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MicroRNAs (miRNAs) are known for their role in the post-transcriptional regulation of messenger RNA (mRNA). However, recent evidence has shown that miRNAs are capable of regulating non-coding RNAs, including miRNAs, in what is known as miRNA:miRNA interactions. There are three main models for the interplay between miRNAs. These involve direct interaction between two miRNAs, either in their mature or primary form, the subsequent changes in miRNA expression due to miRNA-directed transcriptional changes, and the cell-wide impact on miRNA and mRNA levels as a result of miRNA manipulation. Networks of mRNA and miRNA regulatory connections are invaluable to the discovery of miRNA:miRNA pathways, but this cannot be applied without consideration of the specific cell type or condition.In this chapter, we discuss what is understood about miRNA:miRNA interactions, their mechanisms and consequences in disease biology, and suggest further avenues of investigation based on current gaps in the literature and in our understanding of miRNA biology. We also address the pitfalls in contemporary methods relating to the identification of miRNA:miRNA interactions. Future work in this area may ultimately change the definitional role of miRNAs, and have far-reaching impacts on therapeutic and diagnostic developments.

Canonically, microRNAs (miRNAs) control mRNA expression. However, studies have shown that miRNAs are also capable of targeting non-coding RNAs, including long non-coding RNAs and miRNAs. The latter, termed a miRNA:miRNA interaction, is a form of self-regulation. In this Review, we discuss the three main modes of miRNA:miRNA regulation: direct, indirect and global interactions, and their implications in cancer biology. We also discuss the cell-type-specific nature of miRNA:miRNA interactions, current experimental approaches and bioinformatic techniques, and how these strategies are not sufficient for the identification of novel miRNA:miRNA interactions. The self-regulation of miRNAs and their impact on gene regulation has yet to be fully understood. Investigating this hidden world of miRNA self-regulation will assist in discovering novel regulatory mechanisms associated with disease pathways., Summary: MicroRNAs are capable of self-targeting, which has implications on their biogenesis, their canonical role in gene regulation and on cancer development.

miRNAs inherently alter the cellular environment by regulating target genes. miRNAs may also regulate other miRNAs, with far-reaching influence on miRNA and mRNA expression. We explore this realm of small RNA regulation with a focus on the role of the oncogenic miR-21 and its impact on other miRNA species.

Human papillomavirus (HPV), notably type 16, is a risk factor for up to 75% of oropharyngeal squamous cell carcinomas (SCC). It has been demonstrated that small non-coding RNAs known as microRNAs play a vital role in the cellular transformation process. In this study, we used an LNA array to further investigate the impact of HPV16 on the expression of microRNAs in oropharyngeal (tonsillar) cancer. A number of miRNAs were found to be deregulated, with miR-496 showing a four-fold decrease. Over-expression of the high risk E6 oncoprotein down-regulated miR-496, impacting upon the post-transcriptional control of the transcription factor E2F2. These HPV specific miRNAs were integrated with the HPV16 interactome to identify possible mechanistic pathways. These analyses provide insights into novel molecular interactions between HPV16 and miRNAs in oropharyngeal cancers.

MicroRNAs (miRNA) are capable of self-regulation, termed miRNA to miRNA interaction. Very little is known about these interactions and their impact on the cellular milieu. We discuss known miRNA to miRNA interactions, potential mechanisms, and their role in cancer.

The regulation of tumor suppressor genes by microRNAs (miRNAs) is often demonstrated as a one-miRNA-to-one-target relationship. However, given the large number of miRNA sites within a 3′ untranslated region (UTR), most targets likely undergo miRNA cooperation or combinatorial action. Programmed cell death 4 (PDCD4), an important tumor suppressor, prevents neoplastic events and is commonly downregulated in cancer., The regulation of tumor suppressor genes by microRNAs (miRNAs) is often demonstrated as a one-miRNA-to-one-target relationship. However, given the large number of miRNA sites within a 3′ untranslated region (UTR), most targets likely undergo miRNA cooperation or combinatorial action. Programmed cell death 4 (PDCD4), an important tumor suppressor, prevents neoplastic events and is commonly downregulated in cancer. This study investigates the relationship between miRNA 21 (miR-21) and miR-499 in regulating PDCD4. This was explored using miRNA overexpression, mutational analysis of the PDCD4 3′ UTR to assess regulation at each miRNA site, and 50% inhibitory concentration (IC50) calculations for combinatorial behavior. We demonstrate that the first miR-499 binding site within PDCD4 is inactive, but the two remaining sites are both required for PDCD4 suppression. Additionally, the binding of miR-21 to PDCD4 influenced miR-499 activity through an increase in its silencing potency and stabilization of its mature form. Furthermore, adjoining miRNA sites more than 35 nucleotides (nt) apart could potentially regulate thousands of 3′ UTRs, similar to that observed between miR-21 and miR-499. The regulation of PDCD4 serves as a unique example of regulatory action by multiple miRNAs. This relationship was predicted to occur on thousands of targets and may represent a wider mode of miRNA regulation.

Study objective A new generation of designer stimulants marketed as "bath salts" emerged in late 2010. The goal is to describe the epidemiologic emergence of designer stimulants in 9 states in the Midwest. Methods A retrospective review of the National Poison Data System was performed between November 1, 2010, and November 30, 2011. Inclusion criteria were health care–evaluated bath salts or other synthetic stimulants exposures. Cases were excluded if the exposure was unrelated to a designer stimulant. Demographic and clinical characteristics of cases were calculated and differences in outcome and exposure by generation were examined. Results One thousand six hundred thirty-three patients met the inclusion criteria. Age ranged from 1 day to 61 years (mean=29.2 years), with 67.9% male patients. The most common clinical features were agitation (62.2%), tachycardia (55.2%), and hallucinations (32.7%). In addition to 15.5% of patients having a major medical effect, 0.6% died. Reason for use was primarily intentional abuse (88.5%). However, 0.7% of patients reported withdrawal. Treatment involved primarily benzodiazepines (58.5%), with 8.7% of patients being intubated. Baby Boomers were more likely to have a major medical outcome (24.2%) and to report injection as the method of administration (8.6%-12.9%). Conclusion Synthetic stimulants rapidly swept across the Midwest, resulting in more than 1,600 patients seeking medical care. Serious medical effects or death was observed in 16.1% of cases. Older generations were more likely to inject and to have a major medical outcome.

The permanent storage of carbon in mineral form using natural brines found in geologic formations is at the forefront of carbon sequestration research. A complex chemistry describes the ultimate fixation of carbon in stable minerals, such as calcite. However, the parameters that govern carbonate formation are not well understood. Accordingly, the purpose of this study is to induce and characterize calcite formation by reacting natural gas brine with CO2. Brine pH has a significant effect on this conversion and can thus be adjusted to induce calcite precipitation using a laboratory scale reactor operated at temperatures of 75 and 150 °C and pressures of 600 and 1500 psi. Initial pH conditions of at least 9.0 are optimal for carbonate precipitation in reactions of 18 h. Although the reaction duration is not long enough to successfully correlate brine compositional changes with precipitation and pH evolution, X-ray diffraction analysis clearly confirms the presence of calcite. Scanning electron microscopy/en...