Phosphoenolpyruvate carboxykinase (PEPCK) is a rate-limiting enzyme in hepatic gluconeogenesis and therefore plays a central role in glucose homeostasis. The aim of this study was to analyse the nutritional regulation of PEPCK gene expression in rainbow trout (Oncorhynchus mykiss), which are known to use dietary carbohydrates poorly. A full-length hepatic PEPCK cDNA (2637 base pairs with one open reading frame putatively encoding a 635-residue protein) was cloned and found to be highly homologous to mammalian PEPCKs. The presence of a putative peptide signal specific to a mitochondrial-type PEPCK in the deduced amino acid sequence suggests that this PEPCK gene codes for a mitochondrial form. In gluconeogenic tissues such as liver, kidney and intestine, this PEPCK gene was expressed at high levels and, in the liver we found no regulation of PEPCK gene expression by dietary carbohydrates. These results suggest that the first step of the hepatic gluconeogenic pathway in rainbow trout is functional and highly active irrespective of the dietary carbohydrate supply.

REFERENCES

Borrebaek
B.
,
Christophersen
B.
(
2000
).
Hepatic glucose phosphorylation activities in perch (Perca fluviatilis) after dietary treatments.
Comp. Biochem. Physiol
125
,
387
–.
Chomczinski
P.
,
Sacchi
M.
(
1987
).
Single step method of RNA isolation by acid guanidium thiocyanate phenol chloroform extraction.
Analyt. Biochem
162
,
156
–.
Cournarie
F.
,
Azzout-Marniche
D.
,
Foretz
M.
,
Guichard
C.
,
Ferre
P.
,
Foufelle
F.
(
1999
).
The inhibitory effect of glucose on phosphoenolpyruvate carboxykinase gene expression in cultured hepatocytes is transcriptional and requires glucose metabolism.
FEBS Lett
460
,
527
–.
Girard
J.
,
Ferre
P.
,
Foufelle
F.
(
1997
).
Mechanisms by which carbohydrates regulate expression of genes for glycolytic and lipogeneic enzymes.
Annu. Rev. Nutr
17
,
325
–.
Hanson
R. W.
,
Reshef
L.
(
1997
).
Regulation of phosphoenolpyruvate carboxykinase (GTP) gene expression.
Annu. Rev. Biochem
66
,
581
–.
Matte
A.
,
Tari
L. W.
,
Goldie
H.
,
Delbaere
T. J.
(
1997
).
Structure and mechanism of phosphoenolpyruvate carboxykinase.
J. Biol. Chem
272
,
8105
–.
Myers
M. R.
,
Klasing
K. C.
(
1999
).
Low glucokinase activity and high rates of gluconeogenesis contribute to hyperglycemia in barn owls (Tyto alba) after a glucose challenge.
J. Nutr
129
,
1896
–.
Neupert
W.
(
1997
).
Protein import into mitochondria.
Annu. Rev. Biochem
66
,
863
–.
Nielsen
H.
,
Engelbrecht
J.
,
Brunak
S.
,
von Heijne
G.
(
1997
).
Identification of prokaryotic and eukaryotic signal peptides and prediction of their cleavage sites.
Prot. Eng
10
,
1
–.
Panserat
S.
,
Medale
F.
,
Blin
C.
,
Breque
J.
,
Vachot
C.
,
Plagnes-Juan
E.
,
Krishnamoorthy
R.
,
Kaushik
S.
(
2000
).
Hepatic glucokinase is induced by dietary carbohydrates in rainbow trout, common carp and gilthead seabream.
Am. J. Physiol
278
,
1164
–.
Parrizas
M.
,
Planas
J.
,
Plisetskaya
E. M.
,
Gutierrez
J.
(
1994
).
Insulin binding and receptor tyrosine kinase activity in skeletal muscle of carnivorous and omnivorous fish.
Am. J. Physiol
266
,
1944
–.
Pilkis
S. J.
,
Granner
D. K.
(
1992
).
Molecular physiology of the regulation of hepatic gluconeogenesis and glycolysis.
Annu. Rev. Physiol
54
,
885
–.
Scott
D. K.
,
O'Doherty
R. M.
,
Stafford
J. M.
,
Newgard
C. B.
,
Granner
D. K.
(
1998
).
The repression of hormone-activated PEPCK gene expression by glucose is insulin-independent but requires glucose metabolism.
J. Biol. Chem
273
,
24145
–.
Suarez
R. K.
,
Mommsen
T. P.
(
1987
).
Gluconeogenesis in teleost fishes.
Can. J. Zool
65
,
1869
–.
Tranulis
M. A.
,
Dregni
O.
,
Cristophersen
B.
,
Krogdahl
A.
,
Borrebaek
B.
(
1996
).
A glucokinase-like enzyme in the liver of Atlantic salmon (Salmon salar).
Comp. Biochem. Physiol
114
,
35
–.
Valera
A.
,
Pujol
A.
,
Pelegrin
M.
,
Bosh
F.
(
1994
).
Transgenic mice overexpressing phosphoenolpyruvate carboxykinase develop non-insulin-dependent diabetes mellitus.
Proc. Natl. Acad. Sci. USA
91
,
9151
–.
Weldon
S. L.
,
Rando
A.
,
Matathias
A. S.
,
Hod
Y.
,
Kalonick
P. A.
,
Savon
S.
,
Cook
J. S.
,
Hanson
R. W.
(
1990
).
Mitochondrial phosphoenolpyruvate carboxykinase from the chicken: comparison of the cDNA protein sequences with the cytosolic isozyme.
J. Biol. Chem
265
,
7308
–.
Wright
J. R.
,
O'Hali
W.
,
Yuang
H.
,
Han
X.
,
Bonen
A.
(
1998
).
Glut-4 deficiency and severe peripheral resistance to insulin in the teleost fish tilapia.
Gen. Comp. Endocr
111
,
20
–.
This content is only available via PDF.