A novel nuclear inhibitor I-92 regulates DNA binding activity of octamer binding protein p92 during the cell cycle

Abstract

Nuclear DNA binding protein p92 is a sequence specific octamer binding protein with identical molecular weight as the ubiquitous octamer binding protein Oct-1. It binds to octamer related sequences from the enhancer of human papillomavirus type 18. The activity and intracellular distribution of p92 is regulated by extracellular signals. In serum starved Hela-fibroblast hybrid cells p92 is localized to the cytosol. Serum stimulation leads to nuclear import of p92. In fractions of asynchronously growing cells, which were separated according to cell cycle phases into G1, S, and G2 populations by centrifugal elutriation, p92 DNA binding is confined to S phase. In binding site blots however, p92 DNA binding activity is also present in G1 and G2. In G1 and G2 DNA binding activity of p92 is masked by a novel nuclear inhibitor I-92. The cyclic association of p92 with its inhibitor I-92 provides a new mechanism of regulating S phase dependent activity of a sequence specific DNA binding protein.

Cell Cycle Regulation of Nuclear Factor p92 DNA-binding Activity by Novel Phase-specific Inhibitors

“…In addition, the 5Ј-AATTGCTTGCATAA motif is recognized by p92-related factors as was shown by UV cross-linking experiments (3). p92, however, is the most prominent retarded DNA-protein complex in electrophoretic mobility shift assays (4). The HPV18 p92 recognition sequence 5Ј-AATTGCTTGCATAA consists of two partially overlapping octamer-related motifs (1,3).…”

“…We have shown by centrifugal elution experiments that during the cell cycle p92 DNA binding activity is restricted to S phase of 444 cells that contain integrated human papillomavirus type 18 (4). In crude nuclear extracts, we have identified an uncharacterized activity, termed I-92, which inhibits DNA binding of p92 (4). In cell cycle populations of 444 cells, p92 DNA binding activity could not be detected in nuclear extracts from G 1 phase and from G 2 phase cells.…”

“…In cell cycle populations of 444 cells, p92 DNA binding activity could not be detected in nuclear extracts from G 1 phase and from G 2 phase cells. It was, however, possible to detect p92 after treatment of these extracts with the detergent deoxycholate (4), suggesting that p92 was complexed to an inhibitor in G 1 and in G 2 phase of the cell cycle.…”

“…p92 is a sequence-specific nuclear factor that specifically binds to the 5Ј-AATTGCTTGCATAA motif and other related motifs in the HPV18 enhancer (1,3). p92 was originally identified by binding site blotting experiments (1), and retarded p92s containing DNA-protein complexes were identified by preparative electrophoretic mobility shift experiments and analysis of eluted proteins by binding site blotting (4). In addition, the 5Ј-AATTGCTTGCATAA motif is recognized by p92-related factors as was shown by UV cross-linking experiments (3).…”

“…In addition, the intracellular distribution of p92 is regulated by growth factors, because p92 was found in the cytoplasm of serum-starved nontumorigenic HeLa-fibroblast hybrid cells (444 cells) and was translocated to the nucleus upon serum stimulation at the beginning of S phase (1,4). We have shown by centrifugal elution experiments that during the cell cycle p92 DNA binding activity is restricted to S phase of 444 cells that contain integrated human papillomavirus type 18 (4). In crude nuclear extracts, we have identified an uncharacterized activity, termed I-92, which inhibits DNA binding of p92 (4).…”