Cell surface galactosyltransferase structure and function during mesenchymal cell migration

In order to more fully understand the function of surface GalTase on mesenchymal cells, anti-GalTase IgG was used to (a) examine the role of surface GalTase during mouse mesenchymal cell migration on laminin and fibronectin; (b) define the plasma membrane distribution of GalTase by indirect immunofluorescence on migrating cells; (c) quantitate the level of surface GalTase on migrating cells; and (d) determine whether GalTase is associated with the cytoskeleton.^ Results show that anti-GalTase IgG was able to inhibit migration (48-80% as compared to basal rate) when cells were migrating on laminin-containing matrices. Monovalent Fab fragments inhibited migration on laminin by 90% after 4 hours. On the other hand, anti-GalTase IgG had no effect on cells migrating on fibronectin. This illustrates the substrate specificity of GalTase mediated-migration. When anti-GalTase IgG was used to localize surface GalTase on cells migratory on laminin, the enzyme was restricted to the leading and trailing edges of the cell. Assays indicate that GalTase is elevated approximately 3-fold when cells are migrating on laminin-containing matrices as compared to migratory cells on plastic or fibronectin, or as compared to stationary cells on any substrate. Laminin appears to recruit GalTase from preexisting intracellular pools to the growing lamellipodia.^ Double-label indirect immunofluorescence studies indicate that there is an apparent co-localization between some of the surface GalTase and some actin filaments. This relationship was explored by extracting cells prelabeled with anti-GalTase IgG and quantitated by radiolabeled second antibodies. Results show that 79% of the surface GalTase is associated with the cytoskeleton (as judged by detergent insolubility) when monovalent antibodies (Fab) are used. However virtually all (80-100%) of the surface GalTase can be induced to associate with the cytoskeleton when cross-linked with bivalent antibodies. Furthermore, when cells in suspension are incubated with divalent antibodies, an additional 66% of the surface GalTase can be induced to associate with the cytoskeleton. The elevated levels of surface GalTase detectable on cells migrating on laminin also appear to be associated with the cytoskeleton.^ Several lines of evidence suggest that GalTase is associated with F-actin. Data suggest that laminin induces the expression of surface GalTase to the growing lamellipodia where it becomes associated with the cytoskeleton leading to cell spreading and migration. (Abstract shortened with permission of author.) ^

DYSREGULATION OF MEOX2 FOLLOWING WT1 MUTATION IN KIDNEY DEVELOPMENT AND WILMS TUMORIGENESIS

Wilms tumor (WT) is a childhood tumor of the kidney and a productive model for understanding the role of genetic alteration and interactions in tumorigenesis. The Wilms tumor gene 1 (WT1) is a transcriptional factor and one of the few genes known to have genetic alterations in WT and has been shown be inactivated in 20% of WTs. However, the mechanisms of how WT1 mutations lead to Wilms tumorigenesis and its influence on downstream genes are unknown. Since it has been established that WT1 is a transcriptional regulator, it has been hypothesized that the loss of WT1 leads to the dysregulation of downstream genes, in turn result in the formation of WTs. To identify the dysregulated downstream genes following WT1 mutations, an Affymetrix GeneChip Human Genome Array was previously conducted to assess the differentially expressed genes in the WT1-wildtype human and WT1-mutant human WTs. Approximately 700 genes were identified as being significantly dysregulated. These genes were further prioritized based on their statistical significance, fold change, chromosomal region, spatial pattern of gene expression and known or putative cellular functions. Mesenchyme homeobox 2 (MEOX2) was one of the most significantly upregulated genes in WT1-mutant WT. MEOX2 is known to play a role in cell proliferation, apoptosis, and differentiation. In addition to its biological roles, it is expressed during early kidney development in the condensed mesenchyme similar to WT1. Furthermore, the use of the Match® web-based tool from the BIOBASE Biological Data base identified a significant predicted WT1 binding site within the first intron of MEOX2. The similarity in spatial gene expression in the developing kidney and the significant predicted WT1 binding site found in the first intron of MEOX2 lead to the development of my hypothesis that MEOX2 is upregulated via a WT1-dependent manner. Here as a part of my master’s work, I have validated the Affymetrix GeneChip Human Genome Array data using an independent set of Wilms tumors. MEOX2 remained upregulated in the mutant WT1 Wilms tumor by 41-fold. Wt1 and Meox2 gene expression were assessed in murine newborn kidney; both Wt1 and Meox2 were expressed in the condensed, undifferentiated metanephric mesenchyme. I have shown that the in vivo ablation of Wt1 during embryonic development at embryonic day (E) 13.5 resulted in the slight increase of Meox2 gene expression by two fold. In order to functionally demonstrate the effect of the loss of Wt1 on Meox2 gene expression in undifferentiated metanephric mesenchyme, I have generated a kidney mesenchymal cell line to genetically ablate Wt1 in vitro by adenoviral infection. The ablation of Wt1 in the kidney mesenchymal cell line resulted in the upregulation of Meox2 by 61-fold. Moreover, the upregulation of Meox2 resulted in the significant induction of p21 and Itgb5. In addition to the dysregulation of these genes the ablation of Wt1 in the kidney mesenchymal cells resulted in decrease in cell growth and loss of cellular adherence. However, it is uncertain whether the upregulation of Meox2 caused this particular cellular phenotype. Overall, I have demonstrated that the upregulation of Meox2 is Wt1-dependent during early kidney development.

