified CD44 variant isoforms as functional P-, but not E-/L-, selectin ligands on colon carcinoma cells. Furthermore, a approximately 180-kDa sialofucosylated glycoprotein(s) mediated selectin binding in CD44-knockdown cells. Using immunoaffinity chromatography and tandem mass spectrometry, we identify podocalyxin-like protein (PCLP) as an alternative selectin ligand. Blot rolling and cell-free flow-based adhesion assays disclose that PCLP on LS174T colon carcinoma cells possesses E-/L-, but not P-, selectin binding activity. The selectin-binding determinants on LS174T PCLP are non-MECA-79-reactive sialofucosylated structures displayed on O-linked glycans, distinct from the MECA-79-reactive O-glycans on PCLP expressed by high endothelial venules, which is an L-selectin ligand. PCLP on CD44-knockdown LS174T cells exhibits higher HECA-452 immunoreactivity than PCLP on wild-type cells, suggesting that PCLP functions as an alternative acceptor for selectin-binding glycans. The enhanced expression of HECA-452 reactivity on PCLP from CD44-knockdown cells correlates with the increased avidity of PCLP for E- but not L-selectin. The novel finding that PCLP is an E-/L-selectin ligand on carcinoma cells offers a unifying perspective on the apparent enhanced metastatic potential associated with tumor cell PCLP overexpression and the role of selectins in metastasis.

Glomerular epithelial cells in the urine: what has to be done to make them worthwhile?

The significance of the native urine sediment in the differential of glomerular diseases needs no further comment. However, the question arises whether it could be useful to develop a more specific diagnostic approach to identify the origin of renal epithelial cells that can be detected in the urine sediments as well. Especially the detection of podocytes in the urine could be a valuable noninvasive method to get information about the disease activity or disease type and could be used as a follow-up after a biopsy in an outpatient setting. So far, there are only a few studies that analyzed the clinical relevance of renal epithelial cells in the urine systematically or prospectively. The reason for this could be the nature of the material since it will remain unclear whether detachment and changes in the urine milieu have a direct effect on the expression of marker proteins on the detected cells. Dedifferentiation or transdifferentiation of cells that goes along with changed marker expression is certainly also part of the underlying disease process. This review summarizes the available information on marker proteins that have been successfully used in the diagnostic of "podocytes" in the urine. Furthermore, it gives an overview of marker expression on podocytes in situ in development and disease and examines the role of glomerular epithelial shedding in the urine at the interface of basic science and clinical medicine.

Stem cell marker expression in small cell lung carcinoma and developing lung tissue

Histopathologic and clinical findings suggest that small cell lung cancer is derived from a multipotent proximal airway epithelial cell. In order to investigate the histogenetic origin of small cell lung cancer, we compared stem cell marker expression in human fetal lung tissue, human adult bronchial tissue, and a cohort of 64 small cell lung cancers. Supporting derivation of a multipotent precursor cell, 87.5% (56/64) of small cell lung cancers showed a dot-like expression of podocalyxin-like protein 1 (PODXL-1), a marker of embryonic and hematopoetic stem cells. Of small cell lung cancers, 98.4% (63/64) ubiquitously expressed Bmi-1, a key player in self-renewal of stem cells. Oct4 and AP2gamma were not expressed. Although podocalyxin-like protein 1 did not correlate with p53 or Wilms tumor suppressor 1, known regulators of podocalyxin-like protein 1, we could demonstrate demethylated CpG islands in the podocalyxin-like protein 1 promoter in small cell lung cancer, indicating epigenetic regulation. During fetal lung development and within adult bronchial mucosa, Bmi-1 was expressed ubiquitously. In contrast, podocalyxin-like protein 1 was detected in few stromal cells during the pseudoglandular phase (n = 7) and, importantly, in clustered epithelial cells within proximal bronchi and the trachea during the canalicular phase (n = 10). Interestingly, podocalyxin-like protein 1 was not expressed in normal or metaplastic adult bronchial epithelium (n = 36) but was expressed in sparse epithelial cells in half of the cases of normal tumor adjacent bronchial mucosa (20/40). Taken together, we show that small cell lung cancers and clustered epithelial cells in developing proximal bronchi share the expression of stem cell markers, suggesting a possible histogenetic link.

