Figure 6. YTHDC1 and CPSF4 competitively bind to FIP1L1 and regulate the choice of APA sites.

1. Schematic diagram of functional regions of FIP1L1 and CPSF4.
2. YTHDC1 inhibits the interaction between Myc‐FIP1L1 and FLAG‐CPSF4. A substantially suppressed level of interaction between Myc‐FIP1L1 and FLAG‐CPSF4 was observed when FLAG‐YTHDC1 input was increased.
3. Knockdown of YTHDC1 enhances endogenous FIP1L1 recruitment to CPSF4, indicating that YTHDC1 plays an important role in interfering with the 3′ end processing complex interaction.
4. YTHDC1 has little effect on the interaction between Myc‐FIP1L1 and FLAG‐PAPOLA. The interaction between Myc‐FIP1L1 and FLAG‐PAPOLA was not significantly affected when FLAG‐YTHDC1 was increased.
5. Mutation of proline had little effect on the interaction between FIP1L1 and CPSF4 compared with the wild type.
6. The mutation of prolines in FIP1L1 abrogated the inhibitory effect of YTHDC1 on the interaction between FIP1L1 and CPSF4.
7. qRT–PCR validation of APA site switching in a bicistronic dual luciferase system. FIP1L1‐Mut could significantly increase the ratios of Rluc/Fluc compared to FIP1L1‐WT, indicating that YTHDC1 inhibits the use of proximal APA sites by interacting with the proline‐rich domain of FIP1L1. Data are presented as mean ± SEM of three biological replicates. **P = 8.77 × 10⁻⁴, the P values were obtained with unpaired two‐tailed Student's t‐test.

Source data are available online for this figure.