p53 binds the nuclear matrix in normal cells: binding involves the proline-rich domain of p53 and increases following genotoxic stress

The tumour suppressor p53 is a multifunctional protein important for the ma intenance of genomic integrity. It is able to form molecular complexes with different DNA targets and also with cellular proteins involved in DNA tran scription and DNA repair. In mammalian cells the biochemical processing of DNA occurs on a nuclear substructure termed the nuclear matrix. Previously Deppert and co-workers have identified p53 in association with the nuclear matrix in viral- and non-viral transformed cell lines. In the present study we demonstrate, for the first time, that p53 is bound to the nuclear matri x in primary cultures of normal mammalian cells and that this binding incre ases following DNA damage. Analysis of cell lines expressing structural mut ants of p53 revealed that association with the nuclear matrix is independen t of the tertiary and quaternary structure of p53. However, the proline-ric h domain towards the N-terminus of p53 (residues 67 to 98) appeared importa nt for binding to the nuclear matrix. This was demonstrated by TET-ON regul ated expression of p53-derived constructs in p53(-/-) murine embryonic fibr oblasts (MEF p53(-/-)). The proline-rich domain of p53 has potential for SH 3 protein-protein interaction, and has a role in p53-mediated apoptosis and possibly base excision repair of DNA damage. We discuss our observations i n relation to the ability of p53 to facilitate DNA repair and also review e vidence indicating that matrix-bound p53 in SV40-transformed cells may faci litate the transforming potential of SV40 large T antigen.