LEM-4 promotes rapid dephosphorylation of BAF during mitotic exit.

The transitions between the successive cell cycle stages depend on reversible protein phosphorylation events. The phosphorylation state of every protein within a cell is strictly determined by spatiotemporally controlled kinase and phosphatase activities. Nuclear disassembly and reassembly during open mitosis in higher eukaryotic cells is one such process that is tightly regulated by the reversible phosphorylation of key proteins. However, little is known about the regulation of these mitotic events. In particular, although kinase function during entry into mitosis is better studied, very little is known about how proteins are dephosphorylated to allow nuclear reformation at the end of mitosis. We have identified LEM‑4, a conserved protein of the nuclear envelope, as an essential coordinator of kinase and phosphatase activities during mitotic exit. Inhibition of VRK‑1 kinase and promotion of a PP2A phosphatase complex by LEM‑4 tightly regulate the phosphorylation state of BAF, an essential player of nuclear reformation at the end of mitosis. Here I offer extended comments on the contribution of LEM‑4 in the regulation of protein phosphorylation and nuclear reformation.