MARC Record from University of Toronto

LEADER: 03385nam 2200289 4500
001 AAINQ91627
005 20041122101245.5
008 041122s2004 onc|||||||||||||| ||eng d
020 $a0612916278
039 $fws
100 1 $aLiang, Jiyong.
245 10 $aRegulation of p27(KIP1) by the PI3K/PKB pathway and its role in cell cycle progression in human cancer.
260 $c2004.
300 $a137 leaves.
500 $aAdviser: Joyce M. Slingerland.
502 $aThesis (Ph.D.)--University of Toronto, 2004.
506 $aElectronic version licensed for access by U. of T. users.
510 0 $aSource: Dissertation Abstracts International, Volume: 65-05, Section: B, page: 2276.
520 $aTGF-beta induces G1 phase cell cycle arrest in normal epithelial cells. Most tumor cells are resistant to TGF-beta, which is associated with Ras activation. The role played by a Ras effector, the PI3K/PKB pathway, in the cell cycle was investigated in this thesis.The cdk inhibitor p27KIP1 binds to and inhibits cyclin E-cdk2 in response to TGF-beta. This response is defective in TGF-beta resistant cells. We showed increased PKB activation and cytoplasmic mislocalization of p27 in TGF-beta resistant lines. Transfection of constitutively active PKB conferred TGF-beta resistance. PKB phosphorylates p27 on threonine 157 (T157) and impairs its nuclear import. PI3K/PKB inhibition abolished p27T157 phosphorylation and restored TGF-beta-induced cyclin E-cdk2 inhibition by p27 and G1 arrest. Cytoplasmic p27 mislocalization was associated with PKB activation and with poor patient prognosis in 40% of primary breast cancers. This study has brought to light a novel mechanism whereby PKB impairs p27 function during oncogenesis.In summary, constitutive PKB-dependent phosphorylation of p27 leads to cytoplasmic mislocalization of p27, whereas the assembly function of p27 toward cyclin D1-cdk4 is activated through both PKB-dependent and PKB-independent sequential changes in p27 phosphorylation. PKB over-activation leads to p27 sequestration in cytoplasm or in cyclin D-cdk complexes and may contribute to loss of the cyclin E-cdk2 inhibitory function of p27 and TGF-beta resistance.p27KIP1 also acts as an assembly factor for cyclin D-cdk4 or cdk6 in a mitogen-dependent manner. We showed that following growth factor stimulation, PKB activation precedes cyclin D1-cdk4-p27KIP1 assembly in early G1. Inhibition of the PI3K/PKB pathway resulted in loss of cyclin D1 from p27 complexes and a shift of p27 into cyclin E-cdk2. PKB-dependent p27 phosphorylation increased the ability of p27 to assemble cyclin D1-cdk4. Cyclin D1-bound p27 is discretely phosphorylated at multisites including N-terminal S10 and C-terminal S178/T187 and T198, differing significantly from cdk2-bound p27.
653 $aBiology, Neuroscience.
653 $aBiology, Cell.
653 $aBiology, Molecular.
653 $aHealth Sciences, Oncology.
856 41 $uhttp://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=80218&T=F$yConnect to resource
949 $aOnline resource 80218$wASIS$c1$i5312673-2001$lONLINE$mE_RESOURCE$rY$sY$tE_RESOURCE$u10/1/2005
949 $atheses MEDBI 2004 Ph.D. 11229$wALPHANUM$c1$i31761061916755$lTHESES$mGERSTEIN$rY$sY$tBOOK$u10/1/2005
949 $atheses MEDBI 2004 Ph.D. 11229$wALPHANUM$c1$i31761062398243$lMICROTEXT$mMEDIA_COMM$rY$sY$tMICROFORM$u20/1/2005$o.PUBLIC.