Prospero Homeobox Research Articles

Transcriptional regulation of podoplanin expression by Prox1 in lymphatic endothelial cells

Transcription factor prospero homeobox 1 (Prox-1) and podoplanin (PDPN), mucin-type transmembane protein, are both constantly expressed in lymphatic endothelial cells (LECs) and appear to function in an LEC-autonomous manner. Mice globally lacking PDPN (Pdpn-/-) develop abnormal and blood-filled lymphatic vessels that highly resemble those in inducible mice lacking Prox-1 (Prox1-/-). Prox1 has also been reported to induce PDPN expression in cultured ECs. Thus, we hypothesize that PDPN functions downstream of Prox1 and that its expression is regulated by Prox1 in LECs at the transcriptional level. We first identified four putative binding elements for Prox1 in the 5’ upstream regulatory region of Pdpn gene and found that Prox1 directly binds to the 5’ regulatory sequence of Pdpn gene in LECs by chromatin immunoprecipitation assay. DNA pull down assay confirmed that Prox1 binds to the putative binding element. In addition, luciferase reporter assay indicated that Prox1 binding to the 5’ regulatory sequence of Pdpn regulates Pdpn gene expression. We are therefore the first to experimentally demonstrate that Prox1 regulates PDPN expression at the transcriptional level in the lymphatic vascular system.

Bone marrow-derived cells are implicated as a source of lymphatic endothelial progenitors in human breast cancer

Bone marrow-derived endothelial progenitor cells (EPCs) infiltrate into sites of neovascularization in adult tissues and mature into functional blood endothelial cells (BECs) during a process called vasculogenesis. Human marrow-derived EPCs have recently been reported to display a mixed myeloid and lymphatic endothelial cell (LEC) phenotype during inflammation-induced angiogenesis; however, their role in cancer remains poorly understood. We report the in vitro differentiation of human cord blood CD133+CD34+ progenitors into podoplanin+ cells expressing both myeloid markers (CD11b, CD14) and the canonical LEC markers vascular endothelium growth factor receptor 3 (VEGFR-3), lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), and prospero homeobox 1 (PROX-1). These podoplanin+ cells displayed sprouting behavior comparable to that of LECs in vitro and a dual hemangiogenic and lymphangiogenic activity in vivo in an endothelial cell sprouting assay and corneal vascularization assay, respectively. Furthermore, these cells expressed vascular endothelium growth factor (VEGF) family members A, -C, and -D. Thus, bone-marrow derived EPCs stimulate hemangiogenesis and lymphangiogenesis through their ability to differentiate into LECs and to produce angiogenic factors. Importantly, plasma from patients with breast cancer induced differentiation of CD34+ cord blood progenitors into hemangiogenic and lymphangiogenic CD11b+ myeloid cells, whereas plasma from healthy women did not have this effect. Consistent with these findings, circulating CD11b+ cells from breast cancer patients, but not from healthy women, displayed a similar dual angiogenic activity. Taken together, our results show that marrow-derived EPCs become hemangiogenic and lymphangiogenic upon exposure to cancer plasma. These newly identified functions of bone-marrow derived EPCs are expected to influence the diagnosis and treatment of breast cancer.

Novel characterization and live imaging of Schlemm's canal expressing Prox-1.

Schlemm's canal is an important structure of the conventional aqueous humor outflow pathway and is critically involved in regulating the intraocular pressure. In this study, we report a novel finding that prospero homeobox protein 1 (Prox-1), the master control gene for lymphatic development, is expressed in Schlemm's canal. Moreover, we provide a novel in vivo method of visualizing Schlemm's canal using a transgenic mouse model of Prox-1-green fluorescent protein (GFP). The anatomical location of Prox-1+ Schlemm's canal was further confirmed by in vivo gonioscopic examination and ex vivo immunohistochemical analysis. Additionally, we show that the Schlemm's canal is distinguishable from typical lymphatic vessels by lack of lymphatic vessel endothelial hyaluronan receptor (LYVE-1) expression and absence of apparent sprouting reaction when inflammatory lymphangiogenesis occurred in the cornea. Taken together, our findings offer new insights into Schlemm's canal and provide a new experimental model for live imaging of this critical structure to help further our understanding of the aqueous humor outflow. This may lead to new avenues toward the development of novel therapeutic intervention for relevant diseases, most notably glaucoma.

