RESUMO
Deregulated microRNA (miR)/transcription factor (TF)-based networks represent a hallmark of cancer. We report here a novel c-Myc/miR-23b/Sp1 feed-forward loop with a critical role in multiple myeloma (MM) and Waldenstrom's macroglobulinemia (WM) cell growth and survival. We have found miR-23b to be downregulated in MM and WM cells especially in the presence of components of the tumor bone marrow milieu. Promoter methylation is one mechanism of miR-23b suppression in myeloma. In gain-of-function studies using miR-23b mimics-transfected or in miR-23b-stably expressing MM and WM cell lines, we observed a significant decrease in cell proliferation and survival, along with induction of caspase-3/7 activity over time, thus supporting a tumor suppressor role for miR-23b. At the molecular level, miR-23b targeted Sp1 3'UTR and significantly reduced Sp1-driven nuclear factor-κB activity. Finally, c-Myc, an important oncogenic transcription factor known to stimulate MM cell proliferation, transcriptionally repressed miR-23b. Thus MYC-dependent miR-23b repression in myeloma cells may promote activation of oncogenic Sp1-mediated signaling, representing the first feed-forward loop with critical growth and survival role in myeloma.
Assuntos
Regulação Neoplásica da Expressão Gênica , Redes Reguladoras de Genes , MicroRNAs/genética , Mieloma Múltiplo/genética , Proteínas Proto-Oncogênicas c-myc/genética , Fator de Transcrição Sp1/genética , Animais , Sequência de Bases , Sítios de Ligação , Caspase 3/metabolismo , Linhagem Celular Tumoral , Proliferação de Células , Sobrevivência Celular/genética , Metilação de DNA , Modelos Animais de Doenças , Regulação para Baixo , Expressão Gênica , Perfilação da Expressão Gênica , Inativação Gênica , Genes Reporter , Humanos , MicroRNAs/química , Mieloma Múltiplo/metabolismo , Mieloma Múltiplo/patologia , Regiões Promotoras Genéticas , Proteínas Proto-Oncogênicas c-myc/química , Proteínas Proto-Oncogênicas c-myc/metabolismo , Interferência de RNA , RNA Mensageiro/química , RNA Mensageiro/genética , Fator de Transcrição Sp1/química , Fator de Transcrição Sp1/metabolismoRESUMO
We have previously demonstrated that interleukin-17A (IL-17) producing T helper 17 cells are significantly elevated in blood and bone marrow (BM) in multiple myeloma (MM) and IL-17A promotes MM cell growth via the expression of IL-17 receptor. In this study, we evaluated anti-human IL-17A human monoclonal antibody (mAb), AIN457 in MM. We observe significant inhibition of MM cell growth by AIN457 both in the presence and the absence of BM stromal cells (BMSCs). Although IL-17A induces IL-6 production, AIN457 significantly downregulated IL-6 production and MM cell adhesion in MM-BMSC co-culture. AIN457 also significantly inhibited osteoclast cell differentiation. More importantly, in the SCIDhu model of human myeloma administration of AIN457 weekly for 4 weeks after the first detection of tumor in mice led to a significant inhibition of tumor growth and reduced bone damage compared with isotype control mice. To understand the mechanism of action of anti-IL-17A mAb, we report, here, that MM cells express IL-17A. We also observed that IL-17A knockdown inhibited MM cell growth and their ability to induce IL-6 production in co-cultures with BMSC. These pre-clinical observations suggest efficacy of AIN457 in myeloma and provide the rationale for its clinical evaluation for anti-myeloma effects and for improvement of bone disease.
