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 HP1 alpha interacts with the preRC proteins ORC1, ORC2 and CDC6. Immunofluorescence staining and EGFP/DsRed fusion proteins revealed a colocalization of HP1a with ORC1, ORC2 and CDC6 in heterochromatin, supporting the notion that ORC and probably CDC6 play an important role in murine HP1 alpha function. Besides that, we also observed a colocalization of HP1 alpha with gamma-tubulin suggesting a centrosomal localization of HP1 alpha in murine cells. To gain insight into HP1 alpha function, we applied the RNAi technique. Depletion of HP1 alpha 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 HP1 alpha exerts functions in mitosis and cytokinesis. (c) 2006 Elsevier Inc. All rights reserved.