Signal transduction events involved in the control of directed cell migration

Telephone: (301) 435-3701

E-mail: parentc@helix.nih.gov

Office: Building 37, Room 1E24

Mailing Address:
National Cancer Institute (NCI)
37 Convent Drive, MSC 4255 

Bethesda, Maryland 20892-4255

• Biochemical, genetic, and cell biological analyses of directed cell migration 
• Use of the GFP technology to visualize signaling molecules in live migrating Dictyostelium amoebae and human neutrophils

All living cells can sense their environment. The term directional sensing refers to the ability of a cell to determine the direction and proximity of an extracellular stimulus. Directional sensing is needed to detect morphogens that control differentiation and attractants that direct cell migration, as in chemotaxis. This fascinating response is critical in embryogenesis, angiogenesis, neuronal patterning, wound healing, and immunity. Chemotaxis is strikingly exhibited during the life cycle of the social amoebae, Dictyostelium discoideum. During growth, these cells track down and phagocytose bacteria. When starved, they move towards secreted adenosine 3â-5â cyclic monophosphate (cAMP) signals, form aggregates, and differentiate into spore and stalk cells. The fundamental role of chemotaxis in this simple eukaryote provides a powerful system for its analysis at both genetic and biochemical levels. 

Both amoebae and mammalian leukocytes use G protein-linked signaling pathways to respond to chemoattractants. Binding of the attractants to receptors of the seven transmembrane helix class leads to the dissociation of the G proteins into alpha and beta/gamma-subunits. Chemotaxis is likely mediated through the beta/gamma-subunits. In both leukocytes and amoebae, chemoattractants elicit a variety of rapid responses including transient increases in Ca2+ influx, in the intracellular messengers IP₃, cAMP and guanosine 3â-5â cyclic monophosphate (cGMP), and in the phosphorylation of myosins I and II. Chemoattractants also induce actin polymerization, most likely through the activation of the Rho/Rac family of small guanosine trisphosphatases. All these events rapidly subside in the presence of persistent stimulation. This rapid inhibition may allow a migrating cell to "subtract" the ambient concentration of attractant and more accurately sense the direction of a gradient.

This laboratory is interested in studying how specific G protein-coupled signaling events translate into complex cellular responses. We are particularly interested in investigating the role of cAMP in directed cell migration. Using biochemical, cell biological and genetic analyses, our goal is to identify the components involved in the spatial control of signaling. By tagging various signaling proteins with the green fluorescent protein (GFP) we have been able to visualize in live cells where and when various cascades are activated. This has led us to propose a novel mechanism that could explain how chemotactic gradients are amplified. We are currently designing experiments that will allow us to understand how signaling components become asymmetrically distributed upon cellular polarization. In addition to exploiting the genetically tractable model system D. discoideum, we carry out experiments on human neutrophils. This gives us the opportunity to simultaneously develop signal transduction pathways in both systems. Collectively, our research projects are designed to provide insight on the role of various signaling cascades in chemotaxis and will have direct bearing on the understanding of clinically important processes such leukocyte migration to sites of inflammation as well as cancer metastasis.