| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
ARTICLES |
Department of Medical Biochemistry, Ehime University School of Medicine, Shigenobu, Ehime 791–02, Japan
Address all correspondence and requests for reprints to: Yasutake Shimizu, Ph.D., Ehime University School of Medicine, Department of Medical Biochemistry, Shigenobu, Ehime 791–02, Japan. E-mail: yshimizu{at}m.ehime-u.ac.jp
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
-agonist,
phenylephrine, the extent of which being much lower than that by
ß-agonists. The effect of NE was attenuated by the ß-adrenergic
antagonist, propranolol. Dibutyryl cAMP also mimicked the effect of NE.
The phorbol ester, phorbol-12-myristate, 13-acetate (PMA), could induce
activation of MAPK, but pretreatment of the cultured cells with PMA to
down-regulate protein kinase C did not abolish the ability of NE in
activating MAPK. Furthermore, a selective inhibitor of
phosphatidylinositol-3 kinase, wortmannin, did not inhibit the effect
of NE, whereas insulin-induced activation of MAPK was totally
suppressed. These results demonstrate that NE activates MAPK directly
in brown adipocytes and that the effect of NE is not mediated by
PMA-sensitive protein kinase C or wortmannin-sensitive
phosphatidylinositol-3 kinase but rather is likely to be dependent on
ß-receptor-mediated increase in cAMP with a minor contribution of
-receptor-mediated signals. |
Introduction |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
In accordance with the predominant effects of NE on the stimulation of proliferation and differentiation of brown adipocytes, NE also affects the expression of transcription factors. Recent studies demonstrated that gene expression of CCAAT-enhancer-binding protein (C/EBP), which may associate with adipocyte differentiation (5, 6), is under the adrenergic control (7). Furthermore, a protooncogene, c-fos, has been shown to be induced by NE in primary cultures of brown adipocytes (8). However, the signal transduction pathways involved in the adrenergic control of the expression and/or the activation of transcription factors have not, so far, been elucidated.
One of the pivotal molecules participating in the signal transduction of growth factors in a variety of cell types is mitogen-activated protein kinase (MAPK), also known as extracellular signal-regulated kinase (9, 10, 11, 12, 13). MAPK is activated during proliferation and differentiation triggered by growth factors, such as those acting on receptor-tyrosine kinases or on receptors coupled to heterotrimeric guanine nucleotide-binding protein (14). The activated MAPK transmits signals from cell surface receptors to the nucleus by phosphorylating transcription factors.
In view of these facts concerning the predominant roles of MAPK
in regulation of proliferation and differentiation, we consider it of
interest to examine the adrenergic control of MAPK activity in brown
adipocytes. Here we show that cold exposure to rats, a most potent
stimulus for BAT hyperplasia in vivo, activates MAPK through
intermediation of the sympathetic nerves. In addition, analysis with
primary cultures of brown adipocytes demonstrated that NE directly
activates MAPK in the absence of insulin and serum. Further analysis
also revealed that the activation of MAPK by NE is not mediated by
phorbol ester-sensitive protein kinase C or wortmannin-sensitive
phosphatidylinositol-3 (PI-3) kinase but rather seems to depend mainly
on ß-receptor-mediated increase in cAMP with a minor contribution of
-receptor-mediated signals.
|
Materials and Methods |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Cell isolation and culture
Brown fat precursor cells were isolated as the stromal-vascular
fraction from the interscapular BAT of newborn rats according to the
procedure described previously (16). Cells isolated by collagenase
digestion were suspended in DMEM supplemented with 10% FCS, 17
µM D-pantothenic acid, 33 µM
D-biotin, 100 µM ascorbic acid, 1
µM octanoic acid, 100 U/ml penicillin, 0.1 mg/ml
streptomycin, 50 nM insulin, and 50 nM
T3 and were seeded on collagen-coated dishes. The cells
were incubated at 37 C under an atmosphere of 5% CO2 in
air. When the cultured cells reached confluence, they were treated with
1 µM dexamethasone for 48 h to facilitate
differentiation into adipocytes. The cells were used 3–4 days after
reaching confluence. Cells were preincubated with serum- and
supplements-free DMEM for 16 h before use. After incubation for
the indicated times with insulin or NE, cells were taken up in
SDS-sample buffer (2% SDS, 10% glycerol, 62.5 mM Tris, pH
6.8, 5% 2-mercaptoethanol) containing 100 µM sodium
orthovanadate and 1 mM phenylmethylsulfonyl fluoride.