Transcriptional regulation of the mouse $\alpha$2(I) collagen gene

The mouse $\alpha$2(I) collagen gene is specifically expressed in a limited number of cell types in the body including fibroblasts and osteoblasts. We had previously shown that a promoter containing the sequences between $-$350 and +54 bp was expressed at low levels in a cell- and tissue-specific fashion in transgenic mice. Further studies suggested that the sequence between $-$315 and $-$284 bp could mediate cell- and tissue-specific expression of reporter genes in cell culture and in transgenic mice. We report here characterization of the proteins binding to this segment and propose a model for the cell-specific expression conferred by this sequence. In this study we also identified a strong enhancer for the mouse $\alpha$2(I) collagen gene located approximately 13.5 to 19.5 kb upstream of the transcriptional start site. This enhancer segment is characterized by the presence of three cell-specific hypersensitive sites and can drive high levels of cell-specific expression of a heterologous 220-bp mouse $\alpha$1(I) collagen promoter. In the course of this study, we identified a novel zinc finger transcription factor (designated murine epithelial zinc finger, mEZF) which was transiently expressed in the mesenchymal cells which give rise to the skeletal primordia and the metanephric kidney during the early stages of embryogenesis. In newborn mice, the mEZF gene is expressed at high levels in differentiated epithelial cells of the skin, oral mucosa, tongue, esophagus, stomach and colon. Chromosomal mapping suggested that the mEZF gene mapped to mouse Chromosome 4 and that the human homolog of mEZF would likely map to human Chromosome 9q31. This region of the human genome contains tumor suppressor genes for basal cell carcinomas of the skin as well as for squamous cell carcinomas of various organs. We cloned and characterized the human homolog of mEZF and mapped its chromosomal position as a first step in determining whether or not this gene plays a role in the development of these tumors. ^

In vivo definition of genetic and cellular aspects of mammalian sexual differentiation

The differentiation of the reproductive organs is an essential developmental process required for the proper transmission of the genetic material. Müllerian inhibiting substance (MIS) is produced by testes and is necessary for the regression of the Müllerian ducts: the anlagen of the uterus, fallopian tubes and cervix. In vitro and standard transgenic mouse studies indicate that the nuclear hormone receptor Steroidogenic factor 1 (SF-1) and the transcription factor SOX9 play an essential role in the regulation of Mis. To test this hypothesis, mutations in the endogenous SF-1 and SOX9 binding sites in the mouse Mis promoter were introduced by gene targeting in embryonic stem (ES) cells. In disagreement with cell culture and transgenic mouse studies, male mice homozygous for the mutant SF-1 binding site correctly initiated Mis transcription in the fetal testes, although at significantly reduced levels. Surprisingly, sufficient Mis was produced for complete elimination of the Müllerian duct system. However, when the SF-1 binding site mutation was combined with an Mis -null allele, the further decrease in Mis levels led to a partial retention of uterine tissue, but only at a distance from the testes. In contrast, males homozygous for the mutant SOX9 binding site did not initiate Mis transcription, resulting in pseudohermaphrodites with a uterus and oviducts. These studies suggest an essential role for SOX9 in the initiation of Mis transcription, whereas SF-1 appears to act as a quantitative regulator of Mis transcript levels perhaps for influencing non-Müllerian duct tissues. ^ The Mis type II receptor, a member of the TGF- b superfamily, is also required for the proper regression of the Müllerian ducts. Mis type II receptor-deficient human males and their murine counterparts develop as pseudohermaphrodites. A lacZ reporter cassette was introduced into the mouse Mis type II receptor gene, by homologous recombination in ES cells. Expression studies, based on b -galactosidase activity, show marked expression of the MIS type II receptor in the postnatal Sertoli cells of the testis as well as in the prenatal and postnatal granulosa cells of the ovary. Expression is also seen in the mesenchymal cells surrounding the Müllerian duct and in the longitudinal muscle layer of the uterus. ^

