Identification of the fatty acid activation site on human ClC-2

Fatty acids (including lubiprostone and cobiprostone) are human ClC-2 (hClC-2) Cl– channel activators. Molecular and cellular mechanisms underlying this activation were examined. Role of a four-amino acid PKA activation site, RGET691, of hClC-2 was investigated using wild-type (WT) and mutant (AGET, RGEA, and AGAA) hClC-2 expressed in 293EBNA cells as well as involvement of PKA, intracellular cAMP concentration ([cAMP]i), EP2, or EP4 receptor agonist activity. All fatty acids [lubiprostone, cobiprostone, eicosatetraynoic acid (ETYA), oleic acid, and elaidic acid] caused significant rightward shifts in concentration-dependent Cl– current activation (increasing EC50s) with mutant compared with WT hClC-2 channels, without changing time and voltage dependence, current-voltage rectification, or methadone inhibition of the channel. As with lubiprostone, cobiprostone activation of hClC-2 occurred with PKA inhibitor (myristoylated protein kinase inhibitor) present or when using double PKA activation site (RRAA655/RGEA691) mutant. Cobiprostone did not activate human CFTR. Fatty acids did not increase [cAMP]i in hClC-2/293EBNA or T84 cells. Using T84 CFTR knockdown cells, cobiprostone increased hClC-2 Cl– currents without increasing [cAMP]i, while PGE2 and forskolin-IBMX increased both. Fatty acids were not agonists of EP2 or EP4 receptors. L-161,982, a supposed EP4-selective inhibitor, had no effect on lubiprostone-activated hClC-2 Cl– currents but significantl...
Source: AJP: Cell Physiology - Category: Cytology Authors: Tags: RESEARCH ARTICLE Source Type: research