INVESTIGADORES
GONZALEZ BARO Maria Del Rosario
artículos
Título:
Mitochondrial glycerol phosphate acyltransferase directs the incorporation of exogenous fatty acids into triacylglycerol
Autor/es:
IGAL, R.A.; WANG, S; GONZALEZ BARO, M.R.; COLEMAN, R.A.
Revista:
JOURNAL OF BIOLOGICAL CHEMISTRY
Editorial:
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
Referencias:
Lugar: Bethesda, Maryland; Año: 2001 vol. 276 p. 42205 - 42205
ISSN:
0021-9258
Resumen:
The
mitochondrial isoform of glycerol-3-phosphate acyltransferase (GPAT), the first
step in glycerolipid synthesis, is up-regulated by insulin and by high
carbohydrate feeding via SREBP-1c, suggesting that it plays a role in
triacylglycerol synthesis. To test this hypothesis, we overexpressed
mitochondrial GPAT in Chinese hamster ovary (CHO) cells. When GPAT was
overexpressed 3.8-fold, triacylglycerol mass was 2.7-fold higher than in
control cells. After incubation with trace [14C]oleate (~3 uM), control cells incorporated 4.7-fold more label into phospholipid than
triacylglycerol, but GPAT-overexpressing cells incorporated equal amounts of
label into phospholipid and triacylglycerol. In GPAT-overexpressing cells, the
incorporation of label into phospholipid, particularly phosphatidylcholine,
decreased 30%, despite normal growth rate and phospholipid content, suggesting
that exogenous oleate was directed primarily toward triacylglycerol synthesis.
Transiently transfected HEK293 cells that expressed a 4.4-fold increase in GPAT
activity incorporated 9.7-fold more [14C]oleate into triacylglycerol compared with
control cells, showing that the effect of GPAT overexpression was similar in
two different cell types that had been transfected by different methods. When
the stable, GPAT-overexpressing CHO cells were incubated with 100 uM oleate to stimulate triacylglycerol
synthesis, they incorporated 1.9-fold more fatty acid into triacylglycerol than
did the control cells. Confocal microscopy of CHO and HEK293 cells transfected
with the GPAT-FLAG construct showed that GPAT was located correctly in
mitochondria and was not present elsewhere in the cell. These studies indicate
that overexpressed mitochondrial GPAT directs incorporation of exogenous fatty
acid into triacylglycerol rather than phospholipid and imply that (a)
mitochondrial GPAT and lysophosphatidic acid acyltransferase produce a separate
pool of lysophosphatidic acid and phosphatidic acid that must be transported to
the endoplasmic reticulum where the terminal enzymes of triacylglycerol
synthesis are located, and (b) this pool remains relatively separate
from the pool of lysophosphatidic acid and phosphatidic acid that contributes
to the synthesis of the major phospholipid species.