PTBP1 promotes the progression of hepatocellular carcinoma by enhancing the oncogenic splicing switch of FGFR2.

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer accounting for 90% of cases. It is a highly invasive and deadly cancer with a gradual onset. Polypyrimidine tract-binding protein 1 (PTBP1) is an important RNA-binding protein involved in RNA metabolism and has been linked to oncogenic splicing events. While the oncogenic role of PTBP1 in HCC cells has been established, the exact mechanism of action remains unclear. This study aimed to investigate the functional connection between PTBP1 and dysregulated splicing events in HCC. Through immunoprecipitation-mass spectrometry analyses, we discovered that the proteins bound to PTBP1 were significantly enriched in the complex responsible for the alternative splicing of FGFR2 (fibroblast growth factor receptor 2). Further RNA immunoprecipitation and quantitative PCR assays confirmed that PTBP1 down-regulated the FGFR2-IIIb isoform levels and up-regulated the FGFR2-IIIc isoform levels in HCC cells, leading to a switch from FGFR2-IIIb to FGFR2-IIIc isoforms. Subsequent functional evaluations using CCK-8, transwell, and plate clone formation assays in HCC cell lines HepG2 and Huh7 demonstrated that FGFR2-IIIb exhibited tumor-suppressive effects, while FGFR2-IIIc displayed tumor-promoting effects. In conclusion, this study provides insights into the PTBP1-mediated alternative splicing mechanism in HCC progression, offering a new theoretical basis for the prevention and treatment of this malignancy. Mechanistically, the isoform switch from FGFR2-IIIb to FGFR2-IIIc promoted epithelial-mesenchymal transformation (EMT) of HCC cells and activated the FGFR cascades ERK and AKT pathways.

PTBP1 Promotes Growth, Migration and Invasion of Cholangiocarcinoma Cells by Regulating mRNA Alternative Splicing / 中国生物化学与分子生物学报

Cholangiocarcinoma (CCA) is a highly invasive type of cancer with insidious onset and high mortality. Polypyrimidine tract-binding protein 1 (PTBP1) is highly over-expressed in various types of tumor tissues, which contributes to cancer progression. But the role of PTBP1 in CCA has not been explored yet. In this study, we aim to investigate the function of PTBP1 in CCA. Therefore, we used publicly available data from the cancer genome atlas (TCGA) to evaluate the dysregulation of PTBP1 in CCA. The results showed that the PTBP1 is significantly up-regulated in CCA tissues compared to the matched non-tumor tissues (P < 0. 05). We assessed the effects of PTBP1 on the growth of CCA cell lines RBE and HuH28 by performing CCK-8 and plate colony formation assays. The results showed that overexpression of PTBP1 significantly promoted the growth (P < 0. 01) of CCA cells, whereas knockdown of PTBP1 exhibited opposite effects. Transwell and Invasion assays revealed that overexpression of PTBP1 significantly promotes the migration and invasion of CCA cells (P < 0. 001), whereas knockdown of PTBP1 exhibited opposite effects (P < 0. 001). The RNA sequencing (RNA-seq) analysis in PTBP1-depleted cells showed that the up-regulated genes are significantly enriched in p53 signaling pathway, while the down-regulated genes are represented by cholesterol metabolism, Rho GTPase and TGF-β pathways. Then, the alternative splicing analysis revealed that inhibition of PTBP1 led to series of aberrant alternative splicing events, including several cancer-associated ones, such as splicing events within the TGF-β regulator TGIF1 and the p53 activity-correlated gene GNAS. These results indicate that PTBP1 promotes the progression of CCA likely by regulating the transcriptome alternative splicing to influence multiple cancer-associated signaling pathways.