Impact of an Altered PROX1 Expression on Clinicopathology, Prognosis and Progression in Renal Cell Carcinoma

The transcription factor PROX1 (prospero homeobox 1) has a critical role in the development of various organs, and has been implicated in both oncogenic and tumor-suppressive functions in human cancers. However, the role of PROX1 in the development of renal cell carcinomas (RCCs) has not yet been studied. Here, we reported that PROX1 expression was decreased in human RCC tissues compared with adjacent normal tissues. In RCC tissues, however, poorly differentiated RCC expressed higher PROX1 levels compared with well-differentiated RCC. In addition, the PROX1 immunostaining levels were positively correlated with tumor nuclear grade and lymph node metastasis. Further, high PROX1 expression indicated poor survival for patients. These findings imply that in the different developmental stages of RCC, PROX1 may exert distinct functions according to the specific microenvironment of tumor. Moreover, in vitro experiments revealed that PROX1 overexpression enhanced the proliferation and migration of RCC cells; conversely, PROX1 depletion by siRNA attenuated the proliferation and migration of RCC cells. Collectively, these observations suggest that PROX1 plays an important role in RCC development and progression, and PROX1 may be a novel target for prevention and treatment of RCC.

The role of the transcription factor: Prospero homeobox 1: in the biology of differentiated thyroid cancer

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Prox1 and FOXC2 Act as Regulators of Lymphangiogenesis and Angiogenesis in Oral Squamous Cell Carcinoma

Prospero homeobox 1 (Prox1) and forkhead box (FOX) C2 regulate angiogenesis and/or lymphangiogenesis. However, the detailed role and function of Prox1 and FOXC2 in cancer remains controversial. In the present study, we examined the expression of Prox1 and FOXC2 proteins in specimens from 163 cases with oral squamous cell carcinoma (OSCC). Furthermore, the role of Prox1 and FOXC2 in cancer cell growth and invasion was evaluated in cultured OSCC cells. Prox1 expression was significantly associated with local progression of the tumor (P = 0.0023), clinical stage (P<0.0001), lymphovessel density (LVD) (P<0.0001), nodal metastasis (P<0.0001), and worse prognosis (P<0.0001). Immunoreactivity of FOXC2 was strongly correlated with microvessel density (MVD) (P<0.0001) and poor prognosis (P = 0.0076). In vitro analysis demonstrated that Prox1 regulates cell growth, proliferation, invasion, and lymphangiogenesis by activating vascular endothelial growth factor (VEGF)-C expression. Furthermore, FOXC2 enhanced the expression level of Prox1 and promoted angiogenesis by enhancement of VEGF-A expression. Our results suggested that Prox1 and FOXC2 play key roles in OSCC progression and that further studies focusing on these proteins may yield useful insights for diagnosis and therapy of OSCC.

Kaposiform Lymphangiomatosis, a Newly Characterized Vascular Anomaly Presenting with Hemoptysis in an Adult Woman

Disorders of the pulmonary lymphatic system include macro- and microcystic lymphatic malformations, primary or secondary lymphangiectasias, generalized lymphatic anomalies, diffuse pulmonary lymphangiomatosis, and combinations of lymphatic and other tissue anomalies, including lymphangioleiomyomatosis (LAM). We report a case of a patient with a newly defined entity classified as kaposiform lymphangiomatosis (KLA). This 50-year-old nonsmoking Hispanic woman presented with a 20-year history of cough, hemoptysis, chyloptysis, and pleuritic chest pain. Laboratory evaluation demonstrated a low normal platelet count, elevated d-Dimer, low normal fibrinogen, and elevated fibrin split products. Chest computerized tomography imaging showed enlarged hypodense lymph nodes in the mediastinum and hila, and peribronchovascular thickening, without evidence of cystic parenchymal lesions. Magnetic resonance imaging of the chest showed cystic mediastinal lymph nodes with heterogeneously increased T2 and decreased T1 signal intensity. Fiberoptic bronchoscopy revealed hyperemic mucosa with granular appearance suggestive of a submucosal infiltrative process. Pathological specimens revealed dilated, malformed lymphatic channels within the pleura, pulmonary septa, and bronchovascular bundles, and foci of perilymphatic and intralymphatic spindle cells which reacted with the Prospero homeobox protein 1 (PROX-1) immunostain. The morphology and immunohistochemistry results were consistent with a diagnosis of KLA. This newly recognized clinical-pathological entity among intrathoracic lymphatic anomalies is distinguished from generalized lymphatic anomaly and diffuse pulmonary lymphangiomatosis in part by characteristic hematological abnormalities and hemorrhagic complications, including hemoptysis, as experienced by our patient.

