Judith Horev

Dominant negative Met reduces tumorigenicity-metastasis and increases tubule formation in mammary cells

Activation of the Met tyrosine kinase growth factor receptor by its ligand HGF/SF has been shown to increase in vitro invasiveness in epithelial cell lines. To study the effect of Met-HGF/SF signaling in breast cancer cells, we transfected met, hgf/sf and dominant negative (DN) forms of met into the poorly differentiated metastatic murine mammary adenocarcinoma cell line DA3. These cells express moderate levels of endogenous Met, which is rapidly phosphorylated in response to HGF/SF treatment. Met+hgf/sf transfection results in significantly increased tumorigenic and metastatic activity in vivo accompanied by reduced tubule formation. DA3 cells transfected with DN forms of Met (DN-DA3) exhibit reduced Met phosphorylation following exposure to HGF/SF. Furthermore, as compared to the parental cells, the DN-DA3 cells exhibit diminished in vitro scattering and invasiveness, while in vivo they display greatly reduced tumorigenicity and spontaneous metastasis. Tumors emanating from DN-DA3 cells injected to BALB/C mice are highly differentiated and display extensive tubule formation. These results suggest that Met-HGF/SF signaling is a determining factor in the delicate balance between differentiation/tubule formation and tumorigenicity-metastasis.

Molecular imaging of tumors and metastases using chemical exchange saturation transfer (CEST) MRI

The two glucose analogs 2-deoxy-D-glucose (2-DG) and 2-fluoro-2-deoxy-D-glucose (FDG) are preferentially taken up by cancer cells, undergo phosphorylation and accumulate in the cells. Owing to their exchangeable protons on their hydroxyl residues they exhibit significant chemical exchange saturation transfer (CEST) effect in MRI. Here we report CEST-MRI on mice bearing orthotopic mammary tumors injected with 2-DG or FDG. The tumor exhibited an enhanced CEST effect of up to 30% that persisted for over one hour. Thus 2-DG/FDG CEST MRI can replace PET/CT or PET/MRI for cancer research in laboratory animals, but also has the potential to be used in the clinic for the detection of tumors and metastases, distinguishing between malignant and benign tumors and monitoring tumor response to therapy as well as tumors metabolism noninvasively by using MRI, without the need for radio-labeled isotopes.

Cell Motility Dynamics: A Novel Segmentation Algorithm to Quantify Multi-Cellular Bright Field Microscopy Images

Confocal microscopy analysis of fluorescence and morphology is becoming the standard tool in cell biology and molecular imaging. Accurate quantification algorithms are required to enhance the understanding of different biological phenomena. We present a novel approach based on image-segmentation of multi-cellular regions in bright field images demonstrating enhanced quantitative analyses and better understanding of cell motility. We present MultiCellSeg, a segmentation algorithm to separate between multi-cellular and background regions for bright field images, which is based on classification of local patches within an image: a cascade of Support Vector Machines (SVMs) is applied using basic image features. Post processing includes additional classification and graph-cut segmentation to reclassify erroneous regions and refine the segmentation. This approach leads to a parameter-free and robust algorithm. Comparison to an alternative algorithm on wound healing assay images demonstrates its superiority. The proposed approach was used to evaluate common cell migration models such as wound healing and scatter assay. It was applied to quantify the acceleration effect of Hepatocyte growth factor/scatter factor (HGF/SF) on healing rate in a time lapse confocal microscopy wound healing assay and demonstrated that the healing rate is linear in both treated and untreated cells, and that HGF/SF accelerates the healing rate by approximately two-fold. A novel fully automated, accurate, zero-parameters method to classify and score scatter-assay images was developed and demonstrated that multi-cellular texture is an excellent descriptor to measure HGF/SF-induced cell scattering. We show that exploitation of textural information from differential interference contrast (DIC) images on the multi-cellular level can prove beneficial for the analyses of wound healing and scatter assays. The proposed approach is generic and can be used alone or alongside traditional fluorescence single-cell processing to perform objective, accurate quantitative analyses for various biological applications.

