Activation of P13K/PKB Signaling in Breast Cancer may Inhibit TGFB- Induced G1 Arrest through Changes in p27 Function

摘要

TGF-Beta1 plays a pivotal role in maintaining homeostasis of normal tissues including mammary epithelial cell growth, in which TGF-Beta1 induces cell cycle arrest through activating cdk inhibitors including p15(exp INK4B) and p27(expKiP1). Loss of p27(exp KiP1), seminally described in breast cancers, has been found in a plethora of human malignancies. The Slingerland (my mentor) lab found that p27 is subject to complex post-translational regulation, e.g. phosphorylation. To elucidate the mechanisms underlying TGF-Beta resistance in breast cancer cells, this proposal set out to address the hypothesis that changes in phosphorylation serve to switch the cdk inhibitor p27 from an active state that binds avidly to cyclin E/cdk2 in TGF-beta arrest and in G0, to an inactive state in late G1 and mitogenic activation of the P13K/PKB pathways leads to phosphorylation of p27, reducing its affinity for cyclin E/cdk2 and abrogating its inhibitory function. We proposed 3 specific Aims to pursue this hypothesis. Aim 1) Functional difference in p27 will be examined during cell cycle progression in TGF-beta S and R lines by i) assaying differences in p27,s affinity for and inhibition of recombinant cyclin E/cdk2 and ii) correlating changes in p27 function with shifts in its intracellular localization. Aim2) The role of phosphorylation in modulation of p27 in different cyclin/cdk complexes from S and R lines.