Characterization of healing tissue in a tooth extraction socket in a rabbit model

The histology of healing in a tooth extraction socket has been described in many studies. The focus of research in bone biology and healing is now centered on molecular events that regulate repair of injured tissue. Rapid progress in cellular and molecular biology has resulted in identification of many signaling molecules (growth factors and cytokines) associated with formation and repair of skeletal tissues. Some of these include members of the transforming growth factor-β superfamily (including the bone morphogenetic proteins), fibroblast growth factors, platelet derived growth factors and insulin like growth factors. ^ Healing of a tooth extraction socket is a complex process involving tissue repair and regeneration. It involves chemotaxis of appropriate cells into the wound, transformation of undifferentiated mesenchymal cells to osteoprogenitor cells, proliferation and differentiation of committed bone forming cells, extracellular matrix synthesis, mineralization of osteoid, maturation and remodeling of bone. Current data suggests that these cellular events are precisely controlled and regulated by specific signaling molecules. A plethora of cytokines; have been identified and studied in the past two decades. Some of these like transforming growth factor beta (TGF-β), vascular endothelial growth factor (VEGF), platelet derived growth factor (PDGF) and fibroblast growth factors (FGFs) are well conserved proteins involved in the initial response to injury and repair in soft and hard tissue. ^ The purpose of this study was to characterize the spatial and temporal localization of TGF-βl, VEGF, PDGF-A, FGF-2 and BMP-2, and secretory IgA in a tooth extraction socket model, and evaluate correlation of spatial and temporal changes of these growth factors to histological events. The results of this study showed positive correlation of histological events to spatial and temporal localization of TGF-β1, BMP-2, FGF-2, PDGF-A, and VEGF in a rabbit tooth extraction model. ^

ANTI-TUMOR EFFECTS OF THE NOTCH PATHWAY IN GASTROINTESTINAL STROMAL TUMORS

Gastrointestinal Stromal Tumors (GIST) are sarcomas driven by gain-of-function mutations of KIT or PDGFRA. Although, the introduction of tyrosine kinase inhibitors has dramatically changed the history of this disease, evidences emerge that inhibition of KIT or PDGFRA are not sufficient to cure patients. The developmental pathway Notch has a critical role in the cell fate, regulating cell proliferation and differentiation. Dysregulation of Notch pathway has been implicated in a wide variety of cancers functioning as a tumor promoter or a tumor suppressor in a cell context dependent manner. Given that Notch activation deregulates the morphogenesis of mesenchymal cells in the GI track, that Notch acts as a tumor suppressor in neuroendocrine tumors, and finally that the cell of origin of GIST are the Interstitial Cell of Cajal that arise from a mesenchymal origin with some neuroendocrine features, we hypothesized that Notch pathway signaling may play a role in growth, survival and differentiation of GIST cells. To test this hypothesis, we genetically and pharmacologically manipulated the Notch pathway in human GIST cells. In this study, we demonstrated that constitutively active intracellular domain of Notch1 (ICN-1) expression potently induced growth arrest and downregulated KIT expression. We have performed a retrospective analysis of 15 primary GIST patients and found that high mRNA level of Hes1, a major target gene of Notch pathway, correlated with a significantly longer relapse-free survival. Therefore, we have established that treatment with the FDA approved histone deacetylase inhibitor SAHA (Vorinostat) caused dose-dependent upregulation of Notch1 expression and a parallel decrease in viability in these cells. Retroviral silencing of downstream targets of Notch with dominant negative Hes-1 as well as pharmacological inhibition of Notch pathway with a γ-secretase inhibitor partially rescued GIST cells from SAHA treatment. Taken together these results identify anti-tumor effect of Notch1 and a negative cross-talk between Notch1 and KIT pathways in GIST. Consequently, we propose that activation of this pathway with HDAC inhibitors may be a potential therapeutic strategy for GIST patients.

