Publications

It has long been understood that many of the same manipulations that increase longevity in Caenorhabditis elegans also increase resistance to various acute stressors, and vice-versa; moreover these findings hold in more complex organisms as well. Nevertheless, the mechanistic relationship between these phenotypes remains unclear, and in many cases the overlap between stress resistance and longevity is inexact. Here we review the known connections between stress resistance and longevity, discuss instances in which these connections are absent, and summarize the theoretical explanations that have been posited for these phenomena.

miR-155 is a prominent microRNA (miRNA) that regulates genes involved in immunity and cancer-related pathways. miR-155 is overexpressed in lung cancer, which correlates with poor patient prognosis. It is unclear how miR-155 becomes increased in lung cancers and how this increase contributes to reduced patient survival. Here, we show that hypoxic conditions induce miR-155 expression in lung cancer cells and trigger a corresponding decrease in a validated target, FOXO3A. Furthermore, we find that increased levels of miR-155 radioprotects lung cancer cells, while inhibition of miR-155 radiosensitizes these cells. Moreover, we reveal a therapeutically important link between miR-155 expression, hypoxia, and irradiation by demonstrating that anti-miR-155 molecules also sensitize hypoxic lung cancer cells to irradiation. Our study helps explain how miR-155 becomes elevated in lung cancers, which contain extensive hypoxic microenvironments, and demonstrates that inhibition of miR-155 may have important therapeutic potential as a means to radiosensitize hypoxic lung cancer cells.

Neither genetic nor environmental factors fully account for variability in individual longevity: genetically identical invertebrates in homogenous environments often experience no less variability in lifespan than outbred human populations. Such variability is often assumed to result from stochasticity in damage accumulation over time; however, the identification of early-life gene expression states that predict future longevity would suggest that lifespan is least in part epigenetically determined. Such "biomarkers of aging," genetic or otherwise, nevertheless remain rare. In this work, we sought early-life differences in organismal robustness in unperturbed individuals and examined the utility of microRNAs, known regulators of lifespan, development, and robustness, as aging biomarkers. We quantitatively examined Caenorhabditis elegans reared individually in a novel apparatus and observed throughout their lives. Early-to-mid-adulthood measures of homeostatic ability jointly predict 62% of longevity variability. Though correlated, markers of growth/muscle maintenance and of metabolic by-products ("age pigments") report independently on lifespan, suggesting that graceful aging is not a single process. We further identified three microRNAs in which early-adulthood expression patterns individually predict up to 47% of lifespan differences. Though expression of each increases throughout this time, mir-71 and mir-246 correlate with lifespan, while mir-239 anti-correlates. Two of these three microRNA "biomarkers of aging" act upstream in insulin/IGF-1-like signaling (IIS) and other known longevity pathways, thus we infer that these microRNAs not only report on but also likely determine longevity. Thus, fluctuations in early-life IIS, due to variation in these microRNAs and from other causes, may determine individual lifespan.

Originally discovered in C. elegans, microRNAs (miRNAs) are small RNAs that regulate fundamental cellular processes in diverse organisms. MiRNAs are encoded within the genome and are initially transcribed as primary transcripts that can be several kilobases in length. Primary transcripts are successively cleaved by two RNase III enzymes, Drosha in the nucleus and Dicer in the cytoplasm, to produce ∼70 nucleotide (nt) long precursor miRNAs and 22 nt long mature miRNAs, respectively. Mature miRNAs regulate gene expression post-transcriptionally by imperfectly binding target mRNAs in association with the multiprotein RNA induced silencing complex (RISC). The conserved sequence, expression pattern, and function of some miRNAs across distinct species as well as the importance of specific miRNAs in many biological pathways have led to an explosion in the study of miRNA biogenesis, miRNA target identification, and miRNA target regulation. Many advances in our understanding of miRNA biology have come from studies in the powerful model organism C. elegans. This chapter reviews the current methods used in C. elegans to study miRNA biogenesis, small RNA populations, miRNA-protein complexes, and miRNA target regulation.

In normal cells multiple microRNAs (miRNAs) converge to maintain a proper balance of various processes, including proliferation, differentiation and cell death. miRNA dysregulation can have profound cellular consequences, especially because individual miRNAs can bind to and regulate multiple mRNAs. In cancer, the loss of tumour-suppressive miRNAs enhances the expression of target oncogenes, whereas increased expression of oncogenic miRNAs (known as oncomirs) can repress target tumour suppressor genes. This realization has resulted in a quest to understand the pathways that are regulated by these miRNAs using in vivo model systems, and to comprehend the feasibility of targeting oncogenic miRNAs and restoring tumour-suppressive miRNAs for cancer therapy. Here we discuss progress in using mouse models to understand the roles of miRNAs in cancer and the potential for manipulating miRNAs for cancer therapy as these molecules make their way towards clinical trials.

MicroRNAs (miRNAs) are aiding our understanding of cancer biology, and are now coming close to therapeutic use as well. Here, we focus specifically on the interaction between miRNAs and genomic instability. MiRNA regulation is essential to many cellular processes, and escape from this regulatory network seems to be a common characteristic of malignant transformation. Genomic instability may preferentially target miRNAs either because of selective pressure or because of inherent vulnerability related to their location near fragile sites. Furthermore, disruption of miRNA processing elements affords a more global release from miRNA regulation. Finally, we review how miRNAs function as both effectors and modulators of the DNA damage response, intricately weaved with traditional elements such as ATM, P53, and MMR. Thus, miRNAs are important substrates for genomic instability and play a crucial role in cellular DNA sensing and repair mechanisms.

The developmental process of the nematode Caenorhabditis elegans is famously invariant; however, these animals have surprisingly variable lifespans, even in extremely homogenous environments. Inter-individual differences in muscle-function decline, accumulation of lipofuscin in the gut, internal growth of food bacteria, and ability to mobilize heat-shock responses all appear to be predictive of a nematode's remaining lifespan; whether these are causal, or mere correlates of individual decline and death, has yet to be determined. Moreover, few "upstream" causes of inter-individual variability have been identified. It may be the case that variability in lifespan is entirely due to stochastic damage accumulation; alternately, perhaps such variability has a developmental origin and/or genes involved in developmental canalization also act to buffer phenotypic heterogeneity later in life. We review these two hypotheses with an eye toward whether they can be experimentally differentiated.

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 cancer. This review focuses on the function of miRNAs in three of the most well-documented signaling pathways that are dysregulated in tumors: the NFkappaB and Ras prosurvival signaling cascades and the tumor suppressor p53 pathway. Recent findings that connect these pathways through various miRNA families are reviewed, and support for using miRNA therapy as a novel method to counteract these tumor-promoting signaling events are presented.