Oncogene-induced sensitization to chemotherapy-induced death requires induction as well as deregulation of E2F1

Dicer Elicits Paclitaxel Chemosensitization and Suppresses Cancer Stemness in Breast Cancer by Repressing AXL

Paclitaxel is a standard-of-care chemotherapy for breast cancer, despite the increasing recognition of its poor effectiveness in the treatment of patients with advanced disease. Here, we report that adenovirus-type 5 E1A-mediated elevation of the miRNA-processing enzyme Dicer is sufficient to enhance paclitaxel sensitization and reduce cancer stem-like cell properties in this setting. Elevating Dicer expression increased levels of the AXL kinase targeting miRNA miR-494, thereby repressing AXL expression to increase paclitaxel sensitivity. We found that Dicer expression was regulated at the transcription level by E1A, through activation of an MAPK14/CEBPα pathway. Our findings define a mechanism of E1A-mediated chemosensitization for paclitaxel, which is based upon the suppression of breast cancer stem-like cells, with potential implications for the diagnosis and treatment of breast cancer patients. Cancer Res; 76(13); 3916-28. ©2016 AACR.

Loss of autophagy causes a synthetic lethal deficiency in DNA repair

(Macro)autophagy delivers cellular constituents to lysosomes for degradation. Although a cytoplasmic process, autophagy-deficient cells accumulate genomic damage, but an explanation for this effect is currently unclear. We report here that inhibition of autophagy causes elevated proteasomal activity leading to enhanced degradation of checkpoint kinase 1 (Chk1), a pivotal factor for the error-free DNA repair process, homologous recombination (HR). We show that loss of autophagy critically impairs HR and that autophagy-deficient cells accrue micronuclei and sub-G1 DNA, indicators of diminished genomic integrity. Moreover, due to impaired HR, autophagy-deficient cells are hyperdependent on nonhomologous end joining (NHEJ) for repair of DNA double-strand breaks. Consequently, inhibition of NHEJ following DNA damage in the absence of autophagy results in persistence of genomic lesions and rapid cell death. Because autophagy deficiency occurs in several diseases, these findings constitute an important link between autophagy and DNA repair and highlight a synthetic lethal strategy to kill autophagy-deficient cells.

E2F1 drives chemotherapeutic drug resistance via ABCG2

Multidrug resistance is a major barrier against successful chemotherapy, and this has been shown in vitro to be often caused by ATP-binding cassette (ABC) transporters. These transporters are frequently overexpressed in human cancers and confer an adverse prognosis in many common malignancies. The genetic factors, however, that initiate their expression in cancer are largely unknown. Here we report that the major multidrug transporter ABCG2 (BCRP/MXR) is directly and specifically activated by the transcription factor E2F1--a factor perturbed in the majority of human cancers. E2F1 regulates ABCG2 expression in multiple cell systems, and, importantly, we have identified a significant correlation between elevated E2F1 and ABCG2 expression in human lung cancers. We show that E2F1 causes chemotherapeutic drug efflux both in vitro and in vivo via ABCG2. Furthermore, the E2F1-ABCG2 axis suppresses chemotherapy-induced cell death that can be restored by the inhibition of ABCG2. These findings therefore identify a new axis in multidrug resistance and highlight a radical new function of E2F1 that is relevant to tumor therapy.

Network-based differential gene expression analysis suggests cell cycle related genes regulated by E2F1 underlie the molecular difference between smoker and non-smoker lung adenocarcinoma

BACKGROUND

Differential gene expression (DGE) analysis is commonly used to reveal the deregulated molecular mechanisms of complex diseases. However, traditional DGE analysis (e.g., the t test or the rank sum test) tests each gene independently without considering interactions between them. Top-ranked differentially regulated genes prioritized by the analysis may not directly relate to the coherent molecular changes underlying complex diseases. Joint analyses of co-expression and DGE have been applied to reveal the deregulated molecular modules underlying complex diseases. Most of these methods consist of separate steps: first to identify gene-gene relationships under the studied phenotype then to integrate them with gene expression changes for prioritizing signature genes, or vice versa. It is warrant a method that can simultaneously consider gene-gene co-expression strength and corresponding expression level changes so that both types of information can be leveraged optimally.

RESULTS

In this paper, we develop a gene module based method for differential gene expression analysis, named network-based differential gene expression (nDGE) analysis, a one-step integrative process for prioritizing deregulated genes and grouping them into gene modules. We demonstrate that nDGE outperforms existing methods in prioritizing deregulated genes and discovering deregulated gene modules using simulated data sets. When tested on a series of smoker and non-smoker lung adenocarcinoma data sets, we show that top differentially regulated genes identified by the rank sum test in different sets are not consistent while top ranked genes defined by nDGE in different data sets significantly overlap. nDGE results suggest that a differentially regulated gene module, which is enriched for cell cycle related genes and E2F1 targeted genes, plays a role in the molecular differences between smoker and non-smoker lung adenocarcinoma.

CONCLUSIONS

In this paper, we develop nDGE to prioritize deregulated genes and group them into gene modules by simultaneously considering gene expression level changes and gene-gene co-regulations. When applied to both simulated and empirical data, nDGE outperforms the traditional DGE method. More specifically, when applied to smoker and non-smoker lung cancer sets, nDGE results illustrate the molecular differences between smoker and non-smoker lung cancer.

