Role of furin in granular acidification in the endocrine pancreas: identification of the V-ATPase subunit Ac45 as a candidate substrate.
Furin is a proprotein convertase which activates a variety of regulatory proteins in the constitutive exocytic and endocytic pathway. The effect of genetic ablation of fur was studied in the endocrine pancreas to define its physiological function in the regulated secretory pathway. Pdx1-Cre/loxP furin KO mice show decreased secretion of insulin and impaired processing of known PC2 substrates like proPC2 and proinsulin II. Both secretion and PC2 activity depend on granule acidification, which was demonstrated to be significantly decreased in furin-deficient beta cells by using the acidotrophic agent 3-(2,4-dinitroanilino)-3'amino-N-methyldipropylamine (DAMP). Ac45, an accessory subunit of the proton pump V-ATPase, was investigated as a candidate substrate. Ac45 is highly expressed in islets of Langerhans and furin was able to cleave Ac45 ex vivo. Furthermore, the exact cleavage site was determined. In addition, reduced regulated secretion and proinsulin II processing could be obtained in the insulinoma cell line betaTC3 by downregulation of either furin or Ac45. Together, these data establish an important role for furin in regulated secretion, particularly in intragranular acidification most likely due to impaired processing of Ac45.
Louagie
Els
E
Department of Human Genetics, Box 602, Katholieke Universiteit Leuven, Gasthuisberg O/N 1, Herestraat 49, B-3000 Leuven, Belgium.
Taylor
Neil A
NA
Flamez
Daisy
D
Roebroek
Anton J M
AJ
Bright
Nicholas A
NA
Meulemans
Sandra
S
Quintens
Roel
R
Herrera
Pedro L
PL
Schuit
Frans
F
Van de Ven
Wim J M
WJ
Creemers
John W M
JW
D000818:Animals; D001665:Binding Sites; D045744:Cell Line, Tumor; D003594:Cytoplasmic Granules / Q000378:metabolism*; D045683:Furin / Q000172:deficiency / Q000378:metabolism / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D007340:Insulinoma; D007515:Islets of Langerhans / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D018345:Mice, Knockout; D013379:Substrate Specificity; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism*
C484226:Atp6ap1 protein, mouse; D007328:Insulin; D045683:Furin; D025262:Vacuolar Proton-Translocating ATPases