Junxia Min

(Dihydro)ceramide synthase 1-regulated sensitivity to cisplatin is associated with the activation of p38 mitogen-activated protein kinase and is abrogated by sphingosine kinase 1

Resistance to chemotherapeutic drugs often limits their clinical efficacy. Previous studies have implicated the bioactive sphingolipid sphingosine-1-phosphate (S-1-P) in regulating sensitivity to cisplatin [cis-diamminedichloroplatinum(II)] and showed that modulating the S-1-P lyase can alter cisplatin sensitivity. Here, we show that the members of the sphingosine kinase (SphK1 and SphK2) and dihydroceramide synthase (LASS1/CerS1, LASS4/CerS4, and LASS5/CerS5) enzyme families each have a unique role in regulating sensitivity to cisplatin and other drugs. Thus, expression of SphK1 decreases sensitivity to cisplatin, carboplatin, doxorubicin, and vincristine, whereas expression of SphK2 increases sensitivity. Expression of LASS1/CerS1 increases the sensitivity to all the drugs tested, whereas LASS5/CerS5 only increases sensitivity to doxorubicin and vincristine. LASS4/CerS4 expression has no effect on the sensitivity to any drug tested. Reflecting this, we show that the activation of the p38 mitogen-activated protein (MAP) kinase is increased only by LASS1/CerS1, and not by LASS4/CerS4 or LASS5/CerS5. Cisplatin was shown to cause a specific translocation of LASS1/CerS1, but not LASS4/CerS4 or LASS5/CerS5, from the endoplasmic reticulum (ER) to the Golgi apparatus. Supporting the hypothesis that this translocation is mechanistically involved in the response to cisplatin, we showed that expression of SphK1, but not SphK2, abrogates both the increased cisplatin sensitivity in cells stably expressing LASS1/CerS and the translocation of the LASS1/CerS1. The data suggest that the enzymes of the sphingolipid metabolic pathway can be manipulated to improve sensitivity to the widely used drug cisplatin. (Mol Cancer Res 2007;5(8):801–12)

Promises and Challenges of Big Data Computing in Health Sciences

With the development of smart devices and cloud computing, more and more public health data can be collected from various sources and can be analyzed in an unprecedented way. The huge social and academic impact of such developments caused a worldwide buzz for big data. In this review article, we summarized the latest applications of Big Data in health sciences, including the recommendation systems in healthcare, Internet-based epidemic surveillance, sensor-based health conditions and food safety monitoring, Genome-Wide Association Studies (GWAS) and expression Quantitative Trait Loci (eQTL), inferring air quality using big data and metabolomics and ionomics for nutritionists. We also reviewed the latest technologies of big data collection, storage, transferring, and the state-of-the-art analytical methods, such as Hadoop distributed file system, MapReduce, recommendation system, deep learning and network Analysis. At last, we discussed the future perspectives of health sciences in the era of Big Data. We explained the steps for Big Data projects: 1. Formulate your question; 2. Find the right ways (smart devices, Internet, hospitals ?) to collect your data; 3. Store the data; 4. Analyze your data; 5. Generate the analysis report with vivid visualization. 6. Evaluate the project: problem solved or start over. The latest applications of Big Data in health sciences were reviewed. The cutting edge computational technologies of big data collection, storage, transferring, and the state-of-the-art analytical methods were introduced. The future perspectives of health sciences in the era of Big Data were discussed.