Extracellular adenosine sensing-a metabolic cell death priming mechanism downstream of p53

Tumor cells undergo changes in metabolism to meet their energetic and anabolic needs. It is conceivable that mechanisms exist to sense these changes and link them to pathways that eradicate cells primed for cancer development. We report that the tumor suppressor p53 activates a cell death priming mechanism that senses extracellular adenosine. Adenosine, the backbone of ATP, accumulates under conditions of cellular stress or altered metabolism. We show that its receptor, A2B, is upregulated by p53. A2B expression has little effect on cell viability, but ligand engagement activates a caspase- and Puma-dependent apoptotic response involving downregulation of antiapoptotic Bcl-2 proteins. Stimulation of A2B also significantly enhances cell death mediated by p53 and upon accumulation of endogenous adenosine following chemotherapeutic drug treatment and exposure to hypoxia. Since extracellular adenosine also accumulates within many solid tumors, this distinct p53 function links programmed cell death to both a cancer- and therapy-associated metabolic change.

Adenovirus-mediated sensitization to the cytotoxic drugs docetaxel and mitoxantrone is dependent on regulatory domains in the E1ACR1 gene-region

Oncolytic adenoviruses have shown promising efficacy in clinical trials targeting prostate cancers that frequently develop resistance to all current therapies. The replication-selective mutants AdΔΔ and dl922–947, defective in pRb-binding, have been demonstrated to synergise with the current standard of care, mitoxantrone and docetaxel, in prostate cancer models. While expression of the early viral E1A gene is essential for the enhanced cell killing, the specific E1A-regions required for the effects are unknown. Here, we demonstrate that replicating mutants deleted in small E1A-domains, binding pRb (dl1108), p300/CBP (dl1104) and p400/TRRAP or p21 (dl1102) sensitize human prostate cancer cells (PC-3, DU145, 22Rv1) to mitoxantrone and docetaxel. Through generation of non-replicating mutants, we demonstrate that the small E1A12S protein is sufficient to potently sensitize all prostate cancer cells to the drugs even in the absence of viral replication and the E1A transactivating domain, conserved region (CR) 3. Furthermore, the p300/CBP-binding domain in E1ACR1 is essential for drug-sensitisation in the absence (AdE1A1104) but not in the presence of the E1ACR3 (dl1104) domain. AdE1A1104 also failed to increase apoptosis and accumulation of cells in G2/M. All E1AΔCR2 mutants (AdE1A1108, dl922–947) and AdE1A1102 or dl1102 enhance cell killing to the same degree as wild type virus. In PC-3 xenografts in vivo the dl1102 mutant significantly prolongs time to tumor progression that is further enhanced in combination with docetaxel. Neither dl1102 nor dl1104 replicates in normal human epithelial cells (NHBE). These findings suggest that additional E1A-deletions might be included when developing more potent replication-selective oncolytic viruses, such as the AdΔCR2-mutants, to further enhance potency through synergistic cell killing in combination with current chemotherapeutics.

DRAM-1 encodes multiple isoforms that regulate autophagy

Macro(autophagy) is a cellular mechanism which delivers cytoplasmic constituents to lysosomes for degradation. Due to its role in maintaining cellular integrity, autophagy protects against various diseases including cancer. p53 is a major tumor suppressor gene which can modulate autophagy both positively and negatively. p53 induces autophagy via transcriptional activation of Damage-Regulated Autophagy Modulator (DRAM-1). We report here that DRAM-1 encodes not just one mRNA, but a series of p53-inducible splice variants which are expressed at varying levels in multiple human and mouse cell lines. Two of these new splice variants, termed SV4 and SV5, result in mature mRNA species. Different to 'full-length' DRAM-1 (SV1), SV4 and SV5 do not localise to lysosomes or endosomes, but instead partially localise to peroxisomes and autophagosomes respectively. In addition, SV4 and SV5 can also be found co-localised with certain markers of the endoplasmic reticulum. Similar to SV1, SV4 and SV5 do not appear to be inducers of programmed cell death, but they do modulate autophagy. In summary, these findings identify new autophagy regulators that provide insight into the control of autophagy downstream of p53.

Regulation of cell proliferation and apoptosis in neuroblastoma cells by ccp1, a FGF2 downstream gene

BACKGROUND

Coiled-coil domain containing 115 (Ccdc115) or coiled coil protein-1 (ccp1) was previously identified as a downstream gene of fibroblast growth factor 2 (FGF2) highly expressed in embryonic and adult brain. However, its function has not been characterised to date. Here we hypothesized that ccp1 may be a downstream effecter of FGF2, promoting cell proliferation and protecting from apoptosis.

METHODS

Forced ccp1 expression in mouse embryonic fibroblast (MEF) and neuroblastoma SK-N-SH cell line, as well as down-regulation of ccp1 expression by siRNA in NIH3T3, was used to characterize the role of ccp1.

RESULTS

Ccp1 over-expression increased cell proliferation, whereas down-regulation of ccp1 expression reduced it. Ccp1 was able to increase cell proliferation in the absence of serum. Furthermore, ccp1 reduced apoptosis upon withdrawal of serum in SK-N-SH. The mitogen-activated protein kinase (MAPK) or ERK Kinase (MEK) inhibitor, U0126, only partially inhibited the ccp1-dependent BrdU incorporation, indicating that other signaling pathway may be involved in ccp1-induced cell proliferation. Induction of Sprouty (SPRY) upon FGF2 treatment was accelerated in ccp1 over-expressing cells.

CONCLUSIONS

All together, the results showed that ccp1 regulates cell number by promoting proliferation and suppressing cell death. FGF2 was shown to enhance the effects of ccp1, however, it is likely that other mitogenic factors present in the serum can also enhance the effects. Whether these effects are mediated by FGF2 influencing the ccp1 function or by increasing the ccp1 expression level is still unclear. At least some of the proliferative regulation by ccp1 is mediated by MAPK, however other signaling pathways are likely to be involved.