PRKCa: Identification of a Novel Downstream Target of WT1

Wilms tumor is a childhood tumor of the kidney arising from the undifferentiated metanephric mesenchyme. Tumorigenesis is attributed to a number of genetic and epigenetic alterations. In 20% of Wilms tumors, Wilms tumor gene 1 (WT1) undergoes inactivating homozygous mutations causing loss of function of the zinc finger transcription factor it encodes. It is hypothesized that mutations in WT1 result in dysregulation of downstream target genes, leading to aberrant kidney development and/or Wilms tumor. These downstream target genes are largely unknown, and identification is important for further understanding Wilms tumor development. Heatmap data of human Wilms tumor protein expression, generated by reverse phase protein assay analysis (RPPA), show significant correlation between WT1 mutation status and low PRKCα expression (p= 0.00013); additionally, p-PRKCα (S657) also shows decreased expression in these samples (p= 0.00373). These data suggest that the WT1 transcription factor regulates PRKCα expression, and that PRKCα plays a potential role in Wilms tumor tumorigenesis. We hypothesize that the WT1 transcription factor directly/indirectly regulates PRKCα and mutations occurring in WT1 lead to decreased expression of PRKCα. Prkcα and Wt1 have been shown to co-localize in E14.5 mesenchymal cells of the developing kidney. siRNA knockdown, in-vivo ablation, and tet-inducible expression of Wt1 each independently confirm regulation of Prkcα expression by Wt1 at both RNA and protein levels, and investigation into possible WT1 binding sites in PRKCα regulatory regions has identified multiple sites to be confirmed by luciferase reporter constructs. With the goal of identifying WT1 and PRKCα downstream targets, RPPA analysis of protein expression in mesenchymal cell culture, following lentiviral delivered shRNA knockdown of Wt1 and shRNA knockdown of Prkcα, will be carried out. Apart from Wilms tumor, WT1 also plays an important role in Acute Myeloid Leukemia (AML). WT1 mutation status has been implicated, controversially, as an independent poor-prognosis factor in leukemia, leading to decreased probability of overall survival, complete remission, and disease free survival. RPPA analysis of AML patient samples showed significant decreases in PRKCα/p-PRKCα protein expression in a subset of patients (Kornblau, personal communication); therefore, the possible role of WT1 and PRKCα in leukemia disease progression is an additional focus of this study. WT1 mutation analysis of diploid leukemia patient samples revealed two patients with mutations predicted to affect WT1 activity; of these two samples, only one corresponded to the low PRKCα expression cohort. Further characterization of the role of WT1 in AML, and further understanding of WT1 regulated PRKCα expression, will be gained following RPPA analysis of protein expression in HL60 leukemia cell lines with lentiviral delivered shRNA knockdown of WT1 and shRNA knockdown of PRKCα.

Isolation and characterization of cDNAs encoding novel homeoproteins from chondrocytes

