Abstract
To better understand a role of eIF4E S209 in oncogenic translation, we generated EIF4ES209A/+ heterozygous knockin (4EKI) HCT 116 human colorectal cancer (CRC) cells. 4EKI had little impact on total eIF4E levels, cap binding or global translation, but markedly reduced HCT 116 cell growth in spheroids and mice, and CRC organoid growth. 4EKI strongly inhibited Myc and ATF4 translation, the integrated stress response (ISR)-dependent glutamine metabolic signature, AKT activation and proliferation in vivo. 4EKI inhibited polyposis in ApcMin/+ mice by suppressing Myc protein and AKT activation. Furthermore, p-eIF4E was highly elevated in CRC precursor lesions in mouse and human. p-eIF4E cooperated with mutant KRAS to promote Myc and ISR-dependent glutamine addiction in various CRC cell lines, characterized by increased cell death, transcriptomic heterogeneity and immune suppression upon deprivation. These findings demonstrate a critical role of eIF4E S209-dependent translation in Myc and stress-driven oncogenesis and as a potential therapeutic vulnerability.
Highlights
Colorectal cancer (CRC) is a leading cause of cancer-related death worldwide (Siegel et al, 2019)
Compared to HCT 116 parental (WT) cells under normal growth conditions, 4E. Using EIF4E S209A/+ knockin (4EKI) cells showed a strong reduction in p-4E and unexpectedly in p-4E-BP1 (S65/T70), p-AKT(S473), with no change in total eukaryotic translation initiation factor 4E (eIF4E), 4E-BP1, p-4E-BP1(T37/46), p-mTOR (2448), p-S6 or p-ERK (Figure 1A). 4EKI slightly reduced 2D growth after day 5, as well as steady-state ATP levels and proliferation (Figure 1C, Figure 1—figure supplement 1D–F). 4EKI modestly reduced clonogenic and anchorage-independent growth, and severely impaired 3D spheroid growth (Figure 1D–F)
We examined the effects of 4EKI on translation in unstressed HCT 116 cells. 4EKI slightly reduced global mRNA translation, as measured by polysome profiling and activities of cap-dependent Luciferase and GFP reporters (Figure 2A–C, Figure 2—figure supplement 1). eIF4G and 4E-BP1 bind to eIF4E competitively
Summary
Colorectal cancer (CRC) is a leading cause of cancer-related death worldwide (Siegel et al, 2019). The gatekeeper tumor suppressor APC is mutated in 85% of CRCs and leads to increased Wnt/Myc signaling which cooperates with mutational activation of RAS/RAF/ERK (50–80%) and PI3K/AKT/ mTOR pathways (10–15%) to promote CRC initiation and progression (Vogelstein et al, 2013). Emerging evidence suggests that oncogenic drivers such as Myc do not increase ‘physiologic’ proliferation (Dang, 2016), but engender ‘oncogenic’ growth and hallmarks such as altered metabolism, resistance to cell death, metastasis, and immune evasion (Hanahan and Weinberg, 2011). Since direct targeting Myc (Dang et al, 2017) or mutant KRAS (Vogelstein et al, 2013) has not been successful in the clinic, intense interest remains to identify potential druggable targets in their regulatory circuitry
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