Conditional Transgenic System for Mouse Aurora A Kinase: Degradation by the Ubiquitin Proteasome Pathway Controls the Level of the Transgenic Protein

Abstract

Aurora A is a mitotic kinase that localizes to centrosomes. Expression of this protein is normally limited to the mitotic stage (G₂-M) of the cell cycle, whereas human cancer cells frequently exhibit overexpression of Aurora A protein regardless of the cell cycle stage. In the present study, Aurora A transgenic mouse lines were generated with a new conditional expression system (cytomegalovirus immediate early enhancer-chicken beta-actin hybrid promoter-Z-enhanced green fluorescent protein) in order to analyze the function of this protein. Although transcripts for Aurora A were elevated in multiple organs of the transgenic mice, the corresponding protein was not detected in extracts analyzed by immunoblotting. The treatment of transgenic-derived embryonic fibroblasts (MEF) with proteasome inhibitors markedly increased the protein level of transgenic Aurora A, indicating that the transgenic Aurora A protein is readily degraded in normal mouse tissues. Under the exponential growth conditions of MEF cells, transgenic Aurora A was detected within the mitotic stage of the cell cycle and localized to centrosomes. In contrast, the marker of the transgenic promoter (enhanced green fluorescent protein) was continuously expressed throughout the cell cycle, indicating the constitutive transcription of transgenic mRNA. These results indicate that transgenic Aurora A is protected from degradation within G₂-M but is immediately degraded after translation in the G₁-S stage of the cell cycle. The findings obtained with this transgenic model and derived cells support that the transition from protection to degradation by the ubiquitin proteasome system at the end of mitosis is an important step in controlling the level of Aurora A protein during the cell cycle.

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Correction for Fukuda et al., Conditional Transgenic System for Mouse Aurora A Kinase: Degradation by the Ubiquitin Proteasome Pathway Controls the Level of the Transgenic Protein

ACKNOWLEDGMENTS

We are grateful to Jeff Reece, Silbajoris Lydia (confocal microscope core in NIEHS), Naoto Ishii (Department of Immunology, Medical School of Tohoku University), and Shigeto Miura (National Institute of Environmental Health Sciences, Laboratory of Reproductive and Developmental Toxicology) for technical assistance. We thank Harriet Kinyamu, Mitch E. Eddy, Martina Schmitt, and Diane Klotz for helpful advice and discussion. We also thank Hideko Fukuda (National Institute of Environmental Health Studies, Tsukuba, Japan) for her support and encouragement throughout this work.