ATF4 promotes angiogenesis and neuronal cell death and confers ferroptosis in a xCT-dependent manner

Abstract

Activating transcription factor 4 (ATF4) is a critical mediator of metabolic and oxidative homeostasis and cell survival. ATF4 is elevated in response to diverse microenvironmental stresses, including starvation, ER stress damages and exposure to toxic factors. Here we show that ATF4 expression fosters the malignancy of primary brain tumors (WHO grade III and IV gliomas) and increases proliferation and tumor angiogenesis. Hence, ATF4 expression promotes cell migration and anchorage-independent cell growth, whereas siRNA-mediated knockdown of ATF4 attenuates these features of malignancy in human gliomas. Further experiments revealed that ATF4-dependent tumor promoting effects are mediated by transcriptional targeting the glutamate antiporter xCT/SCL7A11 (also known as system Xc-). Thus, xCT is elevated as a consequence of ATF4 activation. We further found evidence that ATF4-induced proliferation can be attenuated by pharmacological or genetic xCT inhibition and ferroptosis inducers such as sorafenib, erastin and GPx4 inhibitor RSL3. Further, fostered xCT expression promotes cell survival and growth in ATF4 knockdown cells. Moreover, increased xCT levels ameliorate sorafenib and erastin-induced ferroptosis. Conversely, ATF4 knockdown renders cells susceptible for erastin, sorafenib and RSL3-induced ferroptosis. We further identified that ATF4 promotes tumor-mediated neuronal cell death which can be alleviated by xCT inhibition. Moreover, elevated ATF4 expression in gliomas promotes tumor angiogenesis. Noteworthy, ATF4-induced angiogenesis could be diminished by ferroptosis inducers erastin and by GPx4 inhibitor RSL3. Our data provide proof-of-principle evidence that ATF4 fosters proliferation and induces a toxic microenvironmental niche. Furthermore, ATF4 increases tumor angiogenesis and shapes the vascular architecture in a xCT-dependent manner. Thus, inhibition of ATF4 is a valid target for diminishing tumor growth and vasculature via sensitizing tumor cells for ferroptosis.

MicroRNA‐214‐3p enhances erastin‐induced ferroptosis by targeting ATF4 in hepatoma cells

“…ATF4 is involved in ferroptosis in cancer cells (Chen, Fan et al, 2017; Chen, Wang et al, 2017). We next detected ATF4 expression in hepatoma cells exposed to erastin.…”

“…The role of ATF4 in regulating ferroptosis in cancer cells is in the debate. In glioma cells, the silencing of ATF4 has been suggested as a solid strategy for impairing glioma growth and vasculature by sensitizing tumor cells to erastin‐ and RSL3‐induced ferroptosis (Chen, Fan et al, 2017). In breast cancer cells, knockdown of ATF4, on the contrary, prevented cystine starvation‐induced ferroptosis (Chen, Wang et al, 2017).…”

“…Besides ER stress damages, diverse microenvironmental stimuli, including exposure to ferroptosis inducers, can also induce its elevation (Lee, Lee, Choudry, Bartlett, & Lee, 2018). ATF4 has recently been demonstrated to act as a negative regulator in ferroptosis (Chen, Fan et al, 2017). Therefore, the knocking down of ATF4 is suggested to render cancer cells susceptible to ferroptosis.…”

Generation and characterization of hepatocellular carcinoma cell lines with enhanced cancer stem cell potential

“…To assess the migratory potential of our HCSC enriched clones 3 and 5 in comparison to that of the parental HepG2 cells, we utilized an adapted spheroid migration assay protocol . For this, 1 × 10 3 cells were seeded into the wells of a GravityPLUS™ Hanging Drop 96‐well plate (ISP‐06‐001, Perkin Elmer) and incubated for 4 days.…”

Endoplasmic reticulum stress signalling – from basic mechanisms to clinical applications

“…However, sustained stress changes the adaptive response to a prodeath response and ultimately, the phosphorylation status of eIF2α appears to codetermine the balance between prosurvival or prodeath signalling . This is accomplished by the above mentioned delayed feedback through which the interplay of GADD34, ATF4 and CHOP results in the activation of genes involved in cell death, cell‐cycle arrest and senescence (Fig. ).…”