A Novel Recombinant Soluble Splice Variant of Met Is a Potent Antagonist of the Hepatocyte Growth Factor/Scatter Factor-Met Pathway

Purpose: The Met receptor tyrosine kinase and its ligand, hepatocyte growth factor/scatter factor (HGF/SF), are involved in a wide range of biological activities, including cell proliferation, motility, invasion, and angiogenesis. The HGF/SF-Met signaling pathway is frequently activated in a variety of cancers, and uncontrolled Met activation correlates with highly invasive tumors and poor prognosis. In this study, we investigated the inhibitory effect of a novel soluble splice variant of Met on the HGF/SF-Met pathway. Experimental Design: Using our alternative splicing modeling platform LEADS, we have identified a novel splice variant of the Met receptor, which encodes a truncated soluble form of the receptor. This variant was produced as a recombinant Fc-fused protein named Cgen-241A and was tested in various cell-based assays representing different outcomes of the HGF/SF-Met pathway. Results: Cgen-241A significantly inhibited HGF/SF-induced Met phosphorylation as well as cell proliferation and survival. In addition, Cgen-241A showed a profound inhibitory effect on cell scattering, invasion, and urokinase up-regulation. The inhibitory effects of Cgen-241A were shown in multiple human and nonhuman cell types, representing different modes of Met activation. Furthermore, Cgen-241A showed direct binding to HGF/SF. Conclusions: Taken together, our results indicate that Cgen-241A is a potent antagonist of the HGF/SF-Met pathway, underlining its potential as a therapeutic agent for the treatment of a wide variety of human malignancies that are dependent on this pathway.

Mimp, a Mitochondrial Carrier Homologue, Inhibits Met-HGF/SF-Induced Scattering and Tumorigenicity by Altering Met-HGF/SF Signaling Pathways

We have recently shown that Mimp, a mitochondrial carrier protein homologue, is induced by Met-hepatocyte growth factor/scatter factor (HGF/SF) signaling and decreases the mitochondrial membrane potential in DA3 mammary adenocarcinoma cells. We show here that induction of Mimp leads to growth arrest in response to HGF/SF by arresting cells at the S phase of the cell cycle. Induction of Mimp or its transient expression does not lead to apoptosis. Mimp also attenuates HGF/SF-induced cellular scattering in vitro and tumor growth in vivo. The exogenous induction of Mimp at levels similar to its endogenous induction by HGF/SF increases the level of the Met protein and its phosphorylation by HGF/SF but reduces the levels of Shc and prevents the HGF/SF-induced tyrosine phosphorylation of Grb2 and Shc. In contrast, the level of phosphatidylinositol 3-kinase (PI3K) increases following Mimp induction and the level of phosphorylated PI3K in response to HGF/SF is unaffected by the exogenous induction of Mimp. Moreover, exogenous Mimp prevents the HGF/SF-induced transcription of the serum response element-luciferase reporter gene. Our results show that Mimp expression reduces Met-HGF/SF-induced proliferation and scattering by attenuating and altering the downstream signaling of Met. These data show a new link between a tyrosine kinase growth factor receptor and a mitochondrial carrier homologue that regulates cellular growth, motility, and tumorigenicity.

Met kinetic signature derived from the response to HGF/SF in a cellular model predicts breast cancer patient survival.

To determine the signaling pathways leading from Met activation to metastasis and poor prognosis, we measured the kinetic gene alterations in breast cancer cell lines in response to HGF/SF. Using a network inference tool we analyzed the putative protein-protein interaction pathways leading from Met to these genes and studied their specificity to Met and prognostic potential. We identified a Met kinetic signature consisting of 131 genes. The signature correlates with Met activation and with response to anti-Met therapy (p<0.005) in in-vitro models. It also identifies breast cancer patients who are at high risk to develop an aggressive disease in six large published breast cancer patient cohorts (p<0.01, N>1000). Moreover, we have identified novel putative Met pathways, which correlate with Met activity and patient prognosis. This signature may facilitate personalized therapy by identifying patients who will respond to anti-Met therapy. Moreover, this novel approach may be applied for other tyrosine kinases and other malignancies.

Mimp/Mtch2, an Obesity Susceptibility Gene, Induces Alteration of Fatty Acid Metabolism in Transgenic Mice.