Bone Morphogenetic Protein 2 Signaling Negatively Modulates Lymphatic Development in Vertebrate Embryos

The emergence of lymphatic endothelial cells (LECs) seems to be highly regulated during development. Although several factors that promote the differentiation of LECs in embryonic development have been identified, those that negatively regulate this process are largely unknown. Our aim was to delineate the role of bone morphogenetic protein (BMP) 2 signaling in lymphatic development. BMP2 signaling negatively regulates the formation of LECs. Developing LECs lack any detectable BMP signaling activity in both zebrafish and mouse embryos, and excess BMP2 signaling in zebrafish embryos and mouse embryonic stem cell-derived embryoid bodies substantially decrease the emergence of LECs. Mechanistically, BMP2 signaling induces expression of miR-31 and miR-181a in a SMAD-dependent mechanism, which in turn results in attenuated expression of prospero homeobox protein 1 during development. Our data identify BMP2 as a key negative regulator for the emergence of the lymphatic lineage during vertebrate development.

Cellular origin of Kaposi's sarcoma and Kaposi's sarcoma-associated herpesvirus-induced cell reprogramming

Kaposi's sarcoma (KS) is the most common malignancy in untreated HIV patients. KS is characterised by abnormal neoangiogenesis, inflammation, and proliferation of tumour cells [KS spindle cells (SCs)]. Kaposi's sarcoma-associated herpesvirus (KSHV) is the aetiological agent of KS. KS SCs are the predominant KSHV-infected cells in KS lesions. In this review, we report advances in understanding of the cellular origin of the KS SC, a contentious topic in KSHV research. KS SCs are now known to be of endothelial cell (EC) origin, phenotypically most similar to lymphatic ECs (LECs), but poorly differentiated. We focus on recent insights into KSHV's ability to exploit the normal differentiation pathway and intrinsic plasticity of ECs, through manipulation of EC-specific transcriptional regulators [i.e., prospero homeobox 1 (PROX1) and MAF] and discuss how this may contribute to viral persistence and KS sarcomagenesis.

Lymphatic Endothelial Differentiation in Pulmonary Lymphangioleiomyomatosis Cells

Pulmonary lymphangioleiomyomatosis (LAM) is a rare, low-grade neoplasm affecting almost exclusively women of childbearing age. LAM belongs to the family of perivascular epithelioid cell tumors, characterized by spindle and epithelioid cells with smooth muscle and melanocytic differentiation. LAM cells infiltrate the lungs, producing multiple, bilateral lesions rich in lymphatic channels and forming cysts, leading to respiratory insufficiency. Here we used antibodies against four lymphatic endothelial markers-podoplanin (detected by D2-40), prospero homeobox 1 (PROX1), vascular endothelial growth factor receptor 3 (VEGFR-3), and lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1)-to determine whether LAM cells show lymphatic differentiation. Twelve of 12 diagnostic biopsy specimens (early-stage LAM) and 19 of 19 explants (late-stage LAM) showed immunopositivity for D2-40 in most neoplastic cells. PROX1, VEGFR-3, and LYVE1 immunoreactivity varied from scarce in the early stage to abundant in the late stage. Lymphatic endothelial, smooth muscle, and melanocytic markers were partially co-localized. These findings indicate that lymphatic endothelial differentiation is a feature of LAM and provide evidence of a previously unidentified third lineage of differentiation in this neoplasm. This study has implications for the histological diagnosis of LAM, the origin of the neoplastic cells, and potential future treatment with drugs targeting lymphangiogenesis.

The role of the transcription factor - Prospero homeobox 1 (Prox1) in the biology of differentiated thyroid cancer - the effect of the expression of Prox1 on migration and invasiveness of thyroid cancer cells