Mobility shift assay for MAPK activation
Activation of two isoforms of MAPK, p42-MAPK and p44-MAPK, was
determined by the appearance of slower migrating forms in gel
electrophoresis caused by phosphorylation of threonine and tyrosine
residues (17). Samples from the tissues or cultured cells were
subjected to SDS-PAGE and transferred to nitrocellulose membranes.
Membranes were blocked with 1% gelatin in PBS and then incubated with
anti-MAPK antibody (Santa Cruz Biotechnology, Inc., Santa Cruz, CA). To
visualize immunoreactive bands, alkaline phosphatase-labeled antirabbit
IgG was used as a second antibody with 5-bromo-4-chloro-3-indolyl
phosphate/nitro blue tetrazolium as substrates. The resultant membranes
were scanned and analyzed with a densitometer. The results were
expressed as mean ± SEM %, regarding the mean value
of control cells as 100%.
In-gel kinase assay
MAPK activity also was measured in SDS-PAGE using the method
described previously (18, 19). Briefly, samples were subjected to
SDS-PAGE in 11% polyacrylamide gel containing 0.5 mg/ml myelin basic
protein (MBP, Sigma, St. Louis, MO). After electrophoresis, SDS was
removed from the gels by washing with 20% 2-propanol in 50
mM Tris-HCl (pH 8.0) followed by washing with 5
mM ß-mercaptoethanol in 50 mM Tris-HCl (pH
8.0). Proteins were denatured with 6 M guanidine
hydrochloride and then renatured by incubation at 4 C with 0.04% Tween
40-containing buffer for 12–18 h. After preincubation of the gels with
a buffer containing 40 mM HEPES (pH 8.0), 2 mM
dithiothreitol, 10 mM MgCl2, and 0.1
mM EGTA, in-gel phosphorylation of MBP was performed in the
same solution containing 25 µM [
-32P]
ATP (25 µCi) for 1 h at room temperature. After extensive
washing with 5% (wt/vol) trichloroacetic acid containing 1% (wt/vol)
sodium pyrophosphate, the gels were dried and analyzed with BAS-1000
image analyzer (Fuji Film, Tokyo, Japan).
In preliminary experiments with insulin-stimulated cell samples, incorporation of radioactive phosphate into MBP increased linearly with increasing amounts of the sample applied onto the gel. The linearity was obtained up to at least triple amounts of the sample used in the present study. The results were expressed as mean ± SEM %, regarding the mean value of control cells as 100%.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
). However, no slower migrating form of MAPK was seen
in this condition. In contrast, cold exposure to rats stimulated
phosphorylation of both the p42-MAPK and p44-MAPK in BAT as judged by
the mobility shift (Fig. 1A). Strikingly, no mobility shift of MAPK was
observed in sympathetically denervated BAT despite the cold
exposure.
|
). Again, the activation was not
observed in denervated BAT (Fig. 1B).
Effects of insulin and NE on MAPK activity in primary cultures of
brown adipocytes
Results shown in Fig. 1 indicate that the sympathetic innervation
is essential for the activation of MAPK in BAT after cold exposure.
However, it is not certain whether the activation is caused by a direct
effect of adrenergic stimulation or by a secondary effect of
sympathetic stimulation. Accordingly, we used primary cultures of brown
adipocytes to ascertain that the MAPK activation is directly affected
by the sympathetic neurotransmitter, NE, together with the effects of
insulin on the enzyme activation.
The appearance of slower migrating forms of MAPK after treatment of the
cultured brown adipocytes with insulin was apparent at concentrations
as low as 10-9 M (data not shown).
Densitometric analysis of the results from four independent experiments
showed that mobility shifts were maximally stimulated with insulin
above 10-8 M (247 ± 12 and 319 ±
16% for p42-MAPK and p44-MAPK, respectively). Then, we examined the
time-course of insulin action on MAPK activation at 10-7
M concentration. The mobility shifts reached the maximal
levels of 275 ± 15% for p42-MAPK and 323 ± 17% for
p44-MAPK, 2 min after addition of insulin (Fig. 2). The
maximal levels were sustained for 15 min, and the responses were
recovered almost to the basal levels by 60 min (114 ± 9 and
118 ± 12% for p42-MAPK and p44-MAPK, respectively). NE above
concentrations of 10-8 M also induced mobility
shifts of p42-MAPK and p44-MAPK in the absence of insulin and serum
factors (data not shown). The maximal levels of the shifts at
10-7 M of NE were 262 ± 24 and 295
± 23% for p42-MAPK and p44-MAPK, respectively, which were comparable
with those obtained with insulin. The appearance of slower migrating
forms in response to 10-6 M of NE was seen
within 2 min and remained essentially unchanged at least for 60 min
(Fig. 3). Activation of MAPK by NE was confirmed further
by in-gel kinase assay. In parallel with the time-course obtained with
mobility shift assay, MBP was phosphorylated at the position
corresponding to p42-MAPK and p44-MAPK (Fig. 4). These
results suggest that NE can stimulate MAPK directly in brown
adipocytes.
|
|
|
, a ß-adrenergic agonist
isoproterenol mimicked the effects of NE, whereas an -agonist
phenylephrine caused only modest effects. A
ß3-adrenoceptor-specific stimulant, BRL37344, apparently
was as effective as NE in stimulating phosphorylation of MAPK (Fig. 5A). Similarly, MBP kinase activities in response to isoproterenol and
BRL37344 were 223 ± 49 and 207 ± 30% of controls,
respectively, which were comparable with the effect with NE (227
± 45%). These results indicate that major adrenoceptors responsible
for the NE-induced activation of MAPK are of ß-subclass, especially
ß3-receptors, which are expressed abundantly in these
cultured cells (20). In accordance with these results, the
ß-antagonist, propranolol, reduced mobility shifts caused by NE (Fig. 5B). Inhibition of the effect of NE by propranolol was 67 ± 17%
(n = 4) as assessed by in-gel kinase assay. On the other hand, an
-agonist, phenylephrine, caused mobility shifts of MAPK, but the
extent was much lower than with ß-agonists (Fig. 5A). Quantitative
analysis with in-gel kinase assay showed that the kinase activity after
treatment with phenylephrine was 134 ± 19% of controls (n =
5). In the antagonistic experiments, an -antagonist
phenoxybenzamine, up to 50 µM, produced little inhibitory
effects, both by mobility shift assay (Fig. 5B) and in-gel kinase
assay.
|
). In-gel kinase assay
gave MBP kinase activity of the MAPK 206 ± 27% of controls
(n = 5) after treatment with the cAMP analogue, which was
equivalent to the activity after NE treatment.
Interaction of the effects of NE and insulin on MAPK activation
To see a possible interaction between the effects of NE and
insulin, these two agents were tested simultaneously to determine their
ability to activate MAPK. As shown in Fig. 6, mobility
shifts induced by NE plus insulin were greater than those by each agent
alone. Quantitative measurements of MAPK activity by in-gel kinase
assay revealed that the effects of NE and insulin were additive (Fig. 6), suggesting that these two agents could stimulate MAPK by different
intracellular mechanisms.
|
). However, the
ability of PMA to induce the activation of MAPK does not necessarily
mean that the protein kinase C pathway is involved in the signaling
pathway leading to activation of MAPK in response to NE. To test this,
the culture cells were pretreated with PMA for 16 h before NE
treatment. The effectiveness of the pretreatment for the
down-regulation of protein kinase C can be proven by the fact that the
acute effect of PMA was totally lost (Fig. 7A). In contrast, the
activation of MAPK by NE was unaffected by pretreatment with PMA (Fig. 7A), which excludes possible involvement of a PMA-sensitive protein
kinase C.
|
, phosphorylation of MAPK induced by NE was
not affected, even though wortmannin was present during the incubation
period, whereas the phosphorylation by insulin was totally abolished.
These results suggest that NE and insulin do not share the same
signaling pathways to activate MAPK, at least at a step in which PI-3
kinase is involved. |
Discussion |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Increased activities of the sympathetic nerves, after cold exposure or overfeeding, cause hyperplasia of BAT, which is accompanied by an increase in cell numbers and mitochondriogenesis (1, 2, 3). The hyperplasia of BAT results in an enhanced capacity of thermogenesis and is thus considered to be an adaptive response to whole body demand for heat generation or energy expenditure. In accordance with this, gene expression of UCP, a key mitochondrial protein responsible for thermogenesis, and some proteins involved in substrate supply for thermogenesis, such as GLUT4 glucose transporter and lipoprotein lipase, are substantially increased during hyperplasia of the tissue (4, 21, 22, 23). The trophic responses of BAT, including the increased expression of these proteins, were also induced by continuous infusion of NE in rats, demonstrating an important role of the sympathetic nervous system in these responses (4). We have shown here that cold exposure to rats results in an activation of MAPK in BAT in vivo. It is noteworthy that cold exposure failed to activate MAPK in the surgically denervated BAT in the same rats. These results indicate that the activation of MAPK in response to cold exposure is attributable to the action of the sympathetic nerves. In other words, other factors being delivered from blood or cells neighboring to this tissue, if any, may not play an essential role for the MAPK activation. It should be noted, however, that this conclusion does not totally rule out possible modulatory roles of other factors.
It has been pointed out that hyperplasia of BAT is accompanied by a coordinated proliferation of endothelial cells forming the capillaries (24). Accordingly, it is possible that MAPK activation in BAT, after cold exposure, originates from an increased mitosis of endothelial cells, and MAPK activity in brown adipocytes may not be influenced by the adrenergic stimulation. However, this is unlikely because NE itself substantially increased MAPK activity in brown adipocytes in primary cultures. It can be thus proven that MAPK activation in BAT is caused (though, perhaps not solely) by a direct effect of the sympathetic nerves on brown adipocytes.
Activation of MAPK is induced by phosphorylation of both threonine and tyrosine residues of the enzyme as a result of successive stimulations of Ras, Raf-1, and MAPK-kinase (9, 10, 13, 14). Recent studies have suggested that PI-3 kinase participates in insulin-induced stimulation of the signaling cascade (25, 26, 27). This apparently is also the case in our brown adipocytes; a selective inhibitor of PI-3 kinase wortmannin abolished the response of MAPK activation to insulin. However, NE-induced activation of MAPK was not discernibly affected by the inhibitor, indicating that NE uses a distinct pathway, different from that of insulin, for stimulating MAPK. In support of this, the stimulative effects of insulin and NE on MAPK activity were completely additive. In addition, we also analyzed a possible involvement of protein kinase C, which is involved in many types of receptor-mediated activation of MAPK cascade (10, 14). Direct stimulation of protein kinase C with PMA led to an activation of MAPK in the cultured brown adipocytes. However, this pathway is not responsible for the effect of NE, because NE was able to activate MAPK, even in the cells in which protein kinase C had been down-regulated. Thus, it can be concluded that NE uses neither wortmannin-sensitive PI-3 kinase nor PMA-sensitive protein kinase C to stimulate MAPK in brown adipocytes.
ß-adrenoceptor-mediated increase in cAMP is responsible for the cell
growth and the expression of specific genes of brown adipocytes (5, 28, 29). Pharmacological analysis with adrenergic agonists and antagonists
has indicated that NE-induced activation of MAPK is mediated mainly
through ß-adrenoceptors, though -receptor-mediated signals also
exert a minor effect. Furthermore, increase in cytosolic cAMP, using
membrane-permeable cAMP analogue, led to activation of the kinase
comparable with NE, indicating that NE uses cAMP as a second messenger.
The effect of cAMP on MAPK cascade is dependent on the cell types; it
antagonizes the growth factor-activated MAPK in some cell types
(30, 31, 32, 33, 34), whereas cAMP itself has a stimulative effect in other cells
(35, 36), and thus the mechanisms involved are likely to be complex.
One of the candidates with a cAMP-dependent pathway confluent with MAPK
cascade is the MAPK kinase kinase (MEKK) that phosphorylates and
activates MAPK-kinase. MEKK is the homologue of Saccharomyces
cerevisiae Ste11, which is activated via a heterotrimeric guanine
nucleotide-binding protein-coupled receptor signal and is considered to
play a similar role in mammalian cells (37). Alternatively, it is to be
noted that NE-induced activation of MAPK was maintained for a
relatively long time, whereas an insulin-induced one was transient and
peaked at 2–15 min. It has been suggested that the transient nature of
MAPK activation by insulin is caused by rapid dephosphorylation by
phosphatases (12, 13). Thus, an inhibition of protein phosphatases
might also be associated with NE-induced phosphorylation of MAPK. This
possibility remains to be examined.
The activation of MAPK leads to the phosphorylation and activation of a number of transcription factors (10, 11, 12). It is thus expected that NE promotes gene expression in brown adipocytes through the MAPK pathway. Indeed, C/EBP ß, which is phosphorylated and activated by MAPK, has been shown to be a transcriptional activator of UCP gene (38, 39). Furthermore, BAT-specific enhancer located in the 5' flanking region of UCP gene contains a consensus sequence including the core motif GGAA, being recognized by a MAPK-substrate ternary complex factor TCF/Elk-1 (40). Alternatively, MAPK induces a protooncogene, c-fos, whose protein product, Fos, combines with Jun protein to form AP-1 transcriptional activator (41). Therefore, elevated AP-1 activity, as a result of MAPK activation after NE, can be used for controlling gene expression. In line with this, Thonberg et al. (8) recently demonstrated that NE induces c-fos in cultured brown adipocytes. Overall, these facts indicate that activation of MAPK by NE would participate in the gene expressions of UCP, as well as some specific proteins, directly through the phosphorylation of transcriptional factors or indirectly through the induction of immediate early genes, such as c-fos, in brown adipocytes.
In summary, we demonstrated that MAPK is activated in brown adipocytes by the sympathetic neurotransmitter, NE, and the activation is not mediated by a phorbol ester-sensitive protein kinase C or wortmannin-sensitive PI-3 kinase but rather is likely to depend mainly on a ß-receptor-induced increase in cAMP. Downstream to the activation of MAPK by NE, which should be associated with DNA synthesis and specific gene expression, are clearly of further interest to establish the physiological significance of the MAPK during hyperplasia of BAT in response to cold exposure or overfeeding.
|
Acknowledgments |
|---|
|
Footnotes |
|---|
Received June 3, 1996.
|
References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
and ß in
brown adipose tissue. FEBS Lett 318:235–241[CrossRef][Medline]
1- and
ß-adrenoreceptors synergetically to maximally induce c-fos
expression in brown adipocytes. J Biol Chem 269:33179–33186-and ß-adrenergic induction of the expression of the
uncoupling protein thermogenin in brown adipocytes differentiated in
culture. J Biol Chem 265:16464–16471 and ß are transcriptional activators of the brown fat
uncoupling protein gene promoter. Biochem Biophys Res Commun 198:653–659[CrossRef][Medline]
This article has been cited by other articles:
 |
|
 |
|
  R. Martinez-deMena and M.-J. Obregon Insulin increases the adrenergic stimulation of 5' deiodinase activity and mRNA expression in rat brown adipocytes; role of MAPK and PI3K J. Mol. Endocrinol., February 1, 2005; 34(1): 139 - 151. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. CANNON and J. NEDERGAARD Brown Adipose Tissue: Function and Physiological Significance Physiol Rev, January 1, 2004; 84(1): 277 - 359. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Klein, M. Fasshauer, M. Benito, and C. R. Kahn Insulin and the {beta}3-Adrenoceptor Differentially Regulate Uncoupling Protein-1 Expression Mol. Endocrinol., June 1, 2000; 14(6): 764 - 773. [Abstract] [Full Text]
|
|
|
|
 |
|
 J. M. Fredriksson, J. M. Lindquist, G. E. Bronnikov, and J. Nedergaard Norepinephrine Induces Vascular Endothelial Growth Factor Gene Expression in Brown Adipocytes through a beta -Adrenoreceptor/cAMP/Protein Kinase A Pathway Involving Src but Independently of Erk1/2 J. Biol. Chem., April 28, 2000; 275(18): 13802 - 13811. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Kimura, M. Ohmichi, K. Tasaka, Y. Kanda, H. Ikegami, J. Hayakawa, K. Hisamoto, K.-i. Morishige, S. Hinuma, H. Kurachi, et al. Prolactin-releasing Peptide Activation of the Prolactin Promoter Is Differentially Mediated by Extracellular Signal-regulated Protein Kinase and c-Jun N-terminal Protein Kinase J. Biol. Chem., February 4, 2000; 275(5): 3667 - 3674. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Klein, M. Fasshauer, M. Ito, B. B. Lowell, M. Benito, and C. R. Kahn beta 3-Adrenergic Stimulation Differentially Inhibits Insulin Signaling and Decreases Insulin-induced Glucose Uptake in Brown Adipocytes J. Biol. Chem., December 3, 1999; 274(49): 34795 - 34802. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. A. Cole Parathyroid Hormone Activates Mitogen-Activated Protein Kinase in Opossum Kidney Cells Endocrinology, December 1, 1999; 140(12): 5771 - 5779. [Abstract] [Full Text]
|
|
|
|
|
|
M. P. Sajan, M. L. Standaert, G. Bandyopadhyay, M. J. Quon, T. R. Burke Jr., and R. V. Farese Protein Kinase C-zeta and Phosphoinositide-dependent Protein Kinase-1 Are Required for Insulin-induced Activation of ERK in Rat Adipocytes J. Biol. Chem., October 22, 1999; 274(43): 30495 - 30500. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Kimura, M. Ohmichi, H. Kurachi, H. Ikegami, J. Hayakawa, K. Tasaka, Y. Kanda, Y. Nishio, H. Jikihara, N. Matsuura, et al. Role of Mitogen-activated Protein Kinase/Extracellular Signal-regulated Kinase Cascade in Gonadotropin-releasing Hormone-induced Growth Inhibition of a Human Ovarian Cancer Cell Line Cancer Res., October 1, 1999; 59(20): 5133 - 5142. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. M. Guardiola-Diaz, S. Rehnmark, N. Usuda, T. Albrektsen, D. Feltkamp, J.-A. Gustafsson, and S. E. H. Alexson Rat Peroxisome Proliferator-activated Receptors and Brown Adipose Tissue Function during Cold Acclimatization J. Biol. Chem., August 13, 1999; 274(33): 23368 - 23377. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Kimura, M. Ohmichi, T. Takeda, H. Kurachi, H. Ikegami, K. Koike, K. Masuhara, J. Hayakawa, T. Kanzaki, M. Kobayashi, et al. Mitogen-Activated Protein Kinase Cascade Is Involved in Endothelin-1-Induced Rat Puerperal Uterine Contraction Endocrinology, February 1, 1999; 140(2): 722 - 731. [Abstract] [Full Text]
|
|
|
|
 |
|
 J Gros, C. Gerhardt, and A. Strosberg Expression of human (beta)3-adrenergic receptor induces adipocyte-like features in CHO/K1 fibroblasts J. Cell Sci., January 11, 1999; 112(21): 3791 - 3797. [Abstract] [PDF]
|
|
|
|
|
|
J. M. Lindquist and S. Rehnmark Ambient Temperature Regulation of Apoptosis in Brown Adipose Tissue. Erk1/2 PROMOTES NOREPINEPHRINE-DEPENDENT CELL SURVIVAL J. Biol. Chem., November 13, 1998; 273(46): 30147 - 30156. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Zhao, B. Cannon, and J. Nedergaard alpha 1-Adrenergic Stimulation Potentiates the Thermogenic Action of beta 3-Adrenoreceptor-generated cAMP in Brown Fat Cells J. Biol. Chem., December 26, 1997; 272(52): 32847 - 32856. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Sawada, M. Ohmichi, K. Koike, Y. Kanda, A. Kimura, K. Masuhara, H. Ikegami, M. Inoue, A. Miyake, and Y. Murata Norepinephrine Stimulates Mitogen-Activated Protein Kinase Activity in GT1-1 Gonadotropin-Releasing Hormone Neuronal Cell Lines Endocrinology, December 1, 1997; 138(12): 5275 - 5281. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. S. Greenberg, W.-J. Shen, K. Muliro, S. Patel, S. C. Souza, R. A. Roth, and F. B. Kraemer Stimulation of Lipolysis and Hormone-sensitive Lipase via the Extracellular Signal-regulated Kinase Pathway J. Biol. Chem., November 21, 2001; 276(48): 45456 - 45461. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. M. Lindquist, J. M. Fredriksson, S. Rehnmark, B. Cannon, and J. Nedergaard beta 3- and alpha 1-Adrenergic Erk1/2 Activation Is Src- but Not Gi-mediated in Brown Adipocytes J. Biol. Chem., July 21, 2000; 275(30): 22670 - 22677. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. Yokoi, M. Ohmichi, K. Tasaka, A. Kimura, Y. Kanda, J. Hayakawa, M. Tahara, K. Hisamoto, H. Kurachi, and Y. Murata Activation of the Luteinizing Hormone beta Promoter by Gonadotropin-releasing Hormone Requires c-Jun NH2-terminal Protein Kinase J. Biol. Chem., July 7, 2000; 275(28): 21639 - 21647. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||
