Inactivation of the ubiquitin conjugating enzyme UBE2Q2 causes a prophase arrest and enhanced apoptosis in response to microtubule inhibiting agents

Abstract

A putative ubiquitin conjugating enzyme known as UBE2Q2 was previously identified in a microarray screen for mitotic regulatory proteins. UBE2Q2 is very similar to another human protein, UBE2Q1 and orthologs from other higher eukaryotic species. In these studies, we demonstrate that UBE2Q2 can covalently bind ubiquitin on the active site cysteine in vitro and show that inhibition of this protein in vivo causes an early mitotic arrest and increased cytotoxicity when cells are treated with microtubule inhibiting agents (MIAs). Changes in cell cycle progression and viability are not observed in the absence of MIA treatment, indicating that UBE2Q2 is involved in the response to MIAs rather than performing a more general function in mitosis. Inhibition of the UBE2Q2 protein causes cells to undergo a prolonged prophase arrest suggesting that UBE2Q2 normally functions to antagonize an early mitotic checkpoint. Furthermore, UBE2Q2 inhibition sensitizes cells to the cytotoxic effects of MIAs through caspase-mediated apoptosis that is correlated with PARP-1 cleavage. These data provide insights into the cellular response to MIAs and demonstrate that inhibition of UBE2Q2 protein function may be useful in the treatment of malignancies.

Characterization of a Novel Ubiquitin-Conjugating Enzyme That Regulates β1,4-Galactosyltransferase-1 in Embryonic Stem Cells

“…A variety of ubiquitin-conjugating enzymes have been shown to be differentially expressed during implantation and embryonic development [37]. UBE2Q1 and UBE2Q2, two E2s that are closely related to GTAP, have been shown to be expressed during the early blastocyst stage [38,39]. Our current results show that the total protein level of GTAP increases during EB development, whereas the Ub-activated form of GalT1-associated GTAP is attenuated.…”

Ubiquitin-Conjugating Enzyme UBE2Q2 Suppresses Cell Proliferation and Is Down-Regulated in Recurrent Head and Neck Cancer

“…Moreover, UBE2Q2 plays an important role in the cellular response to microtubule inhibition, and inactivation of UBE2Q2 causes cells to undergo prophase arrest and apoptosis in M phase, suggesting that UBE2Q2 might promote the development of aneuploidy or malignancy as an oncogene in M phase (22). Because UBE2Q2 inhibition causes mitotic arrest only after treatment with a microtubule inhibitor, it is likely to be related to the function of a mitotic checkpoint rather than perturbing normal mitotic regulation.…”

“…Involvement of UBE2Q2 in reorganization of the epithelial cytoskeleton may be related to characteristics of human UBE2Q2 as an overexpressed gene in hypopharyngeal tumors and its protein as an interacting target for multiple cytoskeletal proteins (18,19). Previous analysis using immunoaffinity purification linked to mass spectrometry showed that UBE2Q2 interacts with several cytoskeletal proteins including actin and six actin-binding proteins (22).…”

“…Human UBE2Q2 protein contains 375 amino acid residues and is characterized by the presence of three functional domains, including a RWD domain, a coiled-coil domain, and an associated UBC domain (20,21). It has been shown that inactivation of UBE2Q2 caused a prophase arrest and enhanced caspase-mediated apoptosis in response to microtubule-inhibiting agents (22). These studies have clearly shown that UBE2Q2 has a pivotal function as a positive regulator in cell cycle progression of carcinoma.…”

“…It has been reported that inactivation of UBE2Q2 using a dominant-negative form causes prophase arrest and enhances apoptosis in response to a microtubule-inhibiting agent (22). To examine the effect of UBE2Q2 on cell proliferation, we established stable NIH 3T3 and HeLa cell lines expressing wildtype UBE2Q2.…”