The feature of malignancy is its ability to infiltrate and metastasis. The differentiated thyroid carcinoma (DTC), which constitutes of more than 80% of all thyroid cancers is spread by two major paths: papillary carcinoma (PTC) usually by the lymphatic vessels, and follicular cancer (FTC) mainly through the circulatory system. It was proposed that the cancers microenvironment induced by lymphangiogenesis could be an important factor affecting the expansion of primary tumour cells to lymph nodes. The aim of our work was to investigate signaling pathways associated with migration and invasiveness of thyroid cancer cells. We were especially interested in the role of Prospero homeobox 1 (Prox1) protein, an important element of the lymphangiogenesis. The studies were performed in a series of thyroid cancer FTC and PTC cell lines. The protein expression level and intracellular localization of the Prox1 gene was determined using molecular biology methods including: Q-RT-PCR, Western Blot and immunocytochemistry. The tumour cells' dynamics and invasiveness were monitored by microscopic observation assay and using invasion test, respectively. Additionally, the cells phenotype under Prox1 gene overproduction and silencing conditions was investigated. We observed significant differences in the level of expression Prox1 between tested thyroid cancer cell lines. Additionally, protein subcellular localization was also variable and correlated with the tumour type. The protein concentration was not directly combined with mRNA level and even under small mRNA concentration in some tissue culture lines, the Prox1 protein was cumulated in the cells over the time. We noticed that the increased expression level of Prox1 gene resulted in a lower rate of cell migration. Interestingly, a similar effect was demonstrated under overexpression conditions of the Prox1 gene, but uniquely, the lower dynamic rate of cells was additionally accompanied by a significantly higher invasive potential of the tested cells. The differences in the expression level and localization of Prox1 protein in various DTC lines may suggest an important role of it in the spreading of follicular and papillary carcinomas. We showed that Prox1 is a factor that has a significant effect on the migration and invasiveness of thyroid cancer cells, and thus affects the spread of the tumour. We propose that Prox1 may lead to changes in the signaling pathway controlling cytoskeleton dynamics in the tumour cells and the turnover of invasiveness. Further on-going studies will precisely determine the role of Prox1 lymphangiogenesis factor in DTC propagation.

Status epilepticus increases mature granule cells in the molecular layer of the dentate gyrus in rats.

Enhanced neurogenesis in the dentate gyrus of the hippocampus following seizure activity, especially status epilepticus, is associated with ectopic residence and aberrant integration of newborn granule cells. Hilar ectopic granule cells may be detrimental to the stability of dentate circuitry by means of their electrophysiological properties and synaptic connectivity. We hypothesized that status epilepticus also increases ectopic granule cells in the molecular layer. Status epilepticus was induced in male Sprague-Dawley rats by intraperitoneal injection of pilocarpine. Immunostaining showed that many doublecortin-positive cells were present in the molecular layer and the hilus 7 days after the induction of status epilepticus. At least 10 weeks after status epilepticus, the estimated number of cells positive for both prospero homeobox protein 1 and neuron-specific nuclear protein in the hilus was significantly increased. A similar trend was also found in the molecular layer. These findings indicate that status epilepticus can increase the numbers of mature and ectopic newborn granule cells in the molecular layer.

Prospero Homeobox 1 Promotes Epithelial–Mesenchymal Transition in Colon Cancer Cells by Inhibiting E-cadherin via miR-9

Prospero homeobox 1 (PROX1) has been shown to function as a tumor suppressor in various types of cancer. However, it promotes colon cancer progression. The aim of this study is to clarify the underlying mechanism by which PROX1 regulates tumorigenicity of colon cancer. Association of PROX1 and clinicopathological features was studied by immunohistochemical staining. Pri-miR-9-2 and miR-9 were detected by quantitative real-time PCR. Assays of cell invasion, adhesion, and matrix metalloproteinase activity were used to study PROX1-mediated epithelial-mesenchymal transition (EMT). PROX1 was overexpressed in 43% (59/136) of colon cancer tissues and its expression was correlated with E-cadherin downregulation (P = 0.00005), advanced tumor staging (P = 0.005), and lymph node metastasis (P = 0.000009). Enforced expression of PROX1 in DLD-1 cells caused downregulation of E-cadherin and integrins and attenuated cell adhesion. These cells showed increase of matrix metalloproteinase activity and invasive ability. Conversely, knockdown of PROX1 in SW620 cells restored E-cadherin protein expression and reduced invasiveness. Unexpectedly, repression of E-cadherin by PROX1 was not mediated by transcriptional inhibition. We found that PROX1 bound to miR-9-2 promoter and triggered its expression to suppress E-cadherin 3'UTR reporter activity and protein expression. Anti-miR-9 restored E-cadherin in SW620 cells, whereas precursor miR-9 inhibited E-cadherin in PROX1-knockdown cells. The miR-9 level was higher in tumor tissues with high PROX1/low E-cadherin than that of tumor tissues with low PROX1/high E-cadherin. Our results provide mechanistic insights by which PROX1 promotes EMT and colon cancer progression. Targeting of PROX1-mediated oncogenic activity may be helpful for the treatment of colon cancer.