Sphingosine-1-Phosphate Lyase Regulates Sensitivity of Human Cells to Select Chemotherapy Drugs in a p38-Dependent Manner

Resistance to cisplatin is a common problem that limits its usefulness in cancer therapy. Molecular genetic studies in the model organism Dictyostelium discoideum have established that modulation of sphingosine kinase or sphingosine-1-phosphate (S-1-P) lyase, by disruption or overexpression, results in altered cellular sensitivity to this widely used drug. Parallel changes in sensitivity were observed for the related compound carboplatin but not for other chemotherapy drugs tested. Sensitivity to cisplatin could also be potentiated pharmacologically with dimethylsphingosine, a sphingosine kinase inhibitor. We now have validated these studies in cultured human cell lines. HEK293 or A549 lung cancer cells expressing human S-1-P lyase (hSPL) show an increase in sensitivity to cisplatin and carboplatin as predicted from the earlier model studies. The hSPL-overexpressing cells were also more sensitive to doxorubicin but not to vincristine or chlorambucil. Studies using inhibitors to specific mitogen-activated protein kinases (MAPK) show that the increased cisplatin sensitivity in the hSPL-overexpressing cells is mediated by p38 and to a lesser extent by c-Jun NH2-terminal kinase MAPKs. p38 is not involved in vincristine or chlorambucil cytotoxicity. Measurements of MAPK phosphorylation and enzyme activity as well as small interfering RNA inhibition studies show that the response to the drug is accompanied by up-regulation of p38 and c-Jun NH2-terminal kinase and the lack of extracellular signal-regulated kinase up-regulation. These studies confirm an earlier model proposing a mechanism for the drug specificity observed in the studies with D. discoideum and support the idea that the sphingosine kinases and S-1-P lyase are potential targets for improving the efficacy of cisplatin therapy for human tumors.

Overexpression of Sphingosine-1-Phosphate Lyase or Inhibition of Sphingosine Kinase in Dictyostelium discoideum Results in a Selective Increase in Sensitivity to Platinum-Based Chemotherapy Drugs

ABSTRACT The efficacy of the chemotherapy drug cisplatin is often limited due to resistance of the tumors to the drug, and increasing the potency of cisplatin without increasing its concentration could prove beneficial. A previously characterized Dictyostelium discoideum mutant with increased resistance to cisplatin was defective in the gene encoding sphingosine-1-phosphate (S-1-P) lyase, which catalyzes the breakdown of S-1-P, an important regulatory molecule in cell function and development and in the regulation of cell fate. We hypothesized that the increased resistance to cisplatin was due to an elevation of S-1-P and predicted that lowering levels of S-1-P should increase sensitivity to the drug. We generated three strains that stably overexpress different levels of the S-1-P lyase. The overexpressor strains have reduced growth rate and, confirming the hypothesis, showed an expression-dependent increase in sensitivity to cisplatin. Consistently, treating the cells with d-erythro-N,N,-dimethylsphingosine, a known inhibitor of sphingosine kinase, increased the sensitivity of mutant and parent cells to cisplatin, while addition of exogenous S-1-P or 8-Br-cyclic AMP made the cells more resistant to cisplatin. The increased sensitivity of the overexpressors to cisplatin was also observed with the cisplatin analog carboplatin. In contrast, the response to doxorubicin, 5-flurouracil, or etoposide was unaffected, indicating that the involvement of the sphingolipid metabolic pathway in modulating the response to cisplatin is not part of a global genotoxic stress response. The augmented sensitivity to cisplatin appears to be the result of an intracellular signaling function of S-1-P, because D. discoideum does not appear to have endothelial differentiation growth (EDG/S1P) receptors. Overall, the results show that modulation of the sphingolipid pathway at multiple points can result in increased sensitivity to cisplatin and has the potential for increasing the clinical usefulness of this important drug.

Novel loci and pathways significantly associated with longevity.

Only two genome-wide significant loci associated with longevity have been identified so far, probably because of insufficient sample sizes of centenarians, whose genomes may harbor genetic variants associated with health and longevity. Here we report a genome-wide association study (GWAS) of Han Chinese with a sample size 2.7 times the largest previously published GWAS on centenarians. We identified 11 independent loci associated with longevity replicated in Southern-Northern regions of China, including two novel loci (rs2069837-IL6; rs2440012-ANKRD20A9P) with genome-wide significance and the rest with suggestive significance (P < 3.65 × 10−5). Eight independent SNPs overlapped across Han Chinese, European and U.S. populations, and APOE and 5q33.3 were replicated as longevity loci. Integrated analysis indicates four pathways (starch, sucrose and xenobiotic metabolism; immune response and inflammation; MAPK; calcium signaling) highly associated with longevity (P ≤ 0.006) in Han Chinese. The association with longevity of three of these four pathways (MAPK; immunity; calcium signaling) is supported by findings in other human cohorts. Our novel finding on the association of starch, sucrose and xenobiotic metabolism pathway with longevity is consistent with the previous results from Drosophilia. This study suggests protective mechanisms including immunity and nutrient metabolism and their interactions with environmental stress play key roles in human longevity.

