Cyclin B1 is significant in the progression of the cell cycle because it regulates initiation of mitosis (Knoblich and Lehner, 1993). Cyclin B1 forms a complex with CDK1, then phosphorylates several substrates, leading to mitotic entry (Abe et al., 2011; Knoblich and Lehner, 1993). Cyclin B1 usually is degraded by the anaphase promoting complex/cyclosome (APC/C) during mitosis in order to facilitate mitotic exit (Pines, 2011). CRL2ZYG11A/B is an E3 ubiquitin ligase that contributes to mitotic slippage by targeting cyclin B1 for degradation when APC/C is inactive (Balachandran et al., 2016). We elucidate the interaction between ZYG11B and cyclin B1, and we explore how this interaction is regulated. We show that cyclin B1’s CBOX1 and CBOX2 domains interact with ZYG11B, but ZYG11B has a preference for binding to CBOX1. The variant leucine rich repeat (vLRR) regions of ZYG11B interact with cyclin B1. Specifically, vLRR regions 4, 5, and 6 seem to play a significant role in the interaction. We identified four cyclin B1 CBOX1 mutants that have reduced interactions with ZYG11B. We also show that ZYG11B interacts with cyclin B1 during S phase and mitosis; however, the interaction during S phase is moderately stronger than the interaction in mitosis. Additionally, the interaction between ZYG11B and its E3 scaffold, CUL2, is not cell cycle regulated. Our data so far suggests that the interaction between ZYG11B and cyclin B1 does not depend on post translational modifications (PTMs).
In addition to studying the interaction between ZYG11B and cyclin B1, we also identified a quiescence pathway in H1299 non-small cell lung cancer (NSCLC) cells that ZYG11A and ZYG11B are involved in. We chose to study H1299 cells because ZYG11A is overexpressed in NSCLC tissue, and ZYG11A expression is positively correlated with progression of NSCLC and poor patient prognosis (Wang et al., 2016). We found that ZYG11A and ZYG11B are important to mediate the levels of MCM7, CSE1L/CAS, and CCT as cells enter quiescence. We also present evidence that ZYG11A and ZYGB interact directly with a subset of these proteins, suggesting direct regulation.
In addition to studying the interaction between ZYG11B and cyclin B1, we also identified a quiescence pathway in H1299 non-small cell lung cancer (NSCLC) cells that ZYG11A and ZYG11B are involved in. We chose to study H1299 cells because ZYG11A is overexpressed in NSCLC tissue, and ZYG11A expression is positively correlated with progression of NSCLC and poor patient prognosis (Wang et al., 2016). We found that ZYG11A and ZYG11B are important to mediate the levels of MCM7, CSE1L/CAS, and CCT as cells enter quiescence. We also present evidence that ZYG11A and ZYGB interact directly with a subset of these proteins, suggesting direct regulation.