Full Research Project Six

Genetic analysis of Egfr signaling and cell adhesion

Co-Principal Investigators:
Bruce Edgar, Full Member, Basic Sciences - FHCRC
Jennifer Curtiss, Assistant Professor, Biology - NMSU

Whether or not metastasis occurs can make the difference between life and death for a cancer patient and whether or not a cancer cell metastasizes lies in its ability and propensity to adhere to other cells. The presence and activity of the cell adhesion molecule E-cadherin in adherens junctions is required for integrity of epithelia and its regulation is critical for morphogenesis of epithelial-derived structures. Little wonder that unregulated E-cadherin activity has been implicated in development and progression of highly malignant invasive carcinomas. But what regulates E-cadherin expression and activity? We have discovered that the Epidermal Growth Factor Receptor (Egfr) signaling pathway, which is also associated with cancer cell invasion, regulates expression of E-cadherin and differential cell affinity in two Drosophila epithelia, the wing and eye-antennal imaginal discs. Furthermore, Egfr signaling and E-cadherin function have interrelated functions in the morphogenesis of structures such as the wing veins and ommatidia, which are derived from the wing and eye discs, respectively. The small molecule GTPase Rap1 also affects E-cadherin localization and the differentiation of Egfr-dependent cell types during both wing and eye development. In an effort to elucidate the relationships between Egfr, Rap1 and E-cadherin, we will use loss- and gain-of-function approaches to determine what role Rap1 plays in the developing wing and eye imaginal discs. We will also use a mutation-based approach to explore the effect of E-cadherin-mediated adhesion on Egfr signaling. We will use Rap1 gain-of-function phenotypes to screen for genes involved in controlling E-cadherin. Finally, we will use a microarray-based strategy to identify transcriptional targets of the Egfr signaling pathway and Rap1. The remarkable similarities between Drosophila and vertebrates in these developmental processes suggest that our discoveries will lead to new tactics in the fight against cancer.

The following questions will be addressed:

1. Aim 1: What role does Rap1 play in Egfr-dependent developmental processes? Using both gain- and loss-of-function approaches, we will determine Rap1Õs function in the developing wing and eye imaginal discs. Our analysis will focus on wing veins and photoreceptors, two cell types that require Egfr signaling for their specification. As part of this analysis, we will determine the epistatic relationship between Egfr and Rap1 signaling in these cells.
2. Aim 2: To what extent is DE-cad-mediated adhesion necessary for Egfr signaling? Using a DE-cad-RNAi transgene, we will compromise DE-cad adhesion in wing and eye cells as Egfr-dependent cell types are being specified. Effects on cell fate and di-phospho-ERK staining (dp-ERK, a readout of Egfr signaling) will be analyzed. As a second test, we will express Egfr ligands in clones lacking either Rap1 or DE-cad function. The ability of these cells to activate dp-ERK staining in adjacent wild-type cells will be tested. Finally, we will target DE-cad to apical regions of the epithelial membrane to determine whether an inflexible pattern of DE-cad subcellular localization affects Egfr signaling and wing and eye cell fates.
3. Aim 3: What are the mechanisms by which Rap1 controls DE-cad localization? As a first step toward understanding how DE-cad localization is controlled during wing vein and photoreceptor differentiation, we will identify genes that suppress or enhance mild Rap1 gain-of-function phenotypes in the wing and eye. Initially, a set of genetic deficiencies will be used to screen a large portion of the Drosophila genome.
4. Aim 4: To what extent do Egfr and Rap1 share a common group of transcriptional targets in differentiating wing and eye cells? We will use microarray analysis to determine the full complement of genes regulated by either Ras or Rap1 in the pupal wing and eye. Both gain and loss-of-function approaches will be used.

The results of these experiments will elaborate a pathway of control from Egfr signaling to cell adhesion and as such, should illuminate parallel studies in vertebrates related to the role of Egfr signaling in cell transformation and metastasis.

For More Information:

Information about Dr. Curtiss' research can be found at http://biology-web.nmsu.edu/webpages/faculty_websites/jennifer_curtiss.html

Faculty and students interested in learning more about this project may contact Dr. Bruce Edgar or Dr. Jennifer Curtiss.