Pitolli, C. | Search bioRxiv

bioRxiv2025

HnRNP C binding to inverted Alu elements protects the transcriptome from pre-mRNA circularization

Back-splicing is a non-canonical splicing event that drives the biogenesis of circular RNAs (circRNAs). Although the molecular mechanisms underlying circRNA biogenesis have been partially elucidated, how this process is globally regulated in tumors, has not been fully investigated. Herein, we uncover a hnRNP C-dependent mechanism that represses a broad repertoire of circRNAs in Group 3 medulloblastoma (MB). HnRNP C binds Alu elements and prevents the circularization of pre-mRNA transcripts. Expression of hnRNP C modulates the balance between linear and circular splicing and guarantees efficient expression of genes that sustain the oncogenic phenotype of Group 3 MB cells. Remarkably, in the absence of hnRNP C, the introns flanking the circularizing exons generate cytoplasmic dsRNAs through base-pairing of inverted Alu elements and trigger an interferon-induced antiviral response. These findings unveil the role of hnRNP C as guardian of transcriptome integrity by repressing circRNA biogenesis. Lastly, targeting hnRNP C in Group 3 MB may trigger an inflammatory immune response, thereby boosting cancer surveillance.

cancer biology↗

bioRxiv2024

Epigenetic modulation of RIPK3 by Transglutaminase 2-dependent serotonylation of H3K4me3 affects necroptosis

The receptor interacting protein kinase 3 (RIPK 3) is the main player in the activation of necroptosis, a pro-inflammatory regulated cell death modality induced by many different stimuli. RIPK3 is epigenetically regulated by DNA methylation and can be expressed when its promoter is associated with H3K4me3 histone. In this study, we show that Transglutaminase 2 protein (TG2) is necessary to induce necroptosis pathway allowing the expression of Ripk3 gene. Indeed, cells lacking TG2 show a strong downregulation of Ripk3 gene and are resistant to necroptotic stimuli. TG2 is known to promote the serotonylation of H3K4me3 histone (H3K4me3Q5ser) regulating in this way the target gene expression. Interestingly, we find that TG2 interacts with both histones H3K4me3 and H3K4me3Q5ser and these post-translational modifications are associated with the Ripk3 promoter only in presence of TG2. In addition, the absence of the H3K4me3Q5ser, in cells lacking TG2, is correlated with Ripk3 gene methylation. Altogether, these results indicate that RIPK3 expression requires TG2 mediated serotonylation of H3K4me3 to prevent Ripk3 promoter methylation, thus favouring its expression and necroptosis induction. HIGHLIGHTS- Transglutaminase 2 protein (TG2) is necessary to induce necroptosis. - Cells lacking TG2 show a strong downregulation of Ripk3 gene. - TG2 allows Ripk3 gene expression by promoting the serotonylation on H3K4me3 histone. SYNOPSIS O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=176 SRC="FIGDIR/small/619049v1_ufig1.gif" ALT="Figure 1"> View larger version (26K): org.highwire.dtl.DTLVardef@12c95c6org.highwire.dtl.DTLVardef@1cfbcaorg.highwire.dtl.DTLVardef@d6be1forg.highwire.dtl.DTLVardef@5bfb31_HPS_FORMAT_FIGEXP M_FIG C_FIG - TG2 serotonylates histone H3K4me3, associated to Ripk3 promoter, favoring its expression. - TG2 dependent serotonylation of histone H3K4me3 prevents DNA methylation. - TG2 favours the expression of Ripk3 making cells susceptible to necroptosis. - In the absence of TG2, neither serotonylation nor methylation occur on histone H3, associated to Ripk3 promoter. - In the absence of TG2, Ripk3 promoter is methylated, thus blocking the activation of necroptosis.

cell biology↗