Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
cAMP-Regulated Cell Proliferation in Brown Preadipocytes
Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As a prototypical second messenger, cAMP is involved in the regulation of multiple cell functions. cAMP has a well established inhibitory effect on cell proliferation in smooth muscle and epithelial cell types. However, there is accumulating evidence also for stimulatory effect on proliferation, mainly in endocrine cell types.

Mechanisms mediating the cAMP stimulatory effect are not well studied. cAMP, produced via β1-adrenoceptor activation, promotes cell proliferation in brown preadipocytes. Due to the importance of brown adipose tissue in energy metabolism and its implication in the treatment of obesity and type II diabetes, understanding the mechanisms of tissue recruitment has clinical implication for the treatment of these metabolic syndromes.

We found that the Erk1/2 family of MAPK, often involved in regulation of cell proliferation, can be activated in response to the stimulation of G protein-coupled receptors, including adrenergic receptors (α1-, α2-, β1- and β3-Adrenoceptors) and mitogenic lysophosphatidic acid (LPA) in primary cultured brown adipocytes. In contrast to the case e.g. in many immortalized cell lines and various primary cultured cells, EGF receptor transactivation is not employed in Erk1/2 activation by any G protein-coupled receptor tested in brown adipocytes. This suggests that EGF receptor transactivation is not an universal mediation process for GPCR activation of MAPK.

cAMP-activated cell proliferation in brown preadipocytes is mediated through PKA rather than Epac under serum-free conditions. This effect is independent of PI3K/Akt, mTOR or Erk1/2 MAPK pathways. Differential responses to two different MEK inhibitors PD98059 and U0126 suggested the involvement of a pathway sensitive to PD98059, but independent of the Erk1/2 family of MAPK. At the transcriptional level, by combining microarray and RT-qPCR, we have identified eight genes, under the regulation of cAMP, that may be involved in the further mediation of the cAMP effect on cell proliferation.

An understanding of cAMP-induced cell proliferation may be of importance both in metabolic and cancer research.

Place, publisher, year, edition, pages
Stockholm: Department of Molecular Biosciences, Stockholm University , 2013. , 78 p.
National Category
Other Biological Topics
Research subject
Physiology
Identifiers
URN: urn:nbn:se:su:diva-88393ISBN: 978-91-7447-664-4 (print)OAI: oai:DiVA.org:su-88393DiVA: diva2:610907
Public defence
2013-04-12, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2013-03-21 Created: 2013-03-13 Last updated: 2013-03-22Bibliographically approved
List of papers
1. Non-transactivational, dual pathways for LPA-induced Erk1/2 activation in primary cultures of brown pre-adipocytes
Open this publication in new window or tab >>Non-transactivational, dual pathways for LPA-induced Erk1/2 activation in primary cultures of brown pre-adipocytes
Show others...
2010 (English)In: Experimental Cell Research, ISSN 0014-4827, E-ISSN 1090-2422, Vol. 316, no 16, 2664-75 p.Article in journal (Refereed) Published
Abstract [en]

In many cell types, G-protein-coupled receptor (GPCR)-induced Erk1/2 MAP kinase activation is mediated via receptor tyrosine kinase (RTK) transactivation, in particular via the epidermal growth factor (EGF) receptor. Lysophosphatidic acid (LPA), acting via GPCRs, is a mitogen and MAP kinase activator in many systems, and LPA can regulate adipocyte proliferation. The mechanism by which LPA activates the Erk1/2 MAP kinase is generally accepted to be via EGF receptor transactivation. In primary cultures of brown pre-adipocytes, EGF can induce Erk1/2 activation, which is obligatory and determinant for EGF-induced proliferation of these cells. Therefore, we have here examined whether LPA, via EGF transactivation, can activate Erk1/2 in brown pre-adipocytes. We found that LPA could induce Erk1/2 activation. However, the LPA-induced Erk1/2 activation was independent of transactivation of EGF receptors (or PDGF receptors) in these cells (whereas in transformed HIB-1B brown adipocytes, the LPA-induced Erk1/2 activation indeed proceeded via EGF receptor transactivation). In the brown pre-adipocytes, LPA instead induced Erk1/2 activation via two distinct non-transactivational pathways, one G(i)-protein dependent, involving PKC and Src activation, the other, a PTX-insensitive pathway, involving PI3K (but not Akt) activation. Earlier studies showing LPA-induced Erk1/2 activation being fully dependent on RTK transactivation have all been performed in cell lines and transfected cells. The present study implies that in non-transformed systems, RTK transactivation may not be involved in the mediation of GPCR-induced Erk1/2 MAP kinase activation

