title: Targeting phospho-MARCKS overcomes drug-resistance and induces antitumor activity in preclinical models of multiple myeloma.
abstract: Multiple myeloma (MM) is incurable in virtually all patients due to the presence of innate and emergent drug-resistance. To identify potential drug resistance mechanisms in MM we used iTRAQ (isobaric tags for relative and absolute quantitation) mass spectrometry to compare protein expression profiles of drug-resistant (RPMI 8226-R5) and sensitive (RPMI 8226-S) isogenic cell lines. We identified selective overexpression of myristoylated alanine-rich C-kinase substrate (MARCKS) in drug-resistant R5 cells. MARCKS overexpression was also observed in several drug-resistant human myeloma cell lines (HMCLs) and in drug-resistant primary MM samples. Functionally, inhibition of MARCKS phosphorylation by enzastaurin or knockdown of the gene by RNAi significantly enhanced the sensitivity of resistant HMCLs and primary MM samples to bortezomib and to other anti-myeloma drugs, providing evidence that MARCKS can modulate drug response. Mechanistically, pMARCKS (phosphorylated form of MARCKS) was found to function as an E2F-1 cofactor to regulate SKP2 transcription. pMARCKS promoted cell-cycle progression by facilitating SKP2 expression, suppressing p27(Kip1) and potentially counteracting drug-induced cell-cycle arrest by promoting Cyclin E/CDK2 activity. Importantly, MARCKS knockdown in combination with bortezomib treatment overcame bortezomib resistance, significantly inhibited tumor growth and prolonged host survival in a MM xenograft model. These data provide a rationale for therapeutic targeting of pMARCKS to improve the outcome of patients with refractory/relapsed MM.
authors.affiliation: 1] Division of Molecular and Cellular Biology, Toronto General Research Institute, Toronto, Canada [2] Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada.
authors.forename: Y
authors.initials: Y
authors.lastname: Yang
authors.affiliation: 1] Division of Molecular and Cellular Biology, Toronto General Research Institute, Toronto, Canada [2] Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada [3] Department of Hematology/Oncology, First Affiliated Hospital, Nanchang University, Nanchang, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.affiliation: 1] Division of Molecular and Cellular Biology, Toronto General Research Institute, Toronto, Canada [2] Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada.
authors.forename: M N
authors.initials: MN
authors.lastname: Saha
authors.affiliation: Ontario Cancer Biomarker Network, Toronto, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Chen
authors.affiliation: Ontario Cancer Biomarker Network, Toronto, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Evans
authors.affiliation: Department of Lymphoma & Myeloma, Institute of Hematology & Blood Diseases Hospital, State Key Laboratory of Experimental Hematology, Chinese Academy of Medical Sciences & Peking Union of Medical College, Tianjin, People's Republic of China.
authors.forename: L
authors.initials: L
authors.lastname: Qiu
authors.affiliation: Department of Laboratory Hematology and Medical Oncology, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Reece
authors.affiliation: Department of Hematology/Oncology, First Affiliated Hospital, Nanchang University, Nanchang, China.
authors.forename: G A
authors.initials: GA
authors.lastname: Chen
authors.affiliation: 1] Division of Molecular and Cellular Biology, Toronto General Research Institute, Toronto, Canada [2] Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada [3] Department of Hematology/Oncology, First Affiliated Hospital, Nanchang University, Nanchang, China [4] Department of Laboratory Hematology and Medical Oncology, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada.
authors.forename: H
authors.initials: H
authors.lastname: Chang
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000235:genetics; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000235:genetics* / Q000401:mortality / Q000473:pathology; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D009368:Neoplasm Transplantation; D010766:Phosphorylation; D061251:Primary Cell Culture; D011719:Pyrazines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D016019:Survival Analysis
chemical_list: D000970:Antineoplastic Agents; D001897:Boronic Acids; C493961:Cdkn1b protein, mouse; D019927:Cyclin E; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D007211:Indoles; D047908:Intracellular Signaling Peptides and Proteins; C000619710:MARCKS protein, human; C000619711:Marcks protein, mouse; D008565:Membrane Proteins; D011719:Pyrazines; D034741:RNA, Small Interfering; D044786:S-Phase Kinase-Associated Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000069286:Bortezomib; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; C504878:enzastaurin