Mitophagy, which selectively eliminates the dysfunctional and excess mitochondria by autophagy, is crucial for cellular homeostasis under stresses such as
hypoxia. Dysregulation of mitophagy has been increasingly linked to many disorders including
neurodegenerative disease and
cancer.
Triple-negative breast cancer (TNBC), a highly aggressive
breast cancer subtype, is reported to be characterized by
hypoxia. However, the role of mitophagy in hypoxic TNBC as well as the underlying molecular mechanism is largely unexplored. Here, we identified GPCPD1 (
glycerophosphocholine phosphodiesterase 1), a key
enzyme in
choline metabolism, as an essential mediator in
hypoxia-induced mitophagy. Under the hypoxic condition, we found that GPCPD1 was depalmitoylated by LYPLA1, which facilitated the relocating of GPCPD1 to the outer mitochondrial membrane (OMM). Mitochondria-localized GPCPD1 could bind to VDAC1, the substrate for PRKN/PARKIN-dependent ubiquitination, thus interfering with the oligomerization of VDAC1. The increased monomer of VDAC1 provided more anchor sites to recruit PRKN-mediated polyubiquitination, which consequently triggered mitophagy. In addition, we found that GPCPD1-mediated mitophagy exerted a promotive effect on
tumor growth and
metastasis in TNBC both in vitro and in vivo. We further determined that GPCPD1 could serve as an independent prognostic
indicator in TNBC. In conclusion, our study provides important insights into a mechanistic understanding of
hypoxia-induced mitophagy and elucidates that GPCPD1 could act as a potential target for the future development of novel
therapy for TNBC patients.Abbreviations: ACTB: actin beta; 5-aza:
5-azacytidine; BNIP3: BCL2 interacting
protein 3; BNIP3L: BCL2 interacting
protein 3 like;
CCCP:
carbonyl cyanide m-chlorophenyl hydrazone; ChIP:
chromatin immunoprecipitation; co-IP: co-immunoprecipitation; CQ:
chloroquine; CsA:
cyclosporine; DOX:
doxorubicin; FIS1: fission, mitochondrial 1; FUNDC1: FUN14 domain containing 1; GPCPD1:
glycerophosphocholine phosphodiesterase 1; HAM:
hydroxylamine; HIF1A:
hypoxia inducible factor 1 subunit alpha; HRE:
hypoxia response element; IF: immunofluorescence; LB: lysis
buffer; LC3B/MAP1LC3B:
microtubule associated protein 1 light chain 3 beta; LC-MS: liquid chromatography-mass spectrometry; LYPLA1:
lysophospholipase 1; LYPLA2:
lysophospholipase 2; MDA231: MDA-MB-231; MDA468: MDA-MB-468; MFN1: mitofusin 1; MFN2: mitofusin 2; MKI67: marker of proliferation Ki-67; OCR: oxygen consumption rate; OMM: outer mitochondrial membrane; OS: overall survival; PalmB:
palmostatin B; PBS:
phosphate-buffered saline; PINK1: PTEN induced
kinase 1; PRKN: parkin RBR E3
ubiquitin protein ligase; SDS:
sodium dodecyl sulfate; TOMM20: translocase of outer mitochondrial membrane 20; TNBC:
triple-negative breast cancer; VBIT-4: VDAC inhibitor; VDAC1:
voltage dependent anion channel 1; WT: wild type.