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Identification and characterization of a maturation-inhibited protein kinase (MIPK)

University of British Columbia

A novel homologue of p38 MAP kinase, called maturation-inhibited protein kinase (MIPK), has been cloned from the Pisaster ochraceus oocyte system. MIPK was first recognized as a major tyrosine phosphorylated protein in the immature oocyte, which underwent dephosphorylation in response to the natural hormone 1 -methyladenine. Using an antipeptide antibody based on the C-terminus of cyclin-dependent kinase 5 (Cdk5-CT) as a probe, MIPK was partially purified from seastar oocyte cytosol. Peptide sequence information was used to clone the full length MIPK cDNA. The predicted amino acid sequence of MIPK was found to be most closely related to the p38 MAP kinase. More specifically, MIPK was 65% identical to human p38, 62% identical to human p38β, 56% identical to human p38γ, and 54% identical to p38δ. Analysis of the known p38 kinase family members from diverse species indicates a high degree of conservation (85-95% for p38) in primary structure. MIPK did not show the same level of identity with p38 as did the known p38 homologues, and was therefore defined as a novel member of the p38 MAP kinase family. MIPK was found to be activated in the oocyte system in response to high osmolarity medium and heat shock, confirming MIPK as a stressactivated protein kinase. Assessment of MIPK phosphotyrosine levels during embryonic development showed a dramatic activation of MIPK 12 h post-fertilization. This time course of activation correlated with the transition from synchronous cell divisions to differential cleavages, at a time when the overall rate of cell division decreased. MIPK appeared to be activated in cells arresting in the cell cycle, during meiotic maturation, under stress conditions, or during embryonic development. MIPK may therefore act as a cytostatic factor in the Pisaster ochraceus oocyte syste

Thesis/Dissertation

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2009-06-02

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http://hdl.handle.net/2429/8618

Medicine

University of British Columbia

UBCV

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