Ecto-F1-ATPase: A moonlighting protein complex and an unexpected apoA-I receptor

Table 1 Ecto-F₁-ATPase subunit detection in various cell types

Cells/tissues	Subunits	Methods	Ref.
K562, A549, Raji	β	B, FC, S	[38]
HUVEC	α, β, IF1	B, FC, CM	[35,39,40]
HepG2, IHH, Human hepatocytes	α, β	SPR, FC, CM	[30]
3T3-L1	α, β	B, CM	[41]
Jurkat	β	RP + MS	[42]
Rat hepatocytes	α, β, δ, γ, b, d, e, F6, OSCP	CM	[37]
HaCat, Human skin	β	RP + MS, CM	[43]
Daudi, RPMI-8226, U937, SK-NEP, G401, G402	α and/or β	FC	[31]
Awells, ST-Emo, HeLa, fibroblasts, Rma-S	α, β	B, CM, FC	[33]
Rat tonsils	β	PM	[44]
Neurons, neuroblastoma, astrocytoma	α	B, CM	[45]
Osteosarcoma	α, β, d	CM	[36]

Studies reporting a cell surface expression of ATP synthase subunits are summarized. The experimental approaches used in these studies are mentioned. B: Cell surface biotinylation; FC: Flow cytometry; S: Sequencing; CM: Confocal microscopy; SPR: Surface plasmon resonance (Biacore); RP + MS: Rafts purification and mass spectrometry; PM: Plasma membrane extraction. Cell lines/tissues are of human origin unless otherwise noted. K562: Erythroleukemia; A549: Lung adenocarcinoma; RPMI-8226: B myeloma; Raji, Daudi: Burkitt lymphomas; Jurkat: T lymphoma; HUVEC: Human umbilical vein endothelial cells; HepG2: Hepatocarcinoma; IHH: Immortalized human hepatocytes; 3T3-L1: Murine fibroblasts (differentiated into adipocytes); HaCat: Immortalized human keratinocytes; U937: Monocytic leukemia; SK-NEP, G401, G402: Renal cell carcinomas; Awells, ST-EMO: EBV-immortalized B cells (ST-EMO was derived from a major histocompatibility complex classI deficient patient); HeLa: Cervix carcinoma; Rma-S: Murine T lymphoma.

Table 2 Ligands and roles of Ecto-F₁-ATPase

Cells/tissues	Ligands	Proposed roles	Ref.
K562, A549, Raji	?	NK/LAK-mediated tumor cell lysis	[38]
HUVEC	Angiostatin HDL/apoA-I	Cell survival through ATP production	[40,60,66]
	FC6	Cell survival through purinergic receptor activation
		Control of blood pressure
Hepatocytes	HDL/apoA-I	HDL endocytosis	[30]
3T3-L1, HaCat	?	Cell survival	[41,43]
Tumor cells	Vγ9/Vδ2 TCR, apoA-I, MHC-I	Tumor cell recognition by Vγ9/Vδ2 T cells/presentation of phosphoantigens	[31,33,46,67]
Tonsils (mouse)	Enterostatin	Food intake regulation	[44]
Neurons	APP, Amyloid β-peptide	Synaptic plasticity regulation	[45]

Major roles of Ecto-F₁-ATPase described in the literature, as well as ligands involved, are summarized here. MHC-I: Major histocompatibility complex class I; NK: Natural killer; LAK: Lymphokine activated killer; HDL: High density lipoprotein; apoA-I: Apolipoprotein A-I; FC6: Coupling factor 6; ATP: Adenosine triphosphate; APP: Amyloid precursor protein. Cells/tissues are of human origin unless otherwise noted. K562: Erythroleukemia; A549: Lung adenocarcinoma; Raji: Burkitt’s lymphoma; HUVEC: Human umbilical vein endothelial cells; 3T3-L1: Murine fibroblasts (differentiated into adipocytes); HaCat: Immortalized human keratinocytes.