LAP2α-binding protein LINT-25 is a novel chromatin-associated protein involved in cell cycle exit

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Abstract
Lamina-associated polypeptide 2α (LAP2α) is a nuclear protein dynamically associating with chromatin during the cell cycle. In addition, LAP2α interacts with A-type lamins and retinoblastoma protein and regulates cell cycle progression via the E2F-Rb pathway. Using yeast two-hybrid analysis and three independent in vitro binding assays we identified a new LAP2α interaction partner of hitherto unknown functions, which we termed LINT-25. LINT-25 protein levels were upregulated during G1 phase in proliferating cells and upon cell cycle exit in quiescence, senescence and differentiation. Upon cell cycle exit LINT-25 accumulated in heterochromatin foci, and LAP2α protein levels were downregulated by proteasomal degradation. Although LAP2α was not required for the upregulation and reorganization of LINT-25 during cell cycle exit, transient expression of LINT-25 in proliferating cells caused loss of LAP2α and subsequent cell death. Our data show a role of LINT-25 and LAP2α during cell cycle exit, in which LINT-25 acts upstream of LAP2α.