Bone morphogenesis is a complex biological process. The multistep process of chondrogenesis is the most important aspect of endochondral bone formation. To study the mechanisms which control this multistep pathway of chondrogenesis during embryonic development, I started by isolating cDNAs encoding novel transcriptional factors from chondrocytes. Several such cDNAs encoding putative homeoproteins were identified from a rat chondrosarcoma cDNA preparation. I have been concentrating on characterizing two of these cDNAs. The deduced amino acid sequence of the first homeoprotein, Cart-1, contains a prd-type homeodomain. Northern hybridization and RNase protection analysis revealed that Cart-1 RNAs were present at high levels in a well differentiated rat chondrosarcoma tumor and in a cell line derived from this tumor. Cart-1 transcripts were also detected in primary chondrocytes, but not in numerous other cell types except very low levels in testis. In situ hybridization of rat embryos at different stages of development revealed relatively high levels of Cart-1 RNAs in prechondrocytic mesenchymal cells and in early chondrocytes of cartilage primordia. It is speculated that Cart-1 might play an important role in chondrogenesis. The second putative homeoprotein, rDlx, contains a Distal-less-like homeodomain. rDlx RNAs were also present at high levels in the rat chondrosarcoma tumor and in the cell line derived from this tumor. In situ hybridization of rat embryos revealed high levels of rDlx transcripts in the developing cartilages and perichondria of mature cartilages. rDlx transcripts were also detected in a number of nonchondrogenic tissues such as forebrain, otic vesicles, olfactory epithelia, apical ectodermal ridge (AER) of limb buds, the presumptive Auerbach ganglia of gastrointestinal tract. The unique expression pattern of rDlx suggests that it might play important roles in chondrogenesis and other aspects of embryogenesis. ^

ELUCIDATING THE ROLE OF CD44 EXPRESSION ON MESENCHYMAL STEM CELLS WITHIN THE TUMOR MICROENVIRONMENT

The tumor microenvironment is comprised of a vast array of heterogeneous cells including both normal and neoplastic cells. The tumor stroma recruitment process has been exploited for an effective gene delivery technique using bone marrow derived MSC. Targeted migration of the MSC toward the tumor microenvironment, while successful, is not yet fully understood. This study was designed to assess the role of CD44 in the migration of MSC toward the tumor microenvironment and to determine the implications of CD44-deficient MSC within the tumor stroma. Inhibition of MSC migration was evaluated through a variety of methods in vitro and in vivo including CD44 receptor knockdown, CD44 antagonists, CD44 neutralizing antibodies and small molecule inhibitor of matrix metalloproteinases. Blocking CD44 signaling through MMP inhibition was characterized by lack of intracellular domain cleavage and lead to the decrease in Twist gene expression. A functional relationship between CD44 and Twist expression was confirmed by chromatin immunoprecipitation. Next, a series of murine tumor models were used to examine the role of CD44 deficient stroma within the tumor microenvironment. Labeled transgenic CD44 knockout (KO) MSC or wild type (WT) C57/B6 MSC were used to analyze the stromal incorporation within murine breast carcinomas (EO771 and 4T1). Subsequent tumors were analyzed for vessel formation (CD31), and the presence of tumor associated fibroblast (TAF) markers, α-smooth muscle actin (α-SMA), fibroblast activation protein (FAP), and fibroblast specific protein (FSP). The tumors with CD44KO MSC cells had less vessel formation than the tumors with WT MSC. The lack of fibroblastic TAF population as defined by FAP/FSP expression by the CD44KO MSC admixed tumors suggest that the bone marrow derived population of MSC were unable to contribute to the fibroblastic stromal population. Subsequently, a bone marrow transplantation experiment confirmed the endogenous migratory deficiencies of the CD44KO bone marrow derived stromal cells toward the tumor microenvironment in vivo. WT mice with CD44KO bone marrow had less CD44KOderived tumor stroma compared to mice with WT bone marrow. These results indicate that CD44 is crucial to stromal cell migration and incorporation to the tumor microenvironment as TAF.

Direct intrathecal implantation of mesenchymal stromal cells leads to enhanced neuroprotection via an NFkappaB-mediated increase in interleukin-6 production.

