Recruitment of protein phosphatase 1 to the nuclear envelope by A-kinase anchoring protein AKAP149 is a prerequisite for nuclear lamina assembly

Subcellular targeting of cAMP-dependent protein kinase (protein kinase A [P KA]) and of type 1 protein phosphatase (PP1) is believed to enhance the spe cificity of these enzymes. We report that in addition to anchoring PKA, A-k inase anchoring protein AKAP149 recruits PP1 at the nuclear envelope (NE) u pon somatic nuclear reformation in vitro, and that PP1 targeting to the NE is a prerequisite for assembly of B-type lamins, AKAP149 is an integral mem brane protein of the endoplasmic reticulum/NE network. The PP1-binding doma in of AKAP149 was identified as K(153)GVLF(157). PP1 binds immobilized AKAP 149 in vitro and coprecipitates with AKAP149 from purified NE extracts. Aff inity isolation of PP1 from solubilized NEs copurifies AKAP149. Upon reasse mbly of somatic nuclei in interphase extract, PP1 is targeted to the NE. Ta rgeting is inhibited by a peptide containing the PP1-binding domain of AKAP 149, abolished in nuclei assembled with membranes immunodepleted of AKAP149 , and restored after reincorporation of AKAP149 into nuclear membranes. B-t ype lamins do not assemble into a lamina when NE targeting of PP1 is abolis hed, and is rescued upon recruitment of PP1 to the NE. We propose that kina se and phosphatase anchoring at the NE by AKAP149 plays in a role in modula ting nuclear reassembly at the end of mitosis.