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PUMA and BIM Are Required for Oncogene Inactivation-Induced Apoptosis and Anoikis
Date of Award
Doctor of Philosophy (PhD)
The clinical efficacy of selective kinase inhibitors supports the hypothesis that some cancer cells may become dependent on a single oncogene for survival, a phenomenon termed "oncogene addiction." Such targeted therapies include lapatinib used to treat HER2-amplified breast cancer and gefitinib or erlotinib used to treat lung cancer harboring activating mutations of EGFR. Although these receptor tyrosine kinase inhibitors (TKIs) have proven useful in cancer therapy, the underlying mechanism of apoptosis is not fully elucidated. Given that the BCL-2 family controls critical checkpoints of intrinsic apoptosis, we sought to explore whether and how BCL-2 family proteins are involved in TKI-induced apoptosis. Here, we demonstrate that BIM and PUMA are the apoptotic effectors of TKIs in both HER2-amplified breast cancer and EGFR-mutant lung cancer. BIM and PUMA are activator BH3-only molecules that can activate BAX and BAK to form holooligomers, leading to cytochrome c efflux and caspase activation. Mechanistically, we have delineated the signaling pathways leading to induction of BIM and PUMA by TKIs. Inhibition of the MEK-ERK signaling cascade leads to BIM induction, whereas antagonizing the PI3K-AKT signaling axis triggers nuclear translocation of FOXO transcription factors that target the PUMA promoter to transactivate PUMA. Induction of Bim and Puma was further demonstrated in a doxycycline-inducible MMTV-HER2/Neu mouse breast tumor model following reduction in HER2/Neu expression. Importantly, deficiency of Bim or Puma prevents caspase activation and thereby impedes tumor regression caused by inactivation of HER2/Neu. Moreover, deficiency of Puma blocks the regression of EGFRL858R-driven mouse lung tumors upon inactivation of EGFR as assessed by magnetic resonance imaging. As in HER2 and EGFR inhibition, BIM and PUMA were found to play a similar function in KRAS inactivation-mediated apoptosis of KRAS-mutant lung cancer. Upon establishing PUMA's role in three models of oncogene inactivation-induced apoptosis, we then applied this knowledge to design a strategy to induce cell death in TKI-resistant cancer cell lines. Additionally, we uncovered a further role for PUMA in executing anoikis, or cell/matrix detachment-induced apoptosis, a physiological barrier to cancer metastasis. Overall, our study identifies BIM and PUMA as the sentinels that interconnect kinase signaling networks and the mitochondrion-dependent apoptotic program.
Chair and Committee
Emily H.-Y. Cheng
Timothy A. Graubert, Ron Bose, Stuart A. Kornfeld, Jason C. Mills, David R. Piwnica-Worms, Brian A. Van Tine
Bean, Gregory, "PUMA and BIM Are Required for Oncogene Inactivation-Induced Apoptosis and Anoikis" (2014). Arts & Sciences Electronic Theses and Dissertations. 79.