Abstract:The oncogenes Cyclin D and cdk4 are overexpressed in a variety of tumors, but the levels of these proteins are not always accurate indicators of oncogenic activity because p27Kip1 is required to assemble this otherwise unstable dimer. However, p27’s association activates or alternatively inhibits cyclin D-cdk4, serving as a bona fide ON/OFF “switch.” Tyrosine (Y) phosphorylation of residues Y88/89 in p27 displaces its C-terminus from the cdk4 active site, permitting both ATP binding and CAK phosphorylation of … Show more
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