Understanding how a cell moves in response to environmental signals is a fundamental challenge in biology. Mena, VASP and EVL, highly related proteins that comprise the Ena/VASP family, play pivotal roles in movement and shape change1 for a variety of cells, including fibroblasts, endothelial cells, epithelial cells, and neurons;Ena/VASP directly regulates actin filament network assembly, modulate morphology and behavior of membrane protrusions, and influences cell motility. One major goal for the current proposal is to study how Ena/VASP function contributes to chemotactic responses in carcinoma cells. Chemotactic cues trigger second messenger pathways that activate kinases, and phosphorylate Ena/VASP proteins. Specific Mena isoforms play key roles in tumor cell invasion and motility in response to Epidermal Growth Factor Receptor (EGFR) signaling. Thus, we propose that Ena/VASP proteins integrate signals from second messenger pathways to execute required motile responses, and are thus not only well positioned to control chemotactic motility, but are in fact generally involved in systems that require guided motility. The study of Mena tumor invasion-specific isoforms is particularly relevant to understanding how tumor cells acquire the ability to move and respond to a chemotactic cue. A second major goal for the current proposal is to examine the requirements for Ena/VASP function in epidermal morphogenesis and wound repair using newly generated conditional knockout mice. Several lines of evidence indicate that Ena/VASP function is required for epithelial morphogenesis and epithelial sheet fusion. Throughout development, there are many morphogenetic episodes involving fusion of two epithelial sheets or shelves of tissue. The most fully explored of these events are fusion and zippering closed of the neural tube, of the two secondary palates, and of the eyelids as the eyes close part way through gestation;embryos deficient in Ena/VASP exhibit all of these defects. While the forces driving these tissues together have been partially described, very little is known about the genetics or cell biology of the final fusion events for any of these processes;if this final knitting together event fails, the consequences can be devastating, resulting in congenital abnormalities as severe as cleft palate or spina bifda. Epithelial sheet migration and fusion is also required during wound repair, another process we will examine in this proposal. Together, these studies will provide valuable insight into the mechanisms controlling cell motility in both normal development and disease.
Drugs that block the EGFR pathway are widely used to treat a variety of cancers; thus, by understanding how invasion-specific Mena isoforms sensitizes carcinoma cells to EGF and amplifies their response, valuable insight into how certain cancers become resistant to therapies that attenuate EGFR signaling will be gained. Epithelial sheet movements during process such as eyelid closure and wound healing are dependent of EGF and EGF-related factors, thus studies of Ena/VASP in epithelial migration and sheet fusion should prove valuable in developing new ways to enhance treatment of wounds.
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