Publications by Author: Frank J Slack

MicroRNAs (miRNA) are short, noncoding RNAs whose dysregulation has been implicated in most, if not all, cancers. They regulate gene expression by suppressing mRNA translation and reducing mRNA stability. To this end, there is a great deal of interest in modifying miRNA expression levels for the treatment of cancer. However, the literature is fraught with inconsistent accounts as to whether various miRNAs are oncogenic or tumor suppressive. In this review, we directly examine these inconsistencies and propose several mechanisms to explain them. These mechanisms include the possibility that specific miRNAs can simultaneously produce competing oncogenic and tumor suppressive effects by suppressing both tumor suppressive mRNAs and oncogenic mRNAs, respectively. In addition, miRNAs can modulate tumor-modifying extrinsic factors, such as cancer-immune system interactions, stromal cell interactions, oncoviruses, and sensitivity to therapy. Ultimately, it is the balance between these processes that determines whether a specific miRNA produces a net oncogenic or net tumor suppressive effect. A solid understanding of this phenomenon will likely prove valuable in evaluating miRNA targets for cancer therapy. Cancer Res; 76(13); 3666-70. ©2016 AACR.

MicroRNA (miRNA) expression is tightly regulated by several mechanisms, including transcription and cleavage of the miRNA precursor RNAs, to generate a mature miRNA, which is thought to be directly correlated with activity. MiR-34 is a tumour-suppressor miRNA important in cell survival, that is transcriptionally upregulated by p53 in response to DNA damage. Here, we show for the first time that there is a pool of mature miR-34 in cells that lacks a 5'-phosphate and is inactive. Following exposure to a DNA-damaging stimulus, the inactive pool of miR-34 is rapidly activated through 5'-end phosphorylation in an ATM- and Clp1-dependent manner, enabling loading into Ago2. Importantly, this mechanism of miR-34 activation occurs faster than, and independently of, de novo p53-mediated transcription and processing. Our study reveals a novel mechanism of rapid miRNA activation in response to environmental stimuli occurring at the mature miRNA level.

In C. elegans, miRNAs are genetic biomarkers of aging. Similarly, multiple miRNAs are differentially expressed between younger and older persons, suggesting that miRNA-regulated biological mechanisms affecting aging are evolutionarily conserved. Previous human studies have not considered participants' lifespans, a key factor in identifying biomarkers of aging. Using PCR arrays, we measured miRNA levels from serum samples obtained longitudinally at ages 50, 55, and 60 from 16 non-Hispanic males who had documented lifespans from 58 to 92. Numerous miRNAs showed significant changes in expression levels. At age 50, 24 miRNAs were significantly upregulated, and 73 were significantly downregulated in the long-lived subgroup (76-92 years) as compared with the short-lived subgroup (58-75 years). In long-lived participants, the most upregulated was miR-373-5p, while the most downregulated was miR-15b-5p. Longitudinally, significant Pearson correlations were observed between lifespan and expression of nine miRNAs (p value<0.05). Six of these nine miRNAs (miR-211-5p, 374a-5p, 340-3p, 376c-3p, 5095, 1225-3p) were also significantly up- or downregulated when comparing long-lived and short-lived participants. Twenty-four validated targets of these miRNAs encoded aging-associated proteins, including PARP1, IGF1R, and IGF2R. We propose that the expression profiles of the six miRNAs (miR-211-5p, 374a-5p, 340-3p, 376c-3p, 5095, and 1225-3p) may be useful biomarkers of aging.

Lung cancer represents the leading cause of cancer-related deaths in men and women worldwide. Targeted therapeutics, including the epidermal growth factor receptor (EGFR) inhibitor erlotinib, have recently emerged as clinical alternatives for the treatment of non-small cell lung cancer (NSCLC). However, the development of therapeutic resistance is a major challenge, resulting in low 5-year survival rates. Due to their ability to act as tumor suppressors, microRNAs (miRNAs) are attractive candidates as adjuvant therapeutics for the treatment of NSCLC. In this study, we examine the ability of 2 tumor suppressor miRNAs, let-7b and miR-34a to sensitize KRAS;TP53 mutant non-small cell lung cancer cells to the action of erlotinib. Treatment with these miRNAs, individually or in combination, resulted in synergistic potentiation of the anti-proliferative effects of erlotinib. This effect was observed over a wide range of miRNA and erlotinib interactions, suggesting that let-7b and miR-34a target oncogenic pathways beyond those inhibited by EGFR. Combinatorial treatment with let-7b and miR-34a resulted in the strongest synergy with erlotinib, indicating that these miRNAs can effectively target multiple cellular pathways involved in cancer cell proliferation and resistance to erlotinib. Together, our findings indicate that NSCLC cells can be effectively sensitized to erlotinib by supplementation with tumor suppressor miRNAs, and suggest that the use of combinations of miRNAs as adjuvant therapeutics for the treatment of lung cancer is a viable clinical strategy.

