Abstract
Sequences with the potential to form RNA G-quadruplexes (G4s) are common in mammalian introns, especially in the proximity of the 5′ splice site (5′SS). However, the difficulty of demonstrating that G4s form in pre-mRNA in functional conditions has meant that little is known about their effects or mechanisms of action. We have shown previously that two G4s form in Bcl-X pre-mRNA, one close to each of the two alternative 5′SS. If these G4s affect splicing but are in competition with other RNA structures or RNA binding proteins, then ligands that stabilize them would increase the proportion of Bcl-X pre-mRNA molecules in which either or both G4s had formed, shifting Bcl-X splicing. We show here that a restricted set of G4 ligands do affect splicing, that their activity and specificity are strongly dependent on their structures and that they act independently at the two splice sites. One of the ligands, the ellipticine GQC-05, antagonizes the major 5′SS that expresses the anti-apoptotic isoform of Bcl-X and activates the alternative 5′SS that expresses a pro-apoptotic isoform. We propose mechanisms that would account for these see-saw effects and suggest that these effects contribute to the ability of GQC-05 to induce apoptosis.
Highlights
G-rich sequences were first identified as functional elements in pre-mRNA splicing when G-triplets were found to be enriched in short introns, where they stimulate splicing and, in particular, the use of adjacent upstream 5 splice sites (5’SSs) [1]
Nucleic Acids Research, 2018, Vol 46, No 2 887 have recently developed a new method based on the use of deazaguanine-substituted RNA (FOLDeR) by which we have shown that two G4s form in functional conditions in Bcl-X pre-mRNA in the G-rich tracts adjacent to the two alternative 5’SS of exon 2 [29]
Bcl-XL isoform predominates [29] (Figure 2, left column). We determined this structure previously using RNase footprinting and RNase H, showing that it forms in the presence or absence of nuclear extract; analysis of deazaguanosinesubstituted pre-mRNA showed that, of six regions that might have had the potential to form G4s, only the regions marked Q2 and Q5 did so [29]
Summary
G-rich sequences were first identified as functional elements in pre-mRNA splicing when G-triplets were found to be enriched in short introns, where they stimulate splicing and, in particular, the use of adjacent upstream 5 splice sites (5’SSs) [1]. They have been shown to be enriched in introns of all sizes, especially near the 5’SS, where they are thought to buffer 5’SS sequences against the effects of mutations [2].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
