Activation of endogenous deltaF508 cystic fibrosis transmembrane conductance regulator by phosphodiesterase inhibition.

Abstract

Many heterologously expressed mutants of the cystic fibrosis transmembrane conductance regulator (CFTR) exhibit residual chloride channel activity that can be stimulated by agonists of the adenylate cyclase/protein kinase A pathway. Because of clinical implications for cystic fibrosis of activating mutants in vivo, we are investigating whether ⌬ F508, the most common disease-associated CFTR mutation, can be activated in airway epithelial cells.

Role of Oxygen Availability in CFTR Expression and Function

“…For example, the A455E mutation results in marginally reduced function of CFTR and clinically mild pulmonary disease, a later age at diagnosis, and a substantially improved prognosis (37). Even classically severe mutations (e.g., the common DF508 allele) have been reported by some (but not all) groups to retain low-level function in humans and mice in vivo (38)(39)(40)(41)(42). If residual CFTR mRNA, protein, and function serve to slow CF pulmonary decline, it is reasonable to imagine that repression of CFTR by low oxygen could contribute to respiratory failure in the disease.…”

cGMP Stimulation of Cystic Fibrosis Transmembrane Conductance Regulator Cl− Channels Co-expressed with cGMP-dependent Protein Kinase Type II but Not Type Iβ

“…Furthermore, the role of cGK II in mediating cGMP-provoked activation of CFTR activation cannot be mimicked by cGK I or cAK in our cell system. In particular, the ascribed role of cAK in the cGMP-induced activation of CFTR in several cell lines (29 -33) may therefore not be widely valid but restricted to cells either expressing a type III cGMP-inhibited phosphodiesterase to elevate cAMP (29) or cells in which very high levels of cGMP can be attained to cross-activate cAK (30 -32). The intestinal cell lines T84 and Caco-2 used to demonstrate the latter mechanism appear nevertheless to be unsuitable models for studying physiological mechanisms, since they do not contain detectable levels of cGK II or cGK I (7).…”

A domain mimic increases ΔF508 CFTR trafficking and restores cAMP-stimulated anion secretion in cystic fibrosis epithelia

“…Even if ⌬F508 CFTR has reduced function and shorter membrane residence (32), previous studies suggest that only a small amount (ϳ10 -15%) of ⌬F508 CFTR activity in the membrane is required to restore epithelial function and moderate disease (15,26). Combined with recent pharmacological studies showing that ⌬F508 hCFTR channel activity can be significantly enhanced by treatment with compounds such as 8-cyclopentyl-1,3-dipropylxanthine (CPX), genistein, or class III phosphodiesterase inhibitors (28), it is clear that correcting ⌬F508 hCFTR trafficking is a viable strategy for treating CF.…”