Biomedical subjects

Patricia Bilan

Publications and source records attributed to Patricia Bilan.

2 recordsLinked to original sources

PubMed2006

Host cell factor-1 and E2F4 interact via multiple determinants in each protein.

Host Cell Factor (HCF-1) is a conserved, essential protein initially identified as a co-regulator for the Herpes Simplex Virus transactivator VP16. HCF-1 is variously involved in regulating transcription, splicing, cell proliferation and cytokinesis; however, its mechanisms of action remain unknown. HCF-1 function is manifested through an increasing assortment of cellular factors that target different regions of the protein. Several HCF-1 partners target the amino-terminal kelch domain of HCF-1 (residues 1-380) via a consensus HCF-binding motif (HBM) comprising the tetrapeptide (D/E)HXY. Searches of sequence databases indicated that this motif is present in E2F1 and E2F4, two members of the E2F family of cell cycle regulators. We show here that E2F4 specifically and directly interacts with HCF-1. Mutational analysis showed E2F4 independently targets the kelch domain and the basic domain (residues 450-902) of HCF-1, both of which are required for normal cell-cycle progression via separate determinants. The HBM-containing domain of E2F4 was necessary for interaction with the kelch domain of HCF-1 but not for interaction with the basic domain. Mutations in the HCF-1 kelch domain known to block cell growth abrogated E2F4 binding to the kelch domain in the absence but not in the presence of the juxtaposed basic region. Functionally, HCF-1 co-activated E2F4/DP-1 in transient transfection assays, while E2F4 blocked HCF-1-dependent rescue of a cell line that harbors a temperature sensitive mutant of HCF-1 that causes growth arrest. Our findings show that HCF-1 and E2F4 interact via multiple determinants and suggest a linkage between E2F4 and HCF-1 cell growth pathways.

Amino Acid Motifs↗

PubMed2002

Host cell factor-1 interacts with and antagonizes transactivation by the cell cycle regulatory factor Miz-1.

Human host cell factor-1 (HCF-1) is essential for cell cycle progression and is required, in conjunction with the herpes simplex virus transactivator VP16, for induction of viral immediate-early gene expression. We show here that HCF-1 directly binds to the Myc-interacting protein Miz-1, a transcription factor that induces cell cycle arrest at G(1), in part by directly stimulating expression of the cyclin-dependent kinase inhibitor p15(INK4b). A domain encompassing amino acids 750-836, contained within a subregion of HCF-1 required for cell cycle progression, was sufficient to bind Miz-1. Conversely, HCF-1 interacted with two separate regions in Miz-1: the N-terminal POZ domain and a C-terminal domain (residues 637-803) previously shown to harbor determinants for interaction with c-Myc and the coactivator p300. The latter functioned as a potent transactivation domain when tethered to DNA, indicating that HCF-1 targets a transactivation function in Miz-1. HCF-1 or a Miz-1-binding fragment of HCF-1 repressed transactivation by Gal4-Miz-1 in transfection assays. Moreover, HCF-1 repressed Miz-1-mediated transactivation of a reporter gene linked to the p15(INK4b) promoter. Protein/protein interaction studies and transient transfection assays demonstrated that HCF-1 interferes with recruitment of p300 to Miz-1, similar to what has been reported with c-Myc. Our findings identify Miz-1 as a novel HCF-1-interacting partner and illustrate cross-talk between these two proteins that may be of consequence to their respective functions in gene regulation and their opposing effects on the cell cycle.

Animals↗