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(American Journal of Pathology. 2003;162:479-489.)
© 2003 American Society for Investigative Pathology

Regular Articles

Localization of the PP2A B56{gamma} Regulatory Subunit at the Golgi Complex

Possible Role in Vesicle Transport and Migration

Akihiko Ito*, Yu-ichiro Koma*, Miwa Sohda{dagger}, Kenji Watabe{ddagger}, Teruaki Nagano§, Yoshio Misumi{dagger}, Hiroshi Nojima§ and Yukihiko Kitamura*

From the Department of Pathology,* Osaka University Medical School/Graduate School of Frontier Bioscience, Suita, Osaka; the Department of Internal Medicine and Molecular Science,{ddagger} Osaka University Medical School, Suita, Osaka; the Department of Molecular Genetics,§ Institute for Microbial Diseases, Osaka University, Suita, Osaka; and the Department of Cell Biology,{dagger} Fukuoka University School of Medicine, Fukuoka, Japan

The BL6 subline was derived from the F10 line, which was derived from the B16 mouse melanoma cell line. BL6 cells are more invasive than F10 cells and differ genetically from F10 cells by an alteration of the gene encoding the B56{gamma} regulatory subunit of protein phosphatase 2A (PP2A). This alteration results in the transcription of mRNA encoding a truncated variant of the B56{gamma}1 isoform ({Delta}{gamma}1). When F10 cells were stained with a polyclonal antibody that recognizes three B56{gamma} isoforms, B56{gamma}1, B56{gamma}2, and B56{gamma}3, the immunofluorescent signals co-localized well with the cis-Golgi marker proteins. When BL6 cells were fractionated in a sucrose gradient, B56{gamma}1 and B56{gamma}2, but not B56{gamma}3, were present in the Golgi-enriched fraction. This fraction also contained the catalytic subunit of PP2A. FLAG-tagged {Delta}{gamma}1 preferentially localized to the trans-Golgi area rather than the cis-Golgi. This localization was the same as that of FLAG-tagged B56{gamma}1. NIH3T3 cells stably expressing {Delta}{gamma}1 transported a mutant viral protein from the endoplasmic reticulum to the plasma membrane much faster than wild-type cells. Their directional migration, as assessed by the advance of cells into a cell-free area, was also elevated. As {Delta}{gamma}1 reduces the activity of the B56{gamma}-containing PP2A holoenzymes, these results suggest that the normal holoenzymes suppress vesicle transport and that {Delta}{gamma}1 might increase the invasive ability of BL6 cells by activating Golgi function.




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