Mesenchymal stromal cell (MSC) therapy has shown promise for the treatment of traumatic brain injury (TBI). Although the mechanism(s) by which MSCs offer protection is unclear, initial in vivo work has suggested that modulation of the locoregional inflammatory response could explain the observed benefit. We hypothesize that the direct implantation of MSCs into the injured brain activates resident neuronal stem cell (NSC) niches altering the intracerebral milieu. To test our hypothesis, we conducted initial in vivo studies, followed by a sequence of in vitro studies. In vivo: Sprague-Dawley rats received a controlled cortical impact (CCI) injury with implantation of 1 million MSCs 6 h after injury. Brain tissue supernatant was harvested for analysis of the proinflammatory cytokine profile. In vitro: NSCs were transfected with a firefly luciferase reporter for NFkappaB and placed in contact culture and transwell culture. Additionally, multiplex, quantitative PCR, caspase 3, and EDU assays were completed to evaluate NSC cytokine production, apoptosis, and proliferation, respectively. In vivo: Brain supernatant analysis showed an increase in the proinflammatory cytokines IL-1alpha, IL-1beta, and IL-6. In vitro: NSC NFkappaB activity increased only when in contact culture with MSCs. When in contact with MSCs, NSCs show an increase in IL-6 production as well as a decrease in apoptosis. Direct implantation of MSCs enhances neuroprotection via activation of resident NSC NFkappaB activity (independent of PI3 kinase/AKT pathway) leading to an increase in IL-6 production and decrease in apoptosis. In addition, the observed NFkappaB activity depends on direct cell contact.

Examination of the engraftment of exogenous mesenchymal stem cells in ovarian tumors and their potential use as delivery vehicles for therapeutic genes

Interactions between neoplastic cells and the host stroma play a role in both tumor cell migration and proliferation. Stromal cells provide structural support for malignant cells, modulate the tumor microenvironment, and influence phenotypic behavior as well as the aggressiveness of the malignancy. In response, the tumor provides growth factors, cytokines, and cellular signals that continually initiate new stromal reactions and recruit new cells into the microenvironment to further support tumor growth. Since growing tumors recruit local cells, as well as supplemental cells from the circulation, such as fibroblasts and endothelial precursors, the question arises if it would be possible to access circulating stromal cells to modify the tumor microenvironment for therapeutic benefits. One such cell type, mesenchymal stem cells (MSC), could theoretically be engrafted into stroma. MSC are pluripotent cells that have been shown to form stromal elements such as myofibroblasts, perivascular tissues and connective tissues. Several reports have demonstrated that MSC can incorporate into sites of wound healing and tissue repair, due to active tissue remodeling and local paracrine factors, and given the similarity between wound healing and the carcinoma induced stromal response one can hypothesize that MSC have the potential to be recruited to sites of tumor development. In addition, gene-modified MSC could be used as cellular vehicles to deliver gene products into tumors. My results indicate that MSC home to and participate in tumor stroma formation in ovarian tumor xenografts in mice. Additionally, once homed to tumor beds, MSC proliferate rapidly and integrate. My studies aim at understanding the fate of MSC in the tumor microenvironment, as well as utilizing them for cellular delivery of therapeutic genes into the stroma of ovarian carcinomas. ^

THE p63 ISOFORM ∆Np63α INHIBITS EPITHELIAL – MESENCHYMAL TRANSITION BY PROMOTING THE EXPRESSION OF MIR-205 IN HUMAN BLADDER CANCER CELLS

p63, a p53 family member, is a transcription factor that has complex roles in cancer. This study focuses on the role of the ∆Np63α isoform in bladder cancer (BC). Epithelial – mesenchymal transition (EMT) is a physiological process that plays an important part in metastasis and drug resistance. At the molecular level, EMT is characterized by the loss of the epithelial marker E-cadherin, and the acquisition of the transcriptional repressors of E-cadherin (ZEB1, ZEB2, TWIST, SNAI1 and SNAI2). Recent publications highlight the role of microRNAs belonging to the miR-200 family and miR-205 in preventing EMT through suppression of ZEB1 and ZEB2. p53, the homologue of p63, is implicated in regulating EMT by modulating the expression of miR-200c; however, the mechanisms underlying miR-205 control remain unclear. Here we show that ∆Np63α regulates the transcription of miR-205 and controls EMT in human BC cells. We observed a strong correlation between the expression of ∆Np63α, miR-205 and E-cadherin in a panel of BC cell lines (n=28) and also in bladder primary tumors from a cohort of patients (n=98). A remarkably inverse correlation is observed between ∆Np63α and ZEB1/2 in cell lines. Stable knockdown (KD) ∆Np63α in UC6, an “epithelial” BC cell line, decreased the expression of miR-205 and induced ZEB1/2 expression, the effects that were reversed by expression of exogenous miR-205. Moreover, overexpressing ∆Np63α in UC3, a “messenchymal” BC cell line, brought about opposite results, an increase in miR-205 expression and a reduction in ZEB1/2 expression. Modulation of ∆Np63α expression resulted in a parallel change in the expression of miR-205 and miR-205 “host” gene (miR-205HG). Nuclear run-on and chromatin immunoprecipitation experiments demonstrated that ∆Np63α regulates the transcription of miR-205 through controlling the recruitment of RNA Polymerase II to the promoter of miR-205HG. Interestingly, high miR-205 expression correlated with poor clinical outcome in BC patients, consistent with our recent publication highlighting the enrichment of ∆Np63 in a lethal subset of muscle invasive BC. In summary, our data present the important roles of ∆Np63α in preventing EMT mediated by miR-205. Our study also identifies miR-205 as a potential molecular marker to predict clinical outcome in BC patients.

