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© The Rockefeller University Press, 0021-9525/1999//1167 $5.00
The Journal of Cell Biology, Volume 147, Number 6, , 1999 1167-1180

Original Article

The a-Kinase–Anchoring Protein Akap95 Is a Multivalent Protein with a Key Role in Chromatin Condensation at Mitosis



Philippe Collasa, Katherine Le Guellecb, and Kjetil Taskéna

a Institute of Medical Biochemistry, Faculty of Medicine, University of Oslo, Blindern, 0317 Oslo, Norway
b Centre National Recherche Scientifique UPR41, Biologie et Génétique du Dévelopement, Faculté de Médecine, 35043 Rennes Cedex, France
Institute of Medical Biochemistry, Faculty of Medicine, University of Oslo, P.O. Box 1112 Blindern, 0317 Oslo, Norway.47-22-85-14-9747-22-85-10-13

philippe.collas{at}basalmed.uio.no

Protein kinase A (PKA) and the nuclear A-kinase–anchoring protein AKAP95 have previously been shown to localize in separate compartments in interphase but associate at mitosis. We demonstrate here a role for the mitotic AKAP95–PKA complex. In HeLa cells, AKAP95 is associated with the nuclear matrix in interphase and redistributes mostly into a chromatin fraction at mitosis. In a cytosolic extract derived from mitotic cells, AKAP95 recruits the RII{alpha} regulatory subunit of PKA onto chromatin. Intranuclear immunoblocking of AKAP95 inhibits chromosome condensation at mitosis and in mitotic extract in a PKA-independent manner. Immunodepletion of AKAP95 from the extract or immunoblocking of AKAP95 at metaphase induces premature chromatin decondensation. Condensation is restored in vitro by a recombinant AKAP95 fragment comprising the 306–carboxy-terminal amino acids of the protein. Maintenance of condensed chromatin requires PKA binding to chromatin-associated AKAP95 and cAMP signaling through PKA. Chromatin-associated AKAP95 interacts with Eg7, the human homologue of Xenopus pEg7, a component of the 13S condensin complex. Moreover, immunoblocking nuclear AKAP95 inhibits the recruitment of Eg7 to chromatin in vitro. We propose that AKAP95 is a multivalent molecule that in addition to anchoring a cAMP/PKA–signaling complex onto chromosomes, plays a role in regulating chromosome structure at mitosis.

Key Words: AKAP • cAMP • chromosome condensation • mitosis • PKA

© 1999 The Rockefeller University Press

Abbreviations used in this paper: AKAP, A-kinase–anchoring protein; CDK1, cyclin-dependent kinase 1; LBR, lamin B receptor; PCD, premature chromatin decondensation; PKA, protein kinase A; R and C, regulatory and catalytic subunit of PKA, respectively; SMC, structural maintenance of chromosome.


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J. Cell Biol. 1999 147: 1-2. [Full Text] [PDF]





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