The evolutionarily conserved gene lin-28 encodes an RNA-binding protein and is an important regulator of the proper temporal succession of several developmental events in both invertebrates and vertebrates. At the cellular level, LIN-28 promotes stemness and proliferation, and inhibits differentiation, a feature best illustrated by its ability to induce pluripotency when ectopically expressed in human fibroblasts in combination with NANOG, OCT4, and SOX2. Mammalian LIN28 functions in part by regulating processing of the let-7 microRNA through a GGAG binding site in the pre-let-7's distal loop region. However, many human and animal let-7 precursors lack the GGAG binding motif. In order to dissect the molecular mechanisms underlying its biological functions in a living animal, we identified a map of LIN-28 interactions with the transcriptome by in vivo HITS-CLIP in Caenorhabditis elegans. LIN-28 binds a large pool of messenger RNAs, and a substantial fraction of the bona fide LIN-28 targets are involved in aspects of animal development. Furthermore, our data show that LIN-28 regulates the expression of the let-7 microRNA by binding its primary transcript in a previously unknown region, revealing a novel regulatory mechanism.

BACKGROUND: Dietary restriction (DR) has been shown to prolong longevity across diverse taxa, yet the mechanistic relationship between DR and longevity remains unclear. MicroRNAs (miRNAs) control aging-related functions such as metabolism and lifespan through regulation of genes in insulin signaling, mitochondrial respiration, and protein homeostasis.

RESULTS: We have conducted a network analysis of aging-associated miRNAs connected to transcription factors PHA-4/FOXA and SKN-1/Nrf, which are both necessary for DR-induced lifespan extension in Caenorhabditis elegans. Our network analysis has revealed extensive regulatory interactions between PHA-4, SKN-1, and miRNAs and points to two aging-associated miRNAs, miR-71 and miR-228, as key nodes of this network. We show that miR-71 and miR-228 are critical for the response to DR in C. elegans. DR induces the expression of miR-71 and miR-228, and the regulation of these miRNAs depends on PHA-4 and SKN-1. In turn, we show that PHA-4 and SKN-1 are negatively regulated by miR-228, whereas miR-71 represses PHA-4.

CONCLUSIONS: Based on our findings, we have discovered new links in an important pathway connecting DR to aging. By interacting with PHA-4 and SKN-1, miRNAs transduce the effect of dietary-restriction-mediated lifespan extension in C. elegans. Given the conservation of miRNAs, PHA-4, and SKN-1 across phylogeny, these interactions are likely to be conserved in more-complex species.

A select group of microRNAs identified in blood samples can differentiate between Alzheimer's disease, other neurological disorders and age-matched healthy controls with high accuracy.

MicroRNAs (miRNAs) have emerged as key genetic regulators of a wide variety of biological processes, including growth, proliferation, and survival. Recent advances have led to the recognition that miRNAs can act as potent oncogenes and tumor suppressors, playing crucial roles in the initiation, maintenance, and progression of the oncogenic state in a variety of cancers. Determining how miRNA expression and function is altered in cancer is an important goal, and a necessary prerequisite to the development and adoption of miRNA-based therapeutics in the clinic. Highly promising clinical applications of miRNAs are the use of miRNA signatures as biomarkers for cancer (for example, for early detection or diagnosis), and therapeutic supplementation or inhibition of specific miRNAs to alter the cancer phenotype. In this review, we discuss the main methods used for miRNA profiling, and examine key miRNAs that are commonly altered in a variety of tumors. Current studies underscore the functional versatility and potency of miRNAs in various aspects of the cancer phenotype, pointing to their potential clinical applications. Consequently, we discuss the application of miRNAs as biomarkers, clinical agents, and therapeutic targets, highlighting both the enormous potential and major challenges in this field.