The regulation of protein phosphatase 2A in signal transduction, cell cycle transit and malignant transformation

• Research unit: EU RFP
• Project number: 98.0176

Key words (English)

Signal transduction; cell cycle; transformation; PP2A; PKB; NDR; kinase; phosphotase

Alternative project number (English)

EU project number: BMH4-98-3328

Research programs (English)

EU-programme: 4. Frame Research Programme - 4.2 Agriculture and agroindustry

Short description (English)

See abstract

Partners and International Organizations (English)

Coordinator: Université Catholique Louvain (B)

Abstract (English)

Signal transduction pathways in mammalian cells function through the coordinated activation, or inactivation, of protein kinases and phosphatases localized in the cell membrane, cytoplasm or nucleus. Many human diseases result from deregulation of signal transduction pathways, for example, diabetes, cancer and immune dysfunction.
Protein phosphatase 2A (PP2A) is a trimeric holoenzyme which has the most diverse substrate specificity of all protein serine/threonine phosphatases identified so far. It is present in the nucleus and cytoplasm of all eucaryotic cells, and therefore PP2A is predicted to be involved in a large number of cellular processes. Recent investigations identified alterations in the regulatory subunit (PR65/A) of PP2A in some human primary lung and colon tumors which supports the hypothesis that PP2A suppresses tumor development through its involvement in cell cycle regulation and cellular growth control.
We are also interested in the signalling pathway that controls PP2A and the targets of this phosphatase. Two of the targets are NDR (nuclear Dbf2 related serine/threonine protein kinase) and PKB/Akt (protein serine/threonine kinase B) are negatively regulated by PP2A. The activation of NDR and PKB/Akt results in several biological effects, including metabolic control,cell survival and cell shape .
We wanted to address the question about functional differences and the regulatory mechanisms affecting the three proteins (PP2A, PKB and NDR) and their isoforms. Therefore, we are generating gene defective mice for the four isoforms of PP2A variable regulatory PR55/B subunit, the three isoforms of PKB and the two isoforms of NDR by selective inactivation of the genes. Gene targeting vecors for PR55a, NDR1, PKB a, b and g have been prepared and introduced into ES cells. Mice with the ablated genes are currently bred to obtain homozygous strains. The phenotypes of PKB a -/-and g -/- are currently being evaluated. Analysis of the knock-out phenotypes for the various genes should provide significant information on the signal transduction pathways controlled by these central regulatory molecules. We also generated isoform specific antibodies for studying the expression profiles of these proteins. These model systems will provide significant information into the in vivo role of these signal transduction pathways.
Further, we focussed on the the identification of MDM2 as a novel substrate of PKB and the positive influence of its phosphorylation on the ubiquitination process in order to gain additional information about cell survival and transformation.
In addition we are studying the regulation and the role of NDR kinase. We believe these studies will provide insights into a novel signalling pathway that regulates neurite outgrowth and cell shape.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 98.0176