MELK is an oncogenic kinase essential for mitotic progression in basal-like breast cancer cells

Despite marked advances in breast cancer therapy, basal-like breast cancer (BBC), an aggressive subtype of breast cancer usually lacking estrogen and progesterone receptors, remains difficult to treat. In this study, we report the identification of MELK as a novel oncogenic kinase from an in vivo tumorigenesis screen using a kinome-wide open reading frames (ORFs) library. Analysis of clinical data reveals a high level of MELK overexpression in BBC, a feature that is largely dependent on FoxM1, a master mitotic transcription factor that is also found to be highly overexpressed in BBC. Ablation of MELK selectively impairs proliferation of basal-like, but not luminal breast cancer cells both in vitro and in vivo. Mechanistically, depletion of MELK in BBC cells induces caspase-dependent cell death, preceded by defective mitosis. Finally, we find that Melk is not required for mouse development and physiology. Together, these data indicate that MELK is a normally non-essential kinase, but is critical for BBC and thus represents a promising selective therapeutic target for the most aggressive subtype of breast cancer. DOI: http://dx.doi.org/10.7554/eLife.01763.001

A Chemical Genetics Approach for the Functional Assessment of Novel Cancer Genes

Assessing the functional significance of novel putative oncogenes remains a significant challenge given the limitations of current loss-of-function tools. Here, we describe a method that employs TALEN or CRISPR/Cas9-mediated knock-in of inducible degron tags (Degron-KI) that provides a versatile approach for the functional characterization of novel cancer genes and addresses many of the shortcomings of current tools. The Degron-KI system allows for highly specific, inducible, and allele-targeted inhibition of endogenous protein function, and the ability to titrate protein depletion with this system is able to better mimic pharmacologic inhibition compared with RNAi or genetic knockout approaches. The Degron-KI system was able to faithfully recapitulate the effects of pharmacologic EZH2 and PI3Kα inhibitors in cancer cell lines. The application of this system to the study of a poorly understood putative oncogene, SF3B1, provided the first causal link between SF3B1 hotspot mutations and splicing alterations. Surprisingly, we found that SF3B1-mutant cells are not dependent upon the mutated allele for in vitro growth, but instead depend upon the function of the remaining wild-type alleles. Collectively, these results demonstrate the broad utility of the Degron-KI system for the functional characterization of cancer genes.

Landscape of dietary factors associated with risk of gastric cancer: A systematic review and dose-response meta-analysis of prospective cohort studies

BACKGROUND The associations between dietary factors and gastric cancer risk have been analysed by many studies, but with inconclusive results. We conducted a meta-analysis of prospective studies to systematically investigate the associations. METHODS Relevant studies were identified through searching Medline, Embase, and Web of Science up to June 30, 2015. We included prospective cohort studies of intake of dietary factors with risk estimates and 95% confidence intervals for gastric cancer. RESULTS Seventy-six prospective cohort studies were eligible and included in the analysis. We ascertained 32,758 gastric cancer cases out of 6,316,385 participants in relations to intake of 67 dietary factors, covering a wide ranging of vegetables, fruit, meat, fish, salt, alcohol, tea, coffee, and nutrients, during 3.3 to 30 years of follow-up. Evidence from this study indicates that consumption of total fruit and white vegetables, but not total vegetables, was inversely associated with gastric cancer risk. Both fruit and white vegetables are rich sources of vitamin C, which showed significant protective effect against gastric cancer by our analysis too. Furthermore, we found concordant positive associations between high-salt foods and gastric cancer risk. In addition, a strong effect of alcohol consumption, particularly beer and liquor but not wine, on gastric cancer risk was observed compared with nondrinkers. Dose-response analysis indicated that risk of gastric cancer was increased by 12% per 5 g/day increment of dietary salt intake or 5% per 10 g/day increment of alcohol consumption, and that a 100 g/day increment of fruit consumption was inversely associated with 5% reduction of risk. CONCLUSION This study provides comprehensive and strong evidence that there are a number of protective and risk factors for gastric cancer in diet. Our findings may have significant public health implications with regard to prevention of gastric cancer and provide insights into future cohort studies and the design of related clinical trials.

Sphingosine Kinase Regulates the Sensitivity of Dictyostelium discoideum Cells to the Anticancer Drug Cisplatin

ABSTRACT The drug cisplatin is widely used to treat a number of tumor types. However, resistance to the drug, which remains poorly understood, limits its usefulness. Previous work using Dictyostelium discoideum as a model for studying drug resistance showed that mutants lacking sphingosine-1-phosphate (S-1-P) lyase, the enzyme that degrades S-1-P, had increased resistance to cisplatin, whereas mutants overexpressing the enzyme were more sensitive to the drug. S-1-P is synthesized from sphingosine and ATP by the enzyme sphingosine kinase. We have identified two sphingosine kinase genes in D. discoideum—sgkA and sgkB—that are homologous to those of other species. The biochemical properties of the SgkA and SgkB enzymes suggest that they are the equivalent of the human Sphk1 and Sphk2 enzymes, respectively. Disruption of the kinases by homologous recombination (both single and double mutants) or overexpression of the sgkA gene resulted in altered growth rates and altered response to cisplatin. The null mutants showed increased sensitivity to cisplatin, whereas mutants overexpressing the sphingosine kinase resulted in increased resistance compared to the parental cells. The results indicate that both the SgkA and the SgkB enzymes function in regulating cisplatin sensitivity. The increase in sensitivity of the sphingosine kinase-null mutants was reversed by the addition of S-1-P, and the increased resistance of the sphingosine kinase overexpressor mutant was reversed by the inhibitor N,N-dimethylsphingosine. Parallel changes in sensitivity of the null mutants are seen with the platinum-based drug carboplatin but not with doxorubicin, 5-fluorouracil, and etoposide. This pattern of specificity is similar to that observed with the S-1-P lyase mutants and should be useful in designing therapeutic schemes involving more than one drug. This study identifies the sphingosine kinases as new drug targets for modulating the sensitivity to platinum-based drugs.

Stress-induced ER to Golgi translocation of ceramide synthase 1 is dependent on proteasomal processing

The ceramide synthase (CerS) enzymes are key regulators of ceramide homeostasis. CerS1 is central to regulating C18 ceramide which has been shown to be important in cancer and the response to chemotherapeutic drugs. Previous work indicated that some drugs induced a novel and specific translocation of CerS1 from the endoplasmic reticulum to the Golgi apparatus. We now show that diverse stresses such as UV light, DTT, as well as drugs with different mechanisms of action induce CerS1 translocation. The stresses cause a specific cleavage of the CerS1 enzyme, and the cleavage is dependent on the action of the proteasome. Inhibition of proteasome function inhibits stress-induced CerS1 translocation, indicating that this proteolytic cleavage precedes the translocation. Modulation of protein kinase C activity shows that it plays a central role in regulating CerS1 translocation. Analysis of the C-terminus of the CerS1 protein shows that several KxKxx motifs are not involved in regulating stress induced translocation. The study suggests that diverse stresses initiate responses through different signaling pathways, which ultimately converge to regulate CerS1 localization. The data provide an increasingly detailed understanding of the regulation of this important enzyme in normal and stressed cells and support the idea that it is uniquely regulated with respect to the other CerS enzymes.