Research

Our laboratory aims to answer the question: How and why cells decide to move, during embryonic development and in pathological conditions such as tumor metastasis. We employ a cross-species experimental strategy by comparing the genetic system Drosophila and human cell cultures. There are five specific areas of interest:

1) The follicular epithelium that envelopes the Drosophila egg is an excellent model for studying developmental regulation of epithelial morphogenesis and for analyzing the epithelial-to-mesenchymal transition that underlies the initiation of tumor metastasis.  We are focusing on the function of two human tumor suppressor gene homologs in this model system: VHL and Nm23.  We are analyzing a novel vesicle transport function of these two genes that is required for maintaining the epithelial integrity and response to extra cellular signals.  We show that such function is conserved in the human cells.

(2) The functions of VHL and another tumor suppressor gene nm23 are studied in the Drosophila vascular development and in human renal carcinoma and primary microvascular endothelial cells. We identified an interesting intra-cellular vesicle transport system that differentially regulates the cell surface localization of different growth factor receptor. Disrupted balance of subcellular localization of these receptors in the VHL mutant, probably acting through the loss of function of nm23, results in abnormal cell invasion and migration. These findings provided an excellent model for studying the control of cell migration in development and in tumor metastasis.

(3) We have demonstrated that the Drosophila homologue of a putative anti-metastasis ETS factor (PDEF) modulates the mesenchymal transition of the primordial germ cells, in a migration and invasion process remarkably similar to that undertaken by metastatic tumors. We are currently comparing the Drosophila and the mouse germ cell migration process, focusing on the function of PDEF.

(4) We have identified a human gene product, mlp-1, that may be important in promoting tumor invasion. It regulates the expression of alpha3 integrin by a novel mRNA localization mechanism. Ongoing studies aim to elucidate this highly interesting cellular mechanism.

(5) VHL patients develop highly vascularized tumor. It has been assumed that VHL tumor cell can attract blood vessel growth (pro-angiogenic). We, however, hypothesized that VHL heterozygosity in the blood vessel cells (microvascular endothelial cells) may also contribute to elevated angiogenic potential. Using a cross-species strategy, comparing the Drosophila trachea, angiogenesis in knockout mice, and 3-dimentional endothelial-tumor cell co-culture, we are examining the role and mechanism of the VHL function in angiogenesis.

Drosophila trachea marked by immunohistochemistry and observed by confocal laser microscopy. The wild-type embryo (upper pane) shows an intricate network of tubular structure. The network is disrupted in mutants of the Drosophila oncogene pnt (lower panel).
nm23 is a potential human metastasis inhibitor but its exact cellular function is unclear. Here we show that the mutations in the Drosophila homolog (78% identity) result in ectopic filopedia formation in the migrating tracheal cells (arrows in bottom panels) as compared to the wild-type cell, which usually sprout one or two filopodia (upper pane).
Confocal laser scanning images of Drosophila egg chambers of wild-type (top panel) and nm23 mutant (lower panels, zoomed-in views) genetic backgrounds. The samples are stained for Nm23 (green), E-cadherin (red), and nuclei (blue). The wild-type egg shows organized single-layer epithelial follicle cells (inset) with E-cadherin at the apical-lateral corners of the cell junctions. In nm23 mutant, E-cadherin becomes diffused and the follicle cells become invasive  (arrows) into the underlying germ cell complex.
	Human renal carcinoma cells 786-0 (VHL mutant) and the counterpart transfected with wild-type VHL gene [786(VHL+)] are examined for FGF receptor (FGFR) and EGF receptor (EGFR) expression, using immunohistochemistry and confocal microscopy. In VHL mutant cells, FGFR is highly concentrated on the cell surface while EGFR accumulates in the Golgi (arrow). In VHL+ cells, FGFR accumulates only at the cell protrusions while EGFR is expressed throughout the cell surface.
	A confocal micrograph showing human primary microvascular endothelial cells (in red) and VHL tumor cells (in green) come together while primitive vessel-like structures are formed. The two cell types are originally separated by 1-mm of collagen gel.
	Current lab members (December 2005): Standing from left to right, Mastan Chintalapudi (postdoc), Vincent Dammai (research assistant professor), Gouthami Nallamouthu (postdoc), Kristen Champion (PhD student), Julie Woolworth (PhD student), Jonathan Sticca (undergraduate student), Nurgun Kose (lab manager), Yair Adereth (postdoc); seated from left to right, Anita Hsouna (postdoc), Maria Guinea (postdoc), Tien Hsu (career counselor).

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