lncRNA - 長い非コーディングRNA

Long non-coding RNAs (lncRNAs) are RNA transcripts longer than 200 nucleotides that are not translated into proteins. Unlike protein-coding genes, lncRNAs are processed similarly to precursor mRNA through splicing and addition of a 5' cap and 3' poly-A tail. They regulate gene expression and cellular processes across plants, animals, bacteria, and viruses, though they show low sequence conservation between species.

RNA synthesis requires less energy and occurs more rapidly than protein synthesis. Since lncRNA is produced in the nucleus, it can be immediately used for gene regulation, providing faster cellular responses than proteins, which must be synthesized and imported from the cytoplasm. This rapid availability makes lncRNAs effective regulators of time-sensitive cellular processes.

LncRNAs can act as scaffolds for proteins by forming multiple stem-loop structures where proteins bind and perform their functions. Chromatin-modifying proteins and transcriptional activators or repressors attach to these structures. This scaffolding mechanism allows lncRNAs to organize protein complexes and direct them to specific cellular locations for coordinated gene regulation.

Like microRNA, lncRNAs can act as guide RNA by binding to protein complexes with one region while another region selectively base pairs with target DNA sequences. This dual-binding capability helps localize protein complexes to specific genomic locations, enabling precise targeting of chromatin modifications and transcriptional regulation at desired genes.

LncRNAs can function as alternative binding sites or sponges, sequestering regulatory molecules away from their target locations. For example, lncRNAs bind to microRNAs and prevent their interaction with target mRNA, effectively blocking microRNA-mediated gene silencing. This sponge mechanism allows lncRNAs to modulate the activity of other regulatory molecules.

LncRNAs can base-pair with complementary regions in mRNA to inhibit pre-mRNA splicing by hiding particular splice sites, or they can block translation of mature mRNA. Some lncRNAs also carry exons and produce small peptides of unknown function. These mechanisms allow lncRNAs to regulate gene expression at both transcriptional and post-transcriptional levels.

LncRNAs play important roles in cancer development, acting as tumor suppressors or promoters. Abnormal expression of specific lncRNAs occurs in tumor-specific patterns; for example, MALAT1 and XIST are associated with brain cancer, while HOTTIP and HOTAIR are linked to lung cancer. These cancer-associated lncRNAs serve as diagnostic biomarkers and potential therapeutic targets for cancer treatment.