Direct interactions with both p27 and Cdk2 regulate Spy1-mediated proliferation in vivo and in vitro

One of these proteins, Spy1, has demonstrated the unique ability to directly bind and activate both Cdk1 and Cdk2, as well as binding and promoting the degradation of at least one Cdk inhibitor, p27 Kip1 . Spy1 accelerates somatic cell growth and proliferation and is implicated in a number of human cancers including the breast, brain and liver.

Herein we isolate key residues mediating the direct interaction with p27. We use mutants of Spy1 to determine the physiological role of direct interactions with distinct binding partners Cdk2 and p27. We demonstrate that disrupting the direct interaction with either Spy1 binding partner decreased endogenous activity of Cdk2, as well as Spy1-mediated proliferation.