Podocalyxin expression in malignant astrocytic tumors

Podocalyxin is an anti-adhesive mucin-like transmembrane sialoglycoprotein that has been implicated in the development of aggressive forms of cancer. Podocalyxin is also known as keratan sulfate (KS) proteoglycan. Recently, we revealed that highly sulfated KS or another mucin-like transmembrane sialoglycoprotein podoplanin/aggrus is upregulated in malignant astrocytic tumors. The aim of this study is to examine the relationship between podocalyxin expression and malignant progression of astrocytic tumors. In this study, 51 astrocytic tumors were investigated for podocalyxin expression using immunohistochemistry, Western blot analysis, and quantitative real-time PCR. Immunohistochemistry detected podocalyxin on the surface of tumor cells in six of 14 anaplastic astrocytomas (42.9%) and in 17 of 31 glioblastomas (54.8%), especially around proliferating endothelial cells. In diffuse astrocytoma, podocalyxin expression was observed only in vascular endothelial cells. Podocalyxin might be associated with the malignant progression of astrocytic tumors, and be a useful prognostic marker for astrocytic tumors.

Expression of podocalyxin enhances the adherence, migration, and intercellular communication of cells

Podocalyxin (PODXL) is an anti-adhesive glycoprotein expressed abundantly in the epithelial cells of kidney glomeruli. In contrast, we report herein that expression of podocalyxin(GFP) (PODXL(GFP)) in CHO cells increased the adherence to immobilized fibronectin, spreading, and migration. The transient knockdown of PODXL or the expression of PODXL lacking the cytosolic carboxyterminal domain (PODXL-Delta(451)) inhibited cell adherence. Moreover, the effect of PODXL was prevented by the ectodomain of podocalyxin (PODXL-Delta(429)), by RGD peptides, or by inhibitors of the vitronectin receptor (alphavbeta3). CHO-PODXL(GFP) also showed adherence to human vascular endothelial cells (HUVEC), exhibiting polarization of granular PODXL and emission of long and thin, spike-like, protrusions with PODXL granules progressing along. We found PODXL colocalized with beta1 integrins at membrane ruffle regions on the leading edge of the cell and a blocking beta1 mAb prevented the spreading of cells. PODXL was also associated with submembrane actin in lamellipodia ruffles, or with vinculin at cell protrusions. The proadhesive effects of PODXL were absent in sialic acid deficient O-glycomutant CHO cells. To conclude, we present evidence indicating that human PODXL enhances the adherence of cells to immobilized ligands and to vascular endothelial cells through a mechanism(s) dependent on the activity of integrins.