High Lymph Vessel Density and Expression of Lymphatic Growth Factors in Peritoneal Endometriosis

To investigate the occurrence of lymph vessels and lymphangiogenic growth factors in peritoneal lesions, we performed immunohistochemical staining of peritoneal lesions of 37 patients with antibodies against podoplanin (D2-40), lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), prospero homeobox protein 1 (Prox-1), vascular epithelial growth factor (VEGF)-C/VEGF-D. Overall, 10 lesions were double stained against D2-40 and von Willebrand factor. The lymph vessel density in peritoneal lesion was significantly higher in comparison with healthy peritoneum. All lymph vessel makers could be detected, whereby the lymph vessel density of LYVE-1- and Prox-1-positive lymph vessels was significantly higher than the lymph vessel density of D2-40-positive lymph vessels. Endometriotic epithelial cells and stromal cells (SCs) showed a moderate-to-strong VEGF-C/VEGF-D expression. The VEGF-C-/VEGF-D-positive macrophages in endometriotic SCs could be observed. The lymphatic vasculature seems to form a further component of peritoneal lesions and could be involved in the inflammatory process. These data demonstrated a further step in the clarification of the pathogenesis of endometriosis.

A transcriptome signature of endothelial lymphatic cells coexists with the chronic oxidative stress signature in radiation-induced post-radiotherapy breast angiosarcomas

Radiation-induced breast angiosarcomas are rare but recognized complication of breast cancer radiotherapy and are of poor prognosis. Little is known about the genetic abnormalities present in these secondary tumors. Herein, we investigated the differences in the genome and in the transcriptome that discriminate these tumors as a function of their etiology. Seven primary breast angiosarcomas and 18 secondary breast angiosarcomas arising in the irradiation field of a radiotherapy were analyzed. Copy number alterations and gene expression were analyzed using Affymetrix SNP 6.0 Array and Affymetrix Exon Arrays, respectively. We showed that two transcriptome signatures of the radiation tumorigenesis coexisted in these tumors. One was histology specific and correctly discriminated 100% of the primary tumors from the radiation-induced tumors. The deregulation of marker genes, including podoplanin (PDPN), prospero homeobox 1 (PROX-1), vascular endothelial growth factor 3 (VEGFR3) and endothelin receptor A (EDNRA), suggests that the radiation-induced breast angiosarcomas developed from radiation-stimulated lymphatic endothelial cells. None of the genes of the histology-specific signature were present in our previously published signature of the radiation tumorigenesis which shows the presence of a chronic oxidative stress in radiation-induced sarcomas of various histologies. Nevertheless, this oxidative stress signature classified correctly 88% of the breast angiosarcomas as a function of the etiology. In contrast, MYC amplification, which is observed in all radiation-induced tumors but also at a low rate in primary tumors, was not a marker of the radiation tumorigenesis.

Minimal Constraints Solution NMR Structure of Prospero Homeobox protein 1 from Homo sapiens. Northeast Structural Genomics Consortium Target HR4660B.

Minimal Constraints Solution NMR Structure of Prospero Homeobox protein 1 from Homo sapiens. Northeast Structural Genomics Consortium Target HR4660B.

Interaction of tumor cells and lymphatic vessels in cancer progression

Metastatic spread of cancer through the lymphatic system affects hundreds of thousands of patients yearly. Growth of new lymphatic vessels, lymphangiogenesis, is activated in cancer and inflammation, but is largely inactive in normal physiology, and therefore offers therapeutic potential. Key mediators of lymphangiogenesis have been identified in developmental studies. During embryonic development, lymphatic endothelial cells derive from the blood vascular endothelium and differentiate under the guidance of lymphatic-specific regulators, such as the prospero homeobox 1 transcription factor. Vascular endothelial growth factor-C (VEGF-C) and VEGF receptor 3 signaling are essential for the further development of lymphatic vessels and therefore they provide a promising target for inhibition of tumor lymphangiogenesis. Lymphangiogenesis is important for the progression of solid tumors as shown for melanoma and breast cancer. Tumor cells may use chemokine gradients as guidance cues and enter lymphatic vessels through intercellular openings between endothelial cell junctions or, possibly, by inducing larger discontinuities in the endothelial cell layer. Tumor-draining sentinel lymph nodes show enhanced lymphangiogenesis even before cancer metastasis and they may function as a permissive 'lymphovascular niche' for the survival of metastatic cells. Although our current knowledge indicates that the development of anti-lymphangiogenic therapies may be beneficial for the treatment of cancer patients, several open questions remain with regard to the frequency, mechanisms and biological importance of lymphatic metastases.

