again in the next S-phase. How can S/M cyclins reappear to shepherd the cell into mitosis? The APC/CCdc20 does not recognize G1/S cyclins. Their concentration rises during G1, activating G1/S Cdks, which in turn phosphorylate Cdh1 and gradually relieve the inhibition on S/M cyclins. Spindle assembly checkpoint CDC20 is also a part of, and regulated by, the spindle assembly checkpoint (SAC). This checkpoint ensures that anaphase proceeds only when the centromeres of all sister chromatids lined up on the metaphase plate are properly attached to microtubules. The checkpoint is held active by any unattached centromere; only when all centromeres are attached will anaphase commence. The APC/CCdc20 is an important target of the SAC, which consists of several different proteins, including Mad2, Mad3(BubR1), and Bub3. In fact, these three proteins, together with CDC20, likely form the mitotic checkpoint complex (MCC), which inhibits APC/CCdc20 so that anaphase cannot begin prematurely. Moreover, Bub1 phosphorylates and thus inhibits CDC20 directly, while in yeast Mad2 and Mad3, when bound to CDC20, trigger its autoubiquitination. Cancer CDC20 is often elevated in cancerous tissues for multiple kinds of cancer. It is correlated with aggressiveness in breast cancer: higher levels are associated with poorer outcomes. CDC20 overexpression has also been reported in lung, gastric, and pancreatic cancers. For gastric and pancreatic cancers, higher levels are correlated with tumor size, histological grade (the abnormality of the cells), and metastases to the lymph nodes. In colorectal cancer and non-small-cell lung carcinoma, it is associated with cancer stage, and thus has been proposed as a biomarker to help predict the prognosis for people with either cancer. References Further reading External links