Nuclear recruitment of A l p 145 subunit of replication factor C in the early GI phase of the cell cycle in Faza 567 hepatoma cell line and hepatocyte primary cultures

Using a combination of immunoprecipitation and Western blotting with Faza 567 hepatoma cell extracts revealed that the large subunit of replication factor C (Alp145; mRFC140) was in a complex with proliferating cell nuclear antigen (PCNA). Western blotting showed that Alp145 was more abundant in nuclear extracts from butyrate-treated hepatoma cells which blocks the cells in the GI phase of the cell cycle than from routinely cultured cells. Indirect immunoperoxidase analysis of G1 blocked Faza hepatoma cells localized Alpl45 protein predominantly in the nucleoli. When hepatoma cells were stimulated to progress toward the S phase, Alp145 protein was then observed in both the cytoplasm and the nucleoplasm of these cells. Studies with early cultured normal hepatocytes which are progressing from G0 towards G1, also showed a nucleolus distribution for Alp145. This is the first demonstration in mammalian cells that the large subunit of replication factor C is associated with PCNA in the nucleus and that its distribution within cells changes during the cell cycle.