Direct modulation of G-proteins by polyunsaturated fatty acids: a novel eicosanoid-independent regulatory mechanism in the developing lung.
Basal and fatty-acid-modulated G-protein function was studied in 1-3-day-pre-term, fetal guinea-pig, type II (fATII) pneumocyte apical membrane. Unstimulated (tonic) high-affinity GTPase activity (measured as [gamma-32P]GTP hydrolysis rate) was high and 77% pertussis toxin-insensitive. Alteration of this activity was used as a marker of G-protein regulation. Arachidonic acid (AA) showed a dose-dependent (IC50 = 48+/-8 microM) inhibition of activity at concentrations significantly below critical micellar concentrations; this effect was mimicked by other polyunsaturated fatty acids (IC50 for linoleic acid = 47 +/- 2 microM; IC50 for oleic acid = 106 +/- 11 microM). Saturated fatty acids showed no effect. The effect of AA on ouabain-insensitive ATPases in the same preparation was significantly lower, suggesting a specificity of the GTPase modulation effect. AA modulation of GTPase activity was not attenuated by blocking eicosanoid metabolism with inhibitors of 5'-lipoxygenase, cyclo-oxygenase and P-450. In order to explore further the mechanism of AA-G-protein interaction, the effect of AA on the time course and equilibrium binding of [35S]GTP[S] to apical membrane was studied. Consistent with our GTPase assay data, AA inhibited binding with an IC50 value of 71+/-1 microM; stearic acid did not mimic this effect. This is the first report of unsaturated-fatty-acid-specific modulation of lung G-protein function: since AA also up-regulates perinatal lung alveolar Na+ transport, we suggest this lipid/G-protein switch helps maintain pulmonary fluid homoeostasis around birth.
Mukhopadhyay
S
S
Lung Membrane Transport Group, Department of Child Health, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY, U.K.
Ramminger
S J
SJ
McLaughlin
M
M
Gambling
L
L
Olver
R E
RE
Kemp
P J
PJ
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D015777:Eicosanoids / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006168:Guinea Pigs; D008168:Lung / Q000196:embryology / Q000378:metabolism* / Q000648:ultrastructure; D015398:Signal Transduction
D015777:Eicosanoids; D005231:Fatty Acids, Unsaturated; D019204:GTP-Binding Proteins