A Novel, Non-Apoptotic Role for Scythe/BAT3: A Functional Switch between the Pro- and Anti-Proliferative Roles of p21 during the Cell Cycle

Abstract

BackgroundScythe/BAT3 is a member of the BAG protein family whose role in apoptosis has been extensively studied. However, since the developmental defects observed in Bat3-null mouse embryos cannot be explained solely by defects in apoptosis, we investigated whether BAT3 is also involved in cell-cycle progression.Methods/Principal FindingsUsing a stable-inducible Bat3-knockdown cellular system, we demonstrated that reduced BAT3 protein level causes a delay in both G1/S transition and G2/M progression. Concurrent with these changes in cell-cycle progression, we observed a reduction in the turnover and phosphorylation of the CDK inhibitor p21, which is best known as an inhibitor of DNA replication; however, phosphorylated p21 has also been shown to promote G2/M progression. Our findings indicate that in Bat3-knockdown cells, p21 continues to be synthesized during cell-cycle phases that do not normally require p21, resulting in p21 protein accumulation and a subsequent delay in cell-cycle progression. Finally, we showed that BAT3 co-localizes with p21 during the cell cycle and is required for the translocation of p21 from the cytoplasm to the nucleus during the G1/S transition and G2/M progression.Conclusion:Our study reveals a novel, non-apoptotic role for BAT3 in cell-cycle regulation. By maintaining a low p21 protein level during the G1/S transition, BAT3 counteracts the inhibitory effect of p21 on DNA replication and thus enables the cells to progress from G1 to S phase. Conversely, during G2/M progression, BAT3 facilitates p21 phosphorylation by cyclin A/Cdk2, an event required for G2/M progression. BAT3 modulates these pro- and anti-proliferative roles of p21 at least in part by regulating cyclin A abundance, as well as p21 translocation between the cytoplasm and the nucleus to ensure that it functions in the appropriate intracellular compartment during each phase of the cell cycle.

Nuclear cathepsin D enhances TRPS1 transcriptional repressor function to regulate cell cycle progression and transformation in human breast cancer cells

“…BAT3 is a nucleo-cytoplasmic shuttling protein that contains an N-terminal ubiquitin homology region, a zinc finger-like domain, a nuclear export signal (NES), an NLS and, in its C-terminal part, a BAG domain that binds to the ATPase domain of HSC70/HSP70. We and others have shown that BAT3 targets the acetyltransferase p300 [ 28 ] and p21 [ 34 ] to the nucleus. We therefore investigated whether BAT3 binds to Cath-D by GST pull-down assay.…”

BAT3 modulates p300-dependent acetylation of p53 and autophagy-related protein 7 (ATG7) during autophagy

“…a relocation of p300 from the cytosol to the nucleus during starvation. BAT3 is also involved in p21 nuclear translocation during G2/M phases, followed by its degradation during the transition between the G1 and S phases (18); however, the mechanism responsible for BAT3 nuclear shuttling remains elusive. A recent study showed that BAT3 variants are generated by alternative splicing of exon11B, leading to a different pattern of expression and intracellular localization.…”

Anisomycin suppresses Jurkat T cell growth by the cell cycle-regulating proteins

“…Twenty five µl of RT-PCR mixture contained 10 µl of RNase free H O, 5 µl of 5 × buffer, 2 µl of 10 mM dNTP, 100 nmol/l of each primer and 1 µg RNA. The following primers were employed in semi-quantitative RT-PCR analysis: p21 [24,30] forward primer: 5'-AGCAGAGGAAGA-CCATGTGGAC-3' and p21 reverse primer: 5'-TTT-CGACCCTGAGA GTCTCCAG-3' p53 forward primer: 5'-TGCGTGTGGAGTATTTG GATG-3' and p53 reverse primer: 5'-TGGTACAGTCAGAGCCAA-CCAG-3'; b-actin [5] forward primer: 5'-AACAGT-CCGCCTAGAAGCAC-3' and b-actin reverse primer: 5'-CGTTGACATCGTAAAGACC-3'. The amplified products were size-fractionated by electrophoresis on 1.5% agarose gel, and analyzed by a FluorChem 8000 system with a software (Alpha Innotech, Santa Clara, CA, USA).…”