The Tootle Lab’s long-term objective is to understand how particular prostaglandin signaling events result in specific biological outcomes. Prostaglandins are locally acting, transient hormones that mediate a wide variety of biological activities, from female reproduction to cancer development and progression. Prostaglandins are synthesized at their sites of action by cyclooxygenase (COX) enzymes, the targets of Aspirin and Advil. As prostaglandin signaling is transient and locally acting, to determine the molecular mechanism of prostaglandin action a cell-cell signaling model is needed. Drosophila is an excellent system to use, as Drosophila genetics has been routinely employed to identify and characterize signaling cascades at single cell resolutions.
Previously, we developed Drosophila oogenesis as a new and powerful model for studying prostaglandin signaling. Using both pharmacology and genetics, we discovered that prostaglandins mediate Drosophila follicle development, identified the Drosophila COX1 enzyme, Pxt, and revealed that genetic perturbation of prostaglandin signaling can be used to exam the function of prostaglandins. This research reveals that prostaglandin signaling modulates actin/membrane dynamics, cell migration, stem cell activity, and the timing of gene expression during Drosophila follicle development.
Prostaglandin signaling regulates the actin cytoskeleton
Prostaglandin signaling regulates actin dynamics during follicle development. Both pharmacology and genetics reveal that prostaglandin signaling is required for nurse cell dumping, a process in which the germline derived nurse cells push all of their cytoplasmic contents into the oocyte. In mutants with no prostaglandin signaling the actin structures required for nurse cell dumping are substantially reduced and often completely eliminated. By using a multifaceted experimental approach that combines Drosophila genetics, cell biology, live imaging, and biochemistry my lab will be able to determine where the prostaglandin signal is coming from, which prostaglandins are involved, whether this is by the canonical signaling pathway, how prostaglandin signaling interacts with known actin regulators, and the downstream changes in gene expression during nurse cell dumping. The results from these studies are likely to provide general insight into how prostaglandins regulate the cytoskeleton at a cellular level. Such mechanisms of prostaglandin action are likely to be reutilized throughout development, including mediating the cytoskeletal changes that occur during cancer progression and metastasis.
The lab had identified a number of actin binding proteins as new downstream effectors of prostaglandin signaling. Fascin, an actin bundling protein, is required downstream of prostaglandins to regulate bundle formation necessary for nurse cell dumping and to maintain cortical actin integrity. Importantly, this work provided the first link between prostaglandins and Fascin. We have identified Enabled as another effector of prostaglandins. Our data suggests that prostaglandins inhibit Enabled early in oogenesis to prevent early and aberrant actin filament and aggregate formation. Later, prostaglandins promote Enabled activity to drive bundle formation necessary for nurse cell dumping. Importantly, prostaglandins and the mammalian homologs of Fascin and Enabled (i.e. Mena) are known to play critical roles in cancer development and metastasis. Thus, the same mechanisms by which prostaglandins regulate Drosophila Fascin and Enabled are likely conserved in the instance of cancer. We plan to directly test this using breast cancer models.
Nuclear actin and actin binding proteins
Observations made during our studies focusing on the roles of prostaglandins in regulating the actin cytoskeleton and the development of tools for examining actin dynamics within the germline, have led to a new area of study - nuclear actin and its regulators. Actin plays critical but poorly understood roles in the nucleus. The structures of nuclear actin and how those structures mediate function remain largely unknown. Which actin binding proteins or regulators localize to the nucleus? What are their roles in modulating nuclear actin structure/function?
Prostaglandins and cancer
The research in the lab is expanding to uncover the molecular mechanisms by which individual prostaglandin signaling cascades and the complement of prostaglandins contribute to tumor initiation, growth, and metastasis.