PROJECT SUMMARY The research proposed in this application seeks to address the physiological basis of inhibition of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) by the enzyme sphingomyelinase (SMase). CFTR is the protein defective in the common genetic disease Cystic Fibrosis (CF). The current major cause of death for CF is pulmonary insufficiency caused by frequent bacterial infections and persistent inflammation of the lungs. Interestingly, both infection and inflammation promote secretion of the enzyme SMase, which our lab has shown to decrease the function of CFTR. To understand if SMase plays a role in worsening disease severity in CF, we will first quantify the amount of SMase in CF lungs by using mass spectrometry and immunohistochemistry. We will then determine the mechanism by which SMase inhibits CFTR by using electrophysiology to study the behavior of CFTR and pharmacological methods to negate the effects of SMase on CFTR activity. Lastly, we will determine the effect SMase-mediated inhibition of CFTR has on the efficacy of the only clinically-approved CFTR potentiator drug (VX-770). Based on our previous findings, we hypothesize that SMase is upregulated in the CF lung, inhibits CFTR via a novel mechanism, and prevents VX-770 from rescuing CFTR activity. Together, these data will help determine if CF patients need co-administration of a drug to nullify the effects of SMase on CFTR.