Adipocyte phosphatases and the antilipolytic action of insulin

Research output: ThesisDoctoral Thesis (compilation)

Abstract

Adipose tissue is the main site of energy storage of the body and an important endocrine organ. Knowledge of the regulation of fat metabolism and the endocrine factors secreted by the adipocyte is crucial for the understanding of diseases such as obesity and diabetes. Insulin is the main antilipolytic hormone. Protein kinase B (PKB) and phosphodiesterase 3B (PDE3B) are both phosphorylated and activated in adipocytes in response to insulin. PDE3B is known to be a key intermediate in insulin's antilipolytic signal transduction pathway and PKB is believed to be the kinase responsible for phosphorylating and activating PDE3B in response to insulin.

This thesis deals with the reversible phosphorylation of PKB and PDE3B in adipocytes and with the purification of membrane associated protein phosphatase 2A (PP2A) from adipose tissue. Using treatment of rat adipocytes with phosphatase inhibitors and in vitro dephosphorylations of PKB and PDE3B with partially purified adipocyte phosphatases, we were able to demonstrate that PP2A has an important role in the dephosphorylation of both PKB and PDE3B. In addition we were able to show that in adipocytes PKB is mainly phosphorylated on a single site, Ser 473 (PKB-alpha sequence), in contrast to previously published reports using cultured cells overexpressing PKB. Finally, since both PKB and PDE3B are membrane associated enzymes we managed to purify a membrane associated form of PP2A from bovine adipose tissue. The PP2A form was identified as being a trimer composed of PP2Ac-beta, PR65-alpha and PR55-alpha.

These results provide information that will make it possible to study the dephosphorylation of PKB and PDE3B in greater detail with the possible goal of finding ways to specifically modify the phosphorylation states of these enzymes.

Details

Authors
  • Svante Resjö
Organisations
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Basic Medicine

Keywords

  • protein phosphorylation, protein purification, adipose tissue, PP2A, protein phosphatase, PDE3B, phosphodiesterase 3B, Insulin signalling, antilipolysis, Klinisk biologi, Clinical biology, PKB, protein kinase B
Original languageEnglish
QualificationDoctor
Awarding Institution
Supervisors/Assistant supervisor
  • [unknown], [unknown], Supervisor, External person
Award date2002 Feb 22
Publisher
  • Svante Resjö, BMC, C11, SE-221 84 LUND, SWEDEN,
Print ISBNs91-628-5112-8
Publication statusPublished - 2002
Publication categoryResearch

Bibliographic note

Defence details Date: 2002-02-22 Time: 13:00 Place: GK-salen, BMC, Sölveg. 19, LUND External reviewer(s) Name: Eriksson, Jan Title: Dr Affiliation: Umeå University Hospital --- Article: Phosphorylation and activation of phosphodiesterase type 3B (PDE3B) in adipocytes in response to serine/threonine phosphatase inhibitors. Deactivation of PDE3B in vitro by protein phosphatase 2AResjö, S., Oknianska, A., Zolnierowicz, S., Manganiello, V. and Degerman, E. (1999) Biochem. J. 341, 839-845Protein phosphatase 2A is the main phosphatase involved in the regulation of protein kinase B in rat adipocytesResjö, S., Göransson, O., Härndahl, L., Zolnierowicz, S., Manganiello, V. and Degerman, E. (2002) Cellular Signalling 14/3 231-238Ser-474 is the major target of insulin-mediated phosphorylation of protein kinase B-beta in primary rat adipocytesGöransson, O., Resjö, S., Rönnstrand, L., Manganiello, V. and Degerman, E. (2002) Cellular Signalling 14/2 175-182Purification of a membrane associated form of protein phosphatase 2A from bovine adipose tissueSvante Resjö, Alina Oknianska, Stanislaw Zolnierowicz, Ulf Hellman, Vincent Manganiello, Eva Degerman Manuscript