Objective Metabolic dysfunctions, such as fatty liver, obesity and insulin resistance, are among the most common contemporary diseases worldwide, and their prevalence is continuously rising. Mimp/Mtch2 is a mitochondrial carrier protein homologue, which localizes to the mitochondria and induces mitochondrial depolarization. Mimp/Mtch2 single-nucleotide polymorphism is associated with obesity in humans and its loss in mice muscle protects from obesity. Our aim was to study the effects of Mimp/Mtch2 overexpression in vivo. Methods Transgenic mice overexpressing Mimp/Mtch2-GFP were characterized and monitored for lipid accumulation, weight and blood glucose levels. Transgenic mice liver and kidneys were used for gene expression analysis. Results Mimp/Mtch2-GFP transgenic mice express high levels of fatty acid synthase and of β-oxidation genes and develop fatty livers and kidneys. Moreover, high-fat diet–fed Mimp/Mtch2 mice exhibit high blood glucose levels. Our results also show that Mimp/Mtch2 is involved in lipid accumulation and uptake in cells and perhaps in human obesity. Conclusions Mimp/Mtch2 alters lipid metabolism and may play a role in the onset of obesity and development of insulin resistance.

H23 Monoclonal Antibody Recognizes a Breast Tumor Associated Antigen: Clinical and Molecular Studies

A monoclonal antibody (MoAb) H23 was generated in our laboratory against particles released by the T47D cell line. H23 MoAb recognized specific antigens in 90% of 590 breast tumor biopsies tested by the indirect immunoperoxidase test. Furthermore, the H23 MoAb detects antigens in sera and body fluids of patients with breast carcinoma. The level of serum antigen in 546 individuals tested correlates with the clinical status of the disease and with poor survival. The cDNA coding for the epitope recognized by H23 MoAb was isolated from a cDNA expression library and its sequence and orientation established. The nucleotide sequence showed that the cDNA insert was composed of 60 bp tandem repeats. We have analyzed the RNA isolated from primary human tumors, and it was demonstrated that breast carcinomas expressed the highest levels of mRNA species hybridizing with this cDNA. The gene coding for the cDNA was isolated from a genomic library and encompasses 7.5 kb. A 2.3 kb segment of this gene was found to be an array of tandem 60 bp repeat units whilst the remaining parts of the gene do not contain these repeats. The fact that these non-repeat sequences hybridize to identical mRNA species, has led to ongoing studies aimed at their further characterization.

Molecular Analysis of H23 Epithelial Tumor Antigen - Differentially Spliced Full Length cDNAs and Gene

The isolation and characterization of the complementary DNAs (cDNAs) and gene which code for an epithelial tumor antigen (H23-ETA), aberrantly expressed in human breast tumor tissue, are described here. A diversity of H23-ETA protein forms, is generated by a series of alternative splicing events that occur in regions located upstream and downstream to a central tandem 20 amino acid (aa) repeat array (TRA) that is rich in proline, serine and threonine residues. The upstream region shows that differential usage of alternative splice acceptor sites generates two protein forms containing putative signal peptides of varying hydrophobicities located at the NH2 terminus. The region downstream to the tandem repeat array indicates that one mRNA transcript is collinear with the gene and defines a 160 aa open reading frame (secreted or sec form). A second cDNA correlates with a mRNA that is generated by a series of splicing events and codes for 149 aa downstream to the TRA, identical with the aa sequence of the unspliced cDNA, after which it diverges and continues for an additional 179 aa. This sequence (transmembrane or tm form) contains a highly hydrophobic transmembrane domain of 28 aa followed by a hydrophilic “transfer-stop signal” (Arg Arg Lys) and a cytoplasmic domain of 72 aa. The various protein forms (alternative signal sequences, secreted and transmembrane) are likely routed to different cytoplasmic, cell membrane and extracellular compartments. Reverse PCR indicates that the relative ratios of the alternatively spliced forms vary in different epithelial tissues. To identify the individual protein species, monoclonal antibodies (mAb) are being generated against synthetic peptides unique to each form. The H23-ETA gene was also isolated and sequenced, demonstrating a putative promoter region that includes a ‘TATA’ box, Spl binding elements and an upstream putative hormone responsive element. Commensurate with these findings, H23-ETA expression was increased following hormonal treatment of BT549 breast tumor cells. These molecular studies have unravelled novel H23-ETA protein and gene structures, and facilitate future investigations that will focus on H23-ETA function and interaction with other cellular proteins.