Interaction between HP1α and replication proteins in mammalian cells

HP1 is an essential heterochromatin-associated protein known to play an important role in the organization of heterochromatin as well as in the transcriptional regulation of heterochromatic and euchromatic genes both in repression and activation. Using the yeast two-hybrid system and immunoprecipitation, we report here that murine HP1α interacts with the preRC proteins ORC1, ORC2 and CDC6. Immunofluorescence staining and EGFP/DsRed fusion proteins revealed a colocalization of HP1α with ORC1, ORC2 and CDC6 in heterochromatin, supporting the notion that ORC and probably CDC6 play an important role in murine HP1α function. Besides that, we also observed a colocalization of HP1α with γ-tubulin suggesting a centrosomal localization of HP1α in murine cells. To gain insight into HP1α function, we applied the RNAi technique. Depletion of HP1α leads to a slow down of cell proliferation, an aberrant cell cycle progression as well as to multinucleated cells with insufficiently organized microtubule. These results together indicate that HP1α exerts functions in mitosis and cytokinesis.