Caspase-mediated Cdk2 activation is a critical step to execute transforming growth factor-beta1-induced apoptosis in human gastric cancer cells.
Although TGF-beta1, a growth inhibitor, is known to also induce apoptosis, the molecular mechanism of this apoptosis is largely undefined. Here, we identify the mechanism of TGF-beta1-induced apoptosis in SNU-16 human gastric cancer cells. Cell cycle and TUNEL analysis showed that, upon TGF-beta1 treatment, cells were initially arrested at the G1 phase and then driven into apoptosis. Of note, caspase-3 was activated in accordance with TGF-beta1-induced G1 arrest. Activated caspase-3 is targeted to cleave p21(cip1), p27(kip1), and Rb, which play important roles in TGF-beta-induced G1 arrest, into inactive fragments. Subsequently, Cdk2 was aberrantly activated due to the cleavage of p21 and p27. We found that the inhibition of Cdk2 activity efficiently blocks TGF-beta1-induced apoptosis, whereas it did not prevent caspase-3 activation or the subsequent cleavage of target proteins. In contrast, the suppression of caspase-3 activity inhibited the cleavage of target proteins, the activation of Cdk2, and the induction of apoptosis. Taken together, our results suggest that activation of caspase-3 by TGF-beta1 may initiate the conversion from G1 cell cycle arrest to apoptosis via the cleavage of p21, p27 and Rb, which in turn causes Cdk2 activation and, most significantly, Cdk2 activation as a downstream effector of caspase is a critical step for the execution of TGF-beta1-induced apoptosis.
Kim
S G
SG
Cancer Research Institute, Seoul National University College of Medicine, Seoul 110-744, Korea.
Kim
S N
SN
Jong
H S
HS
Kim
N K
NK
Hong
S H
SH
Kim
S J
SJ
Bang
Y J
YJ
D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D001973:Bromodeoxyuridine / Q000737:chemistry; D042846:CDC2-CDC28 Kinases; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects*; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D020287:In Situ Nick-End Labeling; D007701:Kinetin; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011687:Purines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism*; D000077546:Roscovitine; D013274:Stomach Neoplasms / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D017304:Annexin A5; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D011687:Purines; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; D000077546:Roscovitine; D050760:Cyclin-Dependent Kinase Inhibitor p27; C090046:olomoucine; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D001973:Bromodeoxyuridine; D007701:Kinetin