Noncoding RNA Epigenetic Regulation

Noncoding RNA Epigenetic Regulation is the set of mechanisms through which RNA molecules that do not encode proteins participate in establishing, guiding, and maintaining chromatin states and gene expression patterns, and the dysregulation of these noncoding RNAs represents an additional layer of epigenetic abnormality contributing to cancer development alongside DNA methylation and histone modification changes.

Categories of Regulatory Noncoding RNA

Long Noncoding RNAs

Long noncoding RNAs are transcripts exceeding a few hundred nucleotides in length that do not code for protein but instead perform regulatory functions, including guiding chromatin-modifying complexes to specific genomic locations, scaffolding the assembly of regulatory protein complexes, and directly influencing three-dimensional chromatin organization.

MicroRNAs

MicroRNAs are short noncoding RNAs that primarily regulate gene expression after transcription by binding to messenger RNA molecules and promoting their degradation or blocking their translation, but they also intersect with epigenetic regulation by targeting the messenger RNAs encoding chromatin-modifying enzymes themselves.

Other Regulatory RNA Classes

Additional classes of small noncoding RNAs contribute to chromatin regulation through mechanisms including guiding DNA methylation machinery to specific sequences and participating in the silencing of repetitive genomic elements, extending the range of noncoding RNA involvement in epigenetic control.

Mechanisms of Noncoding RNA Involvement in Chromatin Regulation

Guiding Chromatin-Modifying Complexes

Certain long noncoding RNAs physically associate with chromatin-modifying protein complexes and direct their activity to specific genomic locations, effectively serving as targeting molecules that determine where a given chromatin modification will be deposited.

Scaffolding Regulatory Complex Assembly

Some noncoding RNAs act as structural scaffolds, bringing together multiple protein components that would not otherwise efficiently assemble into a functional regulatory complex, thereby enabling coordinated chromatin modification at target loci.

Influencing Three-Dimensional Genome Structure

Certain noncoding RNAs contribute to establishing or stabilizing higher-order chromatin structures, including participating in the formation of specific chromatin domains and contributing to the phenomenon of chromosome-wide silencing observed at the inactive X chromosome.

Dysregulation in Cancer

Altered Expression of Regulatory Long Noncoding RNAs

Long noncoding RNAs that normally guide silencing complexes to tumor suppressor gene loci can become overexpressed in cancer cells, driving inappropriate silencing of these protective genes, while long noncoding RNAs supporting normal differentiation programs can become underexpressed, contributing to loss of normal cellular identity.

MicroRNA Dysregulation Affecting Chromatin Regulators

Loss of microRNAs that normally restrain expression of chromatin-modifying enzymes can lead to overexpression of these enzymes, indirectly amplifying epigenetic dysregulation throughout the genome, while gain of microRNAs targeting protective chromatin regulators can suppress their normal restraining function.

Genetic and Epigenetic Alterations Affecting Noncoding RNA Genes

The genomic loci encoding regulatory noncoding RNAs are themselves subject to mutation, copy number alteration, and epigenetic silencing, providing multiple routes through which their normal function can be disrupted in cancer cells.

Functional Consequences

Amplification of Broader Epigenetic Dysregulation

Because many regulatory noncoding RNAs act by directing the activity of chromatin-modifying enzymes, their dysregulation can amplify or redirect the effects of these enzymes across many genomic locations simultaneously, contributing to widespread epigenetic abnormality beyond what enzyme dysfunction alone would produce.

Contribution to Oncogenic and Tumor Suppressive Programs

Individual noncoding RNAs have been characterized as functioning similarly to oncogenes or tumor suppressor genes, promoting or restraining malignant behavior through their downstream effects on chromatin state and gene expression.

Detection and Study

Noncoding RNA Expression Profiling

Sequencing approaches capable of capturing noncoding transcripts allow researchers to identify noncoding RNAs with altered expression in tumor tissue compared to normal tissue, providing candidates for further functional investigation.

Mapping RNA-Chromatin Interactions

Specialized techniques capable of identifying the specific genomic locations to which a given noncoding RNA binds allow researchers to connect a dysregulated noncoding RNA to its direct downstream chromatin targets.

Clinical Relevance

Dysregulated noncoding RNAs are being investigated both as diagnostic and prognostic biomarkers and as potential therapeutic targets, given the feasibility of using synthetic oligonucleotides to directly inhibit or replace specific noncoding RNA molecules, offering an additional therapeutic avenue distinct from targeting chromatin-modifying enzymes directly.