UC Berkeley

Pseudomonas aeruginosa are gram-negative bacteria that colonize the human airway.

They are of great clinical importance, especially for patients with the genetic disorder Cystic

Fibrosis, a disease characterized by persistent infection and hyper-inflammation in the airways

(Hoiby et al., 1977). The innate immune response to P. aeruginosa in airway cells consists of

fluid secretion driven by the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) and

the release of inflammatory cytokines for the recruitment of phagocytes. The present work

addresses the role of two secreted products from P. aeruginosa and their effects on these

processes. Flagellin, the protein monomer of the P. aeruginosa flagellum, has been previously

shown to induce cytokine secretion through Toll-Like Receptor 5 (TLR5) (Zhang et al., 2005)

and to activate CFTR-mediated secretion through an unknown mechanism (Illek et al., 2008). In

the present study I attempted to discover the signaling pathway mediating CFTR secretion from

flagellin. Though this work did not yield a definitive pathway, many possibilities were explored

and the response to flagellin was better characterized than in previous work. In addition to my

study of flagellin, I also studied the effects of a P. aeruginosa quorum-sensing signaling

molecule, N-(3-Oxododecanoyl)-L-homoserine lactone (HSL-C12), on inflammatory signaling

in mammalian cells. Previous work has characterized the response to HSL-C12 as either pro- or

anti-inflammatory depending on the system used and the measurements taken (Telford et al.,

1998, Smith et al., 2001, Smith et al., 2002, Kravchenko et al., 2006, Jahoor et al., 2008,

Kravchenko et al., 2008). In my study I utilized both gene expression and cytokine secretion

measurements to determine that HSL-C12 has anti-inflammatory characteristics in short

treatments but pro-inflammatory characteristics in longer treatments and that both of these

phenotypes stem from an inhibition of host protein synthesis. Together with what is already

known about P. aeruginosa infection, my data helps to paint a picture of how secreted factors

affect the course of infection and inflammatory response to P. aeruginosa in the human airway.