Targeting APA converges on mTORC1 signaling and MYC expression. (A) Metascape analysis of significantly downregulated genes (P < .01, 1.5× fold change) upon FIP1L1 knockdown in Kasumi-1 cells. (B) Plot from GSEA of the RNA-sequencing experiment presented in Figure 3A (supplemental Figure 5A-B) showing genes downregulated upon rapamycin treatment. (C) Western blot showing FIP1L1, phosphorylated p70-S6 Kinase 1 (p-S6K1), S6K1, and actin (loading control) protein in the indicated AML cell lines after transduction with control shRNAs or shRNAs targeting FIP1L1 [shRNA (2) or (3)]. One representative experiment is shown of 2 independent experiments for each cell line. (D) Plot from GSEA of the RNA-sequencing experiment presented in Figure 3A (supplemental Figure 5A-B) showing genes upregulated by the oncogenic MYC transcription factor. (E) Western blot showing FIP1L1, MYC, and actin (loading control) protein in the indicated AML cell lines after transduction with control shRNAs or shRNAs targeting FIP1L1. One representative experiment is shown of 2 independent experiments for each cell line. (F) Cartoon model showing the impact of targeting APA on a positive oncogenic feedback loop. (Left) In cancer, mTORC1 and MYC positively regulate each other, blocking cellular differentiation. (Right) Targeting APA by FIP1L1 knockdown reduced both mTORC1 signaling and MYC transcriptional networks, promoting leukemia cell differentiation. Further work will elucidate the precise posttranscriptional targets responsible for disrupting this oncogenic signaling network. FDR, false discovery rate; NES, normalized enrichment score.