Intravital two-photon microscopy of lymphatic vessel development and function using a transgenic Prox1 promoter-directed mOrange2 reporter mouse

Lymphatic vessels, the second vascular system of higher vertebrates, are indispensable for fluid tissue homoeostasis, dietary fat resorption and immune surveillance. Not only are lymphatic vessels formed during fetal development, when the lymphatic endothelium differentiates and separates from blood endothelial cells, but also lymphangiogenesis occurs during adult life under conditions of inflammation, wound healing and tumour formation. Under all of these conditions, haemopoietic cells can exert instructive influences on lymph vessel growth and are essential for the vital separation of blood and lymphatic vessels. LECs (lymphatic endothelial cells) are characterized by expression of a number of unique genes that distinguish them from blood endothelium and can be utilized to drive reporter genes in a lymph endothelial-specific fashion. In the present paper, we describe the Prox1 (prospero homeobox protein 1) promoter-driven expression of the fluorescent protein mOrange2, which allows the specific intravital visualization of lymph vessel growth and behaviour during mouse fetal development and in adult mice.

Efficient Generation of Hepatoblasts From Human ES Cells and iPS Cells by Transient Overexpression of Homeobox Gene HEX

Human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have the potential to differentiate into all cell lineages, including hepatocytes, in vitro. Induced hepatocytes have a wide range of potential application in biomedical research, drug discovery, and the treatment of liver disease. However, the existing protocols for hepatic differentiation of PSCs are not very efficient. In this study, we developed an efficient method to induce hepatoblasts, which are progenitors of hepatocytes, from human ESCs and iPSCs by overexpression of the HEX gene, which is a homeotic gene and also essential for hepatic differentiation, using a HEX-expressing adenovirus (Ad) vector under serum/feeder cell-free chemically defined conditions. Ad-HEX-transduced cells expressed α-fetoprotein (AFP) at day 9 and then expressed albumin (ALB) at day 12. Furthermore, the Ad-HEX-transduced cells derived from human iPSCs also produced several cytochrome P450 (CYP) isozymes, and these P450 isozymes were capable of converting the substrates to metabolites and responding to the chemical stimulation. Our differentiation protocol using Ad vector-mediated transient HEX transduction under chemically defined conditions efficiently generates hepatoblasts from human ESCs and iPSCs. Thus, our methods would be useful for not only drug screening but also therapeutic applications.

Establishment and Characterization of Human Lymphatic Endothelial Cell in Breast Cancer Patients Undergoing Sentinel Lymphadenectomy

Recently remarkable progress has been made in the understanding of lymphangiogenesis due to the availability of specific biomarkers. A sentinel lymph node (SLN) biopsy has already been established as a common surgical procedure, and the clinical usefulness of an SLN biopsy has been confirmed in patients with various types of cancer. In this study, a novel method has been successfully developed for the isolation of anatomically defined lymphatic endothelial cells (LECs) from human sentinel lymphatic channels during an SLN biopsy in breast cancer patients by the use of collagenase II digestion. The isolated cells were cultured in EGM2MV media with 10% fetal bovine serum (FBS) under hypoxic conditions in an atmosphere of 5% O 2, 5% CO2 and 90% N2 at 37°C. The cultured cells exhibited a monolayer with a cobblestone appearance. Immunofluorescence analysis using selective lymphangiogenesis markers showed expression of vascular endothelial growth factor receptor 3 (VEGFR-3), prospero homeobox 1 (Prox-1) and Podoplanin. Newly established LECs showed expressions of vascular endothelial growth factor (VEGF) family members except VEGF-D and corresponding VEGF receptors by the use of conventional RT-PCR. Treatment with VEGF-C156S (500 ng/mL) apparently induced phosphorylation of the protein kinase Akt, MAPK and JNK in human isolated LECs as determined by Western blot analysis. Peak induction of Akt, MAPK and JNK occurred at 10 to 15 minutes after incubation of the isolated LECs with VEGF-C156S. The use of the MTS cell proliferation assay showed a significant increase in the growth of human lymphatic endothelial cells with VEGF-C156S treatment. The effects of VEGF-C156S (500 ng/mL) on proliferation activity was significantly with 3% FBS condition alone (MTS score: 0.54±0.0104, n=3) and a 3% FBS+VEGFC156S (MTS score: 0.572±0.0061, n=3) condition. The isolated and enzymatic digested method adopted for the culture of human LECs is simple and useful for the investigation of the cellular, molecular and genomic properties of LECs.