Cell Cycle-Dependent Phosphorylation of MAN1

Abstract

The LEM (LAP2beta, Emerin, and MAN1) proteins are essential for nuclear membrane targeting to chromatin via an association with barrier-to-autointegration factor (BAF). Herein, we focused on the mitotic phosphorylation of MAN1 and its biological role. MAN1 was phosphorylated in a cell cycle-dependent manner in the Xenopus egg cell-free system, and the mitotic phosphorylation at the N-terminal region of MAN1 suppressed the binding of MAN1 to BAF. Titansphere column chromatography followed by MS/MS sequencing identified at least three M-phase-specific phosphorylation sites, Thr-209, Ser-351, and Ser-402, and one cell cycle-independent phosphorylation site, Ser-463. An in vitro BAF binding assay involving mutants S402A and S402E suggested that the phosphorylation of Ser-402 was important for regulation of the binding of MAN1 to BAF.

Fission yeast Lem2 and Man1 perform fundamental functions of the animal cell nuclear lamina

“…Phosphorylation, and perhaps other cell cycle dependent protein modifications of components of the lamina, releases chromatin from the NE at mitosis and promotes NEBD (reviewed in refs. 5, 17 and 18). …”

“…At this point in the cell cycle, phosphorylation of lamina proteins releases them from one another and from the DNA to which they were bound (reviewed in refs. 5, 17 and 18) which destabilizes the NE and releases transcriptionally repressed heterochromatin from the nuclear periphery. Plant cells have evolved a different mechanism to regulate NE stability during open mitosis because although they undergo NE breakdown, they have no lamins, LAPs or BAF 19 , 20 …”

Networking in the nucleus: a spotlight on LEM-domain proteins

“…Taken together, these findings suggest external signals are transmitted through PTMs of emerin, leading to changes in the emerin interactome and hence nuclear lamina function. Interactions with partners are also controlled by internal signaling; for example cell cycle-dependent modifications of MAN1 disrupt association with BAF [25]. These findings emphasize that the nuclear lamina includes a dynamic LEM-D protein network that responds to cell signaling.…”

The Cellular Mastermind(?)—Mechanotransduction and the Nucleus

“…180 Other LEM domain proteins similarly show altered interaction upon phosphorylation. In MAN1, phosphorylation of three different residues interrupts binding to BAF; 137,181 changing the phosphorylation state of LAP2α affects its binding to chromatin but not to the nuclear envelope. 182 For lamins and other nuclear envelope proteins, which can also undergo various posttranslational modifications, the functional consequences and prevalence of such modifications outside of their role in mitosis are only beginning to emerge and are likely to produce exciting new insights.…”