Intravenous mesenchymal stem cell therapy for traumatic brain injury.

OBJECT: Cell therapy has shown preclinical promise in the treatment of many diseases, and its application is being translated to the clinical arena. Intravenous mesenchymal stem cell (MSC) therapy has been shown to improve functional recovery after traumatic brain injury (TBI). Herein, the authors report on their attempts to reproduce such observations, including detailed characterizations of the MSC population, non-bromodeoxyuridine-based cell labeling, macroscopic and microscopic cell tracking, quantification of cells traversing the pulmonary microvasculature, and well-validated measurement of motor and cognitive function recovery. METHODS: Rat MSCs were isolated, expanded in vitro, immunophenotyped, and labeled. Four million MSCs were intravenously infused into Sprague-Dawley rats 24 hours after receiving a moderate, unilateral controlled cortical impact TBI. Infrared macroscopic cell tracking was used to identify cell distribution. Immunohistochemical analysis of brain and lung tissues 48 hours and 2 weeks postinfusion revealed transplanted cells in these locations, and these cells were quantified. Intraarterial blood sampling and flow cytometry were used to quantify the number of transplanted cells reaching the arterial circulation. Motor and cognitive behavioral testing was performed to evaluate functional recovery. RESULTS: At 48 hours post-MSC infusion, the majority of cells were localized to the lungs. Between 1.5 and 3.7% of the infused cells were estimated to traverse the lungs and reach the arterial circulation, 0.295% reached the carotid artery, and a very small percentage reached the cerebral parenchyma (0.0005%) and remained there. Almost no cells were identified in the brain tissue at 2 weeks postinfusion. No motor or cognitive functional improvements in recovery were identified. CONCLUSIONS: The intravenous infusion of MSCs appeared neither to result in significant acute or prolonged cerebral engraftment of cells nor to modify the recovery of motor or cognitive function. Less than 4% of the infused cells were likely to traverse the pulmonary microvasculature and reach the arterial circulation, a phenomenon termed the "pulmonary first-pass effect," which may limit the efficacy of this therapeutic approach. The data in this study contradict the findings of previous reports and highlight the potential shortcomings of acute, single-dose, intravenous MSC therapy for TBI.

REGULATION OF HGF EXPRESSION BY ΔEGFR-MEDIATED C-MET ACTIVATION IN GLIOBLASTOMA CELLS

Overexpression of the hepatocyte growth factor receptor (c-Met) and its ligand, the hepatocyte growth factor (HGF), and a constitutively active mutant of the epidermal growth factor receptor (∆EGFR/EGFRvIII), occur frequently in glioblastoma. c-Met is activated in a ligand-dependent manner by HGF or in a ligand-independent manner by ∆EGFR. Dysregulated c-Met signaling contributes to the aggressive phenotype of glioblastoma, yet the mechanisms underlying the production of HGF in glioblastoma are poorly understood. We found a positive correlation between HGF and c-Met expression in glioblastoma, suggesting that they are coregulated. This is supported by the finding that in a c-Met/HGF axis-dependent glioblastoma cell line, shRNA-mediated silencing of c-Met, or treatment with the c-Met inhibitor SU11274, attenuated HGF expression. Biologically, c-Met knockdown decreased anchorage-independent colony formation and the tumorigenicity of intracranial xenografts. Building on prior findings that ∆EGFR enhanced c-Met activation, we found that ∆EGFR also led to increased HGF expression, which was reversed upon ∆EGFR inhibition with AG1478. ∆EGFR required c-Met to maintain elevated HGF expression, colony formation of glioblastoma cells, and the tumorigenicity of orthotopic xenografts. An unbiased mass spectrometry-based approach identified phosphotyrosine-related signaling changes that occurred with c-Met knockdown in a glioblastoma cell line expressing ΔEGFR and in parental cells. Notably, phosphorylation of STAT3, a master regulator of the mesenchymal GBM subtype and a known target of ∆EGFR, also decreased when c-Met was silenced in these cells, suggesting that the signals from these receptors converge on STAT3. Using a STAT3 inhibitor, WP1193, we showed that STAT3 inhibition decreased HGF mRNA expression in ΔEGFR-expressing glioblastoma cells. Consistent with these findings, constitutively active STAT3 partially restored HGF expression and anchorage-independent growth of c-Met knockdown glioblastoma cells that overexpressed ΔEGFR. We found that higher levels of HGF and c-Met expression associated with the mesenchymal GBM subtype. Taken together, these results suggest that the activity of c-Met regulates the expression of HGF in glioblastoma cells, that ∆EGFR feeds positively into this autocrine loop, that signaling of the two receptors together modulate HGF expression via STAT3, and that the HGF/c-Met axis may therefore be a good additional target for therapy of mesenchymal GBM tumors.

LMW-E MEDIATES MAMMARY TUMORIGENESIS BY DEREGULATING ACINAR MORPHOGENESIS & GENERATING CANCER STEM CELLS

Cyclin E is the regulatory subunit of the cyclin E/CDK2 complex that mediates the G1-S phase transition. N-terminal cleavage of cyclin E by elastase in breast cancer generates two low molecular weight (LMW) isoforms that exhibit both enhanced kinase activity and resistance to p21 and p27 inhibition compared to fulllength cyclin E. Clinically, approximately 27% of breast cancer patients overexpress LMW-E and associate with poor survival. Therefore, we hypothesize that LMW-E disrupts normal mammary acinar morphogenesis and serves as the initial route into breast tumor development. We first demonstrate that LMW-E overexpression in non-tumorigenic hMECs is sufficient to induce tumor formation in athymic mice significantly more than overexpression of full-length cyclin E and requires CDK2- associated kinase activity. Further in vivo passaging of these tumors augments LMW-E expression and tumorigenic potential. When subjected to acinar morphogenesis in vitro, LMW-E mediates significant morphological disruption by generating hyperproliferative and multi-acinar complexes. Proteomic analysis of patient tissues and tumor cells with high LMW-E expression reveals that the activation of the b-Raf-ERK1/2-mTOR pathway in concert with high LMW-E expression predicts poor patient survival. Combination treatment using roscovitine (CDK inhibitor) plus either rapamycin (mTOR inhibitor) or sorafenib (b-raf inhibitor) effectively prevented aberrant acinar formation in LMW-E-expressing cells by inducing the G1/S cell cycle arrest. In addition, the LMW-E-expressing tumor cells exhibit phenotypes characteristic of the EMT and enhanced cellular invasiveness. These tumor cells also enrich for cells with CSC phenotypes such as increased CD44hi/CD24lo population, enhanced mammosphere formation, and upregulation of ALDH expression and enzymatic activity. Furthermore, the CD44hi/CD24lo population also shows positive correlation with LMW-E expression in both the tumor cell line model and breast cancer patient samples (p<0.0001 & p=0.0435, respectively). Combination treatment using doxorubicin and salinomycin demonstrates synergistic cytotoxic effects in cells with LMW-E expression but not in those with full-length cyclin E expression. Finally, ProtoArray microarray identifies Hbo1 as a novel substrate of the cyclin E/CDK2 complex and its overexpression results in enrichment for CSCs. Collectively, these data emphasize the strong oncogenic potential of LMW-E in mammary tumorigenesis and suggest possible therapeutic strategies to treat breast cancer patients with high LMW-E expression.