Alcohol is the most commonly abused drug in the world. In the United States about half the adult population regularly consumes alcohol. It has been well established that alcohol has harmful effects on the lung. For example, heavy alcohol intake increases the risk for developing pulmonary diseases such as pneumonia, bronchitis and acute respiratory distress syndrome (ARDS). The first line of defense of the conducting airways is the airway epithelium, which contains tight junctions and expresses Zonula occluden-1 (ZO-1), and occludin. Claudin-1 is a transmembrane protein, which is important in regulating tight junction permeability claudin-1, . ZO-1 is a peripherally associated membrane protein, which links tight junction proteins to the actin cytoskeleton, other tight junction proteins (claudin and occludin) and is believed to be an important component in stabilizing tight junctions. Tight junctions are characteristically located at the apical-lateral borders in airway epithelium where they regulate cell polarity and act to selectively regulate the passage of water, ions, neutral molecules and inflammatory cells through the paracellular pathway. A number of studies have shown that alcohol disrupts tight junctions resulting in barrier leak. In the lung this occurs in the parenchyma compartment resulting in pulmonary edema and alveolar edema. Tight junctions also play a key role in regulating the barrier function in the conducting airways. Airway leak is a cardinal feature of airway diseases such as bronchitis and asthma. Increased leak contributes to airway edema, which is a classic finding of these diseases. However, little is known about the effects of alcohol in the conducting airways. We have recently observed that alcohol impairs ZO-1 and claudin-1 translocation to the cell membrane and increases tight junction permeability resulting in leakier airway epithelial cells. Our data link this leakiness to alcohol-induced changes in airway protein kinase C (PKC) activation resulting in impaired protein translocation to the cell membrane. These findings led us to hypothesize that: Alcohol promotes airway leak linked to the delocalization of ZO-1 and claudin-1 through a PKC-dependent pathway in the airway epithelium. We propose to test this hypothesis with 3 specific aims: 1) Determine the functional consequences of alcohol on tight junctions in the epithelium of the conducting airways; 2) Define the mechanism through which alcohol impairs ZO-1 and translocation; 3) Establish the impact of alcohol-triggered ZO-1 and rearrangement in an in vivo model of alcohol-fed mice. Results for these studies will improve our understanding of the impact alcohol has on airway epithelial barrier functions, which are critical for the understanding and treatment of airway diseases common among alcohol abusers. claudin-1 claudin-1 )