Role for Tyrosine Phosphorylation of A-kinase Anchoring Protein 8 (AKAP8) in Its Dissociation from Chromatin and the Nuclear Matrix

Sho Kubota,Mariko Morii,Ryuzaburo Yuki,Noritaka Yamaguchi,Hiromi Yamaguchi,Kazumasa Aoyama,Takahisa Kuga,Takeshi Tomonaga,Naoto Yamaguchi

doi:10.1074/jbc.m115.643882

Abstract

Protein-tyrosine phosphorylation regulates a wide variety of cellular processes at the plasma membrane. Recently, we showed that nuclear tyrosine kinases induce global nuclear structure changes, which we called chromatin structural changes. However, the mechanisms are not fully understood. In this study we identify protein kinase A anchoring protein 8 (AKAP8/AKAP95), which associates with chromatin and the nuclear matrix, as a nuclear tyrosine-phosphorylated protein. Tyrosine phosphorylation of AKAP8 is induced by several tyrosine kinases, such as Src, Fyn, and c-Abl but not Syk. Nucleus-targeted Lyn and c-Src strongly dissociate AKAP8 from chromatin and the nuclear matrix in a kinase activity-dependent manner. The levels of tyrosine phosphorylation of AKAP8 are decreased by substitution of multiple tyrosine residues on AKAP8 into phenylalanine. Importantly, the phenylalanine mutations of AKAP8 inhibit its dissociation from nuclear structures, suggesting that the association/dissociation of AKAP8 with/from nuclear structures is regulated by its tyrosine phosphorylation. Furthermore, the phenylalanine mutations of AKAP8 suppress the levels of nuclear tyrosine kinase-induced chromatin structural changes. In contrast, AKAP8 knockdown increases the levels of chromatin structural changes. Intriguingly, stimulation with hydrogen peroxide induces chromatin structural changes accompanied by the dissociation of AKAP8 from nuclear structures. These results suggest that AKAP8 is involved in the regulation of chromatin structural changes through nuclear tyrosine phosphorylation.

Highlights

Tyrosine kinases are active in the cell nucleus and involved in global nuclear structure
AKAP8 was tyrosine-phosphorylated by NLS-Lyn and NLS-c-Abl and NLS-4ICD but was not by NLS-Syk (Fig. 1C). These results suggest that AKAP8 is tyrosine-phosphorylated by some nuclear tyrosine kinases such as Src-family tyrosine kinases (SFKs), c-Abl, and 4ICD
AKAP8 is known to associate with nuclear structures such as the nuclear matrix and chromatin and act as a scaffolding protein (24 –26), it has far not been reported that the interaction of AKAP8 with nuclear structures is regulated through posttranslational modifications

Summary

Background

Tyrosine kinases are active in the cell nucleus and involved in global nuclear structure. Results: Phosphorylation of AKAP8 at multiple tyrosine residues by several nucleus-localized tyrosine kinases, including c-Src, induces AKAP8’s dissociation from nuclear structures. Tyrosine phosphorylation of AKAP8 is induced by several tyrosine kinases, such as Src, Fyn, and c-Abl but not Syk. Nucleus-targeted Lyn and c-Src strongly dissociate AKAP8 from chromatin and the nuclear matrix in a kinase activitydependent manner. Stimulation with hydrogen peroxide induces chromatin structural changes accompanied by the dissociation of AKAP8 from nuclear structures These results suggest that AKAP8 is involved in the regulation. Nuclear tyrosine kinases were reported to be involved in the regulation of cytoskeletal structures, DNA damage responses, and gene transcription [20,21,22], the roles of nuclear tyrosine kinases have not been fully understood. We further showed that tyrosine phosphorylation of AKAP8 is involved in nuclear tyrosine kinase-mediated chromatin structural changes

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION