Roles of mitochondrial unfolded protein response in mammalian stem cells

Table 1 List of mitochondrial stress and mitochondrial unfolded protein response modulators in stem cells

Modulator	Functions	Ref.
ATF5	A transcription factor that is highly expressed in undifferentiated neural progenitor cells/stem cells and in a variety of human cancers, including gliomas.	[132]
HD	Antimicrobial peptide.	[14]
CHOP	A transcription factor that is upregulated in response to ER stress and the mitochondrial unfolded protein response, and results in impaired wound healing and reduced IEC proliferation.	[133]
LONP1	The mitochondrial matrix proteases.	[134]
HSP60	A mitochondrion-localized chaperone that is responsible for maintenance of the mitochondrial proteome and is upregulated as a part of the mitochondrial unfolded protein response.	[135]
AKT	A serine-threonine kinase that maintains stem cells by promoting viability and proliferation.	[136]
CLPP	A mitochondrial matrix protease and mitochondrion-localized chaperone that is responsible for maintenance of the mitochondrial proteome and is upregulated as a part of the mitochondrial unfolded protein response.	[134,135]
SIRT3	SIRT3 has been reported to be a tumor suppressor and mitochondrial stress stimulates SIRT3 activity, raising the possibility that SIRT3 plays a dual role in tumorigenesis.	[16]
SIRT7	The strongest deacetylase activity, found in the nucleus, which can result in increased mitochondrial stress and increased tendency to proliferate.	[137]
JNK	New target protein in mitochondrial dependent apoptosis.	[84]
HSP70	Mitochondrial chaperone.	[14]
HSP60	Stem cells without HSP60 lose their ability to self-renew.	[71]

UPR^mt: Mitochondrial unfolded protein response; ER: Endoplasmic reticulum; IEC: Intestinal epithelial cell; CHOP: CCAAT-enhancer binding protein homologous protein; HSP: Heat shock protein; SIRT: Sirtuin; JNK: c-Jun N-terminal kinase; CLPP: Caseinolytic protease proteolytic subunit; LONP1: LON peptidase 1, mitochondrial.