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 ha ve previously been shown to localize in separate compartments in interphase but associate at mitosis, We demonstrate here a role for the mitotic AKAP9 5-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 RI I alpha regulatory subunit of PKA onto chromatin, Intranuclear immunoblocki ng of AKAP95 inhibits chromosome condensation at mitosis and in mitotic ext ract in a PKA-independent manner. Immunodepletion of AKAP95 from the extrac t or immunoblocking of AKAP95 at metaphase induces premature chromatin deco ndensation. Condensation is restored in vitro by a recombinant AKAP95 fragm ent comprising the 306-carboxy-terminal amino acids of the protein. Mainten ance of condensed chromatin requires PKA binding to chromatin-associated AK AP95 and cAMP signaling through PKA. Chromatin-associated AKAP95 interacts with Eg7, the human homologue of Xenopus pEg7, a component of the 13S conde nsin complex. Moreover, immunoblocking nuclear AKAP95 inhibits the recruitm ent of Eg7 to chromatin in vitro. We propose that AKAP95 is a multivalent m olecule that in addition to anchoring a cAMP/ PKA-signaling complex onto ch romosomes, plays a role in regulating chromosome structure at mitosis.