Centromere protein W interacts with beta-transducin repeat-containing protein 1 and modulates its subcellular localization

Beta-Transducin Repeats-Containing Proteins as an Anticancer Target

Beta-transducin repeat-containing proteins (β-TrCPs) are E3-ubiquitin-ligase-recognizing substrates and regulate proteasomal degradation. The degradation of β-TrCPs' substrates is tightly controlled by various external and internal signaling and confers diverse cellular processes, including cell cycle progression, apoptosis, and DNA damage response. In addition, β-TrCPs function to regulate transcriptional activity and stabilize a set of substrates by distinct mechanisms. Despite the association of β-TrCPs with tumorigenesis and tumor progression, studies on the mechanisms of the regulation of β-TrCPs' activity have been limited. In this review, we studied publications on the regulation of β-TrCPs themselves and analyzed the knowledge gaps to understand and modulate β-TrCPs' activity in the future.

FBXW8 regulates G1 and S phases of cell cycle progression by restricting β-TrCP1 function

Sequential alteration in the expression levels of cell cycle regulatory proteins is crucial for faithful cell cycle progression to maintain the cellular homeostasis. F-box protein β-TrCP1 is known to control the expression levels of several important cell cycle regulatory proteins. However, how the function of β-TrCP1 is regulated in spatiotemporal manner during cell cycle progression remains elusive. Here, we show that expression levels of β-TrCP1 oscillate during cell cycle progression with a minimum level at the G1 and S phases of cell cycle. Using biochemical, flow cytometry, and immunofluorescence techniques, we found that oscillation of β-TrCP1 expression is controlled by another F-box protein FBXW8. FBXW8 directs the proteasomal degradation of β-TrCP1 in MAPK pathway-dependent manner. Interestingly, we found that the attenuation of β-TrCP1 by FBXW8 is important for Cdc25A-mediated cell cycle transition from G1 phase to S phase as well as DNA damage-free progression of S phase. Overall, our study reveals the intriguing molecular mechanism and significance of maintenance of β-TrCP1 levels during cell cycle progression by FBXW8-mediated proteasomal degradation.

CENP-W regulates kinetochore-microtubule attachment and meiotic progression of mouse oocytes

Oocyte meiotic maturation failure and unfaithful chromosome segregation are major causes for female infertility. Here, we showed that CENP-W, a relatively novel member of the kinetochore protein family, was expressed in mouse oocytes from the germinal vesicle (GV) to metaphase II (MII) stages. Confocal microscopy revealed that CENP-W was localized in the germinal vesicle in the GV stage, and then became concentrated on kinetochores during oocyte maturation. Knockdown of CENP-W by specific siRNA injection in vitro caused kinetochore-microtubule detachment, resulting in severely defective spindles and misaligned chromosomes, leading to metaphase I arrest and failure of first polar body (PB1) extrusion. Correspondingly, spindle assembly checkpoint (SAC) activation was observed in CENP-W knockdown oocytes even after 10h of culture. Our results suggest that CENP-W acts as a kinetochore protein, which takes part in kinetochore-microtubule attachment, thus mediating the progression of oocyte meiotic maturation.

CENP-W inhibits CDC25A degradation by destabilizing the SCFβ-TrCP-1 complex at G2/M

Skp, Cullin, F-box (SCF)β-TrCP-1 ubiquitin ligases play a central role in cell cycle regulation and tumorigenesis via proteolytic cleavage of many essential cell cycle regulators. In this study, we propose that centromere protein (CENP)-W, a newly identified kinetochore component, is a novel negative regulator of the SCFβ-TrCP-1 complex. CENP-W interacts with Cullin (CUL)-1 and β-Transducin repeat-containing protein (β-TrCP)-1 through highly overlapped binding sites with S-phase kinase-associated protein (SKP)-1. CENP-W is incorporated into the SCFβ-TrCP-1 complex to promote complex disassembly. Unlike other known regulators that increase SCFβ-TrCP-1 ubiquitin ligase activity by promoting complex reassociation, CENP-W-mediated complex disorganization induced β-TrCP1 degradation and consequently decreased its activity. The association between CENP-W and the SCFβ-TrCP-1 complex was prominent during the G2/M transition in the nucleus. Especially, CENP-W knockdown decreased the cell division cycle-25A protein level, leading to a delay in mitotic progression. We propose that CENP-W participates in cell cycle regulation by modulating SCFβ-TrCP-1 ubiquitin ligase activity.-Cheon, Y., Lee, S. CENP-W inhibits CDC25A degradation by destabilizing the SCFβ-TrCP-1 complex at G2/M.