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© The Rockefeller University Press, 0021-9525/2000//341 $5.00
The Journal of Cell Biology, Volume 149, Number 2, , 2000 341-356

Original Article

The Mitotic Phosphorylation Cycle of the Cis-Golgi Matrix Protein Gm130



Martin Lowea, Nicholas K. Gonatasb, and Graham Warrena

a Cell Biology Laboratory, Imperial Cancer Research Fund, London WC2A 3PX, United Kingdom
b Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104
School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK.0161-275-50820161-275-5387

lowe{at}man.ac.uk

The cis-Golgi matrix protein GM130 is phosphorylated in mitosis on serine 25. Phosphorylation inhibits binding to p115, a vesicle-tethering protein, and has been implicated as an important step in the mitotic Golgi fragmentation process. We have generated an antibody that specifically recognizes GM130 phosphorylated on serine 25, and used this antibody to study the temporal regulation of phosphorylation in vivo. GM130 is phosphorylated in prophase as the Golgi complex starts to break down, and remains phosphorylated during further breakdown and partitioning of the Golgi fragments in metaphase and anaphase. In telophase, GM130 is dephosphorylated as the Golgi fragments start to reassemble. The timing of phosphorylation and dephosphorylation correlates with the dissociation and reassociation of p115 with Golgi membranes. GM130 phosphorylation and p115 dissociation appear specific to mitosis, since they are not induced by several drugs that trigger nonmitotic Golgi fragmentation. The phosphatase responsible for dephosphorylation of mitotic GM130 was identified as PP2A. The active species was identified as heterotrimeric phosphatase containing the B{alpha} regulatory subunit, suggesting a role for this isoform in the reassembly of mitotic Golgi membranes at the end of mitosis.

Key Words: Golgi • mitosis • GM130 • phosphorylation • protein phosphatase 2A

© 2000 The Rockefeller University Press

G. Warren's present address is Department of Cell Biology, SHM, C441, Yale University School of Medicine, 333 Cedar Street, P.O. Box 208002, New Haven, CT 06520-8002.

M. Lowe's present address is School of Biological Sciences, University of Manchester, 2.205 Stopford Building, Oxford Road, Manchester M13 9PT, UK.

Abbreviations used in this paper: COPI, coat protein I; IQ, ilimaquinone; MEK1, mitogen-activated protein kinase kinase 1; NRK, normal rat kidney; PKD, protein kinase D.


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