Keyword
Lysophosphatidic acid, Transactivation, Brown adipocytes, Erk1/2, EGF receptor, PI3K
National Category
Other Biological Topics
Research subject
Physiology
Identifiers
urn:nbn:se:su:diva-37122 (URN)10.1016/j.yexcr.2010.05.029 (DOI)000281305800013 ()20576526 (PubMedID)
Available from: 2010-02-10 Created: 2010-02-10 Last updated: 2017-12-12Bibliographically approved
2. In brown adipocytes, adrenergically induced β1-/β3-(Gs)-, α2-(Gi)- and α1-(Gq)-mediated Erk1/2 activation is not mediated via EGF receptor transactivation
Open this publication in new window or tab >>In brown adipocytes, adrenergically induced β1-/β3-(Gs)-, α2-(Gi)- and α1-(Gq)-mediated Erk1/2 activation is not mediated via EGF receptor transactivation
Show others...
(English)Article in journal (Other academic) Submitted
Abstract [en]

Brown adipose tissue is unusual in utilising the neurotransmitter norepineph- rine to influence cell destiny in ways generally associated with classical growth factors: regulation of cell proliferation, apoptosis, progression of differentiation. These effects are thus mediated through G-protein-coupled receptors; mediation of such stimulation to e.g. Erk1/2 activation is generally accepted to occur through transactivation of the EGF receptor (by external or internal pathways). We have examined here the significance of such transac- tivation in brown adipocytes. Stimulation of mature brown adipocytes with cirazoline (α1-adrenoceptor coupled via Gq), clonidine (α2 via Gi) or CL316243 (β3 via Gs) significantly activated Erk1/2. Pretreatment with the EGF receptor kinase inhibitor AG1478 had, remarkably, no significant effect on Erk1/2 activation induced by any of the adrenergic agonists (although it fully abolished EGF-induced Erk1/2 activation), demonstrating absence of transactivation. Results with brown adipocytes in more proliferative states were not qualitatively different. Joint stimulation of all adrenoceptors with norepinephrine did not result in synergism on Erk1/2 activation or in occur- rence of transactivation. AG1478 action on EGF-stimulated Erk1/2 phos- phorylation showed a sharp concentration-response relationship with an IC50 of approx. 0.3 μM; a minor effect of AG1478 on norepinephrine- stimulated Erk1/2 phosphorylation was clearly nonspecific, occurring suc- cessively and only partially over 3 decades of AG1478 concentrations; cau- tion may therefore be required in interpretation of effects of AG1478 at higher concentrations. Transactivation of the EGF receptor is clearly not a universal prerequisite for coupling of G-protein coupled receptors to Erk1/2 signaling cascades. 

