Association of C-Terminal Ubiquitin Hydrolase BRCA1-Associated Protein 1 with Cell Cycle Regulator Host Cell Factor 1

Abstract

Protein ubiquitination provides an efficient and reversible mechanism to regulate cell cycle progression and checkpoint control. Numerous regulatory proteins direct the addition of ubiquitin to lysine residues on target proteins, and these are countered by an army of deubiquitinating enzymes (DUBs). BRCA1-associated protein-1 (Bap1) is a ubiquitin carboxy-terminal hydrolase and is frequently mutated in lung and sporadic breast tumors. Bap1 can suppress growth of lung cancer cells in athymic nude mice and this requires its DUB activity. We show here that Bap1 interacts with host cell factor 1 (HCF-1), a transcriptional cofactor found in a number of important regulatory complexes. Bap1 binds to the HCF-1 ␤-propeller using a variant of the HCF-binding motif found in herpes simplex virus VP16 and other HCF-interacting proteins. HCF-1 is K48 and K63 ubiquitinated, with a major site of linkage at lysines 1807 and 1808 in the HCF-1 C subunit. Expression of a catalytically inactive version of Bap1 results in the selective accumulation of K48 ubiquitinated polypeptides. Depletion of Bap1 using small interfering RNA results in a modest accumulation of HCF-1 C , suggesting that Bap1 helps to control cell proliferation by regulating HCF-1 protein levels and by associating with genes involved in the G 1 -S transition.

Stabilization and targeting of INO80 to replication forks by BAP1 during normal DNA synthesis

“…Although BAP1 can promote cell proliferation by accelerating G1/S progression via host cell factor-1 activation 52,53 , our results suggest that BAP1 can also contribute to cell proliferation by promoting replication fork progression. Indeed, BAP1 depletion results in an accumulation of cells in S phase; conversely, BAP1 re-expression in BAP1-null cells reduces cells in S phase 18,53,54 . Thus, the impact of BAP1 on cell proliferation appears to manifest as the combined effects on DNA replication and other cellular pathways that control cell cycle progression.…”

Mixed Lineage Leukemia 5 (MLL5) Protein Regulates Cell Cycle Progression and E2F1-responsive Gene Expression via Association with Host Cell Factor-1 (HCF-1)

“…We next sought to examine the subcellular localization of these two proteins and determine whether they could colocalize together within cells. Although several previous studies have shown that a short form of the MLL5 proteins (1-560 amino acids) was located mainly in the cell nucleus (20), and the HCF-1 has been detected primarily in the nucleus (30,31,(33)(34)(35)(36)(37)(38)(39), whether they are able to colocalized within the cell nucleus has not been well investigated. To address this, HeLa cells were transiently co-transfected with plasmids encoding HCF-1 protein and FLAGtagged MLL5 protein.…”

BRCA1-associated Protein 1 (BAP1) Deubiquitinase Antagonizes the Ubiquitin-mediated Activation of FoxK2 Target Genes

“…For example, HCF-1 is known to interact with a number of histone-modifying enzymes (39), so deubiquitination of histone H2A by BAP1 could create a different environment for these chromatin regulators. Alternatively, given that BAP1 can deubiquitinate HCF-1 (14,15), it is possible that BAP1 remodels HCF-1 complexes, potentially regulating recruitment of histone-modifying enzymes. Although this study did not find a critical function of HCF-1 at the FoxK2 target genes, further studies will be needed to fully understand the role of the BAP1⅐HCF-1 complex in gene regulation.…”

“…On one hand, BAP1 has been shown to deubiquitinate two BAP1-interacting proteins, HCF-1 (a transcription coregulator) and O-linked N-acetylglucosamine transferase (13)(14)(15). However, the biological significance of this deubiquitination has not been established.…”