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Nuclear localization and cell cycle regulation of a murine protein tyrosine phosphatase
U Tillmann1, J Wagner, D Boerboom
1Laboratory of Mammalian Genes and Development, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
Abstract:
MPTP is a murine homolog of the human T-cell protein tyrosine phosphatase (PTPase) and the rat PTP-S enzyme. Enzymatic activity of this ubiquitously expressed protein was demonstrated in immunoprecipitates from NIH 3T3 cells and in recombinant protein overexpressed in bacteria. Expression of beta-galactosidase-MPTP MPTP chimeric proteins in COS1 cells identified a nuclear localization signal at the carboxyl terminus of the MPTP that was sufficient to direct beta-galactosidase as well as a tagged version of the MPTP to the nucleus. Deletion analysis of amino acids within the nuclear targeting signal showed that this sequence does not conform to the bipartite type of nuclear localization signals. Furthermore, it was shown that the steady-state levels of MPTP RNA fluctuate in a cell cycle-specific manner. On the basis of these experiments, we discuss the possible function of MPTP in the cell cycle and other nuclear processes.
Insights
Murine T-cell protein tyrosine phosphatase (MPTP) is found in the nucleus and its RNA levels change during the cell cycle, suggesting a role in nuclear processes.
Area of Science:
- Molecular Biology
- Cell Biology
Background:
- MPTP is a murine homolog of human T-cell protein tyrosine phosphatase (PTPase) and rat PTP-S.
- Its enzymatic activity has been confirmed in cell lysates and recombinant protein.
Purpose of the Study:
- To investigate the cellular localization and cell cycle regulation of MPTP.
- To identify the nuclear localization signal of MPTP.
Main Methods:
- Immunoprecipitation and Western blotting to detect enzymatic activity.
- Expression of chimeric proteins (beta-galactosidase-MPTP) in COS1 cells.
- Deletion analysis of the MPTP sequence.
- Analysis of MPTP RNA levels during the cell cycle.
Main Results:
- MPTP possesses a nuclear localization signal at its carboxyl terminus.
- This signal directs both MPTP and other proteins to the nucleus.
- The identified nuclear localization signal is not bipartite.
- MPTP RNA levels exhibit cell cycle-specific fluctuations.
Conclusions:
- MPTP is localized to the nucleus via a non-bipartite signal.
- MPTP expression is regulated during the cell cycle.
- MPTP may play a role in nuclear processes and cell cycle regulation.