National Category
Other Biological Topics
Research subject
Physiology
Identifiers
urn:nbn:se:su:diva-88574 (URN)
Funder
Swedish Cancer Society
Available from: 2013-03-20 Created: 2013-03-20 Last updated: 2013-03-20Bibliographically approved
3. cAMP-stimulated cell proliferation in brown preadipocytes is mediated by protein kinase A, but is independent of ERK1/2, PI3K and mTOR
Open this publication in new window or tab >>cAMP-stimulated cell proliferation in brown preadipocytes is mediated by protein kinase A, but is independent of ERK1/2, PI3K and mTOR
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The physiological agonist norepinephrine (NE) promotes cell proliferation of brown preadipocytes during the process of tissue recruitment. In a primary culture system, cAMP was shown to mediate these adrenergic effects in the presence of serum. In the present study, we have demonstrated that in con- trast to other systems where the cAMP mitogenic effect requires the syner- gistic action of growth factors, especially insulin/IGF, the cAMP effect in brown preadipocytes is independent of serum and insulin. Furthermore, we showed that the increase in total DNA resulted from forskolin stimulation of cell proliferation, in addition to the anti-apoptosis effect reported previously. Protein kinase A, rather than Epac, mediated the cAMP mitogenic effect. In a further attempt to elucidate the cell signalling pathways involved in this process, we found that both mTOR complexes and the ERK 1/2 family of MAPK, two cell proliferation hallmarks, are indeed activated by cAMP. However, mTOR inhibition with rapamycin only caused partial inhibition of cell proliferation, and Ku-0063794, another inhibitor of mTOR, showed no inhibitory effect on cAMP-stimulated cell proliferation. The involvement of ERK1/2 was tested with pharmacological inhibitors of ERK1/2. PD98059 brought about a significant inhibitory effect, whereas U0126 did not have any inhibitory effect on cAMP-stimulated cell proliferation, even though ERK1/2 phosphorylation was equally well abolished by both inhibitors. Taken together, these results suggest that in brown preadipocytes under se- rum-free conditions, PKA, rather than Epac, mediated the cAMP mitogenic effect through activation of a pathway sensitive to PD98059 but inde- pendently of PI3K, mTOR complexes and the ERK1/2 family of MAPK. 

National Category
Other Biological Topics
Research subject
Physiology
Identifiers
urn:nbn:se:su:diva-88576 (URN)
Funder
Swedish Cancer Society
Available from: 2013-03-20 Created: 2013-03-20 Last updated: 2013-03-20Bibliographically approved
4. Identifying novel genes involved in cAMP- induced cell proliferation of brown preadi- pocytes
Open this publication in new window or tab >>Identifying novel genes involved in cAMP- induced cell proliferation of brown preadi- pocytes
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Norepinephrine, through the second messenger cAMP, stimulates cell prolif- eration in a variety of cell types including brown preadipocytes. However, the cell signalling pathway mediating the cAMP mitogenic effect is poorly established, especially in physiologically relevant systems. A change in tran- scriptional profile due to the activation of specific transcription factors is an important part of intracellular signalling activated by various extracellular stimulants. In the present study, we have used brown preadipocytes as a model system to investigate novel genes that are involved in cAMP-induced cell growth. Based on data from a genome-wide microarray study, 18 genes upregulated by NE in brown preadipocyte were selected for further study. These genes were later confirmed with RT-qPCR to be upregulated by both norepinephrine and forskolin, indicating that they are truly under the positive regulation of cAMP. We therefore suggest that these genes, namely: Ado- ra2b, Arhgap8, Fgf18, Gpr133, Prr5, Tmem37, Twist2 and Ube2s, may be candidates involved in cAMP-stimulated cell proliferation. 

National Category
Other Biological Topics
Research subject
Physiology
Identifiers
urn:nbn:se:su:diva-88577 (URN)
Funder
Swedish Cancer Society
Available from: 2013-03-20 Created: 2013-03-20 Last updated: 2013-03-20Bibliographically approved

Open Access in DiVA

Comprehensive summary(2260 kB)352 downloads
File information
File name FULLTEXT01.pdfFile size 2260 kBChecksum SHA-512
9e2c9848b7556adebdb706840247a75072c43f550509a3bde8f3dcf7311b0a3c2632cf9ac38e932f3dd4518d8f0217397f868148729289dfd36aaf85e929da29
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Wang, Yanling
By organisation
Department of Molecular Biosciences, The Wenner-Gren Institute
Other Biological Topics

Search outside of DiVA

GoogleGoogle Scholar
Total: 352 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 430 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf