Ferritinophagy is required for the induction of ferroptosis by the bromodomain protein BRD4 inhibitor (+)-JQ1 in cancer cells

Abstract

(+)-JQ1 is an inhibitor of the tumor-driver bromodomain protein BRD4 and produces satisfactory effects because it efficiently increases apoptosis. Ferroptosis is an oxidative cell death program differing from apoptosis. Ferroptosis is characterized by high levels of iron and reactive oxygen species and has been confirmed to suppress tumor growth. In this study, BRD4 expression in cancer and its influence on the prognosis of cancer patients were analyzed using data from public databases. In addition, the effect of the BRD4 inhibitor (+)-JQ1 on ferroptosis was investigated via a series of in vitro assays. A nude mouse model was used to evaluate the function of (+)-JQ1 in ferroptosis in vivo. The potential mechanisms by which (+)-JQ1 regulates ferroptosis were explored. The results showed that BRD4 expression levels were higher in cancer tissues than in normal tissues and were related to poor prognosis in cancer patients. Furthermore, ferroptosis was induced under (+)-JQ1 treatment and BRD4 knockdown, indicating that (+)-JQ1 induces ferroptosis via BRD4 inhibition. Moreover, the anticancer effect of (+)-JQ1 was enhanced by ferroptosis inducers. Further studies confirmed that (+)-JQ1 induced ferroptosis via ferritinophagy, which featured autophagy enhancement by (+)-JQ1 and increased iron levels. Subsequently, the reactive oxygen species levels were increased by iron via the Fenton reaction, leading to ferroptosis. In addition, expression of the ferroptosis-associated genes GPX4 , SLC7A11 , and SLC3A2 was downregulated under (+)-JQ1 treatment and BRD4 knockdown, indicating that (+)-JQ1 may regulate ferroptosis by controlling the expression of ferroptosis-associated genes regulated by BRD4. Finally, (+)-JQ1 regulated ferritinophagy and the expression of ferroptosis-associated genes via epigenetic inhibition of BRD4 by suppressing the expression of the histone methyltransferase G9a or enhancing the expression of the histone deacetylase SIRT1. In summary, the BRD4 inhibitor (+)-JQ1 induces ferroptosis via ferritinophagy or the regulation of ferroptosis-associated genes through epigenetic repression of BRD4.

Iron, Ferritin, Hereditary Ferritinopathy, and Neurodegeneration

“…Ferroptosis is becoming increasingly characterized as a major player in several neurodegenerative diseases (including AD and PD) as well as being understood to be a new form of Programmed Cell Death differing biochemically and morphologically from apoptosis, classical autophagy, and necrosis (Biasiotto et al, 2015;Gao et al, 2016;Angeli et al, 2017;Stockwell et al, 2017). Furthermore, close sequential biochemical linkage between the end point of ferritinophagy (iron release) and the ROS damage in ferroptosis suggests that ferritinophagy iron release is a component of, or perhaps an outright driver of, ferroptosis under certain conditions (Santana-Codina and Mancias, 2018;Sui et al, 2018Sui et al, , 2019. Interestingly, components of the ferroptotic process have been reported in the literature as isolated effects for some time now, but their connections into an overall picture were lacking.…”

Ferroptosis contributes to developmental cell death in rice blast

“…Autophagy has been reported to be involved in the conidial death, since loss of the essential Atg8 function arrests such cell death and renders M. oryzae nonpathogenic, which highlights the close association between conidial cell death and fungal pathogenicity (Veneault‐Fourrey et al ., 2006). In tumor cells, autophagy is found to fine‐tune sensitivity to ferroptosis by degradation of the ferritin complex responsible for intracellular iron storage, thereby modulating the content of available iron and the corresponding iron‐dependent lipid peroxidation (Bauckman & Mysorekar, 2016; Gao et al ., 2016; Hou et al ., 2016; Napoletano et al ., 2019; Sui et al ., 2019). However, it remains unknown whether ferroptosis is also involved in developmental cell death in fungi.…”

Distinct photooxidation-induced cell death pathways lead to selective killing of human breast cancer cells

“…In line with this, it has been recently demonstrated, indeed, that LDCD does not necessarily manifest itself with an apoptotic morphotype and an intriguing connection is emerging between LMP, the adaptive responses to stress, and other RCD subroutines 49,50 . For example, lysosomes have an essential role in autophagy and cellular iron homeostasis, being a major source of free iron due to the degradation of ferritin in a process called ferritinophagy 51–53 . Thus, lysosomal damage could allow this metal to be more bioavailable to peroxidation reactions.…”