The splicing factor DHX38/PRP16 is required for ovarian clear cell carcinoma tumorigenesis, as revealed by a CRISPR-Cas9 screen

Introns with branchpoint-distant 3' splice sites: Splicing mechanism and regulatory roles

The two transesterification reactions of pre-mRNA splicing require highly complex yet well-controlled rearrangements of small nuclear RNAs and proteins (snRNP) in the spliceosome. The efficiency and accuracy of these reactions are critical for gene expression, as almost all human genes pass through pre-mRNA splicing. Key parameters that determine the splicing outcome are the length of the intron, the strengths of its splicing signals and gaps between them, and the presence of splicing controlling elements. In particular, the gap between the branchpoint (BP) and the 3' splice site (ss) of introns is a major determinant of the splicing efficiency. This distance falls within a small range across the introns of an organism. The constraints exist possibly because BP and 3'ss are recognized by BP-binding proteins, U2 snRNP and U2 accessory factors (U2AF) in a coordinated manner. Furthermore, varying distances between the two signals may also affect the second transesterification reaction since the intervening RNA needs to be accurately positioned within the complex RNP machinery. Splicing such pre-mRNAs requires cis-acting elements in the RNA and many trans-acting splicing regulators. Regulated pre-mRNA splicing with BP-distant 3'ss adds another layer of control to gene expression and promotes alternative splicing.

DHX38 enhances proliferation, metastasis, and EMT progression in NSCLC through the G3BP1-mediated MAPK pathway

BACKGROUND

Non-small cell lung cancer (NSCLC) is a prevalent and aggressive malignancy with limited therapeutic options. Despite advances in treatment, NSCLC remains a major cause of cancer-related death worldwide. Tumor heterogeneity and therapy resistance present challenges in achieving remission. Research is needed to provide molecular insights, identify new targets, and develop personalized therapies to improve outcomes.

METHODS

The protein expression level and prognostic value of DHX38 in NSCLC were explored in public databases and NSCLC tissue microarrays. DHX38 knockdown and overexpression cell lines were established to evaluate the role of DHX38 in NSCLC. In vitro and in vivo functional experiments were conducted to assess proliferation and metastasis. To determine the underlying molecular mechanism of DHX38 in human NSCLC, proteins that interact with DHX38 were isolated by IP and identified by LC-MS. KEGG analysis of DHX38-interacting proteins revealed the molecular pathway of DHX38 in human NSCLC. Abnormal pathway activation was verified by Western blot analysis and immunohistochemical (IHC) staining. A molecule-specific inhibitor was further used to explore potential therapeutic targets for NSCLC. The pathway-related target that interacted with DHX38 was verified by co-immunoprecipitation(co-IP) experiments. In cell lines with stable DHX38 overexpression, the target protein was knocked down to explore its complementary effect on DHX38 overexpression-induced tumor promotion.

RESULTS

The protein expression of DHX38 was increased in NSCLC, and patients with high DHX38 expression levels had a poor prognosis. In vitro and in vivo experiments showed that DHX38 promoted the proliferation, migration and invasion of human NSCLC cells. DHX38 overexpression caused abnormal activation of the MAPK pathway and promoted epithelial-mesenchymal transition (EMT) in tumours. SCH772984, a novel specific ERK1/2 inhibitor, significantly reduced the increases in cell proliferation, migration and invasion caused by DHX38 overexpression. The co-IP experiments confirmed that DHX38 interacted with the Ras GTPase-activating protein-binding protein G3BP1. DHX38 regulated the expression of G3BP1. Knocking down G3BP1 in cells with stable DHX38 overexpression prevented DHX38-induced tumor cell proliferation, migration and invasion. Silencing G3BP1 reversed the MAPK pathway activation and EMT induced by DHX38 overexpression.

CONCLUSION

In NSCLC, DHX38 functions as a tumor promoter. DHX38 modulates G3BP1 expression, leading to the activation of the MAPK signaling pathway, thus promoting tumor cell proliferation, metastasis, and the progression of epithelial-mesenchymal transition (EMT) in non-small cell lung cancer.

New insights into pathogen-mediated modulation of host RNA splicing

Alternative splicing (AS) regulation of pre-mRNA has been proven to be one of the fundamental layers of plant immune system. How pathogens disrupt plant AS process to suppress plant immunity by secreted effectors remain poorly understood. In the recent study, Gui et al. revealed that a previously identified effector PSR1 of Phytophthora interferes with host RNA splicing machinery to modulate small RNA biogenesis, leading to compromised plant immunity. The study provided a novel insight into the importance of AS process during pathogen-host interactions.