Prp8 impacts cryptic but not alternative splicing frequency

Pre-mRNA splicing must occur with extremely high fidelity. Spliceosomes assemble onto pre-mRNA guided by specific sequences (5' splice site, 3' splice site, and branchpoint). When splice sites are mutated, as in many hereditary diseases, the spliceosome can aberrantly select nearby pseudo- or "cryptic" splice sites, often resulting in nonfunctional protein. How the spliceosome distinguishes authentic splice sites from cryptic splice sites is poorly understood. We performed a Caenorhabditis elegans genetic screen to find cellular factors that affect the frequency with which the spliceosome uses cryptic splice sites and identified two alleles in core spliceosome component Prp8 that alter cryptic splicing frequency. Subsequent complementary genetic and structural analyses in yeast implicate these alleles in the stability of the spliceosome's catalytic core. However, despite a clear effect on cryptic splicing, high-throughput mRNA sequencing of these prp-8 mutant C. elegans reveals that overall alternative splicing patterns are relatively unchanged. Our data suggest the spliceosome evolved intrinsic mechanisms to reduce the occurrence of cryptic splicing and that these mechanisms are distinct from those that impact alternative splicing.

PRP4 Kinase Domain Loss Nullifies Drug Resistance and Epithelial-Mesenchymal Transition in Human Colorectal Carcinoma Cells

We have investigated the involvement of the pre-mRNA processing factor 4B (PRP4) kinase domain in mediating drug resistance. HCT116 cells were treated with curcumin, and apoptosis was assessed based on flow cytometry and the generation of reactive oxygen species (ROS). Cells were then transfected with PRP4 or pre-mRNA-processing-splicing factor 8 (PRP8), and drug resistance was analyzed both in vitro and in vivo. Furthermore, we deleted the kinase domain in PRP4 using GatewayTM technology. Curcumin induced cell death through the production of ROS and decreased the activation of survival signals, but PRP4 overexpression reversed the curcumin-induced oxidative stress and apoptosis. PRP8 failed to reverse the curcumin-induced apoptosis in the HCT116 colon cancer cell line. In xenograft mouse model experiments, curcumin effectively reduced tumour size whereas PRP4 conferred resistance to curcumin, which was evident from increasing tumour size, while PRP8 failed to regulate the curcumin action. PRP4 overexpression altered the morphology, rearranged the actin cytoskeleton, triggered epithelial-mesenchymal transition (EMT), and decreased the invasiveness of HCT116 cells. The loss of E-cadherin, a hallmark of EMT, was observed in HCT116 cells overexpressing PRP4. Moreover, we observed that the EMT-inducing potential of PRP4 was aborted after the deletion of its kinase domain. Collectively, our investigations suggest that the PRP4 kinase domain is responsible for promoting drug resistance to curcumin by inducing EMT. Further evaluation of PRP4-induced inhibition of cell death and PRP4 kinase domain interactions with various other proteins might lead to the development of novel approaches for overcoming drug resistance in patients with colon cancer.

PRP8-Induced CircMaml2 Facilitates the Healing of the Intestinal Mucosa via Recruiting PTBP1 and Regulating Sec62

BACKGROUND

Multiple organ dysfunction syndrome (MODS) occurs in the gastrointestinal tract and injured intestinal mucosa is the anatomical basis for various diseases. The expression of circular RNAs (circRNAs) is implicated in many diseases; however, the role of circRNAs in intestinal mucosal injury is yet to be discovered. Our preliminary gene microarray analysis revealed a novel circular RNA, circMaml2, with a significant intestinal mucosal protection effect. Its expression was found to decrease in severely burned intestinal mucosal tissue, whereas its overexpression might facilitate the reconstruction of the injured intestinal mucous membrane.

METHODS

The function of circMaml2 in cell proliferation and migration was studied in MC38 cells. The repair function of circMaml2 was tested on the intestinal mucosa of mice. RNA-binding protein polypyrimidine tract-binding protein 1(PTBP1) was selected by pull-down assay and mass spectrometry (MS). RNA immunoprecipitation (RIP) was performed to confirm the binding of circMaml2 and PTBP1 and to study PTBP1 and its downstream target, early B-cell factor 1(Ebf1). Bioinformatics software forecast analysis and dual-luciferase reporter assay were performed to ascertain miR-683 and Sec62 as the downstream targets of circMaml2 and miR-683, respectively. Furthermore, PRP8 was discovered to promote the biogenesis of circMaml2.

RESULTS

CircMaml2 promotes cell proliferation and migration of MC38 cells and the repair of the intestinal mucosa of mice. This effect is brought about by combining with PTBP1 to improve Ebf1 and interacting with miR-683 to regulate Sec2. Furthermore, PRP8 was discovered to promote the biogenesis of circMaml2.

CONCLUSIONS

This is the first reported study of the effect of circMaml2 on intestinal mucosal repair.