Splicing factor FUS facilitates the progression of PIT1-lineage PitNETs by upregulating MDM2.

Background: Splicing factors play pivotal roles in mRNA processing and are implicated in tumor progression. The aberrant expression of splicing factors is closely associated with the invasiveness and secretion profiles of pituitary neuroendocrine tumors (PitNETs). In this study, we explored the involvement of splicing factors in PIT1-lineage PitNET progression and assessed the feasibility of targeting the splicing process as a therapeutic approach. Methods: Statistical data on PitNET subtypes were obtained from the National Brain Tumor Registry of China (NBTRC), and gene expression analysis was conducted on 40 clinical samples collected for this study. Transcriptome analysis and RNA immunoprecipitation sequencing (RIP-seq) were utilized to examine FUS-mediated alternative splicing and to identify mRNA binding sites in PitNET cells. Minigene splicing assays were employed to confirm the specific exonic and intronic regions. Additionally, Annexin V/PI assays and JC-1 staining were conducted to evaluate apoptosis. Results: The expression of the splicing factor FUS was elevated in PIT1-lineage PitNETs and was correlated with increased proliferative capacity and reduced apoptosis levels. Transcriptome sequencing revealed that the knockdown of FUS led to extensive exon skipping and activated the p53 pathway. In addition to RIP-seq analysis, these findings suggest that FUS contributes to the inclusion of exon 3 to generate full-length MDM2, a well-established negative regulator of p53. Antisense oligonucleotides (ASOs) specifically designed to target binding sequences on pre-mRNAs effectively disrupted the FUS-mediated splicing process, consequently impeding the progression of PitNETs. Conclusions: Our study elucidated the critical function of FUS as a splicing factor in PitNETs. Furthermore, we illustrated that targeting the splicing mechanism associated with MDM2 could restore p53 levels, thereby impeding the progression of PitNETs. This discovery presents a potentially novel strategy for the clinical management of PIT1-lineage PitNETs.