No abstract

ϩ uptake, suggesting that all these molecules are carried by the same transport mechanism. These findings demonstrate the existence and functional role of a pHdependent organic cation uptake machinery, namely OCTN1 and OCTN2, in human airway epithelia. We suggest that epithelial OCTN1/2 are involved in the delivery of inhaled cationic bronchodilators to the airway tissue.

Human airway mucosa synthesizes and secretes lactoperoxidase (LPO).

Epithelia express oxidative anti-microbial protection that uses lactoperoxidase (LPO), hydrogen peroxide (H 2 O 2 ) and thiocyanate to generate the reactive hypothiocyanite. Duox1 and Duox2, found in epithelia, are hypothesized to provide H 2 O 2 for use by the LPO. To investigate regulation of oxidative LPO-mediated host defense by bacterial and inflammatory stimuli, LPO and Duox mRNA were followed in differentiated primary human airway epithelial cells, challenged with Pseudomonas aeruginosa flagellin or IFNγ. Flagellin upregulated Duox2 mRNA 20-fold, but only upregulated LPO mRNA 2.5-fold. IFNγ increased Duox2 mRNA 127-fold and upregulated LPO mRNA 10-fold. DuoxA2, needed for Duox2 activity, was also upregulated by flagellin and IFNγ. Both stimuli increased H 2 O 2 synthesis and LPO-dependent killing of Pseudomonas aeruginosa. Reduction of Duox1 by siRNA showed little effect on basal H 2 O 2 production, while Duox2 siRNA markedly reduced basal H 2 O 2 production and resulted in an 8-fold increase in Nox4 mRNA. In conclusion, large increases in Duox2 mediated H 2 O 2 production appear to be coordinated with increases in LPO mRNA and, without increased LPO, H 2 O 2 levels in airway secretion are expected to increase substantially. The data suggest that Duox2 is the major contributor to basal H 2 O 2 synthesis despite the presence of greater amounts of Duox1.

Wnt/β-catenin signaling is an essential pathway that regulates numerous cellular processes, including cell survival. The molecular mechanisms contributing to pro-survival Wnt signaling are mostly unknown. Signal transducer and activator of transcription proteins (STATs) are a well-described family of transcription factors. STAT3 induces expression of anti-apoptotic genes in many tissues and is a downstream mediator of protective growth factors and cytokines. In this study, we investigated whether pro-survival Wnt signaling is mediated by STAT3. The Wnt3a ligand activated Wnt signaling in the retinal pigment epithelium ARPE-19 cell line and significantly increased the viability of cells exposed to oxidative stress. Furthermore, Wnt3a increased STAT3 activation and nuclear translocation, as measured by an antibody against phosphorylated STAT3. Reducing STAT3 levels with siRNA eliminated Wnt3a-dependent protection from oxidative stress. Together, these data demonstrate a previously unknown link between Wnt3a-mediated activation of STAT3 and cell survival, and indicate cross-talk between two important pro-survival signaling pathways.