UC San Diego

Polymorphonuclear leukocytes (neutrophils) utilize an extremely sensitive chemosensory system to detect and migrate towards invading pathogens and damaged tissues in many species, including humans. Chemoattractants, chemical compounds released by such targets, bind to receptors on the neutrophil cell membrane and activate signal transduction cascades that promote directional migration. Neutrophils are capable of correctly orienting themselves in fields of chemoattractant as shallow as 1% across the length of the cell body. To maintain correct polarity in such shallow chemoattractant fields, the cells must be able to amplify these external signals. In this dissertation, ATP is identified as an autocrine/paracrine modulator of neutrophil chemotaxis. In response to stimulation with chemoattractants, neutrophils release ATP into the extracellular space. A novel assay for extracellular ATP was developed and reveals that ATP is released predominantly at the leading edge of stimulated neutrophils. Neutrophils rapidly metabolize released ATP, ultimately to adenosine. Elimination of extracellular ATP or adenosine inhibits chemotaxis, revealing that both compounds play a critical role in this process. Release of ATP at the leading edge establishes polarity in chemoattractant fields through the activation of P2Y2 receptors. Extracellular adenosine drives forward movement by activating A3 adenosine receptors, which localize at the leading edge of migrating cells. The hydrolysis of ATP (and generation of adenosine) is facilitated by ecto- nucleoside triphospho-dihydrolase 1 (E-NTPDase1/CD39), which is also localized at the leading edge. Inhibition of any of these steps leads to aberrant cell migration, revealing a novel autocrine/paracrine signal amplification system in neutrophils that is critical for chemotaxis