January 2000
GLUTAMINE, cAMP, AND ENTEROCYTE MAPKs 99
2
3
4
. Lecce JG, Balsbaugh RK, Clare DA, King MW. Rotavirus and
hemolytic enteropathogenic Escherichia coli in weanling diarrhea
of pigs. J Clin Microbiol 1982;16:715–723.
. Uhnoo I, Olding-Stenkvist E, Kreuger A. Clinical features of acute
gastroenteritis associated with rotavirus, enteric adenoviruses,
and bacteria. Arch Dis Child 1986;61:732–738.
JNKs may be activated during hyperthermia and oxidant
4
0
stress, and are activated during apoptosis. Interestingly,
recent studies from the laboratory of Ko et al.41 have
shown that GLN starvation induces apoptosis in IEC-6
cells. In our GLN-starved cells, JNK was not activated
initially, although there was activation after GLN treat-
ment. Although there is no known specific inhibitor of
the JNK pathway, the use of PD98059 allowed us to
separate 2 MAPK pathways activated by GLN in prolifer-
ating IEC-6 cells. We found no significant effect of
PD98059 on JNK activity (not shown) and only a partial
. Haggard DL. Bovine enteric colibacillosis. Vet Clin North Am
1
985;1:495–514.
5. Rhoads JM, Lecce JG, Keku EO, Kandil H, Woodard PW, Chen W,
Liu SC, Fuller CR, Leary HL, Ulshen MH. Transforming growth
factor–alpha stimulates jejunal mucosal recovery in piglet rotavi-
rus enteritis. Pediatr Res 1995;38:173–181.
6
. Hill CS, Treisman R. Transcriptional regulation by extracellular
signals: mechanisms and specificity. Cell 1995;80:199–211.
3
7. Robinson MJ, Cobb MH. Mitogen-activated protein kinase path-
ways. Curr Opin Cell Biol 1997;9:180–186.
effect of PD98059 in reducing [ H]thymidine incorpora-
tion response to GLN in ‘‘stressed’’ (starved) IEC-6 cells.
While our studies demonstrate an effect of GLN on JNK
in the starved cells, they do not rule out an effect of GLN
on other pathways such as protein kinase C, phosphoino-
sitol-3-kinase, or p38 MAPK.
8
. Derijard B, Hibi M, Wu I-H, Barrett T, Su B, Deng T, Karin M, Davis
RJ. A protein kinase stimulated by UV light and Ha-Ras that binds
and phosphorylates the c-Jun activation domain. Cell 1994;76:
1
025–1037.
9
. Marais R, Wynne J, Treisman R. The SRF accessory protein Elk-1
contains a growth factor–regulated transcriptional activation do-
main. Cell 1993;73:381–393.
GLN Metabolism Bypasses Raf to
Stimulate MEK and ERK Induction
1
0. Miltenberger RJ, Cortner J, Farnham PJ. An inhibitory Raf-1mutant
suppresses expression of a subset of v-raf-activated genes. J Biol
Chem 1993;268:15674–15680.
EGF, insulin, and other growth factors are known
to activate MEK via Raf recruitment to membrane-
bound ras, and Raf activation. There is evidence that
growth signals may stimulate ERK activation in the
absence of Raf activation (Figures 3 and 4). In fact, MEK
is often activated without a corresponding increase in Raf
11. Mansour SJ, Matten WT, Hermann AS, Candia JM, Rong S,
Fukasawa K, Vande Woude GF, Ahn NG. Transformation of
mammalian cells by constitutively active MAP kinase kinase.
Science 1994;265:966–970.
1
2. Graves LM, Lawrence JC. Insulin, growth factors, and cAMP
antagonism in the signal transduction pathways. TEM 1996;7:
4
3–50.
1
3. Wu J, Dent P, Jelinek T, Wolfman A, Weber MJ, Sturgill TW. Inhibition of
the EGF-activated MAP kinase signaling pathway by adenosine
3Ј,5Ј-monophosphate. Science 1993;262:1065–1069.
4. Cook SJ, McCormick F. Inhibition by cAMP of Ras-dependent
activation of Raf. Science 1993;262:1069–1072.
5. Burgering BMT, de Vries-Smits AMM, Medema RH, van Weeren
PC, Tertoolen LGJ, Bos JL. Epidermal growth factor induces
phosphorylation of extracellular signal–regulated kinase 2 via
multiple pathways. Mol Cell Biol 1993;13:7248–7256.
6. Hsueh Y-P, Lai M-Z. c-Jun N-terminal kinase but not mitogen-
activated protein kinase is sensitive to cAMP inhibition in T
lymphocytes. J Biol Chem 1995;270:18094–18098.
1
2
kinase activity. One example is in G protein–coupled
signal transduction in vascular smooth muscle cells. In
these cells, angiotensin II stimulates ERK activation by
an Ras- and Raf-independent pathway requiring activa-
1
1
4
2
tion of protein kinase C.
We do not know the mechanism for initiation of
GLN-stimulated mitogenesis. Research in other cell
types suggests several possibilities. Kilberg et al.43
showed that amino acid starvation induced derepression
of system A amino acid transport activity within 2 hours.
Amino acid refeeding (with A system amino acids or
GLN) increased cellular proliferation when added after
starvation, perhaps by an effect on intracellular amino
acid ‘‘loading.’’ Additionally, cytosolic GLN, aspartate,
and aminoisobutyrate repressed ribosomal protein messen-
1
1
7. Rhoads M, Argenzio R, Chen W, Licato L, Rippe R, Brenner D.
Cyclic AMP blocks intestinal cell proliferation by inhibiting mitogen-
activated protein kinases (abstr). Gastroenterology 1997;112:
A396.
18. Westwick JK, Brenner DA. Methods for analyzing c-Jun kinase.
Methods Enzymol 1995;255:342–359.
1
9. Rhoads JM, Argenzio RA, Chen W, Rippe RA, Westwick JK, Cox AD,
Berschneider HM, Brenner DA. L-Glutamine stimulates intestinal
cell proliferation and activates mitogen-activated protein kinases.
Am J Physiol 1997;35:G943–G953.
4
3
ger RNA levels. When cells were starved and subse-
quently refed, increased messenger RNA translation was
observed. Other possibilities for how GLN signals mito-
genesis include GLN-stimulated release of paracrine
growth factors stored in a rapidly released pool, or a rapid
increase in polyamine synthesis via ornithine decarboxyl-
2
0. Kandil HL, Argenzio RA, Chen W, Berschneider HM, Stiles AD,
Westwick JK, Rippe RA, Brenner DA, Rhoads JM. L-Glutamine and
L-asparagine stimulate ornithine decarboxylase activity and prolif-
eration in a porcine jejunal enterocyte line. Am J Physiol 1995;269:
G591–G599.
2
1. Graves LM, Bornfeldt KE, Raines EW, Potts BC, MacDonald SG,
Ross R, Krebs EG. Protein kinase A antagonizes platelet-derived
growth factor–induced signaling by mitogen-activated protein
kinase in human arterial smooth muscle cells. Proc Natl Acad Sci
USA 1993;90:300–310.
2
0
ase induction.
Re fe re nce s
1
. Thouless ME, DiGiacomo RF, Deeb BJ. The effect of combined
rotavirus and Escherichia coli infections in rabbits. Lab Anim Sci
22. Davis RJ. The mitogen-activated protein kinase signal transduc-
tion pathway. Biol Chem 1993;268:553–556.
1
996;46:381–385.