Understanding the role of miRNA in regulating NF-κB in blood cancer.

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by binding to complementary sequences in mRNAs encoding downstream target genes. A large variety of cellular processes, including differentiation, development, apoptosis and cell cycle progression, are dependent on miRNA-mediated suppression of gene expression for their regulation. As such, it is unsurprising that these small RNA molecules are associated with signaling networks that are often altered in various diseases, including many blood cancers. One such network is the nuclear factor-κB (NF-κB) pathways that universally stimulate transcription of proteins which generally promote cell survival, inhibit apoptosis, allow cellular growth, induce angiogenesis and generate many pro-inflammatory responses. The NF-κB signalling pathway is often constitutively activated in blood cell cancers including myelodysplastic syndrome (MDS), acute myeloid leukaemia (AML), acute lymphocytic leukaemia (ALL), chronic myeloid leukaemia (CML), chronic lymphocytic leukaemia (CLL), lymphomas and in multiple myeloma (MM). This review focuses on the function of miRNAs that directly target NF-κB signaling cascade. Recent findings that connect this pathway through various miRNA families to human blood cancers are reviewed, and support for using miRNA-based therapy as a novel method to counteract this tumour-promoting signalling event is discussed.

Protection of acute myeloid leukaemia cells from apoptosis induced by front-line chemotherapeutics is mediated by haem oxygenase-1.

Haem oxygenase-1 (HO-1) is increasingly regarded as a pro-tumoral target in the treatment of human cancers. Currently, little is known about HO-1 and its role in human acute myeloid leukaemia (AML) to regulate apoptosis in response to chemotherapy. Recently, we showed that HO-1 protects AML samples from tumour necrosis factor-α (TNF)-induced apoptosis - it being regulated by transcription factors Nrf2, NF-ĸB and AP-1. This study aims to analyse the role of HO-1 in regulating apoptosis in AML cells in response to two front-line chemotherapeutic agents used for AML, cytarabine and daunorubicin. Here we show that HO-1 expression in AML samples was increased in response to both cytarabine and daunorubicin treatment, and micro RNA (miRNA) silenced HO-1 expression in combination with either daunorubicin or cytarabine induced a greater apoptotic responses in AML cells. Moreover, we showed that both daunorubicin and cytarabine induced reactive oxygen species (ROS) accumulation to induce apoptosis in AML. However, ROS-dependent induction of HO-1 was limiting the apoptotic response that is seen in AML towards cytarabine and daunorubicin treatment. These findings suggest concurrent inhibition of HO-1 expression in conjunction with chemotherapeutic treatment would improve the number of cases who reach complete remission.