Invalidation of mitophagy by FBP1-mediated repression promotes apoptosis in breast cancer

Abstract

Fructose-1,6-bisphosphatase 1, a rate-limiting enzyme in gluconeogenesis, was recently shown to be a tumor suppressor. However, the functions of fructose-1,6-bisphosphatase 1 in the regulation of mitophagy and apoptosis remain unknown. Here, we investigated the effects of fructose-1,6-bisphosphatase 1 on mitophagy and apoptosis as well as their underlying mechanisms in breast cancer cells. In this work, the messenger RNA and protein expression of various molecules were determined by quantitative realtime polymerase chain reaction and western blot, respectively. Gene-expression correlations were obtained from The Cancer Genome Atlas Breast Cancer database and analyzed using cBioPortal. The levels of cellular reactive oxygen species and apoptotic index were detected by flow cytometry. The mitochondrial membrane potentials were assessed with a JC-1 fluorescent sensor. Subcellular structures were observed under a transmission electron microscope. The intracellular distribution of translocase of outer membrane 20 was detected by immunofluorescence staining. Protein-protein interactions were analyzed by immunoprecipitation. Our results indicated that fructose-1,6-bisphosphatase 1 expression was negatively correlated with autophagy level in breast cancer. Fructose-1,6-bisphosphatase 1 restrained autophagy activity by increasing the level of p62 and decreasing the levels of LC3 and Beclin 1. Additionally, fructose-1,6-bisphosphatase 1 promoted cell apoptosis by upregulating the levels of intracellular ROS and expression of pro-apoptotic proteins such as cleaved PARP, cleaved Caspase 3, and Bax and downregulating the levels of anti-apoptotic proteins such as PARP, Caspase 3, and Bcl-2. Finally, fructose-1,6-bisphosphatase 1 limited the efficient removal of diseased mitochondria and reduced the messenger RNA and protein expressions of HIF-1α, BNIP3L/NIX, and BNIP3. More importantly, fructose-1,6-bisphosphatase 1 facilitated co-action between Bcl-2 and Beclin 1, which may be important in the mechanism of fructose-1,6-bisphosphatase 1-mediated mitophagy inhibition. In summary, loss of mitophagy by fructose-1,6-bisphosphatase 1-mediated repression promotes apoptosis in breast cancer.

Targeting FBPase is an emerging novel approach for cancer therapy

“…FBPase was found to decrease significantly in animal models, basal-like breast cancer (BLBC) cell lines, triple-negative breast cancer (TNBC), and human breast cancer but not in luminal cell lines and brain metastatic cells [ 19 , 21 , 22 , 74 – 76 ]. FBPase inhibits tumourigenicity in vitro and tumour formation in vivo [ 20 , 23 ] as well as the growth of brain metastasis [ 21 ].…”

“…Along with increases in complex I activity and mitochondrial OCR, ROS levels increased when FBPase was expressed [ 12 , 17 , 19 , 22 , 25 ]. ROS amplify tumourigenic phenotypes, such as cancer stem cells (CSCs) [ 103 ].…”

“…Forced FBP1 expression in lung cancer stem cells and breast cancer or FBP2 expression in gastric cancer increased apoptosis by reducing the Bax/Bcl-2 ratio, inducing poly ADP-ribose polymerase (PARP), caspase-3 and caspase-9 activation and suppressing endogenous ROS scavenging systems such as superoxide dismutase (SOD) [ 12 , 19 , 25 ]. In breast cancer cells, FBP1 limited the efficient removal of diseased mitochondria and reduced the expression of hypoxia-induced factor 1α (HIF1α), BCL2/adenovirus E1B 19 kDa interacting protein 3-like (BNIP3L/NIX), and BCL2/adenovirus E1B 19 kDa interacting protein 3 (BNIP3), which disrupts BNIP3/NIX-Bcl-2 complex formation under normal conditions but promotes complex formation between Bcl-2 and Beclin 1 [ 19 ]. Annexin V+/propidium iodide (PI)− and Annexin V+/PI+ cells represent early apoptotic cells and late apoptotic/necrotic cells, respectively [ 106 ].…”

Factor Analysis for Bicluster Acquisition (FABIA) revealed vincristine-sensitive transcript pattern of canine transmissible venereal tumors

“…Additionally, other factors possibly contributing to signaling inhibition were also evidenced. These included enhanced expression of RUBCN—a PI3K inhibitor-encoding gene (Liu et al., 2017), limited expression of STAT1 mediator-encoding gene, limited expressions of ESR1 and TYRO3—the PI3K signaling receptor-encoding genes, and finally, the limited expressions of LRRK2 (Looyenga et al., 2011) and HCK (Poh et al., 2015)—the receptor associated kinase-encoding genes.…”

Potential Roles of NIX/BNIP3L Pathway in Rat Traumatic Brain Injury

“…In addition to inducing apoptosis by means of its own structure, NIX is also thought to combine with p75 NRT (a member of the tumor necrosis factor receptor that is involved in several neuronal populations) 9 , and then induce apoptosis 7 . In further studies, NIX-related mitophagy has been gradually acknowledged 10 , and is another probable pathway for apoptosis 4,11,12 . As previously shown, NIX not only regulates the shift in Parkin and then activates mitophagy by the Parkin-Ubiquitin-p62 pathway 13 , it also induces mitophagy with Atg8-family proteins and serves as an autophagy receptor 14 .…”