标题：Phosphorylation and microtubule association of the Opitz syndrome protein mid-1 is regulated by protein phosphatase 2A via binding to the regulatory subunit α4
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2001
卷号：98
期号：12
页码：6650-6655
DOI：10.1073/pnas.111154698
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Opitz syndrome (OS) is a human genetic disease characterized by deformities such as cleft palate that are attributable to defects in embryonic development at the midline. Gene mapping has identified OS mutations within a protein called Mid1. Wild-type Mid1 predominantly colocalizes with microtubules, in contrast to mutant versions of Mid1 that appear clustered in the cytosol. Using yeast two-hybrid screening, we found that the 4-subunit of protein phosphatases 2A/4/6 binds Mid1. Epitope-tagged 4 coimmunoprecipitated endogenous or coexpressed Mid1 from COS7 cells, and this required only the conserved C-terminal region of 4. Localization of Mid1 and 4 was influenced by one another in transiently transfected cells. Mid1 could recruit 4 onto microtubules, and high levels of 4 could displace Mid1 into the cytosol. Metabolic 32P labeling of cells showed that Mid1 is a phosphoprotein, and coexpression of full-length 4 decreased Mid1 phosphorylation, indicative of a functional interaction. Association of green fluorescent protein-Mid1 with microtubules in living cells was perturbed by inhibitors of MAP kinase activation. The conclusion is that Mid1 association with microtubules, which seems important for normal midline development, is regulated by dynamic phosphorylation involving MAP kinase and protein phosphatase that is targeted specifically to Mid1 by 4. Human birth defects may result from environmental or genetic disruption of this regulatory cycle.