Diagnostic Utility of WT1 Immunostaining in Ovarian Sertoli Cell Tumor

WT1, the Wilms tumor gene product, can be expressed in various tumors from different anatomic sites, including some types of ovarian tumors. Regarding the latter, most studies have focused on surface epithelial-stromal tumors in which serous carcinomas are usually positive and endometrioid carcinomas are negative. Very few studies have specifically investigated this marker in ovarian sex cord-stromal tumors; however, limited data in the literature suggest that WT1 may be frequently expressed in sex cord-stromal tumors. As pure Sertoli cell tumor can be in the histologic differential diagnosis of endometrioid tumors (particularly borderline tumor and carcinoma) and carcinoid, immunostaining for WT1 might be of diagnostic value. Immunohistochemical staining for WT1 was performed in 108 ovarian tumors: pure Sertoli cell tumor (n=26), endometrioid borderline tumor (n=25), classic well-differentiated endometrioid carcinoma (n=23), sertoliform endometrioid carcinoma (n=12), and carcinoid (n=22). Additionally, inhibin and calretinin immunostaining were performed in all cases of Sertoli cell tumor for purposes of comparing expression with WT1. Extent of immunostaining was scored on a 0 to 4+ semiquantitative scale, and immunohistochemical composite scores based on a combination of extent and intensity of immunostaining were calculated in positive cases (possible range, 1 to 12). Nuclear expression of WT1 was present in 96% of Sertoli cell tumors, 16% of endometrioid borderline tumors, 13% of classic well-differentiated endometrioid carcinomas, 25% of sertoliform endometrioid carcinomas, and 0% of carcinoids. In Sertoli cell tumors, expression was diffuse (>50% of positive cells) in all positive cases. When positive in the non-Sertoli cell tumors, the extent of expression tended to be focal to patchy (50% or less positive cells). In Sertoli cell tumors, inhibin and calretinin were expressed in 96% and 54% of cases, respectively. The extent of expression of inhibin tended to be diffuse, similar to WT1; however, the extent of immunostaining for calretinin tended to be focal to patchy. The immunohistochemical composite scores for WT1, inhibin, and calretinin were 11.2, 7.6, and 4.8, respectively. Coordinate patterns for the extent of expression of WT1, inhibin, and calretinin in pure Sertoli cell tumor showed that all 3 markers were positive in 54% of cases; however, 42% were positive for WT1 and inhibin but negative for calretinin. In cases positive for both WT1 and inhibin, expression of both markers was diffuse in 84% of cases, but WT1 was diffuse while inhibin was focal to patchy in 16% of cases. We conclude that ovarian Sertoli cell tumor should be added to the growing list of WT1-positive tumors. This marker is useful for the distinction of Sertoli cell tumor from endometrioid tumors and carcinoid. The diagnostic utility of WT1 in Sertoli cell tumor is similar to inhibin but better than that of calretinin.

Podocalyxin increases the aggressive phenotype of breast and prostate cancer cells in vitro through its interaction with ezrin

Podocalyxin is an anti-adhesive transmembrane sialomucin that has been implicated in the development of more aggressive forms of breast and prostate cancer. The mechanism through which podocalyxin increases cancer aggressiveness remains poorly understood but may involve the interaction of podocalyxin with ezrin, an established mediator of metastasis. Here, we show that overexpression of podocalyxin in MCF7 breast cancer and PC3 prostate cancer cell lines increased their in vitro invasive and migratory potential and led to increased expression of matrix metalloproteases 1 and 9 (MMP1 and MMP9). Podocalyxin expression also led to an increase in mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) activity. To determine the role of ezrin in these podocalyxin-dependent phenotypic events, we first confirmed that podocalyxin formed a complex with ezrin in MCF7 and PC3 cells. Furthermore, expression of podocalyxin was associated with a changed ezrin subcellular localization and increased ezrin phosphorylation. Transient knockdown of ezrin protein abrogated MAPK and PI3K signaling as well as MMP expression and invasiveness in cancer cells overexpressing podocalyxin. These findings suggest that podocalyxin leads to increased in vitro migration and invasion, increased MMP expression, and increased activation of MAPK and PI3K activity in MCF7 and PC3 cells through its ability to form a complex with ezrin.

Erythropoietin modulation of podocalyxin and a proposed erythroblast niche

Epo's erythropoietic capacity is ascribed largely to its antiapoptotic actions. In part via gene profiling of bone marrow erythroblasts, Epo is now shown to selectively down-modulate the adhesion/migration factors chemokine receptor-4 (Cxcr4) and integrin alpha-4 (Itga4) and to up-modulate growth differentiation factor-3 (Gdf3), oncostatin-M (OncoM), and podocalyxin like-1 (PODXL). For PODXL, Epo dose-dependent expression of this CD34-related sialomucin was discovered in Kit(+)CD71(high) proerythroblasts and was sustained at subsequent Kit(-)CD71(high) and Ter119(+) stages. In vivo, Epo markedly induced PODXL expression in these progenitors and in marrow-resident reticulocytes. This was further associated with a rapid release of PODXL(+) reticulocytes to blood. As studied in erythroblasts expressing minimal Epo receptor (EpoR) alleles, efficient PODXL induction proved dependence on an EpoR-PY343 Stat5 binding site. Moreover, in mice expressing an EpoR-HM F343 allele, compromised Epo-induced PODXL expression correlated with abnormal anucleated red cell representation in marrow. By modulating this select set of cell-surface adhesion molecules and chemokines, Epo is proposed to mobilize erythroblasts from a hypothesized stromal niche and possibly promote reticulocyte egress to blood.

Podocalyxin-like protein 1 expression is useful to differentiate pancreatic ductal adenocarcinomas from adenocarcinomas of the biliary and gastrointestinal tracts

Metastases of adenocarcinomas from the pancreas, liver, and gastrointestinal tract are difficult to distinguish from each other because of their similar morphological and immunohistochemical features. So far, no specific marker for pancreatic ductal adenocarcinomas has been described. Podocalyxin-like protein 1 (PODXL-1) is expressed on vascular endothelium, hematopoietic precursor cells, and renal podocytes. We found that 44% (71/160) of pancreatic ductal adenocarcinomas expressed PODXL-1 in a membranous pattern. There was no expression in intrahepatic cholangiocarcinomas (0/18, P < .001), rarely in adenocarcinomas of the extrahepatic bile ducts (1/13, P = .009), and none in duodenal adenocarcinomas (0/5, P = .070). PODXL-1 expression was seen in only 9% of hepatocellular carcinomas (5/56, P < .001), 9% (4/47, P < .001) of gastric carcinomas, 10% of esophageal adenocarcinomas (2/20, P = .003), and 6% of colonic adenocarcinomas (1/17, P = .001). When used as a differential diagnostic marker, ampullary carcinoma needs to be excluded, as 30% (6/20, P = .24) of ampullary carcinomas stain positive, especially those of the signet-ring type (3/3). Adenocarcinomas of the lung and prostate, and liver metastases of colorectal carcinomas lacked PODXL-1 expression. It is concluded that immunoreactivity for PODXL-1 favors a pancreatic origin if ampullary carcinoma is excluded.

The TRA-1-60 and TRA-1-81 human pluripotent stem cell markers are expressed on podocalyxin in embryonal carcinoma

We have previously identified the cell adhesion protein podocalyxin expressed in a human pluripotent stem cell, embryonal carcinoma (EC), which is a malignant germ cell. Podocalyxin is a heavily glycosylated membrane protein with amino acid sequence homology to the hematopoietic stem cell marker CD34. Since the initial discovery of podocalyxin in a cancerous stem cell, numerous new studies have identified podocalyxin in many different human cancers and in embryonic stem cells lines (ES) derived from human embryos. Embryonal carcinoma, as do all human pluripotent stem cells, expresses TRA-1-60 and TRA-1-81 antigens, and although their molecular identities are unknown, they are commonly used as markers of undifferentiated pluripotent human stem cells. We report here that purified podocalyxin from embryonal carcinoma has binding activity with the TRA-1-60 and TRA-1-81 antibodies. Embryonal carcinoma cells treated with retinoic acid undergo differentiation and lose the TRA-1-60/TRA-1-81 markers from their plasma membrane surface. We show that podocalyxin is modified in the retinoic acid-treated cells and has an apparent molecular mass of 170 kDa on protein blots as compared with the apparent 200-kDa molecular weight form of podocalyxin expressed in untreated cells. Furthermore, the modified form of podocalyxin no longer reacts with the TRA-1-60/TRA-1-81 antibodies. Thus, embryonal carcinoma expresses two distinct forms of podocalyxin, and the larger version is a molecular carrier of the human stem cell-defining antigens TRA-1-60 and TRA-1-81.

Podocalyxin is expressed in normal and leukemic monocytes

We have investigated the expression of podocalyxin in primary cultures of leukemic blast cells from 73 patients with acute myeloid leukemia. Podocalyxin was expressed at moderate levels in 15 patients and at high levels in 13 patients. The analysis of membrane markers showed that Podocalyxin expression in leukemic blasts was associated with a monocytic immunophenotype. Cases of podocalyxin-positive acute myelogenous leukemia had high blast cell counts at diagnosis and elevated CD123, CD135, VLA-4 and CXCR4 expression, features associated with poor prognosis. Podocalyxin expression in leukemic blasts was coupled with the concomitant expression of VEGF-R1, -R2, -R3 and Tie-2, the capacity to release VEGF-A and angiopoietin1 and the ability to differentiate into endothelial cells under appropriate culture conditions. These findings show that podocalyxin is a marker of acute myeloid leukemia with a monocytic phenotype and suggest that podocalyxin-positive cases of acute myeloid leukemia originate from the malignant transformation of progenitors common to the myeloid and endothelial lineages. These observations suggest a possible relationship between the monocytic lineage and podocytes.

Role of transcription factor Sp1 and CpG methylation on the regulation of the human podocalyxin gene promoter

Background

Podocalyxin (podxl) is a heavily glycosylated transmembrane protein mainly found on the apical membrane of rat podocytes and also in endothelial, hematopoietic, and tumor cells. Despite of its interest no much is known about the transcriptional regulation of podxl in different cells. Thus, we aimed at studying the functional features of the 5'-regulatory region of the human Podxl gene.

Results

The promoter region of the human Podxl gene has been cloned and its structure and function were analyzed. The primary DNA sequence is rich in G+C and is devoid of TATA or CAAT boxes. The sequence contains recognition sites for several putative transcription factors; however, the basic promoter activity seems to rely entirely on Sp1 transcription factor since supershift analysis was positive only for this factor. The region encompassed by 66 to -111 nts conferred the minimal transcriptional activity that increases as the number of Sp1 sites augmented with the length of the promoter fragment. In Sp1-lacking insect cells the Podxl promoter constructs showed activity only if cotransfected with an Sp1 expression plasmid. Finally, mutation of the Sp1 sites reduced the promoter activity.

We analyzed whether methylation of the CpG dinucleotides present in the first ~600 nts of the promoter region of Podxl could explain the variable rates of expression in different types of cells. Inactivation of methyltransferases by 5'-aza-2'deoxicitidine showed a dose-dependent increase in the podxl content. Moreover, in vitro methylation of the promoter constructs -111,-181 and -210 led to an almost complete reduction of the promoter activity. A correlation was found between the degree of methylation of the CpG promoter dinucleotides and the rate of podxl expression in different cell lines.

Conclusion

Our results indicate that transcriptional regulation of Podxl is supported primarily by Sp1 site(s) and that DNA-methylation of the CpG promoter islands contributes to control the tissue specific expression of podxl.

Podocalyxin variants and risk of prostate cancer and tumor aggressiveness

We previously reported linkage of a prostate cancer tumor aggressiveness locus to chromosome 7q32-q33, a region also associated with a high frequency of allelic imbalance in prostate tumors. The smallest region of allelic imbalance contains the podocalyxin-like (PODXL) gene, which we evaluate here as a candidate prostate cancer aggressiveness gene mapping to 7q32-q33. DNA from probands of linked families was examined for germ-line mutations in PODXL. A variable in-frame deletion, four missense variants and two nonsense variants were identified in linked men. Variants that affected amino acid sequence were further evaluated for association with risk of prostate cancer and tumor aggressiveness in a family-based case-control population (439 cases and 479 sibling controls). The presence of any single in-frame deletion was positively associated with prostate cancer [odds ratio (OR)=2.14, 95% confidence interval (95%CI)=1.09-4.20, P=0.03] and the presence of two copies of any deletion further increased risk (OR=2.58, 95%CI=1.23-5.45, P=0.01). This finding was strengthened when stratifying among men with more aggressive disease (high grade or stage): OR=3.04 for one deletion (95%CI=1.01-9.15) and OR=4.42 for two deletions (95%CI=1.32-14.85, P=0.02). A weak positive association was also observed between prostate cancer risk and PODXL variant 340A (in linkage disequilibrium with another variant, 587T) (OR=1.48, 95%CI=1.02-2.14, P=0.04). These results implicate PODXL as a candidate prostate cancer tumor aggressiveness gene mapping to chromosome 7q32-q33.