The A-kinase-anchoring protein AKAP95 is a multivalent protein with a key role in chromatin condensation at mitosis.
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 RIIalpha 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.
Collas
P
P
Institute of Medical Biochemistry, Faculty of Medicine, University of Oslo, Blindern, 0317 Oslo, Norway. philippe.collas@basalmed.uio.no
Le Guellec
K
K
Taskén
K
K
D000906:Antibodies / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D002457:Cell Extracts; D002843:Chromatin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002877:Chromosomes, Human / Q000737:chemistry / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000037:antagonists & inhibitors / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004527:Egg Proteins / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008938:Mitosis / Q000187:drug effects; D015739:Nocodazole / Q000494:pharmacology; D015530:Nuclear Matrix / Q000187:drug effects / Q000378:metabolism; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D015398:Signal Transduction / Q000187:drug effects; D029867:Xenopus Proteins
C490117:AKAP8L protein, human; D000906:Antibodies; D018797:Cell Cycle Proteins; D002457:Cell Extracts; D002843:Chromatin; D004268:DNA-Binding Proteins; C116601:Eg7 protein, Xenopus; D004527:Egg Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D010446:Peptide Fragments; D029867:Xenopus Proteins; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D015739:Nocodazole