Christopher G Hill

Georgia Institute of Technology, Atlanta, Georgia, United States

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Publications (4)14.36 Total impact

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    ABSTRACT: Documented changes in levels of microRNAs (miRNA) in a variety of diseases including cancer are leading to their development as early indicators of disease, and as a potential new class of therapeutic agents. A significant hurdle to the rational application of miRNAs as therapeutics is our current inability to reliably predict the range of molecular and cellular consequences of perturbations in the levels of specific miRNAs on targeted cells. While the direct gene (mRNA) targets of individual miRNAs can be computationally predicted with reasonable degrees of accuracy, reliable predictions of the indirect molecular effects of perturbations in miRNA levels remain a major challenge in molecular systems biology. Changes in gene (mRNA) and miRNA expression levels between normal precursor and ovarian cancer cells isolated from patient tissue samples were measured by microarray. Expression of 31 miRNAs was significantly elevated in the cancer samples. Consistent with previous reports, the expected decrease in expression of the mRNA targets of upregulated miRNAs was observed in only 20-30% of the cancer samples. We present and provide experimental support for a network model (The Transcriptional Override Model; TOM) to account for the unexpected regulatory consequences of modulations in the expression of miRNAs on expression levels of their target mRNAs in ovarian cancer. The direct and indirect regulatory effects of changes in miRNA expression levels in vivo are interactive and complex but amenable to systems level modeling. Although TOM has been developed and validated within the context of ovarian cancer, it may be applicable in other biological contexts as well, including of potential future use in the rational design of miRNA-based strategies for the treatment of cancers and other diseases.
    BMC Systems Biology 03/2014; 8(1):36. · 2.85 Impact Factor
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    ABSTRACT: MicroRNAs have emerged in recent years as important regulators of cell function in both normal and diseased cells. MiRNAs coordinately regulate large suites of target genes by mRNA degradation and/or translational inhibition. The mRNA target specificities of miRNAs in animals are primarily encoded within a 7 nt "seed region" mapping to positions 2-8 at the molecule's 5' end. We here combine computational analyses with experimental studies to explore the functional significance of sequence variation within the seed region of human miRNAs. The results indicate that a substitution of even a single nucleotide within the seed region changes the spectrum of mRNA targets by >50%. The high functional cost of even single nucleotide changes within seed regions is consistent with their high sequence conservation among miRNA families both within and between species and suggests processes that may underlie the evolution of miRNA regulatory control.
    PLoS ONE 01/2014; 9(12):e115241. · 3.53 Impact Factor
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    ABSTRACT: BACKGROUND: MicroRNAs (miRNAs) are a class of small RNAs that have been linked to a number of diseases including cancer. The potential application of miRNAs in the diagnostics and therapeutics of ovarian and other cancers is an area of intense interest. A current challenge is the inability to accurately predict the functional consequences of exogenous modulations in the levels of potentially therapeutic miRNAs. In an initial effort to systematically address this issue, we conducted miRNA transfection experiments using two miRNAs (miR-7, miR-128) and characterized global changes in levels of gene expression. RESULTS: While ~20% of the changes in expression patterns of hundreds to thousands of genes could be attributed to direct miRNA-mRNA interactions, the majority of the changes are indirect, involving the downstream consequences of miRNA-mediated changes in regulatory gene expression. We find that the changes in gene expression induced by individual miRNAs are functionally coordinated but distinct between the two miRNAs. MiR-7 transfection into ovarian cancer cells induces changes in cell adhesion and other developmental networks previously associated with epithelial-mesenchymal transitions (EMT) and other processes linked with metastasis. In contrast, miR-128 transfection induces changes in cell cycle control and other processes commonly linked with cellular replication. CONCLUSION: The functionally coordinated patterns of gene expression displayed by different families of miRNAs have the potential to provide clinicians with a strategy to treat cancers from a systems rather than a single gene perspective.
    BMC Medical Genomics 08/2012; 5(1):33. · 3.91 Impact Factor
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    ABSTRACT: Ovarian cancer (OC) is the most lethal of all gynecological malignancies primarily due to the sloughing-off of highly metastatic cells from primary tumors and their subsequent spread throughout the peritoneal cavity. Since the epithelial-to-mesenchymal transition (EMT) of OC cells located at the periphery of primary tumors is essential to this process, molecular interventions that can block EMT are of potential clinical significance. Members of the miR200 family of microRNAs have been implicated in EMT in other cancers. Our purpose was to determine if miR200 family microRNAs may be involved in EMT in OC and of potential therapeutic value in reducing OC metastasis. Gene expression profiles of two OC cell lines with different metastatic potentials were monitored using qRT-PCR (quantitative reverse transcription polymerase chain reaction). The effect of over-expression of a miR-200 family microRNA (miR-429) in metastatic OC cells was monitored on molecular (qRT-PCR and microarray) and functional (morphology, migration, invasiveness and anchorage independence assays) levels. Molecular profiling of two OC cell lines with differing metastatic potentials identified significant differences in previously established epithelial and mesenchymal cell biomarkers including E-cadherin, ZEB1, ZEB2, miR-205 and miR-200 family microRNAs. Ectopic overexpression of miR-429, a member of the miR-200 family of microRNAs, in mesenchymal-like OC cells resulted in reversal of the mesenchymal phenotype (mesenchymal-epithelial transition, MET). Our results indicate that miR-429 may not only be a useful biomarker of EMT in ovarian cancer, but also of potential therapeutic value in abating OC metastasis.
    Gynecologic Oncology 04/2011; 121(1):200-5. · 3.69 Impact Factor