Introduction: A long nontranslating RNA is any RNA that is longer than 200 nucleotides (nt). In mammals, several long non-coding RNAs (lncRNAs) are transcribed from the genome, however, these lncRNAs do not code for proteins. The mRNA stability, translation, and post-translational modifications in the cytoplasm contribute to their regulatory effects on gene expression networks through controlling the nuclear architecture and DNA transcription. NEAT-1 (Nuclear paraspeckle assembly transcript 1) is a functionally conserved long non-coding RNA that has been reported to be frequently deregulated in several types of cancer. This gene is located within the human chromosomal region 11q13 and may function as a regulatory factor for various genes and pathways. It also functions as a core component of the paraspeckle in the nucleus. NEAT1 encodes two transcripts, NEAT1_1 and NEAT1_2, which differ in how their 3'untranslated regions (UTRs) are processed. NEAT1_1 is generated by polyadenylation and produces a 3.7 kb transcript. NEAT1_2 forms a triple helix structure that is then cleaved by RNase P into a 23 kb transcript. Different functions are performed by each of these isoforms. Unlike NEAT1_1, NEAT1_2 is not only required for the formation of paraspeckles but is a limiting factor which controls the tendency of the nucleus for creating certain number of paraspeckles according to its concentration. Paraspeckles are dynamic and membraneless nuclear bodies that can influence cellular functions, including stress response. Paraspeckles have been demonstrated to have at least three main functions at the molecular level. Firstly, they are responsible for the biogenesis of microRNAs, a function which is related to NEAT1 and SFPQ (splicing factor proline- and glutamine-rich) protein. Their second role is gene regulation through the adenine to inosine editing process mediated by the adenosine deaminase enzyme RNA specific. Thirdly, paraspeckles act as molecular sponges which trap RNA-binding proteins, therefore modulating gene expression. Paraspeckles are RNase-sensitive structures, therefore, their transcription is dependent on RNA Polymerase II, suggesting that RNAs are necessary for their maintenance. NEAT1_2 is an essential and architectural lncRNA that acts as a scaffold for paraspeckle assembly. Speckles formation initiates by directly binding some paraspeckle proteins (PSPs) also known as RNA binding proteins, to the NEAT1_2 variant, assisting its stabilization and avoiding its possible degradation. Subsequently, Other PSPs form and eventually SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin-remodeling complex mediates the protein-protein interaction network required for paraspeckle assembly, by linking 50 ribonucleoprotein complexes together with NEAT1_2. Various endogenous and exogenous stresses constantly damage DNA, including UV light, ionizing radiation, and reactive oxygen species (ROS). NEAT1 is known as the lncRNA which may regulate the DNA damage repair (DDR) system through multiple signaling pathways, including the ATM and ATR pathways, and the p53 pathway. P53 can be activated by a variety of stress signals, such as DNA-damaging agents, high levels of ROS and hypoxia. In the presence of functional p53, NEAT1_2 is induced followed by DNA damage. It is reported that silencing NEAT1_2 may accumulate DNA damages. It is noteworthy to know that almost all essential PSPs are actively involved in various DDR pathways, such as DNA double-strand breaks. NEAT1 knockdown cells showed decreased ATR-mediated phosphorylation of checkpoint kinase Chk1 and replication protein RPA32, demonstrating that NEAT1 is critical for ATR signaling and checkpoint activation.
Methods: The role of NEAT1 has been investigated by RNA extraction and real-time quantitative PCR, protein extraction and Western blotting, cell cultures and transfection.
Results: lncRNA can regulate the DDR system through the ATM, ATR and the p53 pathway. Many signals can activate p53, which in its turn, may induce the expression of NEAT1_2 and lead to the assembly of PSPs and the formation of paraspeckles.
Conclusion: The current study indicates that cellular stress conditions, known as potential activators of DDR pathways, may stimulate NEAT1 transcription, meanwhile, and initiate the formation and expansion of paraspeckles.
Keywords: lncRNA; NEAT1; paraspeckle; DNA damage repair;