Osteoporosis is one of the most common skeletal diseases, characterized by progressive loss of bone mass and changes in bone microstructure, leading to increased fragility and susceptibility to fractures. The balance between bone formation and resorption is tightly regulated by complex cellular signaling pathways, among which the canonical Wnt/β-catenin pathway plays a key role. A crucial negative regulator of this pathway is sclerostin, a protein encoded by the SOST gene. The expression of this gene is associated with osteoblast differentiation, bone formation, and the development of osteoporosis.
RNA G-quadruplexes are chemically and thermally stable non-canonical secondary structures that can form within guanine-rich sequences. Such sequences are frequently found in the 5′- and 3′-untranslated regions (UTRs) of mRNAs, where they can participate in post-transcriptional regulation.
In this study, we identified a guanine-rich sequence (SOSTwt) in the 3′-UTR of the human SOST gene that is capable of forming an RNA G-quadruplex. By introducing modifications (G to U substitutions), we generated several constructs and demonstrated using 1D H1 NMR spectra that construct U8 forms a predominant RNA G-quadruplex structure within SOSTwt. Using NMR spectroscopy together with CD and UV analyses, we showed that U8 (like SOSTwt) forms a thermally stable, parallel RNA G-quadruplex. The core of the structure consists of two G-quartets and a G-triad, which contains a potential binding site for small molecules such as dGMP, cGMP, or an additional guanine residue. The discovered structure indicates additional structural diversity of RNA G-quadruplexes and their potential role in regulating SOST gene expression. Our work provides the first description of a 4n–1 guanine-containing structure that may form in the 3′-UTR of a gene associated with osteoporosis.
Due to its high thermal stability and specific structural features, the discovered structure in the SOST gene sequence represents an excellent candidate for further studies on translational regulation under cellular conditions. Moreover, it constitutes a promising target for the development of novel therapeutic approaches for the treatment of osteoporosis.
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