CDK2-cyclin E complex phosphorylates p57 at Thr310 of the QT-box domain [53]; Akt, a kinase often deregulated in cancer, phosphorylates p57 at Thr310 or Ser282 [54]; while CHK1 (checkpoint kinase-1) phosphorylates p57 at Ser19 [55]. Here, CHEK1 is linked to cancer.