title: The Mutant KRAS Gene Up-regulates BCL-XL Protein via STAT3 to Confer Apoptosis Resistance That Is Reversed by BIM Protein Induction and BCL-XL Antagonism.
abstract: In colorectal cancers with oncogenic GTPase Kras (KRAS) mutations, inhibition of downstream MEK/ERK signaling has shown limited efficacy, in part because of failure to induce a robust apoptotic response. We studied the mechanism of apoptosis resistance in mutant KRAS cells and sought to enhance the efficacy of a KRAS-specific MEK/ERK inhibitor, GDC-0623. GDC-0623 was shown to potently up-regulate BIM expression to a greater extent versus other MEK inhibitors in isogenic KRAS HCT116 and mutant KRAS SW620 colon cancer cells. ERK silencing enhanced BIM up-regulation by GDC-0623 that was due to its loss of phosphorylation at Ser(69), confirmed by a BIM-EL phosphorylation-defective mutant (S69G) that increased protein stability and blocked BIM induction. Despite BIM and BIK induction, the isogenic KRAS mutant versus wild-type cells remained resistant to GDC-0623-induced apoptosis, in part because of up-regulation of BCL-XL. KRAS knockdown by a doxycycline-inducible shRNA attenuated BCL-XL expression. BCL-XL knockdown sensitized KRAS mutant cells to GDC-0623-mediated apoptosis, as did the BH3 mimetic ABT-263. GDC-0623 plus ABT-263 induced a synergistic apoptosis by a mechanism that includes release of BIM from its sequestration by BCL-XL. Furthermore, mutant KRAS activated p-STAT3 (Tyr(705)) in the absence of IL-6 secretion, and STAT3 knockdown reduced BCL-XL mRNA and protein expression. These data suggest that BCL-XL up-regulation by STAT3 contributes to mutant KRAS-mediated apoptosis resistance. Such resistance can be overcome by potent BIM induction and concurrent BCL-XL antagonism to enable a synergistic apoptotic response.
authors.affiliation: From the Departments of Medicine and Oncology, Gastroenterology Research Unit, and the Mayo Clinic Cancer Center and.
authors.forename: Aziz
authors.initials: A
authors.lastname: Zaanan
authors.affiliation: From the Departments of Medicine and Oncology, Gastroenterology Research Unit, and the Mayo Clinic Cancer Center and.
authors.forename: Koichi
authors.initials: K
authors.lastname: Okamoto
authors.affiliation: From the Departments of Medicine and Oncology, Gastroenterology Research Unit, and the Mayo Clinic Cancer Center and.
authors.forename: Hisato
authors.initials: H
authors.lastname: Kawakami
authors.affiliation: Department of Immunology, Mayo Clinic, Rochester, Minnesota 55905.
authors.forename: Khashayarsha
authors.initials: K
authors.lastname: Khazaie
authors.affiliation: From the Departments of Medicine and Oncology, Gastroenterology Research Unit, and the Mayo Clinic Cancer Center and.
authors.forename: Shengbing
authors.initials: S
authors.lastname: Huang
authors.affiliation: From the Departments of Medicine and Oncology, Gastroenterology Research Unit, and the Mayo Clinic Cancer Center and sinicrope.frank@mayo.edu.
authors.forename: Frank A
authors.initials: FA
authors.lastname: Sinicrope
mesh_terms: D019943:Amino Acid Substitution; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D045744:Cell Line, Tumor; D055785:Gene Knockdown Techniques; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras); D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*; D051020:bcl-X Protein / Q000096:biosynthesis* / Q000235:genetics; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; C494811:BCL2L1 protein, human; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C508600:IL6 protein, human; D015850:Interleukin-6; C117307:KRAS protein, human; D008565:Membrane Proteins; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D051020:bcl-X Protein; D020930:MAP Kinase Kinase Kinases; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins
keywords: B cell lymphoma 2 (Bcl-2) family; BCL-XL; BH3 mimetic; GDC-0623; GTPase Kras (KRAS); MAPK; MEK inhibitor; STAT3; apoptosis; colorectal cancer